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Title: solution Bioinstrumentation Webster
Description: best grade with this solution book the solution is very clear
Description: best grade with this solution book the solution is very clear
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PREFACE
This book describes measurement methods in medicine and biology
...
As a first course in bioinstrumentation for undergraduate biomedical engineers, this
book describes measurement methods used in the growing fields of cell engineering, tissue
engineering, and biomaterials
...
Chapter 1 covers the basics of instrumentation systems, errors, and the statistics
required to determine how many subjects are required in a research study
...
Chapter 3 describes clinical measurements of molecules, such as oxygen and glucose,
to biotechnology measurements such as DNA sequencing
...
Measurements on blood components are the commonest measurements on cells, as
described in chapter 5
...
Chapter 6 covers cellular measurements in biomaterials and tissue engineering,
such as cellular orientation, rolling velocity, pore size, deformation, shear stress, adhesion,
migration, uptake, protein secretion, proliferation, differentiation, signaling and regulation
...
Chapter 8 covers heart and circulation, with
measurements of cardiac biopotentials, pressures, output, sounds, viability—as well as blood
flow and pressure in the periphery
...
Chapter 10 covers measurements of body temperature, fat, and movement
...
A web site contains complete laboratory instructions for 12 laboratories,
examination questions, and quiz questions
...
I would
welcome suggestions for improvement of subsequent editions
...
Webster
Webster@engr
...
edu
January 2002
1
Measurement Systems
Kevin Hugo
1
...
She
can't remember when it started, but her eyesight has increasingly blurred over the course
of the last year
...
She hasn’t been to a doctor for many years, but now she’s decided to see her family physician
...
Although her weight, 90 kg
(198 lb
...
8 in
...
She marveled at the device that took her blood pressure (118/76) and
pulse (63 beats per minute) simultaneously
...
6 °F or 37 °C) from her ear in a few seconds, instead of having to place a
thermometer under her tongue for a minute
...
She is certain that
she did not suffer any injuries
...
The doctor also noted that that Edna has gained a fair
amount of weight
...
There were cotton-like blotches on the normally orange–pink retina
...
Finally, samples of urine and blood were taken
...
The doctor is concerned about the results, and orders an electrocardiogram and further tests on the blood and urine samples before returning to Ms
...
1-1
1-2
Chapter 1 Measurement Systems
1
...
1 Scales of biological organization
The patient in the above story has noninsulin-dependent diabetes mellitus (NIDDM), a
disease in which afflicted persons have high levels of blood glucose
...
However, with early detection and diligent
treatment, the risk of complications can be reduced (Diabetes, 1993)
...
One way to classify the various types of bioinstrumentation is to consider the level
of biological organization involved in taking the measurement
...
The chapters of this
book are presented in the order of these biological levels
...
For example,
every patient has vital signs taken not only because they may be useful in analyzing the
problem that the patient is concerned with, but also because they indicate that person’s
general health
...
An automated thermometer measured Ms
...
This is accomplished by using a temperature-sensing element as well as electronics to derive the temperature based on a mathematical algorithm
...
Measurements of concentrations of glucose and other molecules are performed
by spectrophotometry, as described in Chapter 3
...
Jones may have coronary artery
disease and need an implanted graft vessel
...
Methods used to analyze the blood sample that was drawn are described in
Chapter 5
...
In order to study the urinary casts
(cylindrical protein molds) passed in the urine, Chapter 6 describes the optical microscopes used
...
Jones reported a loss of feeling in her legs
...
Chapter 8 describes the electrocardiogram, which is used to diagnose Ms
...
Ms
...
NIDDM patients are frequently overweight
...
1
...
2 Fields of biomedical engineering
Biomedical engineering is a cross-disciplinary field that incorporates engineering, biology, chemistry, and medicine
...
Table 1
...
Each of these fields is briefly described in the fol-
1
...
The Whitaker Foundation describes various fields of
biomedical engineering at http://www
...
org/glance/acareer
...
Bioinstrumentation
Biomaterials
Biomechanics
Biosignals
Biosystems
Biotransport
Cellular engineering
Clinical engineering
Tissue engineering
Rehabilitation engineering
Table 1
...
Bioinstrumentation applies the fundamentals of measurement science to biomedical instrumentation
...
A physiological variable originates
from a molecular, cellular or systemic process whose nature may be described by a mechanical, electrical, chemical, optical or other event
...
The sensor should be designed to minimize the disturbance
to the measured variable and its environment, comply with the requirements of the living
system, and maximize the signal-to-noise ratio, i
...
the clarity of the signal
...
Bioinstrumentation includes methods for obtaining invasive and noninvasive measurements
from the human body, organs, cells and molecules; electronic instrumentation, principles
of analog and digital signal processing, and typical output devices
...
Biomaterials is the application of engineering materials to the production of
medical devices and diagnostic products
...
These include molecularly engineered materials,
hybrid materials and devices, biomimetic or synthetic biological materials, and other biologically related materials
...
Biomechanics covers the behavior of biological tissues and fluids to incorporate
complexities ranging from nonlinear viscoelasticity to non-Newtonian flows
...
Molecular and cellular biomechanics is integrated with
the macroscopic behavior of tissues and organs
...
An example of biomechanics is ergonomics, wherein everyday devices, such as chairs and desks, are designed to reduce stress and injury to the
body
...
Standard methods
of signal analysis have been used for characterizing rather than for elucidating the
mechanisms
...
Biosystems, which uses modern biology, has given us the tools to identify and
characterize molecules and cells, the fundamental building blocks of organ systems
...
Whereas molecular biology has focused on reductionism, biomedical engineering is in a unique position to move biology to the next frontier where synthesis will lead to an understanding of the function of complex systems
...
Biotransport phenomena covers transport processes from the organ to the subcellular level
...
Transport of ions, substrates, proteins, viruses and cells is a central issue for the quantitative understanding of biological systems
...
While using the fundamentals of transport phenomena for
understanding membrane transport, cellular and tissue energetics, enzymatic regulation
and metabolism, it also considers how data from microsensors, tissue samples or regional
concentrations over time can be acquired, quantified and interpreted
...
Cellular engineering develops and communicates quantitative biochemical and
biophysical design principles that govern cell function
...
Relevant topics are fundamental kinetics, mechanics, and transport processes that use calculus, differential equations and cell biology
...
Techniques from modern biochemistry and molecular biology alter these parameters in order to test model predictions and demonstrate
how the underlying design principles can be applied to manipulate cell function
...
Clinical engineers work with health care workers to determine equipment
needs, search for optimal equipment, specify equipment, perform incoming inspection,
train health care workers in proper operation, provide inventory of equipment, decide
whether to perform maintenance in house or purchase vendor contracts, and perform
safety inspections
...
A rehabilitation engineer works directly with patients such as disabled individuals to assist in
achieving a better standard of life
...
1 Studying Biomedical Engineering
1-5
equipment for such an individual
...
Such a limb would be required of an individual who has lost a leg, but still
desires to run on his or her own power
...
1
...
2 shows that instrumentation can be organized by the biological discipline that
utilizes it
...
For example, medicine can be subdivided into anatomy, anesthesiology, biomolecular chemistry,
biostatistics and medical informatics, family medicine, medical microbiology and immunology, medical physics, neurology, neurophysiology, obstetrics-gynecology, oncology,
ophthalmology, pathology and laboratory science, pediatrics, physiology, preventive
medicine, psychiatry, radiology, rehabilitation medicine, and surgery
...
2 Biomedical engineers work in a variety of disciplines
...
1
...
4 Workplace environments for biomedical engineers
Biomedical Engineers may become a part of the workplace in a variety of different areas,
as shown in Table 1
...
Industry has a demand for biomedical engineers for development
of new technologies and also for testing the theories that others develop
...
Positions in the government often
deal with testing of proposed products for safety and reliability, to safeguard the public
from harm
...
Research institutions are also the place of developing new ideas, and often involve
the dissemination of techniques and practices to others to further the general understanding
...
3 Biomedical engineers may work in a variety of environments
...
2 The need for bioinstrumentation
1
...
1 The scientific method
Figure 1
...
For example, we might hypothesize that exercise reduces high
blood pressure yet experimentation and analysis are needed to support or refute the hypothesis
...
Then the results can be
analyzed statistically to determine the probability (hopefully less than 0
...
Results are reported in scientific journals with
enough detail so that others can replicate the experiment to confirm them
...
1 In the scientific method, a hypothesis is tested by experiment to determine its validity
...
2
...
2 shows that physicians often need instrumentation to obtain data as part of the
scientific method
...
1
...
2 The physician obtains the history, examines the patient, performs tests to determine the
diagnosis and prescribes treatment
...
2
...
3 shows that the measurand is measured by a sensor, which converts the variable
to an electrical signal, which can undergo signal processing
...
As an example, light flashes
stimulate the eye when measuring visual evoked responses from electrodes placed over
the visual cortex of the brain
...
3 A typical measurement system uses sensors to measure the variable, has signal processing and display, and may provide feedback
...
4(a) shows that a patient reading an instrument usually lacks sufficient
knowledge to achieve the correct diagnosis
...
4(b) shows that by adding the clinician to form an effective feedback system, the correct diagnosis and treatment result
...
This is shown in Figure 1
...
An example of such a situation is the day-to-day monitoring of glucose by people suffering from diabetes
...
1-8
Chapter 1 Measurement Systems
Patient
Patient
Instrument
Instrument
Clinician
(a)
(b)
Figure 1
...
(b) The clinician provides knowledge to provide an effective closed loop system
...
5 In some situations, a patient may monitor vital signs and notify a clinician if abnormalities occur
...
3 Instrumentation
1
...
1 Measurands
The measurand is the measured quantity
...
Table 1
...
Measurands can be obtained by invasive or noninvasive methods
...
e
...
An alternative invasive
method is to place the pressure sensor at the distal end of the catheter outside the body
...
3 Instrumentation
1-9
Measurement
Range
Frequency, Hz
Method
Blood flow
1 to 300 mL/s
0 to 20
Blood pressure
Cardiac output
Electrocardiography
Electroencephalography
Electromyography
Electroretinography
pH
pCO2
pO2
Pneumotachography
Respiratory rate
Temperature
0 to 400 mmHg
4 to 25 L/min
0
...
1 to 5 mV
0 to 900 µV
3 to 13 pH units
40 to 100 mmHg
30 to 100 mmHg
0 to 600 L/min
2 to 50 breaths/min
32 to 40 °C
0 to 50
0 to 20
0
...
5 to 150
0 to 10000
0 to 50
0 to 1
0 to 2
0 to 2
0 to 40
0
...
1
Electromagnetic or ultrasonic
Cuff or strain gage
Fick, dye dilution
Skin electrodes
Scalp electrodes
Needle electrodes
Contact lens electrodes
pH electrode
pCO2 electrode
pO2 electrode
Pneumotachometer
Impedance
Thermistor
Table 1
...
A noninvasive method to measure blood pressure is to place a pressure cuff
around the arm and listen for the Korotkoff sounds due to turbulence of the blood under
the cuff
...
Weight and electrocardiography are also examples of noninvasive
measurement methods
...
3
...
Table 1
...
Note that several specifications are designed to prevent
patient electrocution
...
5 Sensor specifications for blood pressure sensors are determined by a committee composed of individuals from academia, industry, hospitals, and government
...
Section 1
...
3 discusses linearity in more detail
...
6
...
Defibrillator withstand is
the amount of energy (in joules) the sensor can withstand if a defibrillator is used while
the sensor is taking measurements
...
6 A hysteresis loop
...
Optimal sensors are designed specifically for the desired measurand, immune to
interference from other variables, and have high gain as shown in Figure 1
...
A sensor
with low gain, as shown in Figure 1
...
Most sensors are analog and provide a continuous range of amplitude values for
output, as shown in Figure 1
...
Other sensors yield the digital output shown in Figure
1
...
Digital output has poorer resolution, but does not require conversion before being
input to digital computers and is more immune to interference
...
Sensor
signal
Sensor
signal
Measurand
(a)
Measurand
(b)
Figure 1
...
(b) A high sensitivity sensor has high gain
...
8 (a) Analog signals can have any amplitude value
...
1
...
3
...
Table 1
...
) The values of the specifications, which have been agreed upon by
a committee, are drawn from research, hospitals, industry, and government
...
05 to 150 Hz
2
...
1 µA
1s
5000 V
10 µA
Table 1
...
The electrocardiogram (ECG), the recording of the electrical activity of the heart,
can have a voltage value of anywhere between 0
...
4)
...
If the measurand exceeds the
input range of the instrument, the output will saturate and cause an error
...
9
shows an input signal that exceeds the ±5 mV input range (a) and the resulting amplified
signal (b)
...
Figure 1
...
Slew rate is the maximum rate at which the system can observe a changing voltage per unit time without distortion
...
The ECG signal is composed of components that vary in frequency from 0
...
4) The electrocardiograph is designed to accommodate this as is
shown by its frequency response range
...
Frequency response is usually plotted as
gain versus frequency
...
11 shows the plotted frequency response of this electrocardiograph
...
2
...
Input impedance is the amount of resistance the signal sees coming into the electrocardiograph
...
5 MΩ,
1-12 Chapter 1 Measurement Systems
so that the majority of the signal will enter the system to be processed and not be lost in
the skin impedance
...
9 (a) An input signal that exceeds the dynamic range
...
Amplitude
Time
(a)
Amplitude
Dc offset
Time
(b)
Figure 1
...
(b) An input signal with dc offset
...
It is important that current flowing to the
patient not exceed very miniscule amounts (i
...
on the order of microamperes)
...
1
...
When switching between the different lead configurations, the electrocardiograph should
take no more than 1 s to adjust itself to correctly display the signal again
...
Overload voltage is the maximum voltage the electrocardiograph can withstand
without damage from defibrillators
...
e
...
) Defibrillators have two paddles that are placed on the patient’s chest
...
This current is what causes the heart to begin beating again
...
0
0
...
05 Hz
Frequency
150 Hz
Figure 1
...
When placing leads on a patient that will be hooked up to instrumentation, it is
of paramount importance to make sure the instrumentation does not shock the patient
...
General Characteristics
Another characteristic that all systems have is whether or not they are linear
...
For example, if you measure some
input (measurand) you get some output
...
This is not the case for nonlinear systems
...
Figure 1
...
1-14 Chapter 1 Measurement Systems
Output
Output
Input
(a)
Input
(b)
Figure 1
...
Note that all variables are italic
...
Finally, Figure 1
...
Continuous signal measurement is most desirable
because no data are lost
...
Amplitude
Amplitude
Time
(a)
Time
(b)
Figure 1
...
(b) Discrete-time signals
are sampled periodically and do not provide values between these sampling times
...
3
...
A display is simply a monitor or some other device attached to the instrumentation
that gives the user a sense of what the input is doing
...
g
...
) Storage is increasingly common as computers are integrated into bioinstrumentation
...
Communication involves transmitting the output to some other location for analysis
...
1
...
5 Panels and series
Certain groups of measurements are often ordered together because they are very commonly used or because they are related
...
3 Instrumentation
1-15
based on different principles or are taken with different sensors
...
7 is an example
of one of these groups of measurements, which are called panels or series
...
5 to 18 g/dL
40 to 54%
4
...
2 × 106/µL
4500 to 11000/µL
Neutrophil 35 to 71%
Band 0 to 6%
Lymphocyte 24 to 44%
Monocyte 1 to 10%
Eosinophil 0 to 4%
Basophil 0 to 2%
Table 1
...
Hemoglobin is the protein which caries oxygen in the bloodstream
...
An erythrocyte is a red blood cell
...
The differential
count tells how many of each type of white blood cell there are in one microliter of blood
...
1
...
4
...
14(a)
...
For example movement of electrodes on the skin may cause an
undesired added voltage called an artifact
...
14(b)
...
Temperature changes in the
amplifier electronic components may cause undesired slow changes in voltage called drift
...
Usually we try to minimize the largest error, since that is the weakest
link in the measurement
...
14 (a) Signals without noise are uncorrupted
...
Frequency filters that can be used to reduce noise and interference are discussed in
Chapter 2
...
15 (a) Original waveform
...
(c) A modifying
input may change the gain
...
15(b) shows that an interfering input may be added to the original
waveform and shift it away from the baseline
...
15(c) shows that a modifying
input may multiply the original waveform to change its gain
...
4
...
For example, a voltmeter with a larger number of digits has a higher resolution than one with fewer
digits
...
However, high resolution does not imply high
accuracy
...
16 shows that precision is the quality of obtaining the same output from
repeated measurements from the same input under the same conditions
...
Repeatability is the quality of obtaining the same output from repeated measurements from the same input over a period of time
...
Figure 1
...
Figure
1
...
Obtaining the highest possible precision, repeatability, and accuracy is a major
goal in bioinstrumentation design
...
4 Errors in Measurements
(a)
(b)
Figure 1
...
(a)
(b)
Figure 1
...
1
...
3 Calibration
1-17
1-18 Chapter 1 Measurement Systems
Measuring instruments should be calibrated against a standard that has an accuracy 3 to
10 times better than the desired calibration accuracy
...
nist
...
If the instrument is linear, its output can be set to zero for zero input
...
Figure
1
...
If the resulting curve
is nonlinear, many points should be measured and plotted to obtain the calibration curve
...
Calibration curves should be obtained at several expected temperatures to determine temperature drift of the zero point and the gain
...
18 (a) The one-point calibration may miss nonlinearity
...
1
...
5
...
The simplest statistic is the estimated sample mean
x=
where i = 1, 2,…n
...
1)
1
...
2)
The standard deviation of the mean s is
x=
s
n −1
(1
...
1 If Person 1 weighs 68 kg, Person 2 weighs 90 kg and Person 3 weighs 95
kg, find the mean, the standard deviation, and the standard deviation of the mean
...
The mean of the data is
x=
∑ xi
n
=
68 + 90 + 95
= 84
...
3)2 + (90 − 84
...
3)2
3 −1
= 14
...
4
3 −1
= 10
...
The
Gaussian distribution is given by
f (X ) =
2
2
e −( X −µ ) (2σ )
2π σ
(1
...
Figure 1
...
Frequency
xs
Estimated mean
standard deviation sx
α
–σ
Population standard
deviation σ
δ
+σ
µ
Mean
x
Figure 1
...
By
measuring samples and averaging, we obtain the estimated mean x s , which has a smaller standard
deviation sx
...
Poisson Probability
The Poisson probability density function is another type of distribution
...
The probability that a particular number of
events K will occur in a measurement (or during a time) having an average number of
events m is
p ( K ; m) = e
–m
mK
K!
The standard deviation of the Poisson distribution is
Poisson distribution
...
5)
m
...
20 shows a typical
1
...
2
0
...
0
0
1
2 K
3
4
5
Figure 1
...
Example 1
...
Calculate the probability that 15 cells will be counted in a sampling period
...
We want to find the probability of 15 cells being counted so K = 15
...
035
K!
15!
1
...
2 Statistical estimations
Suppose we want to know the average weight of adults
...
All adults are called the population
...
This small fraction is called our sample population
...
We want to know if our sample population
average weight is a good estimation of the population average weight
...
If we represent our sample population average weight as a single number, xs ,
then we have made a point estimation of the population average weight
...
The standard deviation of the population is σ
...
We can control the probability of how much x s differs from µ by adjusting
the sample size, N, using the formula
2
2 σ
N = Zα
δ
(1
...
This number is obtained from a statistical table (Distribution Tables, 2002)
...
7)
If we know the standard deviation, σ, of the population average weight, we can use it
...
If it cannot, then the sample standard deviation, s, must be used instead
...
2 s
N = tα
δ
2
(1
...
3 Suppose we know that the standard deviation of the adult average weight is
3 kg
...
(1
...
Lastly, we want a 95% confidence
that the sample size N we calculate will meet our specifications for δ
...
95)/2 = 2
...
025
...
025 and find that it equals 1
...
We can then
find N by using
2
3
N = (1
...
6 ≈ 9
2
which indicates that we would need to take the average of nine weights to get an estimation of the population average weight within ±2 kg with a confidence of 95%
...
Another way to represent estimations is with a confidence interval
...
The sample size
needed for an interval estimation is twice that needed for a point estimation and can be
found with the formula
2σ
N = 2Z α
δ
2
(1
...
We would need 18 samples to be 95% confident that our weight represented
the average weight of the population
...
5 Statistics
1-23
[Lower limit on average weight] ≤ w ≤ [Upper limit on average weight]
In the event that we do not know the standard deviation of the population, we can use the
sample standard deviation, s, and the Student t distribution tα
...
5
...
H0, the null hypothesis, is a hypothesis
that assumes that the variable in the experiment will have no effect on the result and Ha is
the alternative hypothesis that states that the variable will affect the results
...
The goal of hypothesis testing is to find
out which hypothesis is true by sampling the population
...
This leads to four possibilities, as shown in Table 1
...
Usually, the probability of making a Type I error is designated as α and the
probability of making a Type II error is designated as β
...
01, 0
...
1
...
Statistical power is given by 1 – β
...
8, indicating that when H0 is false it will be correctly rejected
more than 80% of the time
...
8 The four outcomes of hypothesis testing
...
A very small p value means that the null hypothesis is unlikely to be true
...
g
...
05, the result is called statistically significant
...
05 means that since the result obtained would happen only once
in 20 times if H0 were true, then H0 should be rejected
...
9 Equivalent table of Table 1
...
Test results about a condition or disease use the terminology in Table 1
...
In this
case H0 states that an individual does not have a condition or a disease, whereas Ha states
that an individual does have a condition or disease
...
9 are useful for defining measures that describe the proportion of, for example, a disease in a population and the success of a test in identifying it
...
Prevalence is the number of cases of a disease at a given time such as y cases per
1000
...
Prevalence =
TP + FN
TN + TP + FN + FP
(1
...
Among all diseased persons, it is the percent who test positive
...
11)
Specificity is the probability of a negative diagnostic result in the absence of the
disease
...
Specificity =
TN
100%
TN + FP
(1
...
PPV =
TP
100%
TP + FP
(1
...
NPV =
TN
100%
TN + FN
(1
...
We can calculate the number of
subjects required in our trial by consulting books on biostatistics (Dawson-Saunders and
Trapp 1990)
...
1
...
Figure 1
...
We set the threshold for the test to maximize true results and minimize false results
...
21 The test result threshold is set to minimize false positives and false negatives
...
We can increase the threshold to make it very difficult to reject H0 in
order to reduce Type I errors (false positives)
...
If we decrease the threshold, the converse is also true
...
15)
where Zα and Zβ are the values for the standard Gaussian distribution corresponding to,
respectively, the tail probabilities of size α and β
...
05, β = 0
...
9, Zα = 1
...
65 and N = 26
...
If the result of the test suggests
1-26 Chapter 1 Measurement Systems
that we accept H0, then there is a 5% probability that H0 is false
...
For a test about the mean m of a normal population, with H0: |m| < δ and Ha: |m|
> δ, the sample size needed is
(
N = Zα + Z β
)2 σ
δ
2
(1
...
(1
...
Kanji (1993) provides a fine
summary of statistical tests
...
All the sample sizes
calculated are estimates based on several assumptions, some of which may be difficult to
prove
...
Hence, it may be convenient to modify some of the relevant factors involved in the equations in order to seek their effect on N
...
1
...
This education should continue throughout their career
through a program of instruction designed by themselves
...
A good place to start is by
reading books, which review a large amount of material, present it in an organized fashion, and provide references for further study
...
amazon
...
”
To obtain recent information, go to www
...
org/BMEnet/ or
www
...
org/BME/BMES/society/, join societies such as the Biomedical Engineering
Society or the Institute of Biomedical Engineering Technology, subscribe to biomedical
engineering journals such as the Annals of Biomedical Engineering, and go to conferences listed there
...
ncbi
...
nih
...
You can search patents at http://www
...
com/
Commercial databases available at universities include ISI, OVID, and INSPEC
...
...
1
...
eng
...
edu
...
html
...
and Trapp, R
...
1990
...
Norwalk,
CT: Appleton & Lange
...
7 References
1-27
Doebelin, E
...
1990
...
4th ed
...
Kanji, G
...
1993
...
Newbury Park, CA: SAGE Publications
...
M
...
Long-term complications of diabetes mellitus
...
Engl
...
Med
...
Distribution Tables 2002
...
statsoft
...
html
The Diabetes Control and Complications Trial Research Group
...
The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus
...
Engl
...
Med
...
Selwyn, M
...
1996
...
Boca Raton:
CRC Press
...
G
...
) 1998
...
3rd ed
...
The Whitaker Foundation [Online] www
...
org
1
...
1
Compare the scientific method with that of making a diagnosis
...
1
...
1
...
1
...
1
...
1
...
Estimate the mean x and standard deviation s
...
7 Your samples from a population are 1, 1, 3, 5, 5
...
1
...
1
...
Calculate the number
of X-ray photons required so that the signal-to-noise ratio (SNR) = (average number of photons)/(standard deviation of the number of photons) = 8
...
10 The results of test X are based on a threshold; positive results are greater than the
threshold and negative results are less than the threshold
...
1
...
1
...
If there are 5 people actually affected by the condition and 60 not affected, then find the number of true positives,
true negatives, false positives, and false negatives
...
13 A test has 83
...
7% specificity
...
1
...
1
...
Calculate the number N of adults we must test to obtain a probability p = 0
...
1
...
Provide the complete reference
...
1
...
Provide
the complete reference
...
2
Basic Concepts of Electronics
Hong Cao
Medical instruments are widely used in clinical diagnosis, monitoring, therapy, and
medical research
...
These instruments contain electric
components such as sensors, circuits, and integrated circuit (IC) chips
...
Biomedical engineers should have a fundamental understanding of their
operations and a basic knowledge of their component electric and electronic s ystems
...
Electrical engineering is too large a topic to cover completely in one chapter
...
It discusses analog components such as resistors, capacitors, and inductors
...
From this it moves to the
digital domain, which includes converters, sampling theory, and digital signal processing
...
2
...
1
...
Most of the electrons are tightly
bound to the atom, while some electrons in the outer orbits are loosely bound and can
move from one atom to another
...
This
process of electron transfer occurs in random directions in materials
...
Title
Suppose there is an imaginary plane in a conductor (Figure 2
...
The loosely
bound outer orbital electrons continuously cross this plane
...
Thus, the net flow of electrons is zero
...
1 Electric current within a conductor
...
(b) A net flow of electrons generated by an external force
...
1(b))
...
If ∆Q is the amount of charge that passes perpendicularly through a surface with
area A, in time interval ∆t, the average current, Iav, is equal to the charge that passes
through A per unit time
...
1)
The rate at which current flows varies with time as does charge
...
(2
...
I = dQ dt
(2
...
242 × 1018 electrons across the plane per second (s)
...
When a negative charge moves in one
direction, it yields the same result as a positive charge moving in the opposite direction
...
Figure 2
...
Section No
...
2
...
2 Voltage and potential
In moving a charge (+ or –) from point A to point B in an electric field, the potential
energy of the charge changes
...
The amount of work is measured in Joules, J
...
3)
where VB and VA are the potential at points B and A, respectively
...
If we choose the potential at infinity to be zero, the
absolute potential of a point in an electric field can be defined as the total work per unit
charge that has been done to move the charge from infinity to the point
...
The potential difference is proportional to the change in potential
energy, where the two are related by ∆U = q0∆V
...
(2
...
We are more interested in
potential difference than the absolute potential for a single point
...
Voltage can be generated in a circuit by a voltage source or by a current source
and resistor in parallel
...
Example 2
...
6×10–19 C)
from 0 V to 4 V?
Rearranging Eq
...
3)
WAB
= q0 (VB − VA ) = 1
...
4 × 10 −19 J
2
...
3 Resistors and Ohm's law
When free electrons move in a conductor, they tend to bump into atoms
...
The unit
of resistance is the Ohm (Ω), in honor of Georg Simon Ohm, who discovered what is
now known as Ohm’s law
...
Title
per unit area) to the electric field that is producing the current, E, is a constant, σ, that is
independent of the electric field
...
J = σE
(2
...
2
...
The potential difference can
be related to the electric field by the relationship
V = El
(2
...
2 A model of a straight wire of length l and cross-sectional area a
...
This electric field
produces a current that is proportional to the potential difference
...
6)
The quantity (l/σa) is defined as the resistance, R, of the conductor
...
7)
Experimental results show that the resistance, R, of a conductor can be rewritten
as
R=ρ
l
a
(2
...
Ohm’s law is written as
V = IR
(2
...
Section No
...
Good electrical
conductors have very low resistivity, where good insulators have very high resistivity
...
Common carbon composition
resistors used in electronic circuits have values between 10 Ω to 22 MΩ
...
2 What is the resistance of a 12
...
7×10–8 Ω⋅m and a radius of 0
...
321 × 10 − 3 m
)2 = 3
...
(2
...
12 m
l
= 1
...
30 × 10 − 3 Ω
a
3
...
Resistors often have their resistance value in ohms color coded
...
The first two
colors give the first two digits in the resistance value
...
The last
color is the tolerance value of the resistor, which is usually 5%, 10% or 20% (Figure 2
...
In equation form, the value of a resistor’s resistance can be calculated using the following
AB × 10 C ± D%
(2
...
Table 2
...
6
Chapter No
...
3 The colored bands that are found on a resistor can be used to determine its resistance
...
The final band
indicates what tolerance value (in %) the resistor possesses
...
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver
Colorless
NUMBER
0
1
2
3
4
5
6
7
8
9
–1
–2
Tolerance (%)
5%
10%
20%
Table 2
...
Each color can indicate a first or second digit, a multiplier,
or, in a few cases, a tolerance value
...
3 What is the resistance value of a resistor where the first band is orange,
second band is blue, third band is yellow, and fourth band is gold?
Using Table 2
...
The second
band gives the second digit, 6
...
The fourth band, or tolerance,
is gold, 5%
...
We define power, the rate at which work is done, as
P = VI
(2
...
V is the voltage between the two terminals of the
resistor and I is the current through the resistor
...
(2
...
(2
...
Title
P=
V2
= I 2R
R
7
(2
...
The power lost as heat in a conductor, for example, is called joule heat and is
referred to as a loss of I2R
...
4 Assume the chest is a cylinder 10 cm in diameter and 40 cm long with a resistivity of
0
...
For a voltage of 2 kV during defibrillation, calculate the current and power
dissipated by the chest
...
(2
...
9) and (2
...
l
0
...
8
= 40
...
1) 2
4
V 2000
= 49 A
I= =
R 40
...
1
...
Some IC chips, such as
the Intel Pentium, contain more than one million components
...
We
can analyze the performance of simple or complex circuits using one theorem and two
laws of linear circuit analysis
...
In other words, if there is more than one source in the network, we can perform
circuit analysis with one source at a time and then sum the results
...
One concept we need to introduce is the polarity of a voltage drop
...
In other words, by
current flowing through an element, a voltage drop is created (as shown by Ohm’s law)
by that element with the polarity of + to – in the direction of current flow (Figure 2
...
Title
R1
+ 10 Ω −
+
V
+ 20 Ω −
V1
R
I
R2
V2
−
I
(a)
VS = 30 V
(b)
Figure 2
...
(b) Kirchhoff’s voltage law
...
Kirchhoff’s voltage law (KVL) states
∑V = 0
(2
...
In other words, starting at any point on
the closed loop, we can use the voltage law to form an equation by adding each voltage
drop across every element (resistors and sources)
...
This law follows from conservation of energy
...
Figure 2
...
If
we sum the voltages counterclockwise around the loop we get
−VS + V1 + V2 = 0
VS = V1 + V2
Notice that the voltage source, VS, has a polarity opposite that of the other voltage drops
...
This is directly
related to Eq
...
9), where the direction of current flow across a resistor affects the
potential change across that resistor
...
In circuit analysis, a node is a junction of two or more branches
...
Title
∑I = 0
9
(2
...
In other words, the currents entering a node must equal the
currents leaving the node (Figure 2
...
5 (a) Kirchhoff’s current law states that the sum of the currents entering a node is 0
...
When we use Kirchhoff’s current law, we can arbitrarily label the current
entering the node + and leaving the node –
...
5(b) is
+3 + 6 − I = 0
I =9A
Kirchhoff’s voltage law and current law are basic laws for circuit analysis
...
We assume unknown currents in the loops and set up the equations using
Kirchhoff’s voltage law and then solve these equations simultaneously
...
4(b) to illustrate loop analysis
...
If we assumed the
current in the other direction, our result would just be negative
...
In this example, the voltage drop for R1 is 10 V
...
Title
a
4W
b
e
10 V
+
+
2W
6W
I1
d
14 V
-
c
I3
I2
f
Figure 2
...
5
...
5 Find the currents I1, I2 and I3 in the circuit shown in Figure 2
...
Applying Kirchhoff’s current law to the current junction at node c, we have
I1 + I 2 = I3
(1)
All together there are three loops, abcda, befcb, and aefda (the outer loop) to which
Kirchhoff’s voltage law can be applied
...
Title
11
Substituting this value into (5), we find I2 = –3 A
...
The other type of analysis is nodal analysis
...
We solve these
equations to yield the voltage at each node
...
7 shows an example using nodal
analysis
...
7 Example of nodal analysis
...
7, we are given the voltage at A as 30 V and at B as 20 V
...
We apply Kirchhoff’s current law at node C
30 − V 20 − V V − 0 50 − 3V
+
−
=
=0
20
20
20
20
V = 16
...
With an equal number of
equations and unknowns, large numbers of unknowns can be solved for using a matrix
and linear algebra
...
1
...
For example,
Figure 2
...
12
Chapter No
...
8 The 1 mV signal from the electrocardiogram is attenuated by the resistive divider
formed by the 100 kΩ skin resistance and the 1 MΩ input resistance of the oscilloscope
...
91 nA
R 100 kΩ + 1 MΩ
The output voltage Vo is
Vo = iRi = (0
...
91 mV
Thus the input voltage (ECG) has been undesirably attenuated by an amount that we can
calculate from the voltage divider equation
Vo
Ri
=
Vi Rs + Ri
(2
...
91
Vi Rs + Ri 100 kΩ + 1 MΩ
Figure 2
...
With two resistors in series,
the output voltage is part of the input voltage
...
A potentiometer is a three-terminal resistor with an adjustable sliding contact
that functions as an adjustable voltage divider or attenuator
...
9 shows that if the
slider is at the top, vo = vi
...
If the slider is in the
middle, vo = 0
...
Potentiometers are usually circular with a rotatable shaft that can be
turned by hand or a screwdriver
...
Alternatively, a potentiometer can
be used as a two-terminal variable resistor by using the variable resistance between the
slider and only one end
...
Title
vi
13
Slider
vo
Figure 2
...
The input signal vi is attenuated by the potentiometer to yield an adjustable smaller
voltage vo
...
1
...
A common type of galvanometer consists of a coil of wire mounted in such a
way that it is free to deflect or rotate in the presence of a magnetic field provided by a
permanent magnet
...
The torque is
proportional to the amount of current that passes through the galvanometer, such that the
larger the current, the greater amount of deflection or rotation of the coiled wire
...
Also, the fact that the
galvanometer gives a full-scale deflection for low currents (1 mA or less) makes it
unusable for currents greater in magnitude
...
Most of the current that
is measured will pass through this resistor (Figure 2
...
If an external resistor, Rs, is placed in series with the galvanometer, such that its
resistance value is relatively larger than that of the galvanometer, the device can be used
as a voltmeter
...
10(b))
...
14
Chapter No
...
10 (a) When a shunt resistor, Rp, is placed in parallel with a galvanometer, the device can
be used as an ammeter
...
Wheatstone bridge
Often in biomedical instruments, unknown resistances or changes in resistance are
measured within a circuit
...
The Wheatstone bridge has several
applications and is widely used in electronics
...
One parallel branch contains one known resistance (R1) and an unknown
resistance (Rx) as shown in Figure 2
...
The other parallel branch contains resistors of
known resistances, R2 and R3
...
Title
I1
+
I2
R1
R1
−
15
b
a
R3
Rx
Figure 2
...
The circuit is often used to measure an
unknown resistance Rx, when the three other resistances are known
...
In order to determine the resistance of the unknown resistor, the resistances of
the other three are adjusted and balanced until the current passing through the decreases
to zero
...
Similarly, the potential difference across R3 must also equal Rx
...
16)
From Eq
...
16), we can calculate the value of the unknown resistor
...
This device, commonly used in biomedical instruments to measure
experimental stresses, often consists of a thin wire matrix attached to a flexible plastic
backing and glued to the stretched metal
...
The resistance measurement is made with the
strain gage as one or more elements in the Wheatstone bridge
...
Title
the diaphragm of an silicon integrated circuit blood pressure sensor are formed into a
Wheatstone bridge
...
1
...
Now we investigate two elements with different
relationships between voltage and current
...
A capacitor is a two terminal element in which the current, i, is proportional to
the change of voltage with respect to time, dv/dt, across the element (Figure 2
...
19)
where C is capacitance and is measured in farads (F)
...
Common capacitor
values are 10 pF to 1 µF
...
3) in
biomedical instruments
...
12 (a) Capacitor current changes as the derivative of the voltage
...
We can also represent v as a function of i and t
v(t ) = v(t0 ) +
1 t
∫ idt
Ct
0
(2
...
Title
17
where t0 and t are the beginning and ending times over which we observe the current, v(t0)
is the initial voltage across the capacitor
...
A capacitor usually consists of two conductors that are separated by an insulator
...
A
parallel-plate capacitor consists of two parallel plates of equal area A, separated by a
distance d (Figure 2
...
One plate has a charge +Q and the other –Q, where the charge
per unit area on either plate is σ = Q/A
...
+Q
−Q
Area = A
d
Figure 2
...
The component consists of two parallel plates of
area A separated by a distance d
...
We can then see that the electric field between the plates is
E = σ εo = Q εo A
(2
...
85 pF/m))
...
22)
Capacitances can be found in many different configurations within a circuit
...
For the series capacitances in
Figure 2
...
Title
−1
1
C1C2
1
Ce =
C + C = C +C
2
1
2
1
1
1
1
1
=
+
+
+ mm
Ce C1 C2 C3
2 capacitors
(2
...
14(b), the equivalent capacitance, Ce, can be
calculated by
2 capacitors
Ce = C1 + C2
Ce = C1 + C2 + C3 + mm multiple capacitors
(2
...
14 (a) A series combination of two capacitors
...
1
...
15), or
v=L
di
dt
(2
...
Its unit is the henry (H)
...
This is usually taken to
be the defining equation for the inductance of any inductor, regardless of its shape, size
or material characteristics
...
The inductance of an
element often depends on its geometry
...
Title
19
V
L
i
+
v
1
di/dt
L
−
(b)
(a)
Figure 2
...
(b) Symbol of the
inductor
...
26)
0
+
? 0e?
i
t
L=2H
−
Figure 2
...
Example 2
...
16, an inductor is connected, at time t = 0 by a switch, to a
voltage source whose signal can be described as –10e–5t V
...
Using Eq
...
26) we can solve for i(t)
...
i (t ) = i (t0 ) +
1 t
∫ vdt
Lt
0
1 t
1 − 10
i (t ) = 0 +
∫ − 10e−5t V dt = 2 − 5 e−5t
2H0
i (t ) = e −5t A
20
Chapter No
...
27)
For multiple inductors in parallel, Le can be calculated by
1
1
1
1
=
+
+
+ ll
Le L1 L2 L3
(2
...
1
...
17(a)
...
For vC(t)
when t ≥ 0, we have
VC(t)
1
+
+
R
−
iR
VC(0)
C
−
iC
τ
(a)
t
(b)
Figure 2
...
(b) Normalized voltage
across the capacitor for t ≥ 0 (normalized means the largest value is 1)
...
29)
Upon rearranging, we get
dvC
1
+
v =0
dt
RC C
(2
...
This is a
first-order differential equation
...
Section No
...
31)
Figure 2
...
Also, we have
t
iC (t ) = −iR (t ) =
vC (t )
v (0) −
=− C
e RC
R
R
(2
...
The voltage and current in this
circuit can be described by equations of the form
−
t
f (t ) = Ke τ
(2
...
The constant τ is called the time constant of the first-order
system
...
When time t reaches τ, the amplitude of vC (t = τ) is vC(0)E–
1
...
We can
assume the value of vC(t) is practically zero after five time constants
...
17(a), there was no independent source (or
input), only an initial state of the circuit
...
Example 2
...
17(a)
...
How long will it take for the
capacitor to discharge to half of its original voltage?
This simple RC circuit can be solved with a first-order differential equation
...
Using Eq (2
...
−
t
vC (t ) = vC (0)e RC
v (t )
t
ln C = −
v ( 0)
RC
C
vC (t )
t = − RC ln
v (0) = −(1 kΩ )(40 µF)ln (0
...
7 ms
C
Now let us consider the case of nonzero input using the circuit shown in Figure
2
...
From t = –∞ to just before t = 0 (t = 0–), the switch has been open
...
Title
current has been flowing and no charge is in the capacitor
...
+
V
+
−
vR
+
R
C
−
VC(t)
V
I
vC
−
1
VC(t)
τ
t
(a)
(b)
Figure 2
...
(b) Normalized voltage across
the capacitor
...
34)
for t ≥ 0
The solution of the equation is
vC = V − Ve
−
t
RC
The voltage across the resistor, vR, and current, i, are
(2
...
Title
t
RC
t
−
e RC
vR = Ve
i=
V
R
23
−
(2
...
18(b)
...
From the definition of a capacitor, we know the voltage across it cannot change abruptly
or the current will become infinite
...
As
time increases, the capacitor becomes charged and as time approaches infinity, all the
source voltage is across the capacitor while the voltage drop across the resistor is zero
...
8 Consider the circuit in Figure 2
...
Suppose that V = 12 V, R = 1 kΩ and
C = 10 µF
...
Sketch the voltage across the capacitor versus
time
...
35):
vC = V − Ve
−
vC = 12 − 12e
t
RC
−
t
0
...
8 V
...
vC (V)
12
10
...
023
Time (s)
Figure 2
...
8
...
05
24
L/R
...
Title
We can also use a resistor and an inductor to make a first-order circuit where τ =
2
...
10 Frequency
Sinusoidal waves are widely used in electrical circuits
...
20 shows two sinusoidal
waveform, which can be represented as
A sin( 2πft + θ ) = A sin(ωt + θ ) = A sin(
where
2π
t +θ)
T
(2
...
20 One period, T, of the sine and cosine waveforms
...
Example 2
...
21 and 2
...
In Figure 2
...
By doubling the frequency
the period is reduced by half by T = 1/f
...
Title
25
1
v (V)
0
...
5
–1
0
1
2
3
t (s)
4
5
6
Figure 2
...
In Figure 2
...
The
minus sign in front of the phase angle shifts this waveform to the right and can be said
that it is leading the original waveform
...
1
v (V)
0
...
5
–1
0
1
2
3
t (s)
4
5
6
26
Chapter No
...
22 Sinusoidal waveforms with 0º phase angle (solid) and 180º phase angle (dashed)
...
Since sinusoidal sources
change with time and its differential is still sinusoidal, a more efficient way to solve the
equations is to use complex sinusoidal forms
...
38)
This representation comes from Euler's identity and has the same amplitude, frequency,
and phase angle as the noncomplex form
...
39)
A = A∠φ
by
(2
...
Equation (2
...
"
Let us consider a resistor
...
41)
v = Ri
Ve j (ω t +θ ) = RIe j (ω t +φ )
Ve jθ = RIe jφ or V∠θ = RI∠φ
(2
...
(2
...
23(a))
...
43)
As to an inductor, the voltage across it is given by
v=L
The V-I relationship can be written as
di
dt
(2
...
Title
27
Ve jθ = jωLIe jφ or V∠θ = jωLI∠φ
(2
...
46)
Therefore
and θ = φ + 90°, which shows that current lags the voltage by 90° (Figure 2
...
Using the methods presented in Eq
...
44) through (2
...
47)
and θ = φ – 90°, which shows that current leads the voltage by 90° (Figure 2
...
Imax
iR
Imax
Vmax
vR
Vmax
iC
Imax
vL
t
Vmax
vC
t
t
iL
(a)
(c)
(b)
Figure 2
...
(a) With a resistor both the
current and the voltage vary as sin(ωt), the current is in phase with the voltage, meaning that when
the current is at a maximum, the voltage is also
...
(c) For a capacitor, the current leads the voltage by 90°
...
That equation is
V = ZI
(2
...
For the three elements,
ZR = R
ZC =
1
jωC
Z L = jωL
(2
...
(2
...
1
...
Phasor equations simplify the circuit analysis and can be used by
computers to solve the problem
...
Therefore, the performance of the circuit will also change with frequency
...
28
Chapter No
...
10 The current through a 50 mH inductor is 100∠0° mA
...
(2
...
V = jωLI
V = j1000(0
...
1
...
2
...
Figure 2
...
These two impedances, and in general infinitely many of them,
can be combined into one equivalent impedance
...
24(a), the equivalent impedance, Ze, can be calculated by
Z e = Z1 + Z 2
(2
...
50b)
For the parallel impedances in Figure 2
...
51a)
For multiple impedances in parallel, the equivalent impedance Ze is
1
1
1
1
=
+
+
+
Z e Z1 Z 2 Z3
(2
...
(2
...
Using these definitions, it is possible to reduce large complicated circuits down
to (ideally) one or two impedances and a voltage source
...
24(c) shows the
equivalent impedance of the combined series or combined parallel circuit
...
Title
29
Z1
Z2
Z1
Z2
(a)
(b)
Ze
(c)
Figure 2
...
(b) Parallel circuit
...
2
...
12 Electrical safety
Because safety is paramount in considering biomedical devices in the real world setting,
great emphasis is placed on currents and voltages that exist in an apparatus and what
dangers these may pose to a patient or operator who might use the device
...
Often the degree of damage depends on the magnitude of current that is
applied, how long the current acts, and through which point on the body the current
passes
...
Currents larger than 10 mA tend to cause muscles to contract,
making the person unable to let go of a live wire
...
The heart can go into ventricular fibrillation, which is fatal (macroshock)
...
Contact with live wires or voltages above 24 V is
not recommended
...
In the following sections, we will explore ways
in which this can be done
...
2 Amplifiers
Most bioelectric signals have a very small magnitude (on the order of millivolts or
microvolts) and therefore require amplification so that users can process them
...
30
Chapter No
...
2
...
An op amp is made of many transistors
and other components that are integrated into a single chip
...
Focusing on the
terminal behavior of op amps allows us to see many applications for this circuit in
bioinstrumentation
...
25(a) shows the equivalent circuit of an op amp
...
25(b) shows
the symbol of the op amp
...
The gain (A in Figure 2
...
Gain is also called amplification
RS
v1
vo
+
Rd
−
A(v2 − v1)
v1
−
v2
+
V+
A
vo
V−
v2
(a)
(b)
Figure 2
...
(b) Symbol of op amp
...
2
...
2 Ideal op amp
When designing a circuit, we assume that we are using an ideal op amp
...
If they do,
we revise the initial design to accommodate the nonideal characteristics
...
A = ∞ (gain, or amplification of the input, is infinity)
2
...
Rd = ∞ (differential input impedance is infinity)
4
...
Bandwidth = ∞
...
27 and 2
...
)
Two basic rules should be stated before we discuss designing circuits with op amps
...
Title
31
Rule 1: The two input terminals are at the same voltage
...
This is not realistic
...
Also the op amp saturates about ± 13 V, which means that when
vo exceeds ± 13 V, it saturates and further increases in vi will not produce change in the
output
...
This is true because we assume the input impedance of an op amp is infinity and no
current flows into an infinite impedance
...
2
...
26 shows an inverting amplifier, or inverter
...
Note that Rf is connected from the output to the negative input terminal
and thus provides negative feedback
...
Rf
i
i
−
vi
Ri
A
+
vo
Figure 2
...
The gain of the circuit is –Rf/Ri
...
26, the positive input terminal of the op amp is connected to ground
and is always at 0 V
...
This
clamping of the negative input to 0 V is called a virtual ground
...
Therefore, the current
flows through Ri and then through Rf to the output terminal, then through the output
circuit of the op amp to ground
...
52)
32
Chapter No
...
When using op amps in circuits it is important to consider the output impedance
of any source that they are connected to, as this value will affect the total input resistance
and the gain of the op amp
...
27 Inverter circuit attached to a generator that contains an internal resistance
...
11 Suppose in Figure 2
...
(2
...
However if
the signal generator shown in Figure 2
...
Rs would therefore change vo as well as the gain of the circuit
...
48
vs
Ri + Rs
which is much less than our desired value
...
2
...
28(a) shows the circuit for a noninverting amplifier
...
From Figure 2
...
53)
Section No
...
28 (a) A noninverting amplifier has a gain of (Rf + Ri)/Ri
...
Notice the output vo has the same sign as the input voltage vi
...
If we choose Ri = ∞ (open circuit), the circuit can be simplified as Figure
2
...
The gain, (Rf + Ri)/Ri, would be unity
...
At first glance, this circuit does nothing, since the output equals
the input
...
Loading can be expressed by the voltage divider equation (Eq
...
15)
...
8, if Ri is a significant fraction of Rs, we would get an attenuated signal for Vo
...
This can be seen mathematically in
Eq
...
15as Rs increases to infinity, Vo/Vi approaches zero
...
It provides an extremely high input
impedance and an extremely low output impedance
...
12 Suppose the signal generator in Figure 2
...
29), will the generator’s output impedance affect the
gain?
No, since no current will flow into the positive input terminal, vi = 1 V and the
gain would remain (Rf + Ri)/Ri
...
34
Chapter No
...
29 The gain of the noninverting amplifier is not affected by the addition of the impedance
Rs due to the generator
...
2
...
30 is a simple one-op-amp differential amplifier
...
Thus, R1 and R2 act as a
voltage divider
...
30 A differential amplifier uses two active inputs and a common connection
...
The top part of the amplifier works like an inverter
...
54)
Section No
...
55)
Combining these two equations yields
vo =
R2
(v − v )
R1 2 1
(2
...
If the two inputs are hooked
together and driven by a common source, then the common-mode voltage is equal to Vc
(v1 = v2)
...
When v1 ≠ v2, the differential voltage (v2 – v1)
produces a differential gain (Gd), which equals R2/R1
...
Take ECG for example, the wires from patient to ECG machine are
about 1 ~ 2 m in length and are exposed to different interference such as power line
interference
...
(2
...
The output of the amplifier solely depends on the input
from the patient
...
From Eq
...
56) we know that only different signals input
into the differential amplifier will be amplified
...
No differential amplifier perfectly rejects the common-mode voltage
...
57)
In real applications a CMRR greater than 100 may be acceptable, depending on
the situation
...
To measure CMRR, We have to know both Gd and Gc
...
Then we can
connect one input to ground and apply a voltage to the other one
...
With these two numbers, we can calculate the CMRR from Eq
...
57)
...
Title
As with the inverting amplifier, we must be careful that resistances external to
the op amp circuit do not affect the circuit
...
This is especially a problem when the added impedance fluctuates (for
example, skin resistance fluctuates)
...
31
...
Thus, there is no loss of voltage
...
31 Differential amplifier attached to a differential voltage that contains varying
impedances
...
R4 = 1 kΩ
R5 =1
...
32 Differential amplifier for Example 2
...
13 For the differential amplifier in Figure 2
...
Using KCL, we can solve for vo
...
v3 =
R3
1 kΩ
8V =
8V =6V
(R1 || R2 ) + R3
(1 kΩ || 500 Ω ) + 1 kΩ
Section No
...
4 V − v3 v3 − vo
=
R4
R5
4 V − 6 V 6 V − vo
=
1 kΩ
1
...
2
...
The voltage output flips from one saturation limit to the other as the negative input of the
op amp passes through 0 V
...
Otherwise, the output is the positive saturation voltage
...
The simplest comparator is the op amp itself
...
However the circuit in Figure 2
...
R1
Saturated
voltage
vi
vo
−vref = vi
−
A
vref
+
R1
(a)
vi
vo
(b)
Figure 2
...
(b) The input–output characteristic of the comparator in (a)
...
Because the current
flows from vi to vref through two equal resistors, the voltage at the negative input is their
average value (vi + vref ) 2
...
Because the op amp is open loop and its
gain is infinite, the output voltage vo saturates at the negative saturation value, which is
usually about –13 V
...
An application of the comparator is for detecting heartbeats from the ECG signal
as shown in Figure 2
...
The normal ECG signal contains a P wave, a QRS complex, and
38
Chapter No
...
The QRS complex normally has a much larger amplitude than the other two
waves
...
Every time a QRS complex passes through the comparator, the comparator gives
out a pulse, which corresponds to the heart beat
...
R
Threshold
T
P
Q
S
Figure 2
...
2
...
7 Frequency response
An ideal op amp has unlimited bandwidth; its gain is same for low frequency and high
frequency
...
Each of the stages has some stray capacitance or junction capacitance associated
with it
...
Figure 2
...
It would appear that an open-loop op amp has very poor frequency response,
since its gain is reduced when the frequency exceeds 10 Hz
...
Instead, we introduce large negative
feedback to control the gain of the amplifier circuit
...
35), the frequency response is flat up to 100 kHz and is
reduced above that frequency
...
Title
Gain
Circuit bandwidth
Ideal
gain
Typical open
loop gain
Circuit gain of 10
10
1
39
100
102
104
Frequency (Hz)
106
Figure 2
...
However the in circuit bandwidth is larger than the open loop bandwidth
...
The gain–bandwidth product is the product of gain and bandwidth at a
particular frequency
...
35 shows that the unity gain bandwidth is 1 MHz
...
Thus, for any amplifier circuit, we can obtain the bandwidth by dividing the unity gain–
bandwidth product by the amplifier circuit gain
...
3 Filters
To obtain a specific output from a device, it is sometimes necessary to electronically sort
through and pick out exactly what is desired from the incoming mass of signals
...
In most applications, the signal we obtain contains more frequency
components than we want, so we use a filter to reject undesired components
...
It also has oscillator circuitry (band pass filter) to tune to
different radio stations
...
More specifically,
a filter is an electronic circuit that, by design, attenuates sinusoidal voltage signals at
undesired frequencies and passes signals at preferred frequencies
...
Similarly, in the case of biomedical
applications, filters are useful when recording physiological signals such as the ECG
(electrocardiogram) and EEG (electroencephalograph)
...
3
...
Generally a filter is inserted between an input source and an output
...
Title
vi = Vm sin(ωt + φ )
vo = Vm T (ω ) sin(ωt + φ + θ (ω ))
(2
...
Thus the filter multiplies the amplitude of the input sine wave by |T( ω)| and adds
to the phase of the sine wave θ(ω)
...
For example, the ideal low-pass filter has a magnitude response of
1
T( f ) =
0
if f < f c
if f ≥ f c
(2
...
The low-pass filter passes all frequency components lower than fc and rejects all
frequency components higher than fc
...
Figure 2
...
All these filters have a passband, where the
filter passes the frequency components, and a stopband, where the filter rejects or
attenuates the frequency components
...
Title
T(f)
41
T(f)
PB
1
...
0
0
...
1
0
...
01
100 f
fc 10
10 fc
1
(a)
T(f)
(b)
100 f
T(f)
PB
1
...
0
0
...
1
0
...
01
100 f
1
(c)
f1
10
f2
100 f
(d)
Figure 2
...
(b) High-pass filter
...
(d) Bandstop filter
...
The closer the actual circuit
characteristics approach the ideal response (i
...
the steeper the transition band), the better
the approximation
...
2
...
2 Low-pass filter
Low-pass filters pass low-frequency signals and attenuate high-frequency signals
...
The first-order RC and RL networks are approximations of a low-pass filter
...
37 shows the RC and RL filter
...
Title
R
L
+
vi
−
−
(a)
+
+
C
vo
−
+
vi
R
vo
−
(b)
Figure 2
...
(a) RC circuit
...
For the RC filter in Figure 2
...
60)
where
ωc =
1
RC
(2
...
37(b), we have
T (ω ) =
R
1
=
R + jωL 1 + j ω ωc
(2
...
63)
The magnitude and phase responses of these filters are similar to those in Figure
2
...
At ω = ωc (f = fC), the magnitude is 1 2 times the magnitude at ω = 0
...
This frequency is also known as the half power
frequency because at ω = ωc the power delivered to the load is half of what it is at ω = 0
...
A combination of unshielded ECG
electrode leads and long electrode-to-amplifier connecting wires causes RF signals from
other medical equipments to couple to the amplifier
...
However, frequency
components of the ECG also lie below 150 Hz
...
Title
43
through a low-pass filter before it is amplified in order to filter out radio-frequency
signals
...
37(a), which will minimize RF interference
...
3
...
38)
...
38 High pass filter
...
(b) RL circuit
...
64)
where
1
RC
R
ωc =
L
ωc =
for the RC circuit
(2
...
36(b)
...
The ECG signal always has some dc offset and low-frequency artifacts due to
the electrodes
...
05 Hz is used to filter the
signal
...
2 MΩ and a capacitor of 1 µF can be used to make a high-pass
filter that passes frequencies only higher than 0
...
2
...
4 Other filters
More complex circuits, such as second, third, or higher order circuits, can be used to
make the changes in magnitude from passband to stopband more abrupt
...
Title
Second order circuits, such as RLC circuits, can be used to realize bandpass and
bandstop filters
...
For example, a device requires a bandpass filter with corner frequencies ω1 and
ω2 ( ω1 < ω2)
...
These two filters can be cascaded so the
signal will first go through the low-pass filter and then through the high-pass filter
...
As a result, only the frequency
components between ω1 and ω2 will pass through the cascaded filter
...
39)
...
39 A low-pass filter and a high-pass filter are cascaded to make a bandpass filter
...
However, keep in mind that the response of cascaded filters is more
complex than that for a single filter
...
4 Analog-to-digital (ADC) and digital-to-analog (DAC) conversion
The past sections discuss analog signals, which are usually continuous in amplitude,
phase, and time
...
The most common digital system employs two
number values and is defined as a binary system
...
The simplest binary system is a switch to control light
...
When the switch is open and then the
light is turned off, the state is 0
...
The main advantage of digital signals is their high error tolerance
...
For example, in TTL logic circuits, we define a voltage of 4 V to 5 V to be high and
0 V to 1 V to be low
...
0 V and 4
...
If a high state
(5 V) signal is corrupted to 4
...
0 V
...
Section No
...
They
are employed in almost every aspect of electronics, including communications, control,
instrumentation, and computing
...
The circuit complexity of a digital IC ranges
from a small number of transistors (~100 to 10,000) to a complete computer chip (42
million transistors for a Pentium 4 chip)
...
4
...
D
...
A decimal number is represented by a string of digits
...
For example, the decimal number of 215, can be computed as
215 = 2 × 102 + 1 × 101 + 5 × 100
Conventionally, we only write the digits and infer the corresponding powers of
10 from their positions
...
A1 A0
(2
...
The decimal number system is base 10 because the coefficients are multiplied by
powers of 10 and the system uses 10 distinct digits
...
+ A1r1 + A0 r 0
(2
...
A1 A0 )r
(2
...
These are base-2, 8, and 16 number systems, respectively
...
Title
The binary number system is a base-2 system that uses the digits 0 and 1
...
g
...
A binary number can be converted to a
decimal number using Eq
...
67)
...
The
remainders at every division form the binary number
...
For example
11 ÷ 2 = 5 with remainder 1 (LSB)
5÷2 = 2
1
2÷2 =1
0
1÷ 2 = 0
1 (MSB)
so
(11)10 = (1011)2
Binary digital impulses, alone, appear as long strings of ones and zeros, and
have no apparent meaning to a human observer
...
Examples
of this output might be a computerized voice, a picture, or a voltage to control
mechanical motion
...
4
...
Often an analog signal must be sampled discretely with an analog-to-digital
converter (ADC)
...
A digital signal needs to be converted to an analog signal with a digital-toanalog converter (DAC), since many devices need an analog signal for controlling,
monitoring or feedback
...
The DAC changes digital input to analog output
...
40 shows the static
behavior of a 3-bit DAC
...
The
maximum analog output is 7/8 of the reference voltage Vref
...
The difference between the consecutive analog outputs is
Section No
...
In general, for an n-bit DAC or ADC, the
resolution is
resolution =
1
Vref
2n
(2
...
40 The ideal static behavior of a 3-bit DAC
...
Equation (2
...
DACs are available in 4, 8, 10, 12, 16, 20 or more bits
...
A variety of circuit configurations are suitable for a DAC
...
Figure 2
...
48
Chapter No
...
41 is the reference voltage of the DAC
...
The accuracy and stability of the reference should be carefully
considered in the circuit design
...
The digital inputs are decoded by the decoder and
the corresponding switch is closed
...
Voltage scaling is suited to IC technology because this technology is optimized
for making many copies of the same structure
...
The output of the DAC is discrete and not continuous
...
Interpolation could be implemented by an
electronic circuit with a voltage holder, linear interpolation, or low-pass filter
...
Title
b2
b0
3-to 8 decoder
Vref
R
b1
49
7
6
5
4
3
2
1
0
R
R
Vo
R
R
R
R
R
Figure 2
...
2
...
3 Analog-to-digital converters (ADC)
Many signals used in biomedical engineering such as voltage, temperature, pressure,
strain, flow and speed, will originally be in analog form
...
The objective of an
ADC is to convert analog input data to an equivalent output digital word
...
Figure 2
...
Title
characteristic of a 3-bit ADC
...
42 shows that the resolution of an ADC depends
on the number of bits of the ADC
...
(2
...
111
110
Digital output
101
100
011
010
001
000
0/8
1/8
2/8
3/8
4/8
5/8
6/8
7/8
Vref
Figure 2
...
Many circuit configurations could be employed in an ADC, such as a counter
ADC, dual slope ADC, successive approximation ADC, or parallel ADC
...
Figure 2
...
It
consists of a comparator, a DAC, and digital control logic
...
This digital value
is sent to the DAC and generates an analog value of 0
...
The comparator compares
this generated value with the input analog signal
...
Otherwise, the MSB is changed to 0
...
Section No
...
43 Block diagram of a typical successive approximation ADC
...
44 shows the possible conversion paths for a 3-bit converter
...
Vout
111
110
101
100
1/2 Vref
011
010
001
0
1
111
110
101
100
011
010
001
000
2
3
4
Conversion cycle
Figure 2
...
2
...
A continuous signal is converted into a sequence of samples by the ADC
...
Title
sequence is processed by algorithms to yield an output sequence
...
In some cases, the input samples can be stored in memory and the processing
will be implemented after all the samples are obtained
...
Compared with analog signal processing, digital signal processing has some
advantages: (1) A digital filter is highly immune to interference because of the way it is
implemented (digital signals are far less susceptible to noise than analog signals)
...
(3) With the help of modern computers, digital
signal processing is much more flexible and powerful than analog signal processing
...
Because of these advantages, digital signal processing is widely used in
communication systems, radar and sonar, speech and video coding and enhancement, and
biomedical engineering
...
The greatest drawback is
its relatively slow speed
...
One is the sampling speed
of the ADC and DAC
...
The other is the speed of the signal processing hardware
...
In digital signal processing, it
depends on the complexity of the algorithms and the clock speed of the processor
...
5
...
Digital signals are discrete in time
and amplitude
...
Such sequences are usually
obtained by the periodic sampling of an analog signal xa(t)
...
70)
where T is the sampling period and its reciprocal is the sampling frequency
...
45(a) shows a segment of a sine wave and Figure 2
...
Section No
...
45 (a) Continuous signal
...
2 s
...
5
...
We are also assuming
that we will be able to reconstruct the original signal perfectly with just these sampled
points
...
It states that,
for a continuous band-limited signal that contains no frequency components higher than
fc, the original signal can be completely recovered without distortion if it is sampled at a
frequency of at least 2fc
...
Suppose the original signal can be represented by function Xc(f) in the frequency
domain and its highest frequency component is fc
...
71)
54
Chapter No
...
Figure 2
...
We know the sampled signal consists of periodically
repeating copies of Xc(f)
...
Figure 2
...
In Figure 2
...
This overlap will corrupt the
original signal and we will not be able to reconstruct the original signal from the sampled
signal
...
72)
Here we present an example of a moving window digital filter for an ECG signal
...
We can use a low-pass digital filter to attenuate the
EMG using the following equation
y[n] =
1
( x[n] + 2 x[n − 1] + x[n − 2])
4
(2
...
This is more flexible than the analog filter, which would
require a change in components or even construction of a new circuit
...
Title
fC
Frequency
Sampling
function
Magnitude
(a)
fS
2fS
Frequency
2fS
Frequency
Sampled
signal
Magnitude
(b)
fS−fC
fC
fS
Low-pass
filter
Magnitude
(c)
fn
Frequency
Reconstructed
signal
Magnitude
(d)
fC
Frequency
(e)
Figure 2
...
(b) Spectrum of sampling function
...
(d) Low-pass filter for reconstruction
...
2
...
In the last
twenty years, computer technology, especially microcomputer technology, has had a
significant impact on bioinstrumentation
...
Title
computers), and microprocessor-based (or micro-controller) systems
...
2
...
1 Structure of a microcomputer
A microcomputer is composed of its CPU (central processing unit), memory, I/O devices,
and buses, as shown in Figure 2
...
Bus (address, data, control signal)
ROM
RAM
CPU
I/O
Figure 2
...
The CPU plays an important role in a computer
...
The most commonly used
CPU in microcomputers is the Intel Pentium 4, which contains 42 million transistors on
one chip
...
The core programs, such as startup instructions and interface instructions for the CPU, are generally stored in ROM
...
Because it holds basic programs,
a modern microcomputer contains tens of kilobytes of ROM
...
Data
and instructions are also stored in RAM
...
In 2002, most computers have
more than 256 megabytes (MB) of RAM, with some having several gigabyte (GB)
memory
...
There may be one or more functionally separate buses linking the various
microcomputer modules
...
47)
...
The first IBM PC had an Intel 8088 with a clock speed of
4
...
In 2002, the Intel Pentium 4 has a clock speed of 2
...
Intel or other
companies will manufacture much faster chips in the future
...
These devices can be divided into several categories
...
A user gives the computer instructions or data through these devices
...
Section No
...
They are used to permanently store software and data on mass
storage media
...
Network
devices include a modem or network card, and a network
...
In bioinstrumentation, ADC and DAC devices are widely used to collect the
data for processing and to send out signals to control other equipment
...
6
...
For example, a clinical ECG monitoring system
contains a microprocessor, ROM for a program, RAM for data and an I/O port for ECG
signals
...
When something abnormal occurs, it gives out an alarm from a speaker and
light signals
...
The
advantages are its small size and flexibility
...
2
...
6 discussed the components of a computer system
...
) describe the hardware of the computer
system
...
The computer itself can do nothing without software
...
Figure 2
...
It is the application software that gives the computer its bioinstrumentation
abilities
...
Title
Problem
Application software
Editor
Complier
Linker
Operating System
CPU
Figure 2
...
Two aspects should be considered for developing a biomedical system: (1) the
choice of operating system to support the task, and (2) the choice of the programming
language to implement the application
...
2
...
1 Operating system
The operating system (OS) is a set of procedures that handle the resources of the
computer system
...
The OS manages the file system control, CPU control, memory control and system
security
...
The operating system also provides some frequentlyused functions so that users can work more efficiently
...
In a
computer, there are several storage media such as a floppy disk, hard disk, or tape
...
The OS
provides an interface between the user and media
...
The OS takes care of the details automatically
...
Below is a brief discussion of three common operating systems: Unix,
DOS/Windows, and Mac
...
It is very flexible, provides the
capability to maximally manipulate a computer system, and gives excellent control of
input/output and other facilities
...
e
...
Because of this great flexibility, Unix requires considerable expertise to use all of its
Section No
...
Different hardware companies (such as HP, IBM and others) provide their
own versions of Unix for their products
...
The Macintosh is a computer hardware/software system by Apple
...
Macintosh is equipped with a very
easy to use graphical user interface (GUI) by sacrificing a great deal of direct user control
of the hardware system
...
Without training, an
individual can sit down and quickly learn to use the Macintosh because of its intuitive OS
...
It
became the most popular operating system on personal computers because of the wide
use of the IBM PC
...
1, NT, 2000,
XP), which has graphical user interface
...
A typical need for bioinstrumentation is the ability for real-time processing
...
Sometimes this is critical,
especially in the intensive care unit of a hospital
...
The Unix system is not
desirable because of its multi-user/multitask property
...
2
...
2 Programming languages
The OS takes care of talking to the hardware but the user still has to give the computer
instructions on how to implement the solution (i
...
program the computer)
...
For
example, the binary code for PC machines that use DOS cannot be used on Macintosh
machines
...
When the computer was first invented, engineers had to
remember instructions in binary code and write their own programs in binary format
...
The codes developed in the programming
language are called source codes
...
One advantage of programming languages is
ease of use
...
There are numerous programming languages, but all languages can be classified
in one of two categories
...
Every
instruction in assembly language corresponds to a binary instruction code for the CPU
...
Assembly language can achieve the
greatest run-time performance because it provides the direct manipulation of the
60
Chapter No
...
However it is also the most difficult language to write since we have to think
about the problem in the way the processor does
...
Once we want to use another system, we have to write the code
again from scratch
...
The
instructions are similar to the way we think of the problem and programs are relatively
easy to write
...
The tradeoff
is that the programs usually are not as efficient as those in assembly language, especially
for real-time processing
...
FORTRAN was developed for scientific calculation (FORmula TRANslation)
...
The C language is the most popular language and is used to develop Unix
systems
...
C++ is a modern version of the C language
and allows object-oriented structure
...
There are two other special languages worth mentioning
...
It is optimized for laboratory
applications
...
Thus,
unlike traditional programming by typing command statements, LabVIEW is a purely
graphical, block diagram language
...
MATLAB is general purpose software for matrix manipulation
...
MATLAB is very useful for
digital signal processing, which in turn is very important for biomedical instrumentation
...
7
...
Such a description should be
precise enough to be used in a completely automatic manner (i
...
by a computer)
...
There are several aspects of the correctness of an algorithm
...
Also for every satisfying input, the
algorithm should execute to the end and not abort in the middle
...
The algorithm should also terminate in a finite number of steps
...
Another consideration for an algorithm is its efficiency
...
Before implementing an algorithm on a computer, we
have to investigate whether it is feasible to use the algorithm to solve the problem
...
Title
61
of known algorithms grow too computationally expensive as the size of the input
increases
...
2
...
4 Database systems
A database is a collection of stored operational data used by applications
...
The database itselfa collection of data stored on
some storage media; A set of ordinary programs for users to get access to the data for
performing the functions such as retrieving, updating, inserting and deleting; The
database is integrated, which means that it contains data for many users
...
Why are databases important? One general answer is that they provide users
with centralized control of the operational data
...
A typical use of database systems is in hospitals
...
Even if it is the first time
that patient is admitted to a certain hospital, doctors can obtain his or her former
information from the other hospitals using a database system
...
First, the amount of data redundancy in the stored data can be reduced
...
For example, a patient’s files for different doctors all contain his or her name,
social security number, address, age, gender and so on
...
Second, the data can be shared
...
Third, data security restrictions can be applied
...
This can protect data from abuse
...
Most applications are data-dependent, which means the way in which the data
are stored and the way in which they are accessed are both dictated by the application
...
By using the same commands, the application
can get access to different databases without the knowledge of the physical storage and
access format
...
The architecture of the database determines the performance of the application
...
There are different ways to
implement a database
...
62
Chapter No
...
8 Display devices
For improved understanding of the processes of the instrument or of an object, it is
important to display the results as either characters or graphically
...
The
main part of an oscilloscope is a cathode ray tube (CRT)
...
49 is a sketch of a
CRT
...
Electrons are accelerated by the axial high voltage,
hit the screen, and light is emitted due to fluorescence
...
The deflection control unit controls the location of the
spot on the screen
...
The heart of a TV monitor is also a CRT, but it is a little different from the CRT
for the oscilloscope
...
If many electrons hit the spot, it will emit more light and we observe that the location is
white
...
The
deflection control unit controls the location of the spot (scanning) and we can see an
image on the screen
...
These three colors compose the different colors we
observe
...
49 Sketch for cathode ray tube (CRT)
...
Section No
...
9 Recording devices
In many applications, we want to save the data permanently as record
...
A strip of paper travels at a constant speed (i
...
, 5 cm/s, 10 cm/s) and an
ink pen is in contact with the paper
...
It records
(plots) the electric signal on the paper
...
A tape recorder is also a common device for recording analog signals
...
The main difference being
that we record the input electric signal instead of music
...
In recent years, technological advances have made digital techniques more
widely used in recording signals
...
It also has an interface that can be used to save data on a floppy disk or
to send data to a computer, which can save the file
...
Another commonly used device is a PC data acquisition system, such as
LabVIEW Biobench
...
It can also display the signal on the screen for manual or
automatic measurement, in which case it is similar to the oscilloscope
...
This makes the system more flexible than an oscilloscope
...
10 References
Alexandridis, N
...
1984
...
Rockville, MD:
Computer Science Press
...
, Kreczmar, A
...
1991
...
Reading, MA: Addison-Wesley
...
S
...
Elementary Linear Circuit Analysis
...
Date, C
...
1977
...
Reading MA: Addison-Wesley
...
B
...
Operating System Principles
...
Hilburn, J
...
and Julich, P
...
1979
...
Englewood Cliffs, NJ: Prentice-Hall
...
N
...
Electric Circuits
...
Oppenheim, A
...
and Schafer, R
...
1989
...
Englewood
Cliffs, NJ: Prentice-Hall
...
J
...
1993
...
Englewood Cliffs,
NJ: Prentice-Hall
...
Title
Webster, J
...
(ed
...
Medical Instrumentation: Application and Design
...
New
York: John Wiley & Sons
...
11 Problems
2
...
2
2
...
4
2
...
6
2
...
8
2
...
10
2
...
12
2
...
14
2
...
16
2
...
18
One ampere flows through an electrosurgical dispersive electrode that has a
resistance of 50 Ω
...
Discuss the possibility of burns
under the electrode
...
Calculate the equivalent resistance for a 400 Ω and 1 kΩ resistor in parallel
...
An operational amplifier has limited current output of 20 mA
...
From a 2 kV source in series with a 20 kΩ resistor, calculate the time required to
charge a 100 µF defibrillator capacitor to 1
...
Calculate the time response of a 10 kΩ, 30 mH high-pass and low-pass RL circuits
(similar to the two cases of RC circuit, but τ = L/R) to a 1 V step input
...
If a voltage of 2sin(2ωt) is
applied, sketch the waveform of the output and label axes
...
If a voltage of 2sin(2ωt) is
applied, sketch the waveform of the output and label axes
...
30, R1 = 1 kΩ, the two R2 are 10 kΩ and 9 kΩ respectively (the one
connected to ground is 9 kΩ)
...
Design a comparator to detect an amplified electrocardiogram whose Q wave is 0
V and R wave is 4 V
...
Calculate by what factor it reduces 1 MHz interference from an
electrosurgical unit
...
Explain the advantages and disadvantages of digital signals versus analog signals
...
For a signal that contains frequency components up to 1
kHz, calculate the minimum sampling frequency
...
The students randomly select a DSP that takes 360,000 samples per
minute
...
Explain the function of the following devices in a microcomputer: CPU, RAM,
ROM, I/O port, data bus
...
Title
65
2
...
Also state on
which platform each operates
...
20 Describe how a CRT functions
...
21 Go to www
...
org/BMEnet/
...
Find an industrial (not university)
job and describe in a few sentences
...
22 A radio-frequency (RF) catheter is introduced into the heart to inject power at 500
kHz to ablate (destroy) tissue that causes tachycardia
...
Design a filter that reduces this interference to
0
...
3
Analysis of Molecules in Clinical Medicine
Mat Klein
Methods used to measure molecules in clinical chemistry, toxicology, and pulmonary
medicine, have a tremendous impact on the fields of bioengineering and medicine
...
This chapter presents various techniques used to measure different molecules in the body, along with the importance and
impact of their measurement
...
1 Spectrophotometry
Photometry is based on measurements of electromagnetic energy emitted, absorbed, or
transmitted under controlled conditions
...
Spectrophotometry is based on the use of light intensity measurements at a particular wavelength or a discrete portion of wavelengths to determine the concentration of the desired molecules in solution by the amount of radiant
energy absorbed by the desired molecules
...
1
...
Figure 3
...
Radiant energy sources
The purpose of the light source in a spectrophotometer is to provide incident light of sufficient intensity to the sample
...
The most common source for substances that absorb
3-1
3-2
Chapter 3 Analysis of Molecules in Clinical Medicine
radiation in the visible, near infrared, and near ultraviolet regions, is a glass enclosed
tungsten filament
...
To increase the lifetime of the tungsten filament, there is usually low-pressure iodine or bromine vapor in the bulb
...
High-pressure hydrogen or deuterium discharge lamps are
sufficient for measurements in the near ultraviolet region
...
Two advantages deuterium lamps have is that they produce about three times the light intensity of hydrogen lamps and have a longer lifetime
...
These lamps may require thermal insulation with or without auxiliary
cooling to protect surrounding components since they become extremely hot during operation
...
1 Block diagram of a single beam spectrophotometer
...
The exit slit is moveable in the vertical direction so that those portions of the power spectrum produced by the power source (light source) that are to be used can be selected
...
The
term monochromator refers to the dispersing device and associated slits and components
used to isolate the desired wavelength
...
Both components separate white light into a
spectrum from which the desired wavelength may be chosen
...
As white light passes through the prism,
shorter wavelengths are refracted, or bent, more than longer wavelengths
...
A diffraction grating separates white light, such as that produced by a tungsten
filament, into a continuous linear spectrum
...
1 Spectrophotometry
3-3
with a polished aluminum or aluminum–copper alloy
...
The amount of
bending is dependent upon the wavelength of the light
...
Wave fronts are formed as the light waves move past the corners
...
Cuvette
Spectrophotometry ascertains the absorption of the desired molecules (the solute) in a
solvent
...
Cuvettes can be round, square, or rectangular, and have a light path of constant length,
most commonly 1 cm
...
They are made from glass tubing, are not
perfectly round or polished, and contain surface aberrations
...
Detector and readout device
There are two requirements for a detector of radiant energy in a spectrophotometer
...
The most common devices used to detect the amount of
radiant energy leaving the cuvette include barrier layer cells, photodiode arrays, and photomultiplier tubes
...
A readout device displays the electric energy from the detector onto some type
of scale such as absorbance or transmittance
...
In a direct readout meter, there is a linear
relationship between milliamperes and %T (percent transmittance) and a log relationship
between millivolts and absorbance
...
In a null point system, the meter is calibrated (zeroed) by a potentiometer
...
3
...
2 Theory
The determination of the concentration of a light-absorbing substance in a solution using
a spectrophotometer is based on the discoveries of four individuals
...
Beer and Bernard observed that the concentration of a substance in solution [less
3-4
Chapter 3 Analysis of Molecules in Clinical Medicine
than 10–2 M (molar)] is directly related to its absorbance
...
” (Wheeler,
1998) This relationship is
I = I 010 −aLc
(3
...
2)
Absorbance (A) is exponentially related to the reciprocal of transmittance
...
3)
As the concentration of the substance in solution increases (or decreases), the transmittance varies logarithmically and inversely
...
Let the length of the light path (usually the outer diameter of
the cuvette) be a constant, L, and the concentration of the substance in solution be c
...
4)
where a is in liters per gram times centimeters, L is in cm, and c is in grams per liter
...
Epsilon is a constant corresponding to a 1 molar solution of the absorbing
substance, with a light path of L = 1 cm and a given wavelength
...
5)
3
...
6)
where Au is the absorbance of the unknown concentration and cu is the unknown concentration
...
1
...
This ensures that measurements made with the spectrophotometer are accurate and reproducible
...
1
...
1 lists common molecules measured in the clinical laboratory and their normal
and toxic levels
Molecule
Type of test
Normal levels
US units
(mg/dL)
Normal levels
SI units
(mmol/L)
Toxic levels
(mg/dL)
Total bilirubin
Indirect
Direct
Blood (serum)
0
...
0
0
...
8
0
...
3
High levels result in jaundice
...
4–17
...
4–12 × 10–3
1
...
1 × 10–3
0
...
3
Urea
Blood (serum)
10–20
53–97 × 10–3
62–115 × 10–3
3
...
1
Glucose
Blood
70–105
3
...
8
Adult male:
<50 or >400
Adult female:
<40 or >400
Sodium
Blood (serum)
136–145 mEq/L
136–145
<120 or >160 mEq/L
Potassium
Blood (serum)
3
...
1
<3 or >7
...
0 mEq/L
0
...
1
0
...
2
0
...
2 mEq/L
>45
>4
>100
Table 3
...
NA denotes “not available”
...
1
...
The basic principle is to mimic the function of a capillary blood vessel by perfusing a thin
dialysis tube implanted into the tissue with a physiological liquid
...
Microdialysis is thus a
technique whereby substances may be both recovered from and supplied to a tissue
...
However, the latter feature renders the
technique unsuitable for sampling large molecules such as proteins
...
3
...
Hemoglobin transports oxygen from the lungs, where oxygen tension (partial pressure of oxygen) PO2 is
high, to the tissues, where oxygen tension is low (See Chapter 6)
...
HbO 2SAT=
[HbO 2 ]
[RHb] + [HbO 2 ]
(3
...
Oxygen saturation is calculated
as a percent or fraction
...
8)
Oxygen saturation measurements are made in order to determine the response to
therapeutic intervention (e
...
supplemental oxygen administration or mechanical ventilation) and/or diagnostic evaluation (e
...
the effect of exercise on O2 levels)
...
SO2 can be determined by using spectrophotometry on a venous whole blood
sample
...
An oximeter uses
a spectrophotometer to measure light transmission at two wavelengths to calculate SO2
...
2 Oxygen saturation
3-7
By using four wavelengths, the CO-oximeter also measures carboxyhemoglobin ([COHb])
and methemoglobin ([MetHb])
...
But
then we measure a mixed sample of venous and arterial blood
...
Light emitting diodes (LEDs)
transmit light at 660 nm and 940 nm and a photodiode measures the transmission at the
minimum blood pressure (diastole) and at the maximum blood pressure (systole)
...
The OxiFirst™ Fetal Oxygen Saturation Monitoring System is inserted into the
mother’s uterus and placed against the fetus’s temple or cheek when fetal heart rate indicates that the baby may be in distress
...
3
...
Bilirubin is waste resulting from the removal of old red blood cells
...
Each subunit has one chain of protein,
also referred to as globin, and one molecule of heme
...
When a
red blood cell is destroyed, the body recycles the iron
...
Unconjugated bilirubin is produced in
the spleen when the porphyrin is broken down
...
Unconjugated bilirubin is produced when red blood cells are destroyed
...
This condition is
known as jaundice
...
In general, blood
samples can be taken and used to measure bilirubin concentration when diagnosing liver
and/or biliary disease
...
This technique is used to measure total and conjugated
bilirubin in blood serum or plasma
...
3
...
Lactic acid is a metabolic intermediate involved in many biochemical
processes including glycolysis and gluconeogenesis (the formation of new glucose from
3-8
Chapter 3 Analysis of Molecules in Clinical Medicine
noncarbohydrate sources)
...
Some of these diseases include diabetes mellitus,
neoplasia (tumor growth), and liver disease
...
Lactic
acidosis (very high levels of lactate in the blood) is caused by hypoperfusion: a decreased
blood flow through an organ
...
Lactic acid is measured from a sample of whole blood or plasma
...
8
...
This latter reaction is
lactate oxidase
L-lactate + O2 → pyruvate + H2O2
(3
...
10)
Coupling these two enzymes enables measurements of lactate as low as 80 nM (Canh,
1993)
...
3
...
During this conversion, creatine is produced
...
However, when creatine needs to be
excreted, it is dehydrated and converted to creatinine
...
Therefore, it
is an ideal candidate for being used to measure the condition of the kidneys
...
Elevated levels of
creatinine in the blood result from muscle damage or as a result of strenuous physical
activity
...
Therefore, measurement of creatinine in blood
(serum) is a rough estimate of the health of the kidneys
...
The most common method used to measure creatinine is based on the Jaffe reaction
alkaline
Creatinine + Picric Acid → Picrate–creatinine Complex
(3
...
5 Creatinine
3-9
In an alkaline (basic) medium, creatinine and picric acid form a red–orange compound
whose structure has been postulated but not confirmed
...
The complex can
be measured spectrophotometrically at wavelengths between 505 to 520 nm
...
Most methods use a 0
...
One of the main
problems with the Jaffe reaction is that it is nonspecific when used to measure creatinine
in plasma
...
As a result, several modifications
exist which increase the specificity of the reaction (Burtis and Ashwood, 1994)
...
3
...
Figure 3
...
Protein
Amino acids
Proteolysis
Liver
NH3
Ammonia
Removal of NH2
Urea
Enzymatic
synthesis
Figure 3
...
The liver produces urea by first
breaking proteins down into their building blocks, amino acids, by a process that breaks the peptide
bonds between the amino acids (proteolysis)
...
Over 90% of urea is excreted through the kidneys to the urine
...
Ammonia is produced by the liver as a waste product of gluconeogenesis and
the liver converts it into urea
...
Although the urea nitrogen measurement is often referred to
as BUN, it is never measured from whole blood
...
An above normal amount of urea in the blood is an indicator of decreased kidney function, and therefore possibly kidney disease
...
The first method measures urea indirectly by quantifying the concentration of the ammonium ion spectrophotometrically
...
12)
→
3-10 Chapter 3 Analysis of Molecules in Clinical Medicine
Two ways of quantifying the ammonium ion concentration are Berthoelot’s reaction and
the enzymatic assay with glutamate dehydrogenase
...
The second method measures urea directly
...
It has been used in several automated systems,
such as the Dupont Dimension 380
...
13)
Diazine can be measured using spectrophotometry and absorbs electromagnetic energy at
540 nm
...
14)
3
...
Diabetes mellitus is a group of
metabolic disorders of carbohydrate metabolism in which glucose is underutilized, producing hyperglycemia (high blood sugar levels)
...
When a person has high blood glucose, glucose shows up in the urine
...
Insulin is one of the hormones that controls whether or not glucose is going to
be taken out of storage and put into the blood, or vice versa
...
Type II patients produce insulin, but cells do not recognize it (i
...
they have
defective insulin receptors)
...
Type II is seen in much older
people, and for many, careful control of diet and exercise will be enough for treatment
...
Self-monitoring of blood glucose is required for diabetic patients, especially
insulin dependent, in order to maintain normal blood glucose levels (glycemia)
...
By regulating blood glucose levels, patients are mimicking the body by providing themselves with the correct
amount of insulin
...
One reason the level of blood glucose needs to be tightly regulated is that glucose is the only source of energy neurons can consume (they do not have the enzymes to
consume anything else)
...
When this
occurs, an individual’s neurons have no source of energy and if low enough, the person
will go into a coma and die
...
When
blood glucose becomes too high, the glucose molecules will denature (alter the shape of)
proteins, such as collagen and hemoglobin, throughout the body
...
7 Glucose
3-11
lining of blood vessels (the basement membrane)
...
This leads to decreased blood flow in the arms and legs
(lower perfusion)
...
Diabetes mellitus is the leading
cause of amputation because decreased blood flow causes tissue to die and damaged
nerves hinder the sensation thus making widespread damage much more likely
...
The
glucose oxidase method is a very popular manual procedure used for self-monitoring
...
3
...
1 Glucose oxidase method
The glucose oxidase method is used in a large number of commercially available strip
tests
...
A strip
test product, One Touch II (Lifescan, Milpitas, CA), depends on the glucose oxidase–
peroxidase chromogenic reaction
...
(3
...
glucoseoxidase
Glucose + 2H 2 O + O 2 → GluconicAcid + 2H 2 O 2
(3
...
peroxidase
o - dianisine + H 2 O 2 →oxidized o - dianisine + H 2 O
(3
...
In the Lifescan system (Figure 3
...
The device
automatically starts and times the test and has a range of 0 to 600 mg/dL
...
7
...
The general reactions are
hexokinase
Glucose + ATP → glucose–6–phosphate + ADP
(3
...
18)
Glucose is phosphorylated to glucose-6-phosphate in the presence of ATP, Mg2+, and the
enzyme hexokinase
...
(3
...
3
...
The NADH produced
absorbs electromagnetic energy at 340 nm and is proportional to the glucose concentration
...
There are
several other techniques based on the hexokinase method (Burtis and Ashwood, 1994)
...
3 LifeScan, Inc
...
3
...
8
...
An amperometric sensor that measures the partial pressure of O2 (PO2)
is the Clark electrode
...
The silver/silver chloride anode is in a phosphate buffer containing potassium chloride to
buffer the hydroxyl ions produced at the cathode (Eq
...
20))
...
4 shows the main
components of the Clark (PO2) electrode
...
19)
At the cathode, the following reaction occurs:
O 2 + 2H 2 O + 4e − 2H 2 O 2 + 4e − 4OH −
→
→
(3
...
According to the Nernst
3-13
3
...
3
...
A cell reaction will spontaneously proceed to the left if the potential for the cell is less
than zero (E < 0)
...
Platinum cathode
Glass rod
0
...
4 In the PO2 electrode, O2 dissolved in the blood diffuses through a permeable membrane
...
, 1987)
...
059
2
log
n
CO
(3
...
E0 is the standard half-cell
potential
...
A dc voltage between 600 and 800
2
2
mV allows the electron transfer reaction between O2 and H2O to occur
...
These steps include the transport of O2 from the solution to the working electrode,
the transfer of electrons from O2 to H2O, interactions between O2 and H2O (the oxidized
and reduced forms of the species of interest), and the transport of H2O back to the solution
...
Because
O2 is consumed at the cathode, there is a concentration gradient from the dissolved O2 to
the cathode
...
The cathode may be vibrated to ensure that fresh O2 is available at the cathode
...
The rate of electrons transferred from O2 to H2O is
directly proportional to the concentration of O2
...
8
...
5)
...
Glucose + O2
H2O2
O2
O2
Glucose oxidase
Glucose acid
Pt cathode
0
...
5 In the glucose enzyme electrode, when glucose is present, it combines with O2, thus
decreasing the O2 that reaches the cathode
...
This glucose
sensor uses the PO2 electrode and the enzyme glucose oxidase immobilized on a membrane
...
22)
Glucose and oxygen react in the presence of the enzyme glucose oxidase
...
(The concentration of glucose is indicated by the
consumption of O2 by the enzyme glucose oxidase
...
A dual oxygen electrode glucose sensor (Peura, 1998) eliminates the problem of
variations in PO2 that the single oxygen electrode is sensitive to
...
An enzyme within a gel covers one electrode, thus depleting oxygen when
glucose is present
...
The amount of glucose is determined as a function of the difference between the
electrode responses
...
8 Amperometric Biosensors for Oxygen and Glucose
3-15
responses
...
A more recent approach to amperometric enzyme glucose electrodes involves
the use of the electron transfer mediator dimethyl ferrocene
...
There are several advantages in using mediators
...
Second, they
allow glucose measurements that are independent of the variations in PO2 of the sample
(Burtis and Ashwood, 1994)
...
6, a reduced
form of the mediator dimethyl ferrocene reduces the oxidized form of glucose oxidase
...
One of the disadvantages of
this technique is that dimethyl ferrocene (as well as all mediators) is not very soluble and
ends up adsorbing to the electrode surface
...
6 The sequence of reactions involved in the mediated reaction of a glucose sensor (Taylor
and Schultz, 1996)
...
The use of the mediator dimethyl ferrocene
reduces the sensor’s dependence on oxygen tension
...
has developed a GlucoseWatch
...
Within the hydrogel, the
extracted glucose undergoes a reaction with the enzyme, glucose oxidase to produce gluconic acid and hydrogen peroxide in the presence of oxygen
...
, 1998)
...
9 Ion-selective electrodes for pH and CO2
Ion selective electrodes are used to measure the activity of a specific ion in a cell or solution
...
In the presence of the specific ion, a membrane potential results which
indicates the amount of ion activity
...
3-16 Chapter 3 Analysis of Molecules in Clinical Medicine
pH = –log10[H+]
(3
...
To prevent pH measurement errors that occur due to other ions, a highly selective H+ glass membrane is desired
...
1 | glass membrane | 2
(3
...
(3
...
When the pH of
the solutions on side 1 and 2 differ, a potential across the membrane develops, V = V1 –
V2
...
The potential of solution 2 can be recorded with a calomel electrode
...
303
RT
) log(a i)
ZF
(3
...
The activity of an
ion, ai, equals the activity coefficient λi times its concentration c
...
26)
Factors such as other ions in the solution and the strength of H+ in the solution
influence λi
...
λi for plasma is about 0
...
74 for K+,
and 0
...
In solutions where the primary ion (H+) is of very low concentration
(µM), the membrane potential is not directly proportional to the logarithm of the activity
of the diffusible ion H+ in solution 1 or 2
...
Or the potential can also be calculated from
E = −0
...
27)
where [H+]i is the concentration of H+ inside the cell and [H+]o is the concentration of H+
ions outside the cell
...
A
stainless steel probe has a silicon chip sensor and can be stored dry
...
Deposited on the substrate between the source and drain is a silicon
electrical insulator
...
9 Ion-Selective Electrodes for PH and CO2
3-17
tween the source and drain
...
The pH can then be derived from
this voltage to a very high level of accuracy
...
The pH
level in the body is more strictly regulated than glucose
...
36
to 7
...
A pH of less than 7
...
If the pH is less than 7
...
A pH greater than 7
...
8 causes the body’s muscles to seize up, a condition known as tetany
...
Molecules in the body, particularly proteins, have sites where protons can associate or dissociate, and when the body’s pH is
altered, the charge of that particular portion of the molecule is essentially changed
...
As a result, proteins do not fold properly and DNA does not form as it
should, among other things
...
With the
exception of vomiting, protons leave the body via the kidney
...
Carbonic acid spontaneously breaks down into water and carbon dioxide
...
An individual can exhale too much or too little carbon dioxide, thus changing the acidity
of the blood
...
Both the lungs and the kidneys regulate the
body’s pH level
...
If the pH level is abnormal, there are three things that can be
measured: carbon dioxide concentration, pH, and bicarbonate concentration
...
If the problem is abnormal CO2 concentration, then we know the problem is
with the lungs
...
Further studies are required for abnormal bicarbonate concentration such as sodium concentration or chloride concentration measurements of the blood
...
Holes in
the membrane permit gas to diffuse through, but block everything else
...
The reaction for this process is
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3–
Since CO2 concentration is proportional to H+ concentration; measurements from the pH
electrode yield PCO2
...
10 Flame photometry
Flame photometry, a subset of emission photometry, is a technique commonly used to
quantify sodium, potassium, and lithium concentrations in bodily fluids
...
Figure 3
...
The purpose of the flame is to provide energy to the elements such that their
valence electrons will be excited from ground states to higher excited states
...
The wavelength(s) of the light emitted by an element is
characteristic of that element
...
The intensity of the light given off is directly proportional to the number of photons being emitted, which in turn is directly proportional to
the number of atoms, or concentration of cations, in the solution
...
7 The flame photometer aspirates a sample containing metal ions and heats it to incandescence
...
In flame photometry, the monochromator and detector are similar to those found
in the spectrophotometer, although the detector is measuring emission as opposed to absorption
...
The
atomizer draws the sample solution containing the cations through an aspirator and into
the flame
...
The
fuel used to generate the flame can be either propane, natural gas, or acetylene mixed
with compressed air or oxygen
...
A
known concentration of lithium is added to the sample
...
3
...
10
...
The purpose of lithium measurement is to measure lithium carbonate, which is used in the treatment of the psychiatric disorder manic depression (also known as bipolar disorder)
...
10
...
To keep these cells
working properly, the amount of sodium and potassium in the body must be regulated
...
Sodium and potassium enter
the body via eating
...
For example, if an individual eats a lot of salt, the excess salt in their blood will be passed in the urine
...
Too much potassium can kill a person by stopping their heart as a result of decreasing the
concentration gradient, and hence the ability to generate an action potential in the heart
muscle cells
...
11 Mass spectrometry
Mass spectrometry is a powerful analytical technique that is used to identify unknown
compounds, quantify known materials, and to elucidate the chemical and physical properties of molecules
...
A mass spectrometer separates a material according to its atomic or molecular mass and the sample of
molecules can be a gas, liquid, or solid, as long as the specimen is not too volatile
...
As far as the scope of mass spectrometry is concerned, many
different techniques and types of instrumentation have been devised to accomplish each
of the above processes
...
3
...
1 Sample inlet
Figure 3
...
Several types of sample inlet systems exist that accommodate certain aspects of the sample such as its temperature, vapor pressure, and its volatility
...
3
...
2 Ion source
Figure 3
...
Many different methods
to ionize the sample exist, one of which is the heated filament
...
Typical current flow is about 500 µA
...
Electron energy is typically 70 to 80 eV
...
Sample inlet
Sampling
device
Interface
Porous plug
Ion
source
Mass
analyzer
Vacuum
system
Detector
ADC
Figure 3
...
By bombarding molecules of the vaporized sample with electrons from a heated
filament, electrons can be removed from the molecules
...
Since the mass of an electron is negligible relative to the mass of a molecule, the mass of the molecular ion remains essentially the same
+
ABC + e − → ABC• + 2e −
− → ABC−
ABC + e
(3
...
11 Mass Spectrometry
Pole of magnet
Filament
3-21
Focusing elements
(electric field)
N
Repeller
e–
Electron trap
(positively
charged target)
To mass
analyzer
S
Pole of magnet
Figure 3
...
The electron collisions with ion ABC (Eq
...
28)) produce
both positive and negative ions
...
For a time span of 0
...
+
ABC• → AB+ + C +
A + + BC +
+
AB• + C (Loss of neutral)
+
(3
...
Not all of the positively charged molecular ions undergo fragmentation
...
An electric field then appropriately focuses and accelerates them into the mass analyzer
...
Figure 3
...
A mass spectrum is a plot that represents the relative ion abundance at each value of m/z (mass to charge ratio)
...
10 The mass spectrum displays the relative abundance of charged molecular ions and
fragments
...
11
...
This is usually done with a magnetic field
...
11 shows the main components of a quadrupole mass analyzer
...
11 A quadrupole mass analyzer accelerates ions from the ion source
...
Ions that do not stabilize collide with the rods and do not reach the detector
...
11
...
, 1995)
...
12 shows the main
components of an electron multiplier
...
11 Mass Spectrometry
3-23
cathode, thus releasing secondary electrons
...
A larger number of tertiary electrons are released and attracted to the second dynode, etc
...
Dynodes
Cathode
Anode
Horn
Collector
Ion+
Dynodes
Quadrupole
mass analyzer
rods
X-ray shield
Figure 3
...
An electron multiplier is sensitive enough to
detect the presence of a single ion
...
(Haven et al
...
3
...
The intensities depend on the medium(s) the waves pass through
...
Spectra are formed by
a spectroscope—an optical instrument that physically breaks up electromagnetic radiation
into its component parts, usually with a prism or grating
...
The majority of carbon dioxide in the body is expired through the lungs as an
end product of the respiration cycle
...
Gases with dipole moments such as CO2, N2O, or
water vapor (H2O), absorb a specific wavelength of light in the infrared region of the
spectrum
...
Carbon dioxide concentration can be measured by passing a particular wavelength of infrared light through a chamber containing a sample of carbon dioxide
3-24 Chapter 3 Analysis of Molecules in Clinical Medicine
and noting the power of the infrared light transmitted to the sample, and the power of the
infrared light transmitted through the sample
...
30)
where Pt is the power per unit area of transmitted infrared light received by the detector,
P0 is the power per unit area of infrared light entering the sample, a is the absorption coefficient, L is the path length of light through the gas, and c is the concentration of gas
...
13 shows the basic components of an infrared spectroscopy system (Primiano,
1998)
...
The detector compares transmission through the sample cell with transmission through a reference cell
...
13 An infrared transmission spectroscope measures the absorption of infrared light by a
sample drawn through the sample cell by a vacuum pump
...
13 Nitrogen by emission spectrometry
The concentration of nitrogen, N2, in a sample of a mixture of gases can be measured by
emission spectrometry
...
Emission spectrometry involves applying a
voltage of 600 to 1500 V dc between two electrodes on opposite sides of an ionization
chamber in which the pressure is low (1 to 4 mm Hg or 150 to 550 Pa)
...
Figure 3
...
25
3
...
14 Emission spectroscopy measures ultraviolet light emitted by ionized nitrogen
(Primiano, 1998)
...
14 Drugs by fluorometry and chromatography
3
...
1 Fluorometry
Fluorescence is the emission of energy in the form of light as a result of the electrons of a
molecule returning to their ground state
...
As
the electrons of the molecule return to their ground states, they fluoresce
...
Thus, fluorometry is defined as measuring the relationship between the concentration of a substance and the intensity of the fluorescence
produced by that compound when it is excited by radiation
...
g
...
Figure 3
...
Although the components of a fluorometer are basically the same as those of a
spectrophotometer, fluorometry is up to four orders of magnitude more sensitive than
spectrophotometry (Wheeler, 1998)
...
When the absorbance of the unknown solution is relatively small,
small errors in the measurement of the zero absorbance solution can cause relatively large
errors in the final determination
...
Though a disadvantage of fluorometry is that measurements are also susceptible to inner-filter effects
...
Primary filter
Cuvette
I0
If
Secondary filter
Detector
Readout
Figure 3
...
The primary filter passes only wavelengths that excite
the fluorescent molecule
...
The secondary filter and detector are at a right
angle to the primary beam in order to avoid direct transmission of the light source through the sample to the detector
...
31)
3
...
32)
We can expand through a Taylor’s series, rearrange, and convert the logarithm base to
yield
IF = φI0 (2
...
Fluorometry is limited by several factors, including concentration of the sample
...
Spectrofluorometers replace the fixed secondary filter with an emission monochromator and sweep it at 5 to 50 nm increments to yield a spectrum of emission magnitude versus wavelength
...
In time-resolved fluorometers, long-lived
fluorescent molecules are excited by pulsed light and their decay is monitored over 0
...
Laser-induced fluorometers measure emission from individual fluorescent or
fluorescent-labeled molecules, cells, or particles passing through a flow cell cuvette
...
14
...
Some components include drugs such as antibiotics, therapeutic drugs, or abused drugs
...
Chromatographic separation relies on the components in a mixture being
separated by the stationary phase
...
The greater the affinity for the stationary phase, the less a component will move
...
In order for separation to occur, the mobile phase must move past the stationary
phase
...
The components in a chemical mixture react differently with each of the phases in the column
...
As a result, the components in the mixture become separated in
the column
...
3-28 Chapter 3 Analysis of Molecules in Clinical Medicine
A chromatogram is a plot of the relative amounts of the components in the mixture as a function of the amount of time it takes for them to get washed (eluted) off the
column or pass through the column
...
The number of peaks plotted indicates the complexity of the mixture
...
Measuring the area under each peak yields a quantitative evaluation of the relative concentrations of the components
...
14
...
GC is used to separate compounds that are volatile at the temperature in the
column of the chromatograph
...
Figure 3
...
Column
Column oven
Injector
Flow meter
Detector
Flow control
Carrier gas
Figure 3
...
There are several advantages of GC: it is fast, extremely sensitive, and requires a very
small sample
...
The carrier gas has very little effect on the rate of retention of components in the solute
...
14 Drugs by Fluorometry and Chromatography
3-29
Column
The column in GC is usually enclosed in an oven with computerized temperature regulation
...
When the column is heated over a range of temperatures, components in the solute with lower boiling points will elute off the column
first, followed by components with higher boiling points
...
The column (stationary phase) separates the components in the sample because
they each have different retention times
...
Packed columns are typically between 1
and 4 mm in diameter and 1 to 4 m in length (Burtis and Ashwood, 1994) They are
packed with a solid support material such as diatomaceous earth (a type of algae with cell
walls containing Ca++) and then coated with a liquid (the stationary phase)
...
2 and 0
...
In capillary columns, the inner wall of the tube is coated
with the stationary phase
...
The advantage of
glass is that it is inert and the advantage of stainless steel is that oxide films do not develop on the surface, thus preventing reactions with solutes
...
The advantage of packed columns is that they can handle a large sample size and
require less maintenance
...
It does this by
providing an electric signal proportional to the amount of the component coming off the
column
...
The combination of mass spectrometry and GC is ubiquitous in clinical chemistry laboratories in hospitals and is a very
powerful tool
...
17 shows that the detector yields a chromatogram
...
The volume that has passed before the peak is
the peak volume and is given by Vr(A) = trF
...
An efficient column minimizes band spreading
...
The width of a Gaussian peak at 1/2 its height, w1/2, is 2
...
54[Vr(A)/w1/2(A)]2
...
17 In chromatography, the peak appears after retention time tr
...
33)
where w(A) and w(B) are the peak widths measured at the corresponding base
...
8 and baseline separation occurs for Rs > 1
...
, 1994)
...
1 For a gas chromatograph with a flow rate of 1
...
5 min
...
5 L and the peak width for solute B is 1
...
(3
...
w(A) = 0
...
5 L
Vr (A) = t rA F = 1 min × 1
...
5 L
Vr (B) = t rB F = 2
...
5 L/min = 3
...
75 L − 1
...
25
[ w(A) + w(B)]/2 [0
...
5 L] 2
Since Rs > 1
...
3
...
Combining the gas chromatograph
with the mass spectrometer (MS) is a powerful tool
...
When interfacing gas chromatography with mass spectrometry, several compatibility issues arise
...
In most cases, an interface is required to minimize these incompatibilities
...
For
a packed column, the jet separator is commonly used
...
The advantage of the direct interface
is total inertness from the head of column to the ion source
...
e
...
5 m narrow bore (0
...
3 mm) columns
...
It can remove about
90% of a light carrier gas such as helium, yet pass all but a few percent of the heavier
sample compounds
...
As the gas from the GC passes through a nozzle expanding into an evacuated region, the momentum of the heavier sample gas is increased
relative to the carrier gas
...
The jet separator operates with maximum efficiency at column flows of 25
mL/min and is capable of transmitting a wide range of molecular weights from permanent gases to high molecular weight compounds
...
3
...
4 Liquid chromatography
Liquid chromatography (LC) is a type of chromatography that uses a liquid of low viscosity as the mobile phase
...
One commonly
used type of liquid chromatography is high-performance liquid chromatography (HPLC)
...
Figure 3
...
An HPLC instrument operates by injecting a liquid sample via a syringe into the
stream of mobile phase that is being pumped into the column
...
The detector can observe changes in refractive
index, UV light absorption and fluorescence
...
3-32 Chapter 3 Analysis of Molecules in Clinical Medicine
Flow
splitter
Vacuum
pump
Solvent 1
Sample
injection port
Solvent 2
Degasser 1
Pressure
gage
Degasser 2
Mixing
vessel
Pre-column
Differential
detector
High pressure
pump
To waste
To waste or
fraction collector
Figure 3
...
3
...
5 Ion exchange chromatography
Another type of chromatography that is widely used in the separation and purification of
biological material is ion exchange chromatography
...
Due
to the high affinity of charged molecules for opposite charges, this method is highly selective
...
Ion exchange chromatography is used in the separation of both
proteins and amino acids
...
15 Electrophoresis
Electrophoresis is a technique used to separate charged molecules in a liquid medium
with an electric field
...
3
...
1 Components of an electrophoretic system
An electrophoretic system consists of a power supply, a chamber containing a support
medium, and an anode and cathode made of metal, such as platinum
...
19)
...
Positively
charged cations migrate to the cathode (–)
...
Several
3
...
Electrophoresis works because when
a charged molecule is placed in an electric field, the molecule sustains a force, which is
proportional to the charge of the molecule and the strength of the electric field
...
19 In an electrophoresis system, charged molecules move through a support medium because of forces exerted by an electric field
...
Most power supplies for electrophoresis systems provide between 50 and 200 V
...
34)
where V is voltage, I is current, and t is time
...
In a system with a constant voltage supply, the migration rate increases with time
because the resultant current generates heat, which results in thermal agitation of the dissolved ions
...
Increasing the current generates more heat and water starts to evaporate more quickly
...
Migration rates that are too fast or that change with time are undesirable because of decreased resolution of the solutes in the gel
...
Presentday systems regulate the voltage in an attempt to maintain constant current
...
3-34 Chapter 3 Analysis of Molecules in Clinical Medicine
Support medium
One of the most commonly used support mediums is agar
...
Clinically,
electrophoresis is performed on a plastic support covered with a thin (1 mm) layer of agarose gel
...
Another commonly used support medium is cellulose acetate
...
These membranes
consist of about 80% air in pockets in-between interconnected cellulose acetate fibers
...
Cellulose
acetate electrophoresis (CAE) has the advantage of being relatively quick (20 to 60 min)
...
Electrodes and chamber
Electrodes may be made of metal such as platinum, or of carbon
...
3
...
2 Electrophoretic mobility
There are several factors that cause different migration rates among the molecules in a
mixture
...
A molecule in the medium experiences a force FE = qE in the direction of the electric field that is proportional to the strength of the electric field, E, and the
net charge of the molecule, q
...
FE = FD
(3
...
36)
The mobility of a charged particle is defined as its steady state velocity divided by the
strength of the electric field
...
15 Electrophoresis
electrophoretic mobility µ =
vss = q
E
f
3-35
(3
...
Analysis and quantification
Electrophoresis plates are usually dried before analysis to prevent diffusion of the migrated solutes
...
There are cameras available that can photograph the electrophoresis gel, using
filters specific for different stains
...
The bands
appearing in the gel, or on the plate, can be identified by inspection under the Woods
lamp, but a densitometer is required for accurate quantification
...
A densitometer measures the transmittance of light through a solid electrophoretic sample, similar to how a
spectrophotometer operates
...
The plate or sample is then slowly moved past the
exit slit while the amount of transmitted light is measured
...
Serum protein electrophoresis
Electrophoresis is used to separate the proteins in blood serum
...
20 and 3
...
It is produced in the liver and performs many tasks
...
The other
three peaks are referred to as alpha, beta, and gamma
...
The most prevalent gamma globulins are antibodies
(the term antibodies and immunoglobulins are synonymous since antibodies are part of
the immune system)
...
For example, if the albumin is low, that can be a sign of liver disease
...
21 is a spread of many types of antibodies as a result of
a B-lymphocyte tumor (bone tumor)
...
16 DNA sequencing
There are 20 standard amino acids that make up all proteins
...
They are distinguished by their different side
chains (R groups)
...
In high-performance liquid chromatography (HPLC), 0
...
Amino acids in a buffer solution are pumped through the column at about
13 MPa for about 40 min
...
Amino acids with more positive charge bind
more tightly to the resin and elute later
...
,
1993)
...
20 This serum protein electrophoresis demonstrates a normal pattern, with the largest
peak for albumin
...
21 This serum protein electrophoresis demonstrates a decrease in the albumin and an
increase in gamma globulins
...
Peptides can be obtained by
purification from tissue, by genetic engineering, or by direct chemical synthesis
...
16 DNA Sequencing
3-37
the cell, amino acids are synthesized into a longer polypeptide sequence (a protein)
through the translation of information encoded in messenger RNA by an RNA–protein
complex called a ribosome
...
Differential centrifugation may yield subcellular fractions
...
Size-exclusion
chromatography separates by size
...
The purified protein is characterized
by ion-exchange chromatography to measure the amount of the protein of interest and the
contaminants
...
The nucleic acids RNA and DNA are polymers of nucleotides
...
A dideoxynucleoside phosphate
(ddNTP) analog specific for one of the nucleotides interrupts DNA synthesis to prematurely terminate the fragment at that nucleotide, for example A
...
When each of these radiolabeled (with a radioactive compound) four fragments is separated electrophoretically, it yields the autoradiogram (by
darkening photographic film) pattern in Figure 3
...
A
G
T
G
T
C
A
C
G
•
T
•
•
•
•
•
Figure 3
...
The sequence is read from the rows of bands from the bottom up as ACTGTG
...
Then all four fragments can be combined and analyzed
by a single lane during electrophoresis
...
A computer displays the colored peaks and also the sequence
...
3
...
1996
...
its
...
edu
...
html
Berger, S
...
1996
...
New York: Oxford University Press
...
J
...
Biosensor Principles and Applications
...
3-38 Chapter 3 Analysis of Molecules in Clinical Medicine
Bowers, L
...
, Ullman, M
...
and Burtis, C
...
1994
...
In C
...
Burtis
and E
...
Ashwood (eds
...
2nd ed
...
B
...
Burtis, C
...
and Ashwood, E
...
(eds
...
Tietz Textbook of Clinical Chemistry
...
Philadelphia: W
...
Saunders
...
M
...
Biosensors
...
Carrier, R
...
1994
...
[Online]
http://www
...
edu/dept/chem-eng/Biotech-Environ/CHROMO/chromequip
...
M
...
D
...
) 1995
...
New York: Van Nostrand Reinhold
...
, Liu, P
...
2000
...
Advanced Drug Delivery Reviews 45: 189–216
...
DS-34 Camera for Electrophoresis Gel Recording by Polaroid
...
dmscientific
...
html
Hall, E
...
H
...
Biosensors
...
Hicks, M
...
, Haven, M
...
, Schenken, J
...
, and McWhorter, C
...
1987
...
3rd ed
...
B
...
Haven, M
...
, Schenken, J
...
, Tetrayktm J
...
1995
...
4th ed
...
IQ Scientific Instruments
...
The ultimate source for non-glass ISFET technology pH
systems [Online] http://www
...
com
Kurnik, R
...
, Berner, B
...
, and Potts, R
...
1998
...
J
...
Soc
...
[Online] http://www
...
com/monitor/journals
...
L
...
L
...
M
...
Principles of Biochemistry
...
New York: Worth Publishers
...
2001
...
mallinckrodt
...
Melcher, U
...
Gel Electrophoresis
...
[Online]
http://opbs
...
edu/~melcher/MG/MGW4/MG422
...
1989
...
Chicago:
American Society of Clinical Pathologists
...
D
...
J
...
Mosby’s Diagnostic and Laboratory Test Reference
...
St
...
Peura, R
...
1998
...
In J
...
Webster (ed
...
3rd ed
...
Primiano, F
...
Jr
...
Measurements of the respiratory system
...
G
...
)
Medical Instrumentation: Application and Design
...
New York: John Wiley &
Sons
...
F
...
S
...
Handbook of Chemical and Biological Sensors
...
Tissue, B
...
2000
...
[Online]
http://www
...
vt
...
html
Tissue, B
...
2000
...
[Online] http://www
...
vt
...
html
Tissue, B
...
2000
...
[Online]
http://www
...
vt
...
html
3
...
M
...
Mass Spectroscopy (MS)
...
chem
...
edu/chemed/scidex
...
G
...
) 1997
...
Bristol, UK: IOP Publishing
...
G
...
) 1988
...
New
York: John Wiley & Sons
...
A
...
Clinical laboratory instrumentation
...
G
...
) Medical
Instrumentation: Application and Design
...
New York: John Wiley & Sons
...
18 Problems
3
...
2
3
...
4
3
...
6
3
...
8
3
...
10
3
...
12
3
...
14
3
...
16
3
...
18
3
...
20
3
...
22
Give the equation for Beer’s law, define each term, and give units
...
List the components
of a spectrophotometer
...
Assume Beer’s law holds and calculate the unknown concentration for a
transmission of 70%
...
4 in a spectrophotometer
...
25
...
Define oxygen saturation and state the physiological meaning of SaO2
...
Describe how NADH is used to measure lactate concentration and why lactate
concentration isn’t ascertained by measuring lactate directly
...
Describe why and how to measure urea and the body fluids it can be measured in
...
Describe how to measure glucose in automated equipment
...
Describe the most common enzymatic electrode method for measuring glucose
...
Draw a pH electrode and explain its principle of operation
...
Explain the relation of the CO2 electrode to the
pH electrode
...
Explain the principle of operation and give an example of use for mass spectrometry
...
Explain why and how N2 is measured by emission spectroscopy
...
Describe one of the advantages of
fluorometry
...
Explain the two principles that are
the primary factors affecting interactions in chromatography
...
3-40 Chapter 3 Analysis of Molecules in Clinical Medicine
3
...
List the factors that cause differential
migration rates among the component molecules of a mixture
...
24 Explain how protein purity is measured
...
25 Explain how the DNA code is determined
...
Monzon
This chapter discusses measurements of molecular variables that are needed for research
and development in the rapidly growing areas of biomaterials and tissue engineering
...
1 Molecules and Biomaterials
The following sections present some biomaterials fundamentals
...
4
...
1 Integrated approach
Over the years, a number of different types of materials have been used in medical
practice, either for treating wounds and diseases or for cosmetic purposes
...
This definition suggests that
the development of materials for biological use can be accomplished only through an
integrated approach of several disciplines: science and engineering, especially material
sciences for detailed study and testing of the structural properties and phenomena of
materials; biology and physiology, to provide the necessary tools for experimentation
based on immunology, anatomy, cellular and molecular biology; clinical sciences, as
many medical specialties are directly related to the actual use of biomaterials (Park,
1995)
...
4
...
2 Types of biomaterials
2
Surface Characterization in Biomaterials and Tissue Engineering
Materials for biological use can be classified according to their base structure as ceramics,
composites, metals, and polymers
...
1 summarizes different types of biomaterials
and their most common applications (Silver, 1994; Park and Lakes, 1992)
...
Synthetic polymers constitute the vast majority of biomaterials used in
humans (Marchant and Wang, 1994)
...
1 Classification of biomaterials in terms of their base structure and some of their most
common applications
...
1 Molecules and Biomaterials
Polymers
Nylon
Synthetic rubber
Crystalline polymers
3
Replacement of soft tissues: skin,
blood vessels, cartilage, ocular lens,
sutures
Orthopedic
Figure 4
...
(from
http://www
...
com/Biomedical/ionguard
...
1
...
CH3
CH
Figure 4
...
This is the monomer for poly(ethylene), a
common biomaterial used for medical tubing and many other applications
...
, 1995)
...
e
...
Synthetic polymers are obtained through two basic chemical processes: addition
polymerization and condensation polymerization
...
Condensation polymers include poly(esters), poly(amides), and
poly(urethanes) (Marchant and Wang, 1994; Park and Lakes, 1992; Silver, 1994)
...
Table 4
...
Table 4
...
Biomedical polymer
Poly(ethylene) (PE)
Low density (LDPE)
High density (HDPE)
Ultra high molecular weight
(UHMWPE)
Application
Bags, tubing
Nonwoven fabric, catheter
Orthopedic and facial implants
Poly(methyl methacrylate) (PMMA)
Intraocular lens, dentures, bone
cement
Poly(vinyl chloride) (PVC)
Blood bags, catheters, cannulae
Poly(ethylene terephthalate) (PET)
Artificial vascular graft, sutures,
heart valves
Poly(esters)
Bioresorbable sutures, surgical
products, controlled drug release
Poly(amides) (Nylons)
Catheters, sutures
Poly(urethanes) (PU)
Coat implants, film, tubing
Properties
Biomaterials for implants should be nontoxic, noncarcinogenic, nonallergenic, functional
for its lifetime, and biocompatible (Billotte, 2000)
...
1 Molecules and Biomaterials
5
Polymeric biomaterials exhibit reasonable cost of processing and can be
manufactured with various shapes showing desired mechanical and physical properties
...
, 1995)
...
Biocompatibility
The most important requirement for an implant is its biocompatibility, that is, the
acceptance of an artificial device by the surrounding tissues and by the body as a whole
(Park, 1995)
...
(1996) suggest that biocompatibility does not mean lack of
biological response—as might be expected—but rather the presence of a desirable set of
biological responses
...
Figure 4
...
(from
http://www
...
com/products/heartvalves/mechanical/mastersseries
...
2 Molecules and Tissue Engineering
As is the case with biomaterials, molecular phenomena also play an important role in
tissue engineering research
...
4
...
1 Tissue engineering
Tissue engineering can be defined as the application of engineering and life sciences
toward the design, growth, and maintenance of living tissues (Berthiaume et al
...
This discipline uses living cells and their extracellular products to develop more
biological replacements instead of using only inert implants (Skalak et al
...
Tissue
engineering activities can be performed either in vivo (in the body) or in vitro (in
solution), the latter being of more interest to bioengineers
...
Although many bioartificial tissues are still in a developmental stage, it is expected that
in the future bioartificial organs and tissues will be able to regenerate and perform
complex biochemical functions, similar to the natural organs and tissue they will replace,
a behavior that pure artificial implants cannot exhibit (Berthiaume et al
...
4
...
2 Cellular composites
Tissues are multiphase systems of cellular composites
...
, 1996)
...
, 1994)
...
,
1996)
...
3 shows some current examples of applications and in vitro research in
tissue engineering (Berthiaume et al
...
Table 4
...
Not all of the listed
applications are at the same developmental stage
...
2 Molecules and Tissue Engineering
Cardiovascular
Endothelialized synthetic vascular
grafts (angiogenesis)
Regeneration of the arterial wall
Compliant vascular prostheses
Liver and pancreas
Bioartificial pancreatic islets
Bioartificial liver
Musculoskeletal
Cartilage reconstruction
Bone reconstruction
Neural
Neurotransmitter-secreting cells
(polymer-encapsulated)
Neural circuits and biosensors
Peripheral nerve regeneration
Skin
7
Bioartificial skin substitutes
Of the structural components of tissues mentioned earlier, the scaffolding
architecture is, for tissue engineers, a synthetic biomaterial
...
The characteristics of the synthetic material will directly affect the recruitment,
attachment, proliferation and differentiation of living cells, that is, defining the quality of
the new tissue
...
, 1996)
...
In the next sections we discuss some of the most important molecular variables,
and we present the necessary tools for quantitatively studying them
...
3 Surface Analysis
The successful use of a synthetic polymer—either as a biomaterial implant or as a
scaffolding architecture for tissue growth—relies on the qualitative and quantitative
knowledge of several properties of such a polymer
...
It is not possible to determine which of these variables prevails over the
others, so researchers are continuously designing instruments, procedures and techniques
for better understanding of these variables, and for relating them to the overall behavior
of material implants
...
A complete description of the chemistry and morphology of a surface cannot be
accomplished using one single technique
...
Basic characterization using microscopy, the study of the chemical composition
by means of spectroscopy, and the evaluation of the polymer–water interface using
contact angle methods, are the main variables and procedures currently used in polymer
surface analysis (Andrade, 1985a)
...
References describe the principles governing the
procedures and instruments that are presented
...
4
...
1 Topography
Andrade (1985c) points out that the very first characterization to be performed on any
surface is to look at it
...
Microscopes are needed for observing other qualities such as roughness,
surface texture, or topography (or microtopography for a molecular scale)
...
Next we discuss the
different types of electron microscopes that are used for observation of surface
topographies
...
Developed several decades ago, TEM made
possible a relevant increase in magnification compared to visible light optical
microscopes
...
Resolution and magnification: The resolving power, or resolution, of a microscope is its
ability to discriminate two closely placed structures
...
Higher magnification
does not necessarily mean better resolution
...
The resolving power of a microscope is a function of the wavelength, λ, of the
source of illumination
...
3 Surface Analysis
λ=
h
mv
9
(4
...
Better
resolution is achieved by using lower wavelengths
...
Electrons accelerated in an electric field will reach a velocity:
v=
2eV
m
(4
...
By
substitution in Eq
...
1), and by replacing the constants by their values (see Appendix),
we obtain
λ=
1
...
3)
which shows that short wavelengths can be obtained by using high voltages (on the order
of kilovolts)
...
3) is not useful for calculating the resolution because lens
aberrations, refractive index of the medium, and aperture angles limit the resolution
...
4
to 1 nm (4 to 10 Å), with a practical magnification of 100,000 to 200,000
...
4(a) shows the basic components of a TEM
...
The simplest electron source is a heated, pointed
tungsten wire, although higher resolution microscopes are equipped with a lanthanum
hexaboride (LaB6) cathode to which typically voltages of 40 to 120 kV are applied
(Dykstra, 1992)
...
4 (a) TEM microscope
...
(b) SEM microscope
...
Both TEM and SEM operate in a particle free (vacuum) environment
...
Lenses for an electron microscope are not made of glass as for
optical microscopes, but rather they are magnetic coils (solenoids) that can bend the
electron path (Bozzola and Russell, 1991)
...
3 Surface Analysis
11
Below the sample plane, the objective lens assembly focuses and magnifies the
specimen image
...
Scattered elements of the electron beam
emerging from the sample are also eliminated by the objective lens system (Dykstra,
1992)
...
This screen can be observed through a viewing window (not
shown) or the image can be photographically reproduced by exposing a photographic
plate immediately beneath the fluorescent screen (Packer, 1967)
...
This process is lengthy and involves several steps, most of which are
chemical processes: fixation, washing, dehydration, infiltration with transitional solvents
and with resins, embedding, and curing
...
This procedure is
called ultramicrotomy and is performed to allow the beams of electrons to pass through
the sample material (Bozzola and Russell, 1991)
...
g
...
There are some alternative methods of specimen preparation that
overcome this difficulty
...
However,
this can be overcome by using a defocused conventional TEM; a defocused beam also
avoids sample damage or destruction (Goodman et al
...
One major disadvantage of TEM is its limitation for a proper three-dimensional
view (Dykstra, 1992)
...
Using multiple
views could permit reconstruction of the three-dimensional structure
...
, 1988)
...
Scanning Electron Microscope (SEM)
SEMs and TEMs have many features in common—they both use electron beams to
visualize a sample
...
The principle of SEM operation makes it very useful for topographic analysis, as we will
see in the next paragraphs
...
The
incident beam (primary electrons) displaces orbital electrons from the sample atoms,
giving rise to secondary electron emission (Figure 4
...
5 Principle of SEM operation
...
Some primary electrons pass by the nucleus to become backscattered electrons
...
Some primary
electrons may not collide with orbital electrons
...
These are not the only emissions arising at the atomic level, as we explain in
section 4
...
2 (see Figure 4
...
Operations: Figure 4
...
Notice the similarities with the TEM in Figure 4
...
Some components of the SEM are
identical to those of the TEM, such as a vacuum system for operation in a particle-free
environment
...
Magnetic lenses of various types are in
the TEM and in the SEM they are all condensers
...
Deflector coils bend the primary beam for scanning across the specimen
...
Some of
these secondary electrons contact a positively charged detector, also called a collector,
connected to a cathode ray tube (CRT), giving a point of illumination on the CRT screen
4
...
Deflector coils in the SEM are connected to the
deflector plates of the CRT so that as the SEM beam is scanned over the specimen, the
CRT gun is synchronously swept over the screen
...
Resolution and images: Image resolution in SEM is a more complex concept than in
TEM because time is an integral part of the image formation process in scanning
microscopes (Dykstra, 1992)
...
However, some backscattered electrons, as they leave the atom (Figure 4
...
These extraneous
secondary electrons produced by backscattered radiation are also detected by the
collector and displayed on the CRT screen, giving a blurred or noisy signal
...
Some backscattered
electrons can also be collected by a special detector
...
A very attractive feature of the SEM is its ability to generate images that appear
to have three dimensions
...
Secondary electrons are emitted from various parts of the
specimen, but those that face the primary beam and are in line of sight with the detector
will appear bright on the CRT screen, whereas a dark appearance corresponds to areas
not reached by the beam, and not emitting secondary electrons
...
This variation in contrast contributes to the generation of an image that appears
to have depth, although that image is visualized on a two-dimensional CRT screen
(Bozzola and Russell, 1991)
...
The three dimensional effect on SEM-generated images is very useful for
topographical studies
...
3
...
The sample can be probed to
depths of tenths of micrometers making it possible to convert a chemical structure into
topographical relief
...
, 1988)
...
Mostly dry samples
are used
...
The remarkable depth of focus
allows the examination of uneven surfaces with the SEM
...
Scanning Tunneling Microscope (STM)
The scanning tunneling microscope, along with the scanning force microscope (SFM)
that we discuss later, belongs to the more general group of scanning probe microscopes
(SPM or SXM)
...
In
this way, it is possible to obtain information on surface topography, and on some
mechanical and electronic properties at the atomic level (Marti, 1993)
...
Properties of the surface derive from atoms not being completely
surrounded by other atoms, as they are in the interior of a solid (Dykstra, 1992)
...
This rather complicated function of kinetic and
potential energies—which is related to the probability of electrons crossing a gap
between two conducting surfaces—can be synthesized in our discussion of the STM by
saying that if a voltage is applied between the probe tip and the sample surface, a current
will develop across the junction (tunneling current)
...
Distances of an atomic diameter can cause a relevant decrease in the tunneling current,
thus allowing precise measurements of the vertical position of atoms at the specimen
surface (Dykstra, 1992)
...
The resolution of the STM is a function of the geometry of the tip, the
topography of the sample, and of their electronic structures
...
However, on an atomic
scale, resolution is governed by the stability of the tunnel barrier width (i
...
the distance
between tip and sample)
...
Calculation of STM resolution is not a straightforward process
...
Stable and precise STMs can measure distance
variations of 1 pm, provided the instrument is in a vibration-free environment (Dykstra,
1992)
...
3 Surface Analysis
15
(a)
(b)
Figure 4
...
The tip is very small,
and can be ruined on a sample, which is seen in Figure 4
...
(from
http://www
...
soton
...
uk/~wsb/stm/photos
...
8 shows a block diagram of the STM
...
The piezoelectric effect is
the mechanical expansion and contraction of a material in response to an electric field
...
A widely used piezoscanner made of ceramic material is
the piezotube, which has inner and outer electrodes for movements along the three
Cartesian axes x, y, and z
...
The sample is connected to a tunnel voltage source
...
The output of the I/V converter
is further processed at the voltage processor block for display
...
A scan controller generates the voltages needed for
movements along the x–y plane
...
A
Sliding
surfaces
B
The assembly A slides
inside the assembly B,
driven by the Zapproach drive piezo
...
7 This is a sample of a piezotube
...
(from
http://www
...
com/cryosxm
...
8 STM schematics
...
Three-dimensional
movements of the sample under the tip are accomplished using a voltage-controlled piezoscanner
...
4
...
In the constant current mode, very high-gain voltage amplifiers are used, so as
to keep the tunneling current constant and to force the tip to follow the contours
...
Any suitable recording device can be used for such purpose: chart recorder, oscilloscope,
or computer
...
In this mode the tip is held at a constant height and no longer follows the sample
topography
...
Three disadvantages of the STM are the need for an environment free of
vibrations, very stable temperatures and the requirement for highly conductive samples to
develop tunneling currents
...
However, careful data
acquisition and interpretation are highly recommended (Ratner, 1988)
...
They share many of the same features
...
All of
these microscopes measure forces generated between a probe and a sample surface
(Dykstra, 1992)
...
The force between a tip and the sample is used to obtain an image of
the surface topography
...
Contact SFMs require the tip to actually touch the sample
...
,
1996)
...
9 shows the SFM
...
As the tip moves toward the sample, two types of forces develop: at
large distances the interaction is attractive due to the van der Waals forces; at short
distances repulsive forces develop due to the exclusion principle of quantum mechanics
(Marti, 1993)
...
9 Sketch of an SFM
...
The difference in output from each segment is proportional to the
deflection amplitude of the cantilever scanning the sample
...
Although the tip radius is very
small (~10 nm), the forces acting on it can deflect the entire cantilever
...
, 1996)
...
The
most common method is the optical lever, shown in Figure 4
...
A laser beam is focused
on the cantilever and reflected back to a photodiode in the middle of two subdiodes (twosegment photodetector)
...
This differential current signal at the output of the
photodetector is then proportional to the cantilever deflection and thus to the surface
topography
...
9) to control the movements of the sample
with respect to the tip according to the modes of operation discussed next
...
, 1996; Marti, 1993)
...
3 Surface Analysis
19
Modes of operation: Similar to the STM, piezoelectric elements are used to control the
motion of the sample or the tip
...
We said
previously that these forces are in the nanonewton range, but due to the action on tiny
areas of contact (about 0
...
As the tip scans the surface,
an upward deflection of the cantilever indicates a topographic obstacle and the sample
retracts, by means of the feedback loop, to keep the force constant
...
In the constant height mode the cantilever
can deflect in both directions, and the sample is kept at a constant height
...
A combined mode, the error
signal mode, requires fast feedback response to follow the surface as in the constant force
mode, but recordings correspond to cantilever deflection and not to the sample motion
...
, 1996)
...
In contact SFM (repulsive force
operation), some lateral forces between the tip and the sample may develop, giving
distorted images and thus reduced resolution
...
The magnitude of the lateral forces is a function of the tip dimension and shape, so
careful design of the tip is necessary
...
Although very useful for imaging soft samples,
they exhibit some mechanical instability due to their attractive force operation
(Bustamante et al
...
The AFM is widely used in surface analyses of biomaterials
...
The
AFM can work very easily in liquid (Descouts, 1995)
...
3
...
Accurate
quantitative information on chemical composition is achieved by means of spectroscopic
methods
...
X-ray Photoelectron Spectroscopy (XPS)
X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for
Chemical Analysis (ESCA), is a widely used technique for surface analysis
...
20
Surface Characterization in Biomaterials and Tissue Engineering
Researchers rely on XPS’s high surface specificity, which takes its information
from within 10 nm (100 Å) of the surface, because it allows the studying of biomaterials
interfaces with living tissue
...
XPS is based on the photoelectric effect, shown in Figure 4
...
The basic equation for this photoemission process and thus for XPS is
E k = hν − E b − φ s
(4
...
The value of φs is predetermined for
each spectrometer
...
10 When an X-ray photon (a) interacts with an atomic orbital electron of the sample, a
photoelectron (b) is emitted verifying Eq
...
4)
...
The relaxation process can be accomplished by either of two mechanisms: (1) an outer orbital
electron releases energy as fluorescent radiation (c) while occupying the place of the emitted
photoelectron, or (2) the excess energy is used to unbind and emit another outer orbital electron
called an Auger electron (d)
...
4
...
e
...
An electron analyzer,
also known as an electron spectrometer, can measure the number of these electrons
...
Figure 4
...
Distinct peaks correspond to specific
atomic orbitals so that the binding energy position of each peak allows elemental
identification
...
All of the elements in the periodic
table exhibit binding energies in the approximate range of 0 to 1000 eV (electron volts),
therefore positive identification is possible
...
Many detected
electrons lose energy in interactions with the sample, leading to lower kinetic energies
and higher binding energies recordings (see Eq
...
4)) adjacent to every intense peak,
giving the spectrum a stair-step shape (Andrade, 1985b)
...
11 A typical XPS spectrum, showing photoelectron intensity as a function of binding
energy
...
Some peaks may also represent Auger radiation
...
12 shows the basic schematic of an XPS instrument
...
The resulting photoelectron
22
Surface Characterization in Biomaterials and Tissue Engineering
radiation is captured by an analyzer
...
12) for minimal sample
contamination and for easy passage of the photoelectrons to the analyzer (Paynter, 1988)
...
12 Basic schematics of an XPS instrument
...
These electrons enter the hemispherical analyzer where they are
spatially dispersed due to the effects of the retarding grid and of the electrostatic field of the
concentric hemispheres
...
At
the other end of the analyzer electrons are detected, counted, and a spectrum of photoelectron
intensity versus binding energy is displayed
...
An electrically biased grid at the entrance of the analyzer retards the kinetic
energy of the photoelectrons, which are then spatially dispersed as they initiate their
semicircular trajectory between the hemispheres
...
Ramping voltages in the pre-retardation stage allows actual kinetic
energy scanning with a constant resolution mode of typically ~0
...
0 eV
...
3 Surface Analysis
23
that counts the number of light pulses arising at the screen (Andrade, 1985b; Paynter,
1988)
...
12)
...
The detection system must compensate for this reduced
intensity in order to obtain suitable signal levels
...
High cost of the instrument, large area of analysis, high vacuum required and
low speed (several minutes per peak) are major disadvantages of the XPS technique
(Andrade, 1985b)
...
Imaging X-ray Photoelectron Spectroscopy (iXPS)
The lack of spatial resolution has also been an inherent weakness of XPS
...
13, uses the capability of parallel imaging to produce
photoelectron images with spatial resolution better than 5 mm
...
A combination of lenses before and after the energy analyzer
focus the photoelectrons on a channel plate detector
...
Neither the X-ray nor
the photoelectrons are scanned to produce an image
...
In ESCALAB, images are formed on a
channel plate detector
...
The advantage of iXPS is that it produces images much more quickly than the
conventional methods (for comparable spatial resolution) because the entire field of view
is imaged simultaneously
...
e
...
This
makes setting up experiments much quicker
...
24
Surface Characterization in Biomaterials and Tissue Engineering
Hemispherical
analyzer
Spectroscopy
detector
Lenses
Imaging
detector
Irises
X rays
Sample
Camera
Zoom
microscope
Figure 4
...
thermo
...
html)
and schematics of an ESCALAB
...
Auger Electron Spectroscopy (AES)
4
...
10) are complementary to XPS for surface analysis, being
especially useful for quantitative analysis of certain elements
...
AES
found practical applications earlier than XPS, but due to the need of electron
bombardment to the sample (instead of photons), it is a highly destructive technique not
recommended for modern polymer surface analysis (Andrade, 1985b)
...
Secondary-Ion Mass Spectroscopy (SIMS)
Secondary-ion mass spectroscopy (SIMS) is another technique for studying the nature of
biomaterial surfaces
...
However, it can provide useful information for the understanding of the
composition and structure of an implant material surface (Andrade, 1985c; Castner and
Ratner, 1988)
...
If enough ionizing
energy is present, sample molecules are even dissociated, forming ionic fragments
...
The pattern of product ions formed is dependent on
the structure of the intact compound (Wait, 1993)
...
14 illustrates the SIMS procedure and instrument schematics
...
As with XPS,
ultrahigh vacuum (UHV) chambers are used to avoid not only external contamination but
also collisions with particles that may be present in a nonvacuum environment
...
14 Schematic diagram of a SIMS instrument
...
A mass analyzer separates these ions in terms of
their mass-to-charge ratio
...
The display presents the SIMS spectra, consisting of the count of ions versus
their mass-to-charge ratio
...
The size,
energy, mass, and flux of the incident beam are directly proportional to secondary ion
emission and sample damage
...
The use of such low-energy inert gas ion beams is called static SIMS and is
the most commonly used technique
...
A high-energy and high-flux beam technique,
called dynamic SIMS, is used to profile the depth of minerals and semiconductors
(Andrade, 1985c)
...
One way of avoiding this charge
buildup is by using a neutral atom incident beam, a technique referred to as fast atom
bombardment (FAB) SIMS (Castner and Ratner, 1988)
...
3 Surface Analysis
27
Charge neutralization: For suitable reading of secondary ion emission, the charge that
builds up on the surface of an insulating sample must be neutralized
...
Even for the case of neutral FAB SIMS, the use of
neutralizing electrons has shown to increase the quality of detected data (Castner and
Ratner, 1988)
Mass analyzer: The counts of secondary emitted ions versus their mass-to-charge ratio
(measured in Daltons, where 1 D = 1/12 the mass of C12) constitute the data obtained
through a SIMS instrument
...
(4
...
5)
which can be rearranged to give the fundamental mass spectrometer equation
m 2V
= 2
z
v
(4
...
The quadrupole mass spectrometer, which determines mass divided by charge
m/z by scanning voltages, is used for analyzing fragments of up to 500 D
...
Quadrupole spectrometers are commonly used because they
are inexpensive and most polymers yield fragment ions in their detection range (Castner
and Ratner, 1988)
...
The TOF mass analyzer measures velocity instead of voltages
...
4
...
For precise time
measuring, pulsed ionization techniques must be employed for primary beam generation,
which accounts for the higher cost of TOF-based instruments
...
The electric signal is amplified, computer processed, and
visualized
...
Static SIMS is used for determining the types, structures, and quantity of the
chemical compounds on a surface
...
This
28
Surface Characterization in Biomaterials and Tissue Engineering
is mainly due to the different ionic particles—some of them fragments of molecules—
that are detected
...
Nevertheless, careful SIMS experiments allow full
identification of polymeric chains, and also some composition up to a depth of 1
...
SIMS complements XPS for polymer composition studies (Castner and Ratner,
1988)
...
Incident ions lose
energy in these elastic collisions, a loss that depends on the mass of the atom in the
surface
...
Infrared Spectroscopy (IR)
Next we present some infrared spectroscopy techniques, which are usually combined to
allow surface analysis
...
Dispersive infrared spectroscopy: The infrared region of electromagnetic radiation
includes wavelengths in the range of 700 nm to 1
...
Usually only the mid-infrared
region is used for measuring, and this includes wavelengths from 2
...
For convenience, spectroscopists use the wavenumber,
expressed in cm–1 and defined as 1/λ, rather than wavelengths
...
The underlying principle of infrared spectroscopy states that the absorption of
electromagnetic radiation of the appropriate energy excites the atom
...
The absorption process depends on the relative masses and geometry of the atoms
and on the forces between bonds within the sample molecules
...
The vibrational and rotational motions take place at particular
frequencies (or wavelengths) according to the molecular structure
...
A spectrum (energy vs
...
An unlimited
number of spectral libraries are available to verify tentative identifications (Grim and
Fateley, 1984)
...
3 Surface Analysis
29
The dispersive infrared spectroscope is similar to the spectrophotometer (see
Chapter 3)
...
Dispersive spectrometry has some limitations, which are
overcome by the use of interferometric techniques as we discuss next
...
This interference can be constructive (sum of amplitudes of
radiations in phase) or destructive (amplitudes of out of phase radiations cancel each
other)
...
An interferogram is the plot of
amplitude vs
...
A major component in interferometry instruments is the interferometer, a device
for developing a difference in phase between two waves (Grim and Flateley, 1984)
...
15 shows schematically the optical configuration of a Michelson interferometer,
the first designed and still the most common interferometer in use today
...
The beamsplitter transmits half of the source
radiation to the fixed mirror and the other half to the sliding mirror (Fink and Larson,
1979)
...
The
changes in the mirror position change the path length for each beam
...
If the path lengths to
the fixed and sliding mirrors are the same, constructive interference occurs to yield a
maximum at the detector
...
For a monochromatic source, as the sliding mirror
moves distance x, the detector yields an output I = I0 cos(2πx/λ)
...
30
Surface Characterization in Biomaterials and Tissue Engineering
Infrared
detector
Sliding
mirror
Beamsplitter
Source
Fixed mirror
Figure 4
...
A beamsplitter transmits half of the source radiation to the
fixed mirror and the other half to the sliding mirror
...
The
detector provides the interferogram, a plot of energy as a function of differences in optical paths
...
Fourier Transform infrared spectroscopy (FT-IR): For a polychromatic source, the
interferogram will show a center burst (maximum) only when the two path lengths are
equal
...
Then if absorption from one path is
present at one wavelength, an inverted cosine wave will appear across the interferogram
...
This operator allows the display of the interferogram (and in fact of any time
signal) in the frequency domain
...
Calculations for the FT for displaying
interferograms in the frequency domain were a lengthy and tedious process that has since
been all but eliminated by the use of digital computers
...
It has improved the benefits of interferometry over dispersive
4
...
Attenuated internal total reflection (ATR): Total internal reflection is a special case of the
more general phenomenon of reflection and refraction of incident electromagnetic
radiation at an interface of two media having different indexes of refraction (Knutson and
Lyman, 1985)
...
16 shows that when an incident beam with an angle θ traveling in a
medium of refractive index ηc encounters the interface with a second medium of
different refractive index ηs, the beam will be reflected back into the first medium and
transmitted into the second medium with an angle other than the incident (refraction)
according to Snell’s Law of Refraction:
η c sin θ = η s sin φ
(4
...
From Eq
...
7) and from Figure 4
...
e
...
Also, there is a value for θ that will make φ = 90° and is called the critical angle
θc
...
(4
...
8)
Values of θ larger than θc will cause total reflection of the incident beam (i
...
no
refractive beam develops)
...
16 When an incident beam traveling at an angle θ in a medium of refractive index ηc
encounters another medium of refractive index ηs, it will reflect in a direction given by θ and
refract in the direction given by φ, verifying Snell’s Law of Refraction (Eq
...
7))
...
A more
rigorous treatment would have required the use of tools provided by electromagnetic
wave theory
...
The electromagnetic radiation is totally internally reflected (ATR) through an
optically transparent material in contact with the sample (see Figure 4
...
The
reflectivity exhibited by the surface depends upon the interactions of the electromagnetic
field established within the sample
...
Finally, the addition of the Fourier Transform led the method known as Fourier
Transform Infrared Spectroscopy-Attenuated Total Internal Reflection, FTIR-ATR,
which ultimately combines the versatility of the infrared spectrum and the convenience of
computers for fast digital processing, represents a key technique for surface analysis
...
3
...
3 Surface Analysis
33
Biomedical polymers are usually implanted within a liquid environment
...
Contact angle method
The contact angle method requires relatively simple and inexpensive equipment, although
it is one of the most sensitive methods used to obtain information about the outermost
layer of solid surfaces (Andrade et al
...
This method allows the determination of the excess free energy per unit area, the
surface tension, whose SI unit is N/m
...
A surface tension develops in these
phase boundaries when the equilibrium is altered giving rise to an excess energy, which
will minimize the surface area
...
Figure 4
...
At equilibrium, Young’s equation is
γ SV − γ SL = γ LV cos θ
(4
...
, 1985)
...
(4
...
10)
γ LV
γ SV
θ
γ SL
Figure 4
...
γ is the interfacial free energy for each of the phases
...
34
Surface Characterization in Biomaterials and Tissue Engineering
The values of θ describe the wetting characteristic of a surface; a complete
wetting is represented by a value of zero for θ
...
17)
...
10 shows that the value of θ
represents ratios and not absolute values of surface tension
...
Several conditions must be satisfied for a straightforward interpretation of the
contact angle: the solid surface is rigid, very smooth, uniform, homogenous, and does not
interact with the liquid other than the three-phase equilibrium; the liquid surface tension
is well known, constant, and the liquid vapor does not adsorb on the solid surface to
change its surface free energy (Andrade et al
...
The contact angle can be measured, among another methods by: (1) direct
microscopy with a goniometer or protractor for direct measurement of the angle, (2)
calculation of the angle from known dimensional measures of the drop, such as diameter,
volume and trigonometric relationships and (3) capillarity of a liquid of known surface
tension (Andrade et al
...
4
...
The interaction of proteins with solid surfaces, which is protein adsorption,
represents an important process for the fields of biomaterials due to its role in blood
coagulation and in the reaction of tissues to artificial implants
...
Diverse processes are affected by protein adsorption: thrombosis and hemostasis,
healing of hard and soft tissues, infection and inflammation
...
For orthopedic applications, surface properties affect bone
healing (Chinn and Slack, 2000)
...
This blood compatibility or
incompatibility is considered to be related to adsorption processes involving gamma
globulins, fibrinogen, fibronectin, albumin, and several other proteins (Andrade, 1985d)
...
Whether or not the
biomaterial used for such purpose is biodegradable, its surface properties (affected by
adsorbed proteins) will influence the initial cellular events (cell attachment) at the cellmaterial interface (Boyan et al
...
Implantation of biomaterials or engineered tissues,
for example, generally leads to an inflammatory response aimed at destroying the foreign
material
...
This cell adhesion to the vessel walls is
mediated by a family of protein receptors (Jones et al
...
4
...
e
...
, 1996)
...
4
...
Carbon, nitrogen, oxygen, and hydrogen atoms are the basic elements in a
protein molecule; in many cases, sulfur atoms are also a part of the protein molecule
...
There are 20 different amino acids
...
18 shows the structure of an amino
acid molecule, which has a central carbon atom
...
Also in Figure 4
...
R
NH2
C
C
H
OH
O
Figure 4
...
To a central carbon atom, an amino group, a carboxyl group
and a hydrogen atom are bonded
...
Different amino acids combine to form polypeptides and these in turn give rise
to the very high number of complex structures (proteins)
...
This spatial
relationship between the amino acid chains giving rise to the structure of a protein is
called conformation
...
The particular regions of a protein to which antibodies or cells can
bind are called epitopes
...
4
...
2 Protein adsorption fundamentals
36
Surface Characterization in Biomaterials and Tissue Engineering
For a single protein solution, the rate of adsorption to the substrate depends upon
transport of the protein to the substrate
...
For constant temperature and static systems, transport is exclusively by
diffusion, and the net rate of adsorption can be described by Langmuir’s theory of gas
adsorption (Chinn and Slack, 2000)
...
11)
where rA is the net rate of adsorption, kA is the adsorption rate constant, Cb is the bulk
concentration of the protein in solution, θ is the fraction of surface occupied by the
adsorbed molecules and kD is the desorption rate constant
...
(4
...
12)
Equation (4
...
It is most applicable to
dilute solutions (Chinn and Slack, 2000)
...
The Vroman effect designates a set of transient phenomena related to protein
adsorption: the layer composition on the surface appears to be evolutionary and varies
from surface to surface, and that proteins may replace one another in some ordered
sequence during adsorption, giving rise to the concept of protein multilayers
...
4
...
3 Protein adsorption measurements
In order to understand protein adsorption, quantitative evaluation of the adsorption
process must be performed, along with information on the properties and characteristics
of the protein molecule itself that will affect the adsorption mechanisms
...
The amount of adsorbed protein (adsorbed isotherms) can be
measured using XPS and ATR-IR (see section 4
...
2)
...
The conformation and
conformational changes (denaturation) of the protein molecule can be determined using
IR techniques (section 4
...
2), circular dichroism (CD) and calorimetry
...
For studying the heterogeneity of
4
...
3
...
The
use of radiolabeled proteins allows direct measurement of protein adsorbed to a substrate
...
The result of these processes is a
generation of heat, which can be measured in a calorimeter
...
The heat developed in the reaction vessel is
completely transferred through a thermopile to a surrounding heat sink of large capacity
...
In a twin
calorimeter, two vessels are within a single heat sink
...
The detectors are in opposition so the
differential signal indicates the heat from the reactor vessel and rejects disturbances from
the surroundings that affect both vessels (Feng and Andrade, 1994)
...
They are called optically active or chiral
...
That is, a vertical band of polarized light will rotate to the left or right if
passed through an optically active substance
...
This is the difference in absorption
of LCP and RCP light (Hatano, 1986)
...
Total Internal Reflection Fluorescence (TIRF)
Most proteins fluoresce naturally due to the intrinsic fluorescence of one or more of the
aromatic amino acids comprising them: tyrosine (Tyr), phenylaline (Phe), or tryptophan
(Trp) (Hlady et al
...
Light from xenon, or other light source, passes through an
excitation monochromator to emit a narrow band of usually ultraviolet wavelengths
...
The emission passes through an
emission monochromator and is measured by a photomultiplier
...
It requires optically flat, reflective surfaces and provides
information on the thickness and optical contents of adsorbed film as a function of time
...
38
Surface Characterization in Biomaterials and Tissue Engineering
Autoradiography
The distribution of a radiolabeled compound within a specimen can be imaged using
autoradiography, which is more sensitive than pulse counters (Dykstra, 1992)
...
Silver halide photographic emulsions are placed over the radiolabeled
specimen, then developed
...
Radiolabeling
Radiolabeling permits measurement of the affinity for a given protein onto materials
(Baquey et al
...
During testing, peristaltic pumps cause biological fluids to flow
through tubing segments of material samples such as PVC, silicone elastomer,
polyurethane or polyethylene
...
Detectors based on junctions of semiconductors are preferred because of their
good energy resolution
...
4
...
A laser emits polarized light focused on the solution in a
scattering cell
...
This is known as static or Rayleigh scattering
...
This is
also known as quasi-elastic or photon correlation spectroscopy (PCS)
...
Coherent light from two particles scatters and can add or interfere at the
photosensor
...
The photosensor output fluctuates as the
particles move relative to each other
...
Thus the fluctuations are slow for large particles because they do not move
very far between measurements
...
Figure 4
...
G(τ) =
(4
...
5 Molecular Size
where:
G(τ) = ACF
I(t) = intensity at time t
I(t + τ) = intensity at (t + τ)
τ = delay time
< > = time average
1
G(τ)
0
τ
Figure 4
...
A PCS measurement can be thought of as a measure of the time it takes for a
particle to diffuse a distance 1/K, where K is the scattering vector
K = 4πn
sin (θ / 2)
λ
(4
...
333 for water)
θ = scattering angle
λ = wavelength (λ = 633 nm for He–Ne laser)
The ACF function for identical particles is a single decaying exponential
G(τ) = exp(–2Γτ)
(4
...
37, 1/(2Γ) = τ
...
From the diffusion constant, we can use the Stokes–
Einstein equation to calculate the diameter of a spherical particle
...
16)
where DT is the diffusion coefficient, the Boltzmann constant is k = 1
...
001 Pa·s for water at 20
°C), and d is the diameter of the particle
...
1 Given autocorrelation function data obtained from experiment, calculate the
particle size of polystyrene latex in the sample solution
...
8 nm
...
4 gives the data for τ and
the corresponding intensity
...
33, η = 0
...
Table 4
...
1
...
001
0
...
003
0
...
35
0
...
051
0
...
4 yield an exponential plot, but it doesn’t provide a useful
mathematical model for calculation
...
The given data yield the linear approximation
ln (G (τ )) = −1077
...
0852
To calculate the diffusion coefficient, Γ needs to be calculated first
...
37
when 1/(2Γ) = τ, the linear approximation can be used to find τ when G(τ) = 0
...
τ=
ln (0
...
0852
= 1
...
2
Now using the relationship 1/(2Γ) = τ, Γ = 498
...
Solve for K using Eq
...
14) and the known constants
K = 4πn
sin (θ / 2)
sin (45)
= 4π (1
...
87 *10 7
−9
λ
632
...
427×10–12 and solve for the particle
diameter using the rearranged Stokes–Einstein equation, Eq
...
16)
4
...
38 × 10 −23 (293)
kT
=
= 301 nm
3πηDT 3π (0
...
427 × 10 −12
(
)
4
...
D
...
Introduction to surface chemistry and physics of polymers
...
D
...
) Surface and Interfacial Aspects of Biomedical Polymers, Vol
...
New York: Plenum
...
D
...
X-ray photoelectron spectroscopy (XPS)
...
D
...
)
Surface and Interfacial Aspects of Biomedical Polymers, Vol
...
New York: Plenum
...
D
...
Polymer surface analysis: conclusions and expectations
...
D
...
) Surface and Interfacial Aspects of Biomedical Polymers, Vol
...
New York: Plenum
...
D
...
Principles of protein adsorption
...
D
...
) Surface and
Interfacial Aspects of Biomedical Polymers, Vol
...
New York:
Plenum
...
D
...
M
...
E
...
The contact angle and interface
energetics
...
D
...
) Surface and Interfacial Aspects of Biomedical
Polymers, Vol
...
New York: Plenum
...
G
...
Ceramic biomaterials
...
D
...
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Engineering Handbook
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Boca Raton, FL: CRC Press
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, Lespinasse, F
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, Baquey, A
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F
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Dordrecht, Holland: Kluwer Academic Publishers
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, Tompkins, R
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and Yarmush, M
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In R
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Boca Raton, FL: CRC Press
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D
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W
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D
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Biomaterials, 17 (2): 137–46
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...
D
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Electron Microscopy: Principles and Techniques
for Biologist
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Brown, W
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) 1993
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Oxford: Clarendon Press
...
1984
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In T
...
) Fourier
Transform Infrared Spectroscopy
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Reidel Publishing
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, Eire, D
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and Yang, G
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Scanning force microscopy of biological
macromolecules: present and future
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) Nanofabrication and Biosystems: Integrating Materials Science,
Engineering and Biology
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Castner, D
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and Ratner, B
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Publishers
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A
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D
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Boca Raton, FL:
CRC Press
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T
...
D
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The effect of biomaterials on the host
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S
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Descouts, P
...
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Nanoscale probing of biocompatibility of materials
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A
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Dordrecht, The Netherlands: Kluwer Academic Publishers
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and Bilge, F
...
1986
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In A
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New York: Macmillan
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J
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Biological Electron Microscopy: Theory, Techniques and
Troubleshooting
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Feng, L
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D
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Protein adsorption on low-temperature isotropic
carbon: I
...
J
...
Materials Res
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Ferraro J
...
and Basile, L
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(eds
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Fourier Transform Infrared Spectroscopy:
Applications to Chemical Systems, Vol
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Orlando, FL: Academic Press
...
61
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and Larson, H
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Ferraro and
L
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Basile (eds
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2
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Fischbach, F
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4th ed
...
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Goodman, S
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, Li, C
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B
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L
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M
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and bulk morphology of polyurethanes by electron microscopies
...
D
...
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Greisler, H
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, Gosselin, C
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, Kang, S
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and Kim, D
...
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Biomaterials, 17 (3): 329-36
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M
...
G
...
Introduction to dispersive and interferometric
infrared spectroscopy
...
Theophanides (ed
...
Dordrecht, Holland: D
...
Hatano, M
...
Induced circular dichroism in biopolymer-dye systems
...
Okamura
(ed) Advances in Polymer Science, Vol
...
Berlin: Springer Verlag
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, Van Wagenen, R
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and Andrade, J
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In J
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2
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Hutton B
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Introduction to XPS
...
chem
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ac
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Jones, D
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and Mcintire, L
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and Lyman, D
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In J
...
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1 Surface Chemistry
and Physics
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4
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B
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In J
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Bronzino (ed
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2nd ed
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Marchant, R
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and Wang, I
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humans
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S
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Biomedical Devices
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Marti, O
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SXM: an introduction
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Marti and M
...
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in Biology
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Morrissey, B
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Ann
...
Y
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Norde, W
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New York: Plenum
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O
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A
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D
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Biomedical Engineering Handbook
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Boca Raton, FL: CRC Press
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1967
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New York: Academic Press
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D
...
J
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Reference
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St
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Park, J
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Bronzino (ed
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2nd ed
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and Lakes, R
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2nd ed
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Paynter, R
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(ed
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Publishers B
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Ratner, B
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1988
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D
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Biomaterials
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S
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San Diego: Academic Press, 1996
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D
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F
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microscope
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F
...
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Scientific, Technical and Clinical Testing of Implant Materials
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Silver, S
...
1994
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London: Chapman & Hall
...
, Bujia, J
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, Reitzel, D
...
W
...
R
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Tissue engineering and autologous transplant formation: practical approaches with
resorbable biomaterials and new cell culture techniques
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Skalak, R
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F
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) 1988
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New York: Alan R
...
Skalak, R
...
F
...
1988
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In Skalak, R
...
F
...
Tissue Engineering
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Liss
...
Biotreatments
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...
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Spire Biomedical
...
[Online]
http://www
...
com/bio_technologies
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Materials Science Program
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uah
...
1999
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vgscientific
...
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...
Mulloy and A
...
Thomas (eds
...
Totowa, NJ: Humana Press
...
, Mayer, J
...
, Eckert, K
...
, Lüscher, P
...
1996
...
Biomaterials, 17 (2): 83–91
...
7 Problems
4
...
2
4
...
4
4
...
6
4
...
8
4
...
10
4
...
12
4
...
14
4
...
16
4
...
18
4
...
20
4
...
22
4
...
24
4
...
26
Search the literature to find a biomaterial listed in Table 4
...
Search the literature to find a polymer listed in Table 4
...
Describe how polymers are made more rigid
...
Search the literature to find an application listed in Table 4
...
State the highest practical resolution of TEM and calculate the accelerating
voltage required to achieve it
...
Describe the principle and sample preparation for a TEM
...
Describe the principle and sample preparation for 2 modes of STM
...
Describe the principle and sample preparation for XPS
...
Describe the principle and sample preparation for SIMS
...
Describe the principle and sample preparation for dispersive infrared
spectroscopy
...
Describe the principle and sample preparation for FT-IR
...
Describe the principle and sample preparation for FTIR-ATR
...
Describe the principle of DSC
...
Describe the principle of TIRF
...
Describe the principle of autoradiography
...
4
...
27
4
...
5 and when G(τ) = 0
...
We wish to view the topography of a biomaterial surface and the molecules that
adsorb to it in a liquid
...
Name other
instruments you rejected and why you rejected them
...
6
Cellular Measurements in Biomaterials and Tissue
Engineering
Jeffrey S
...
Major advances have been made over the past
several years allowing for the observation of cells and their structure
...
One area that has benefited the most is
tissue engineering and the development of biomaterials
...
Researchers are using live cells,
chemicals, and other synthetic materials to develop biomaterials for implantation in the
human body (Lewis, 1995)
...
6
...
Microscopy, or using a microscope to
study an object, has made significant advances since then
...
First let’s briefly look at a basic cell, different types of
cellular measurements, and some of the parameters of interest to the biomedical researcher
...
1
...
It is the basic unit of life and all organisms are composed of one or more cells
...
Eukaryotic cells are composed of three main features: a nucleus, surrounded by cytoplasm, which in turn is surrounded by a sack-like plasma membrane
...
Cells are 90% fluid (cytoplasm),
which consists of amino acids, proteins, glucose, and numerous other molecules
...
On a molecular level, the cell contains
50% protein, 15% nucleic acid, 15% carbohydrates, 10% lipids, and 10% other
...
1
shows the contents of the typical cell
...
1 Typical cell content
...
Membranous sacs within the cytoplasm
...
Site of protein and lipid synthesis and a transport network for molecules
...
Does not have ribosomes and is tubular
...
Lysosomes
Microtubules
Mitochondria
Nucleus
Peroxisomes
Ribosomes:
Main point of digestion
...
Site of aerobic respiration and the major energy production center
...
Use oxygen to carry out catabolic reactions
...
RNA goes
here for translation into proteins
...
2 shows the typical sizes for some of the cell features
...
2 Typical sizes of cellular features
0
...
8 nm
2 nm
4 nm
6 nm
7 to 10 nm
17 to 20 nm
25 nm
50 to 70 nm
100 nm
200 nm
200 to 500 nm
200 to 500 nm
1 µm
2 µm
3 µm
3 to 10 µm
9 µm
90 µm
100 µm
Diameter of hydrogen atom
Amino acid
Thickness of DNA membrane
Protein
Microfilament
Cell membranes
Ribosome
Microtubule
Nuclear pore
AIDS virus
Centriole
Lysosomes
Peroxisomes
Diameter of human nerve cell
Bacteria
Mitochondrion
Nucleus
Human red blood cell
Amoeba
Human egg
Many processes that occur within cells are still not well understood
...
The human body contains over 200 types of
cells of various shapes, sizes and functions, yet each contains the same genetic material
...
1
...
The traditional method of fixed cell evaluation is through the viewing of cells that have been permanently affixed to a microscope slide
...
g
...
Fixed cells
In some cases, with relatively loose or transparent tissue, the object under examination
can be placed on a slide and then placed under the microscope
...
If the
object is generally opaque, then the slice either must be very thin or some other method
must be used as discussed in Chapter 4
...
Therefore, dyes are used which react with some of the cell’s
structures but not others
...
Because of this, the cells are normally preserved or fixed for observation
...
In fixing the cells, the general
structure of the cell and organelles may be preserved but enzymes and antigens within the
cell may be destroyed
...
6-4
Chapter 6 Cellular Measurements
Another method involves the freezing or cryofixing of cells for observation
...
A cryostat is a microtome mounted in a freezing
chamber
...
However, this method has the disadvantage
that ice crystals formed during the freezing process may distort the image of the cell and
the specimens have a tendency to freeze-dry
...
This is good when trying to make a diagnosis while a patient is on the operating
table but not so good for long-term research studies
...
The characteristics of individual cells at different stages of response to the stimulus are
examined and then these individual responses are pieced together into one response that
describes the entire process
...
The process of breaking open cells is called homogenization and the separation of
organelles is called fractionation
...
Homogenization is normally accomplished by using force to break the cell
membrane
...
When the pestle is inserted and turned rapidly in the tube containing small pieces of tissue, intracellular connections are broken and membranes of whole
cells are ruptured
...
Ultrasonic waves are also used where the cell membrane is broken,
but the organelles remain intact
...
For some
materials, this can be accomplished by simply using gravity
...
The most widely used instrument for
separation, however, is the centrifuge
...
At each level, the material which sediments
can be saved and the supernatant can be centrifuged at higher forces
...
A centrifuge that operates at speeds greater than 20,000 rpm
is called an ultracentrifuge
...
Live cells
Live cells have the advantage that time is not typically a factor when viewing
...
One of the three general categories of live cell research is the division of cell
population studies
...
With
this configuration, not only the activity within the cell can be studied, but also the interaction between cells and other substances or objects external to the cellular structure such
as man-made materials
...
This may be the physical features of the cell, its topology, or the relative
chemical/molecular structure of the cell
...
Single cell imaging involves one of two different techniques
...
Using digital (computer) techniques, characterization
of single cells can be done by the cell researcher
...
This involves the use of video cameras and video recording systems
...
Cell motility is assessed by timelapse video microscopy of individual cells crawling on sheets of polydimethylsiloxane
...
2 Light Microscopy
Since there is a theoretical limit (Rayleigh limit) on how much an object can be magnified and still be seen clearly, scientists have resorted to a variety of new technologies and
have developed a number of techniques to enhance their understanding of the cellular
world
...
When a curved
lens is used, light rays pass straight through the center of the lens while rays passing
through the outer edges of the lens are bent
...
1(a)
...
Figure 6
...
1)
Object
Image
F
LO
LF
(a)
LI
(b)
Figure 6
...
(b) The light rays are
bent by the lens and refocus as an image
...
2 shows that a conventional (wide field and bright field) compound
microscope is composed of two lenses
...
It forms a much larger primary (intermediate)
image just below the eyepiece
...
This is the
enlarged virtual image seen when looking into a microscope
...
Eye
Eyepiece
Objective
Slide
Sample
Condenser
Field
iris
Light
source
Figure 6
...
The compound microscope contains a light source for sample
illumination, a field iris to control the light field, a condenser to focus the illuminating light, an
objective lens, and an eyepiece
...
If light is reflected from the object instead of
passing through, the light microscope becomes a dissecting microscope
...
6
...
1 Resolution versus magnification
The microscope’s function is to allow viewing of objects that cannot be seen with the
human eye
...
As previously discussed in Chapter 4, magnification
refers to the size of the image as compared to the original object and is usually expressed
as × mm, where mm is the amount of magnification
...
As
a general rule, the greater the magnification, the greater the resolution
...
If an image of a cell is magnified by a factor of ten, the image will get larger, but not necessarily any clearer
...
Regardless of how
much you increase the size of the image, no more detail can be seen
...
This is also known as the resolving power of the lens
and is only a function of the lens
...
1 mm apart at a distance of 100 mm
...
01 mm apart, they cannot be
distinguished unless we magnify their image by × 10
...
1 mm to 0
...
Unfortunately, a lens can magnify an image without increasing the resolution
...
Thus, even
though they can be made to appear 0
...
While microscope lenses are typically expressed in terms of magnification, the important value is the resolution
...
resolution = 0
...
2)
where λ is the wavelength of the illuminating light, n is the refractive index of the medium between the objective and the specimen, and the cone angle α is 1/2 the angle of the
acceptance of light onto the lens (Figure 6
...
The value n sinα is known as the numerical
aperture (n
...
Objective
α
Specimen
Figure 6
...
There are three ways to improve resolution
...
This is typically done using filters
...
The cone
angle can be increased by placing the objective as close as possible to the specimen
...
95 (GEK, 1997)
...
Immersion oil is sometimes used in place of the air between the objective
and the slide to increase n
...
Since the shortest wavelength of visible light is blue, almost all microscopes have incorporated a blue filter, which is often
referred to as a daylight filter
...
2 to 0
...
Resolution can
be enhanced by reducing the wavelength to the ultraviolet range
...
Thus, this form of microscopy requires a detector or photographic film that is sensitive to UV
...
The best resolution is not attainable, however, unless the lenses are corrected for
problems common to lens design
...
Chromatic and spherical distortions (aberrations) occur in all lenses to some
extent due to the fact that a 3-D object is being viewed as a 2-D image
...
In general, the smaller the optical distortion, the greater the cost
...
2
...
Bright field microscopy is
used to view stained or naturally pigmented organelles in the cell
...
If an object contains colored features, the eye detects those colors
...
Therefore,
the light that passes through the sample is seen as a color that is distinctly different from
the background or direct light that does not pass through the sample
...
The easiest way to enhance the contrast of the relatively transparent cells is to
stain them
...
If the cells
are fixed, this is not a problem except for possible damage to the cellular integrity from
the dye
...
One way to achieve this is by using a filter
...
Blue light, about 450 nm, is
usually the shortest wavelength used in light microscopy
...
In order to see a specific structure of the
cell, it must be large enough to be able to perturb the wave motion of the light rays that
strike it
...
Organelles that are smaller than this cannot be resolved be-
6-10
Chapter 6 Cellular Measurements
cause they are small compared to the wavelengths of visible light and are not able to perturb the wave motion of light traveling to our eyes
...
This type of microscopy is used to view living cellular structures because they are not pigmented, thus
unable to be seen under bright field microscopy, and the structures within the cell tend to
differ in refractive indices
...
This causes interference, which in turn
causes different areas to appear as differences in brightness when seen by the eye
...
If the normal phase shift is increased by 1/4 or 1/2 wavelength, the
differences will be magnified in intensity
...
A standard compound microscope is modified for phase contrast microscopy, as
shown in Figure 6
...
Some light transmitted from the lower annular ring passes
through the specimen and is imaged on an upper semitransparent ring
...
Since the rays of light travel
slightly different distances, when they meet up again, they will be slightly out of phase
with one another
...
5)
...
6)
...
4 In phase contrast microscopy, light from the lower annular ring is imaged on a semitransparent upper annular ring
...
Figure 6
...
The amplitude of the wave is doubled by this interaction
...
6 Interaction of light waves that meet one-half wavelength out of phase results in destructive interference
...
If the upper annular ring is opaque instead of semitransparent, it will block all
light except that which is refracted, thus yielding a dark field phase contrast microscope
...
Contrast is obtained by converting these phase
changes into amplitude changes
...
These rays are routed through two different optical paths and then recombined
...
The advantage to this method is
that the phase difference can be shifted in phase by a variable amount
...
In microscopy, the term Normarski is synonymous with the differential interference contrast
technique
...
DIC imaging provides good rejection of out-of-focus interference
...
The technique essentially acts as a filter that emphasizes edges and lines
...
Dark field
Figure 6
...
With dark field illumination, the background field is dark because the condenser light comes from outside the
collecting angle of the objective
...
Small objects, even those below the limits of resolution, can be detected easily since objects scatter light and appear to emit light on a dark field
...
7 Example of darkfield illumination
...
Imagine the object in the darkfield view glowing like
the moon at night
...
This method is similar to conventional darkfield illumination
except that the central opaque light stop at the base of the substage condenser is substituted for a colored central stop
...
If a colored transparent annular filter is added, the
sample is colored
...
The light source and
condenser are above the stage pointing downward
...
As a result, one is looking up through the bottom of the specimen and rather
than looking at the specimen from the top, typically through a cover glass, as on a conventional microscope
...
By adding
phase contrast capabilities, cells can be observed without stains
...
Near field scanning optical microscopy (NSOM)
NSOM offers dramatic improvement in resolution from about 1 µm to about 10 nm
(Paesler and Moyer, 1996)
...
The sample is
raster scanned in close proximity to the fixed probe, which detects light only from the
surface in the immediate vicinity
...
Electrodes on the left and right sides are driven with 200 V to achieve 15 µm side movement
...
An interior electrode permits 1
...
6-14
Chapter 6 Cellular Measurements
6
...
3 Electronic microscopy
A photographic, video, or solid-state camera can be attached to a microscope to make a
permanent record of an observation
...
A camera can be adapted to each of these viewing heads
...
The microscope itself usually acts as the camera lens
...
The use of a still camera is called photomicroscopy and the still picture is called the micrograph
...
The most recent instrumentation involves the use of specially
configured microscopes, new types of high-resolution solid-state cameras, image digitization, and digital image processing
...
However, as a result of these developments, the field
is now usually called electronic microscopy or optodigital microscopy (Shotten, 1990)
...
The
typical solid-state camera uses a technology called a charge-coupled device or CCD
...
8)
...
The charge for each pixel is collected and sent to an output amplifier so that the level of light incident to each pixel is recorded
...
The intensity of each pixel is displayed as a video matrix on the computer, yielding a two-dimensional image of incident light
...
The CCD camera has very high signal-to-noise ratio and is available in high
resolution arrays of 2032 × 2044 pixels or greater at 1
...
These array cameras
have a response in which the output is linearly related to the input light intensity over a
very wide range of light levels
...
A lower resolution array of 1300 ×
1030 pixels at 12 frames/s is still below the 60 Hz standard video scan rate
...
Also, many times these
devices are operated at low temperatures to maximize the signal-to-noise ratio and are
therefore termed cooled
...
8 CCD Array
...
Each pixel can independently sense light level and provide this information to a computer
...
9)
that can be done with these microscopes
...
The device
is focused on a plane of the object and a two-dimensional picture is directly recorded
...
In contrast, a point-scanned device is focused on a single point of the object
...
This is
typically done in the two horizontal (x–y) planes so the resulting picture would look the
same as the wide field image (Shotten, 1990)
...
Objective
Objective
Sample
Sample
(a) Wide field
(b) Point scan
Figure 6
...
(a) wide field collects an
entire image while (b) point scan image must be assembled point by point
...
2
...
These markers are used for a variety of purposes
from locating a certain structure within a cell, identifying which cells contain a particular
substance, how much of the substance they contain, where it is located within the cell,
how that substance may move over the cell’s cycle, if the substance moves between cells,
and even how much of the substance is present within a cell
...
Some are naturally taken up by the cells when introduced into their environment
...
Once put into cells, some are analyzed immediately, others are given some time to bond
to specific cellular structures, while others are activated at a later time when the researcher wants to observe time specific cellular dynamics
...
These systems all involve the excitation of a fluorescent material, the subsequent fluorescence emission by the material, and
the detection of this fluorescence by a detector (Haugland, 1997)
...
There are a number of different
ways that these probes are used with the cells:
•
•
•
•
•
the probe binds directly to the cellular structure of interest,
the probe binds to another molecule that has an affinity or reactivity towards
some cellular structure,
the probe binds to an antibody that in turn binds to some cellular structure,
the probe does not bind but its fluorescence depends on local concentration of a
solute,
nonfluorescent molecules are converted to fluorescent molecules through an enzymatic reaction
...
First the excitation wavelength is different from the emission wavelength
...
Also, different types of probes emit fluorescence at different wavelengths
...
In addition, the entire excitation/fluorescence cycle can
be repeated
...
First, probes must
be chosen based on sensitivity, or the amount of substance that is labeled within the cell
...
Specificity is provided by fluorochromes
...
Some
types of fluorochromes are generated by the activity of enzymes, or are sensitive to the
presence of specific ions
...
The advantages of using probes include the high signal levels against a low
background (noise) level, they are not prone to motion artifact, and they can be used to
monitor very small changes
...
Photobleaching is the breakdown of the fluorescent probe within the sample as it
is exposed to light
...
Photobleaching causes several problems
...
In a flow cytometer, a laser excites fluorescence of individual cells in an interrogation volume
...
cell type
...
Fluorescence video microscopy can capture multiple images at differing wavelengths of light simultaneously at video rates
...
Radioactive tracers
Radioactive tracers are used in a number of areas of cell research as an effective and safe
means of monitoring cellular interactions
...
These tracers have the advantages of high precision and specificity but suffer the
disadvantages of extensive radiation handling safety procedures, the inability to distinguish more than one probe at a time, and a relatively long time (hours to days) to obtain
results
...
Tritium (3H) is an important tracer
used for cellular research
...
Tritium is most prominent because replacing hydrogen with tritium in a molecule does not cause chemical or physiological changes in molecular activity (Heidecamp, 1996)
...
It is nearly impossible to predict
which individual element will radioactively decay, but predictions can be made about
large numbers of the elements
...
It is measured in becquerels
...
To monitor this ionization effect, a device called an ionization chamber is
used
...
These chambers have two electric plates separated by an inert gas with
a voltage applied across them with a battery or power supply
...
10
...
This causes a small voltage change in the form of a pulse
to temporarily occur across the plates
...
The output pulse is then read by some measuring
device
...
High-energy alpha particles are significantly easier to detect than beta particles,
and they require lower voltage
...
Consequently, ionization chambers are most useful for measuring alpha
emissions
...
Resistor
+
Voltage
supply
Capacitor
+++++++++++++++
Particle
−
−
−
+ +
Ions
+
− − − − − − − − − − −−
Pulse
count
Plates
Freq to volt
counter
Meter
Figure 6
...
The power supply has a voltage source and series
resistor
...
A pocket dosimeter is a modification of the basic ionization chamber
...
Essentially it is just a capacitor, which is charged by a base unit
and carried as a portable unit
...
When
exposed to ionizing radiation, the capacitor discharges slightly
...
Since dosimeters carry lower voltage potentials, they are used for the measurement
of X-ray and high-energy gamma radiation, but do not detect beta emissions
...
They use a substance in the counting chamber, called a scintillant, to produce a flash of light
...
A circuit then converts
each light flash to an electric current pulse
...
If the efficiency of the system (or the percent of actual radioactive decays that were detected) is known, the disintegrations per minute (dpm) can be calculated using Eq
...
3)
...
3)
Autoradiography is the process of using radioactivity to trace cellular activity
...
Carbon and phosphorous are also used, but are more radioactive so they
require more handling precautions and provide poorer resolution of intracellular details
...
The picture of a cell on photographic film that has been labeled with radioactive
tracers is called an autoradiogram
...
The number and distribution of these
grains are therefore proportional to the amount and distribution of the cellular radioactive
label
...
Alpha particles produce straight, dense tracks a few micrometers in length
...
Beta particles or electrons produce single grains or tracks of
grains
...
Low-energy beta particles (3H and 14C) produce silver grains within a few
micrometers of the radioactive area thus providing excellent resolution
...
2
...
These microscopes remove the out-of-focus
blur from the 2-D image directly through hardware rather than requiring a software deblurring technique (discussed in section 6
...
1)
...
A standard light
microscope can be used for CLSM with some technically simple, yet expensive, modifications
...
A CLSM normally uses a laser beam as a light source because a laser provides high intensity, wellfocused, monochromatic light, which is able to easily illuminate individual points within
a specimen
...
This interference is known as halation
...
To obtain an image of the specimen,
the light from the specimen is routed to a detector
...
11
...
This signal is then typically sent to
an imaging system where the current is converted to a voltage, digitized, processed to
reduce noise, and an image is reconstructed for display on a monitor
...
CLSM provides
high-contrast images of specimens without the image artifacts normally present with
conventional contrasting techniques
...
The disadvantages of this technique are relatively high cost and possible damage to the specimen
from the laser illumination
...
Detector
Pinhole
detector
aperture
Pinhole
illumination
aperture
or laser
Dichroic
mirror
Objective
Specimen
Focal plane
Out of focus
In focus
Figure 6
...
The microscope removes out-of-focus (z-plane)
blur by keeping out of focus light from reaching the detector using a pinhole
...
2
...
This technique is based
on the principle that two photons of longer wavelength light simultaneously excite a
probe that would normally be excited by one photon of a shorter wavelength, as shown in
Figure 6
...
This method has the advantage that less photobleaching occurs because only
the focal point is being excited as compared to the entire depth of the specimen as in confocal and wide-field imaging
...
In addition, TPEM can obtain optical sections from deeper into a specimen
...
Two-photon excitation has several limitations
...
This can be eliminated by the use
of a confocal aperture at the expense of a loss in signal
...
Detector
Two beam excitation
Dichroic
mirror
Objective
Specimen
Focal plane
Figure 6
...
This microscope doesn’t require a pinhole but is
able to excite single points within the sample by having two photons excite the sample only at the
exact location of interest
...
2
...
Several of these techniques correct the image in software as opposed to hardware
...
Computational deblurring
A computational deblurring (digital deconvolution) light microscope system is a relatively new system that offers an alternative to confocal microscopy
...
By a fairly complex mathematical algorithm, each 2-D slice
of the object is stored in the computer as a digital image (Richardson, 1997)
...
It mathematically makes a first estimate as
to which 2-D plane light has originated from based on the characteristics of the lens system used
...
Then the adjusted image is compared to the original image and the error is determined
and used to adjust the estimate
...
High-resolution fluorescence images are achieved
...
Image processing and analysis is typically
done after imaging has been completed although some systems process the data real-time
...
This process is similar
to the technique used for X-ray and magnetic resonance imaging discussed in Chapter 7
...
An algorithm fills in structures
and builds a single 3-D image
...
Tracing can be done within the entire volume or in a series of overlapping thick
sections
...
The contour data are also assigned 3-D coordinates to calculate volumes, surface
areas, and perimeters
...
Manipulations can be done to create a stereoscopic image of the image so it can be viewed in 3-D
...
3 Cell Orientation
Cell orientation refers to both the orientation of cells within tissue and the orientation of
cellular components within the cell
...
Understanding how cells are oriented in relation to one another, and thereby the mechanical properties of natural tissue, is an important aspect in
the development of artificial tissue (Tranquillo, 1997)
...
Another aspect involves the way in which cells orient themselves and migrate in
response to different types of stimuli
...
6
...
1 Orientation chamber
One way to measure orientation is by using an orientation chamber
...
The chamber is similar to a hemocytometer (see Chapter 5)
...
6
...
2 Video enhanced contrast microscopy
Video enhanced contrast microscopy (VECM), as shown in Figure 6
...
By using both the analog and digital contrast enhancement as well as background image subtraction, this method is able to observe objects with dimensions an order of magnitude smaller than the resolution limits of the microscope alone (Shotten,
1990)
...
This method involves three steps (Figure 6
...
First the light microscope’s DIC optics is adjusted to just
under the saturation level of the video camera
...
Then the gain control is adjusted to
amplify this dark-low intensity signal
...
In this step, the specimen free background that has been previously recorded
is subtracted from the live image
...
13 Video-enhanced contrast microscope (VECM) system
...
Intensity
A
Intensity
Distance
B
Intensity
Distance
C
Intensity
Distance
D
Distance
Figure 6
...
(b) The threshold is set just under the saturation
level
...
(d) Gain is adjusted to amplify dark-low intensity signal
...
3 Cell Orientation
25
Figure 6
...
(b) The same image with digital contrast enhancement, the single structures
become apparent
...
(c) Subtraction of the background and resulting
with further contrast enhancement
...
4 Cell Rolling Velocity
Cell rolling velocity involves the tracking of cells, particularly blood cells, as they start to
tumble or roll as the body responds to infection or foreign matter
...
When an infection occurs in an area of the body, white blood cells
are responsible for attacking the infection
...
Recruitment of white blood cells from the blood to
the area of infection is required
...
These Velcro-like cell adhesion molecules (CAMs) start
the rolling process and cause the white blood cells to roll along the endothelium wall of
the blood vessel
...
This is typically measured using fluorescent probes, intensified fluorescence microscopy,
cell tracking techniques, and the artificial introduction of CAMs
...
High-sensitivity video
cameras use video image tubes with sensitivities about two orders of magnitude greater
than conventional video cameras
...
Recently, these cameras have been replaced with solidstate slow-scan cooled CCD cameras of high resolution
...
IFM images do have one major problem—out-of-focus
blur
...
This problem is compensated for in software and is detailed in the image processing section 6
...
7
...
Figure 6
...
IFM is typically used
with the lowest level of excitation light possible so that the probe can be traced for a relatively long period of time
...
6-26
6
...
16 Intensified Fluorescence Microscopy system
...
The video image is typically time stamped and sent
to the frame grabber
...
The processed signal is then sent to a monitor for display by the operator and permanently recorded for later playback and analysis
...
5 Cell Pore Size Determination
Cell pore size is an important parameter for a number of reasons
...
Also, the first indication that two cells
are going to fuse is the formation of a small pore connecting the two cells
...
6
...
1 TEM
The transmission electron microscope (TEM) (discussed in Chapter 4) is a useful tool for
determining pore sizes because of its resolution in the 0
...
Electron microscopes did not typically view larger objects well so it was difficult to view the cell as a
whole, locate a point of interest, and then zoom in on it
...
TEMs work in a vacuum, so living cells cannot be
observed with this type of microscope
...
Thus it is possible that the cellular structure
being imaged may have been altered by the dye
...
17 A TEM image of skeletal muscle cells
...
5
...
The 3-D structure is obtained through the
process of Secondary Emission Ion Scanning
...
The particles are analyzed with each scan of the electron beam
...
The data from each layer are then analyzed and reconstructed to
6-28
6
...
Since electrons are relatively small, the etching is sometimes enhanced by bombarding the surface with ions rather than electrons
...
18 A SEM image of stressed liver cells
...
6 Cell Deformation
Cell deformation involves measuring the mechanical properties of cells and the forces
involved in cell activation
...
The deformation of cells, in response to some mechanical force outside the cell, is an area of great interest to biomedical researchers
...
This research involves in vitro biological experiments, mathematical modeling of
cellular mechanical behavior, and computer simulation of cell mechanics
...
Typically video microscopy is
used to monitor, record, and measure the amount of deformation in these experiments
...
6
...
1 Micropipet technique
Several methods can be used to deform cells (Hochmuth, 1990)
...
This technique involves aspirating part or
all of a cell into a glass micropipet
...
The rigidity and other cell deformation properties can be found as a
function of the force on the cell and the displacement of the cell inside the micropipet
...
1 µm can be measured
...
19 In the micropipet technique, force causes a displacement to determine cell deformation
properties
...
6
...
5 Cell Pore Size Determination
31
Another technique used is called optical tweezers or a laser trap
...
The optical trapping system uses an inverted microscope in differential interference contrast mode and a motorized x–y stage
and two associated lasers
...
The optical tweezers can be moved
throughout the viewing field and cell deformations as small as 0
...
6
...
Shear stresses
are generated due to regions of the liquid flowing at different speeds
...
20)
...
Cell
shear stress is defined as the cellular response to this mechanical effect within the body
...
The production rate and the release of these compounds are modulated by blood flow and the associated shear stress
...
For example, bone marrow cells cultivated in a petri dish
produce only two of ten types of blood cells
...
There are two problems in dealing with cell shear stress
...
The other is what effect the shear
stress has on the cells
...
20 Parabolic distribution of velocities and the shear stress it causes on a blood cell
...
7
...
However, the cone and plate method solves this problem
...
The cone
is rotated at a constant speed
...
7 Cell Shear Stress
33
proportional to their distance from the axis of rotation since the slope of the cone is constant
...
4)
where η is the viscosity of the liquid (0
...
Figure 6
...
If the
viscosity remains relatively constant, as is the case with blood, the shear stress remains
constant
...
Liquid
Cone
dv/dx
Plate (microscopic slide)
v=0
vmax
Figure 6
...
The cone is immersed in a liquid and then rotated at a constant
rate
...
6
...
2 Fluorescent ratiometric imaging
Shear stress is reported to induce calcium increase in the cell
...
13
...
The fluorescent image is an image pair acquired at two different wavelengths and
obtained by a silicon-intensified target camera
...
6
...
In some cases reduction of adhesion is the aim, in others an increase is desired
...
In addition, the strength of adhesive bonds is of prime
interest to the tissue engineer
...
6
...
1 Laser trap
The optical tweezer, or laser trap, method is used for generating controlled forces in the
piconewton range
...
Although piconewton sized forces are quite small, they are sufficient to
stop the motion of highly mobile cells or single enzymes
...
6
...
2 Interferometry
Interference microscopy is used for examining cell adhesion
...
An interferometer splits a light beam into two
beams, which are then recombined so they can interfere (Chapter 5)
...
Changes in optical
path length occur with changes in refractive index (changes in density) of the structure on
which the beams are focused
...
Interference microscopes are operated in both the reflectance and transmittance modes
...
8
...
This is used to study the cell adhesion molecule
...
6-34
6
...
Cell migration is an area of
great interest for tissue engineering applications such as tissue growth and biomedical
implantation
...
9
...
First, a single point image is scanned over a 2-D plane
...
This process must be repeated for each point in time
...
Typically, this animation is recorded on a
video recorder for ease of repetitive observation and analysis or is assembled into a computer animation file
...
One problem with this technique is the large amount of storage space and computing power required for the image processing
...
Four fields of view, each
containing 5 to 20 cells, are collected at 15 to 30 min intervals and the position of each
cell is recorded in each frame at every event interval
...
6-35
6
...
Cell capacitance has been used as an index of secretion in cells
...
Fluorescent microscopy is commonly used since fluorescent probes are now available to
measure pH, sodium, magnesium, potassium, calcium and chloride ions
...
10
...
Submicron colloidal gold particles coupled to antibodies are useful for this purpose (Geerts et al
...
These small particles
can be detected with a light microscope since the particles scatter a small amount of light,
which is detectable using video contrast enhancement microscopy
...
The
biggest advantage of this technique is its ability to label specific molecules within the cell
...
A final advantage is the
small size of these particles, which allow diffusion throughout the cytoplasm
...
10
...
This allows cell uptake of various biological molecules
...
With the proper pulse shape, the cell completely recovers, the pores reseal, and the cell
continues to grow
...
6-36
6
...
Epithelial cells from certain organs produce and secrete many
important proteins that are stimulated by specific hormones and neurotransmitters
...
As such, cellular engineers are focusing on the regulation of the external and internal environments of the cell that promote the secretion of specific proteins
...
11
...
This resolution allows for observation of individual protein molecules in action
...
For example, AFM permits study of wear debris a few hundred nanometers in size from ultrahigh molecular weight polyethylene (UHMWPE) used
in hip implants
...
11
...
This method is also known as Time-Resolved Fluorescence Microscopy (TRFM)
and is analogous to magnetic resonance imaging (MRI) discussed in Chapter 7
...
The fluorescence lifetimes of the
probes are mostly independent of their concentration and are not normally affected by
photobleaching
...
Therefore, FLIM allows quantitative imaging using visiblewavelength illumination
...
Figure 6
...
In
this system, the time difference between the start of an excitation laser light pulse’s arrival at the sample and the arrival of the fluorescence photon at the detector is measured
...
6-37
6-38
Chapter 6 Cellular Measurements
Microscope
Light
source
Beam
splitter
Photomultiplier
tube
Sample
Start timer
circuit
Stop timer
circuit
Timer
Time-toamplitude
converter
Multichannel
analyzer
Figure 6
...
When a light source
provides an excitation pulse, some of the light is deflected to the start timer circuit while the rest
illuminates the sample
...
The time difference is then converted to an amplitude
...
The other method using this technique simply monitors the fluorescent intensity
over time
...
The sample is excited and the fluorescent
intensity of the sample is recorded over time
...
11
...
First, a probe is introduced that binds to plasma membrane
proteins
...
This causes the probe in that area to fluoresce
...
1 to 1
...
This causes the probes in
that area to photolyse (convert to a nonfluorescent product)
...
With time, plasma membrane proteins from neighboring areas diffuse into the circular area and the fluorescence recovers with time as in Figure 6
...
39
6
...
23 A sample graph of fluorescence of proteins during FRAP
...
If not all the proteins are mobile within the membrane, the percentage of mobile proteins
can be calculated using
Rm =
F (∞ ) − F (+ )
F (− ) − F (+ )
(6
...
6
...
Many tissue engineering
studies depend on the ability to determine the effect of various factors on cell proliferation
...
These studies that help in the understanding of the regulation of cell
proliferation are key in the development of new tissue engineering methods and the biomaterials used to support them
...
Cell proliferation studies are used when measuring growth
factor, drug screening, and the study of toxic, mutagenic, and carcinogenic effects of
chemical compounds on cells (Roche Molecular Biochemicals, 2000)
...
Density of cells growing on a vessel surface is useful for
tissue engineering applications
...
Cell density is recorded and then
plotted on a log scale against time in culture
...
There are two general methods of measuring cell proliferation in cell populations including measuring DNA synthesis and measuring metabolic activity
...
12
...
Over time, some of the radioactive material is retained in the DNA of the
cells
...
Knowing the radiation level of the original tracer in the cell and comparing it to the current radiation level
of the cell provides a ratio that is proportional to the number of times the cell has divided
...
12
...
Fluorescent probes are fed to cells, which are given time to incorporate them into their
DNA (typically 2 to 24 h)
...
One other method involves using special salts and detects whether cell proliferation is occurring
...
6-40
6
...
There are 200 different kinds of
cells in our bodies, yet all are developed initially from a single cell
...
Most research on cell differentiation focuses on understanding the mechanisms involved
in cell differentiation
...
Learning what
cell types are involved in tissue regeneration is critical in building tissue
...
Staining techniques are widely used to visualize those components that are otherwise too difficult to see under an ordinary light microscope because of the lack of color
contrast between the object under examination and the background or because of the limited resolving power of the light microscope
...
The dye used in
staining varies with the cell types
...
13
...
This is accomplished by taking advantage of the property
that fluorescent probes have a wavelength shift when they bind with ions in the cell
...
This ratio of fluorescence intensities at the two wavelengths is then
used to calculate the relative concentration of the probe to the concentration of the ion
(Bolsover et al
...
First the background must be subtracted from the two signals
...
6)
where λ1 and λ2 are the two excitation wavelengths, Iλ1 and Iλ2 are the fluorescence
intensities, Bλ1 and Bλ2 are the background light levels, and Sλ1 and Sλ2 are the shading
6-41
6-42
Chapter 6 Cellular Measurements
corrections that compensate for the small spatial distribution between the two excitation
beams
...
6
...
2 Cell sorter
Flow cytometry systems (Chapter 5) examine cells previously labeled with fluorochromes one at a time and then separate the cells on the basis of their color of fluorescence
...
The system uses multiple excitation wavelengths in the visible and UV range
...
The PC can be used for statistical purposes providing histograms of
the various distributions of cells
...
14 Cell Signaling and Regulation
Cell signaling and regulation involves the complex processes that occur within cells to
maintain life (regulation) and trigger new events to occur (signaling)
...
To do
this, engineers must study the processes of signaling and regulation within the cell and
develop an understanding of how and why they work as they do
...
NMR provides noninvasive images of cellular structure and chemical composition
...
Microscope Laser Light Scattering Spectroscopy (MLLSS) is used
for motion studies of intercellular macromolecules during diffusion or flow
...
Fluorescent
probes are used to mark specific membrane proteins, which can in turn be microinjected
into cells
...
With these systems, both quantitative and qualitative observation of membrane flow in
live cells can be monitored
...
However, two of the
most common methods are described below
...
14
...
In situ hybridization is the
process of attaching a small fragment of DNA to a specific target strand of DNA or RNA
in a preserved cell
...
Then the point of attachment along the chromosome is identified (Figure 6
...
This
method is useful if the identity of a particular gene is known but the chromosome on
which it is located is not
...
Another application is in the study of embryo development and the mechanisms involved in the sequence of gene selection, activation, and location
...
To do this,
the spectrum of the fluorescence emission must be determined since it may contain light
that is a mixture of several different colors
...
, 1996)
...
By changing the length of the optical path difference between beams, an
intensity versus optical path difference is obtained
...
Since the probes used typically have a relatively
6-43
6-44
Chapter 6 Cellular Measurements
large span between emission wavelength, the intensity peaks where each probe is fluorescing is readily apparent from the spectral image
...
A
Fluorescent probe
B
Chromosome target
Figure 6
...
(b) The fluorescent probe binds to the target gene
...
25 Human chromosomes probed and counterstained to produce a FISH image
...
(from Fluorescence Detection: Anti-Dye Antibodies
...
[Online] Available:
www
...
com/lit/fish/part4
...
14
...
A radioactive tracer is added to the cellular environment for a short period of time
...
The cells are then fixed and
autoradiography is used to locate the sites of newly synthesized DNA
...
14 Cell Signaling and Regulation
45
tion of a particular molecule is determined by pulse-chase labeling: cells are again exposed to a radioactive tracer for a short period of time and then washed away
...
When these cells are examined,
the radioactivity will have moved to the site of utilization in the cell
...
15 References
Bolsover, S
...
, Silver, R
...
and Whitaker, M
...
Ratio imaging measurements of
intracellular calcium
...
Shotton (ed
...
New York: Wiley-Liss
...
P
...
Liquids
...
F
...
) Biomechanics – Materials
...
Geerts, H
...
, Nuydens, R
...
1991
...
In R
...
Cherry (ed
...
Boca Raton, FL:
CRC Press
...
H
...
Cell Biology Laboratory Manual
...
gac
...
html
Hochmuth, R
...
1990
...
Trans
...
Biomech
...
, 112 (3): 233-4
...
1997
...
Am
...
, [Online] Available:
www
...
org/amsci/Issues/Sciobs97/Sciobs97-03pits
...
P
...
Handbook of Fluorescent Probes and Research Chemicals
...
LOCI 2000
...
[Online] Available:
www
...
wisc
...
html
Lewis, R
...
Tissue engineering now coming into its own as a scientific field
...
9: 15
...
2000
...
Fluorescence Detection: Anti-Dye Antibodies
...
probes
...
html
Paesler, M
...
and Moyer, P
...
1996
...
New York: John Wiley & Sons
...
B
...
Handbook of Biological Confocal Microscopy
...
Peters, R
...
1991
...
In R
...
Cherry
(ed
...
Boca Raton,
FL: CRC Press
...
CCD Grading
...
photomet
...
shtml
Richardson, M
...
Three Dimensional Deconvolution of Microscope Data
...
[Online] Available: www
...
com/technical
...
Guide to Cell Proliferation and Apoptosis Methods
...
roche
...
html
Soenksen, D
...
, Garini, Y
...
1996
...
In Asakura, T
...
L
...
C
...
V
...
J
...
) Optical Diagnostics of Living Cells and Biofluids
...
SPIE,
2678
...
15 References
47
Shotton, D
...
) 1993
...
New York: Wiley-Liss
...
M
...
Video and opto-digital imaging microscopy
...
J
...
)
New Techniques of Optical Microscopy and Microspectrometry
...
Stine, B
...
High Resolution Imaging of Biological Samples by Scanning Probe Microscopy
...
[Online] Available:
www
...
com/AppNotes/ANMain
...
and Rodgers, M
...
J
...
Time-resolved fluorescence microscopy
...
J
...
) New Techniques of Optical Microscopy and Microspectrometry
...
Wright, S
...
Introduction to confocal microscopy and three-dimensional reconstruction
...
Matsumoto (ed
...
San Diego: Academic Press
...
16 Problems
6
...
2
6
...
4
6
...
6
6
...
8
6
...
10
6
...
12
6
...
14
6
...
16
6
...
18
6
...
20
List the size of an atom, molecule, virus, cell
...
Calculate the focal length for a
magnification of 20
...
2 and a cone
angle of 80° that is operated at a wavelength of 770 nm
...
Sketch a phase contrast microscope
...
Explain how the phase contrast microscope is changed to
achieve a dark field
...
Describe the term fluorescent probe as it applies to cell microscopy
...
Describe the effect of photobleaching in fluorescence microscopy
...
10 has a voltage supply of 100
V
...
Name the electric circuit component that converts the
analog voltage at the right of the capacitor to a digital signal suitable for input to
a pulse counter
...
The detector has an
efficiency of 0
...
Determine the actual number of decays per minute
...
For a confocal laser scanning microscope, for fixed optics, explain how scanning is accomplished in the x, y, and z directions
...
Explain how scanning is accomplished in the x, y, and z directions
...
Explain the reason for using and the basic principles of operation of deconvolution image processing
...
Explain the reason for and the basic principles of measuring cell rolling velocity
...
Explain the reason for and the basic principles of measuring cell deformation
...
6-48
6
...
21
6
...
23
6
...
25
6
...
27
6
...
29
49
Calculate the shear stress for water at 20 °C in a cone and plate viscometer with
a diameter of 10 cm, a separation gap of 1 mm at the circumference, and rotation
at 1 revolution per second
...
Explain the reason for and the basic principles of measuring cell adhesion
...
Explain the reason for and the basic principles of measuring cell uptake
...
Using fluorescence recovery after photobleaching, calculate the fraction of mobile protein where F(–) = 4, F(+) = 1, F(∞) = 2
...
Explain the reason for and the basic principles of measuring cell differentiation
...
7
Nervous System
Jang-Zern Tsai
The nervous system is defined as all cells, tissues, and organs that regulate the body’s
response to both internal and external stimuli (Costello, 1994)
...
Biomedical engineers need to understand how the nervous system works in order to
design this equipment
...
1 Cell Potential
The nervous system is comprised of neuron cells
...
Only
these and muscle cells are able to generate potentials and therefore are called excitable
cells
...
, 1999)
...
1
...
Across this membrane
there is an electric charge referred to as the resting potential
...
In the cells, potassium (K+)
channels allow diffusion of K+ ions out of the cell while sodium (Na+) ions diffuse into
the cell
...
K+ and Na+ ions are
continuously diffusing across the membrane from where they were just pumped, but at a
slower rate
...
The magnitude of the equilibrium membrane resting potential is given, at body
temperature, by the Nernst equation
1
2
Nervous System
Vm = (RT/nF)ln[K+]e/[K+]I
Vm = 0
...
1)
At 37 °C (body temperature), where Vm is the transmembrane potential in millivolts, R is
the universal gas constant, T is absolute temperature in K, n is the valence of the ion, F is
the Faraday constant, [K+]e is the extracellular potassium concentration, and [K+]i is the
intracellular potassium concentration
...
7 mV
...
3 mV (Clark, 1998)
...
, 1999)
...
1
...
Other cells, such as nerve and muscle
cells, are excitable
...
Later the K+
permeability increases and K+ ions flow out to counter this effect
...
Finally, the resting potential is regenerated
...
2
...
It
propagates in nerves at about 60 m/s and carries sensation from the periphery toward the
brain via sensory nerves
...
Figure 7
...
We can calculate the
action potential propagation velocity v = d/t, where d = distance and t = time
...
1 Cell Potential
3
Indifferent
electrode
Electronic
stimulator
Micropipet electrode
1m
Stimulus
0V
Action potential
0
20 ms
Time
Resting potential
–70 mV
Figure 7
...
The
depolarization process first occurs at the stimulation site
...
4
Nervous System
Na+
Na+
++++
−−−−
+ + + Outside cell
Plasma membrane
−−−
Inside cell
++
−−
++++
++
+++
−−−−
−−
−−−
K+
1
K+
3
Resting phase
Na+
Repolarizing phase
Na+
−−−−
−−
−−−
++++
++
+++
++++
++
+++
−−−−
−−
−−−
K+
Depolarizing phase
4
Membrane potential
(mV)
2
K+
2
+50
0
1
Undershoot phase
3
4
−50
−100
t
Figure 7
...
The circled numbers on
the action potential correspond to the four diagrams of voltage-gated sodium and potassium
channels in a neuron's plasma membrane (Campbell et al
...
+7
...
2
...
The cerebellum is a coordinator in the voluntary (somatic) muscle system and
acts in conjunction with the brainstem and cerebral cortex to maintain balance and
provide harmonious muscle movements
...
3 shows the cerebrum, which occupies a special dominant position in
the central nervous system
...
Figure 7
...
From A
...
McNaught and R
...
, 1975
...
7
...
2 Electroencephalography (EEG)
5
6
Nervous System
The electroencephalogram (EEG) provides information about the health and function of
the brain by detecting electric impulses in the brain
...
By removing a portion of the skull, it is possible to insert microelectrodes into
the brain and record action potentials from single cells
...
4
...
Some localization is possible by using the monopolar
connection, which is a recording from a single electrode referenced to the average of all
other electrodes
...
The EEG is
typically 100 µV in amplitude with a frequency response of 0
...
Sixteen
channels are usually recorded simultaneously (Hughes, 1994)
...
4 The 10–20 electrode system for measuring the EEG
...
H
...
The EEG is typically recorded with the subject awake and resting
...
5(b)
shows that when the eyes are closed, alpha waves with a frequency of about 10 Hz appear
...
2 Brain, EEG and Evoked Potentials
7
amplitude increases
...
Alpha waves correspond to when the subject is awake, theta waves
indicate sleep, delta waves indicate sleeping well, and finally beta waves indicate REM
sleep (Clark, 1998)
...
5(a)
...
Grand mal epilepsy spreads throughout the brain, causes
convulsions, and is diagnosed by large amplitude recording from all parts of the scalp
...
Psychomotor epilepsy is identified by 2 to 4 Hz waves with
superimposed 14 Hz waves and causes amnesia or unwanted motor action
...
5(c)
shows various epilepsy waveforms, though other abnormal waveforms also exist that help
to diagnose other disease
...
(c)
8
Nervous System
Figure 7
...
(b) When the eyes are opened, alpha waves disappear
...
From A
...
Guyton, Structure and Function
of the Nervous System, 2nd
...
, Philadephia: W
...
Saunders, 1972
...
2
...
The
response is usually of low amplitude (<5 µV), especially in relation to the background
EEG signal (50 to 100 µV), so that stimulus-related cerebral evoked potentials usually
cannot be identified in routine EEG recordings
...
For example, a stimulus
occurs N = 100 times and each time the response is recorded
...
All 100 responses at 1 ms are added, etc
...
ms
...
The interfering
noise potentials from the EEG are random and have an amplitude equal to N
...
,
1993)
...
They permit the lesions of these pathways, which may not have any
visible symptoms, to be detected and localized
...
The electric potentials associated with cognitive
processes can also be recorded through the scalp and are helpful in the evaluation of
patients with suspected dementia
...
Clinical abnormalities can be detected by an
increase in latency (the delay between the stimulus and the wave response)
...
The pattern consists of a counterphase
alternation of dark and light squares without any change in total luminance
...
The evoked potential generated in the occipital cortex is
detected by an electrode placed on the scalp in the midoccipital position with reference to
either the linked mastoids or a midfrontal electrode
...
The
procedure is usually done twice to ensure reproducibility and the two eyes are tested
separately
...
It may
help diagnose certain visual or brain disorders (Gevins and Aminoff, 1988) (WFUBMC,
2000)
...
2 Brain, EEG and Evoked Potentials
9
Brainstem auditory evoked potentials
During brainstem auditory evoked potential (BAEP) testing, rarefaction or condensation
clicks at about 10 Hz stimulate one ear of the subject and white noise masks the
contralateral ear
...
The evoked responses are smaller than 1 µV measured from the vertex with
reference to the lobe of the stimulated ear
...
At least two separate results
are recorded for each ear to ensure reproducibility
...
It may help uncover the cause of hearing and
balance problems as well as other nervous system disorders (Gevins and Aminoff, 1988)
(WFUBMC, 2000)
...
Electrodes placed on the subject’s scalp and along the spinal cord can detect a
series of positive and negative potentials following the peripheral stimulation
...
About 1000 responses are averaged to
reduce the interference from endogenous cardiac, motor, and EEG activities and
exogenous electric noise
...
SSEP assesses the neurological pathways from the nerves in
the arms or legs through the spinal cord to the brain
...
7
...
X rays are
very short wavelength electromagnetic waves produced when fast-moving electrons
collide with substances in their path
...
Because of this short
wavelength, X rays can penetrate very dense substances to produce images or shadows
that can then be recorded on photographic film
...
Dense structures, such as the skull appear white, whereas air-filled areas,
such as the lung are black
...
6 shows an X-ray system
...
An aluminum filter
stops low-energy X rays, because they would not pass through the body to form an image
...
Secondary radiation could fog
the film, but is stopped by a grid shaped like Venetian blinds
...
To lower X-ray dose, an image intensifier may be used
...
Many light photons stimulate a photocathode to emit
many electrons
...
Figure 7
...
Unlike a camera, there are no lenses
...
4 Brain Imaging: CT
Figure 7
...
It measures X-ray
attenuation of many parallel paths in one plane
...
The
information is processed by computer to yield a 2-dimensional image of a slice through
the body
...
Figure 7
...
Thus if there is high attenuation at
one picture element (pixel), the assignment from many angles increases that pixel more
than other pixels
...
Water is
used as the benchmark substance as it has a CT value of zero
...
CT can produce cross-sectional
images (slices) of anatomic structures without superimposing tissues on each other
...
CT yields images of soft tissue within the brain not possible with
conventional X ray, which is largely blocked by the dense skull
...
CT is used in the differential
diagnosis of intracranial neoplasms (brain tumors), cerebral infarctions (lack of blood
7
...
However there do
exist limitations of CT as with all imaging devices
...
For, example, if a
tissue (i
...
tumor) in the body has attenuation similar to that of water, it will not be
detected
...
7 In computed tomography, a thin X-ray beam measures the attenuation along a single
path
...
The information is processed to yield attenuation at every element in the
2-dimensional slice
...
A
...
Di Chiro, Theory of image reconstruction in
computed tomography
...
12
Nervous System
Y
1
1/3 + 1/3
=
2/3
1/3 + 1
=
4/3
1/3 + 1/3
=
2/3
3
1 + 1/3
=
4/3
1+1
=
2
1 + 1/3
=
4/3
1
1/3 + 1/3
=
2/3
1/3 + 1
=
4/3
1
3
1/3 + 1/3
=
2/3
1
X
Figure 7
...
Each row and column signifies a certain path
angle
...
These sum to the maximum value of 2, thus indicating an object in that cell
...
A sum of these two
numbers that is significantly greater relative to the others indicates an object
...
5 Brain Imaging: MRI
Magnetic resonance imaging (MRI) provides two-dimensional images that are slices of
1H isotope concentration in three-dimensional objects
...
The charged 1H electrons spin and precess like
a spinning top at the Larmor frequency of 42
...
The magnetic field is perturbed
to produce a small magnetic gradient along the y-axis
...
9 shows that there is only
one slice at a particular Larmour frequency
...
The magnetic field is quickly perturbed
along the x-axis
...
The z-axis magnetic field can be perturbed to
produce additional scan lines
...
The strengths of MRI include: sensitivity to flow (i
...
blood); electronic
adjustment of imaging plane (opposed to physical adjustment in CT); no ionizing
radiation (only magnetism and radio waves); and high soft tissue resolution (see Figure
7
...
However some of the weaknesses are contraindications due to implanted medical
devices and metal plates in patients, slow image acquisitions and high cost
...
5 Brain Imaging: MRI
13
z
One slice
in x axis
One slice
in y axis
Single line
y
x
Figure 7
...
An RF receiver measures from one slice
in the x-axis
...
10 MRI images of the brain
...
(b) A sagittal view of a
patient with an arterio-venous malformation (AVM) which is an explosive growth of the capillary
bed
...
The regions of the brain
that were "activated" by the visual stimulus are displayed in white on the images
...
7
...
In an attempt to reach stability, the
radionuclide emits one or more types of radiation, the most common examples being
alpha particles, beta particles, and gamma electromagnetic radiation
...
Computerized radiation detection equipment, particularly scintillation
detectors, detects gamma rays by giving off a light flash (scintillation)
...
It is used mainly to allow visualization of organs
and regions within organs that cannot be seen on a simple X-ray film
...
A radiopharmaceutical is administered orally or intravenously to the patient
...
An
imaging device records the position and concentration of the radiation that emerged from
the radionuclide
...
With a nuclear medicine scan, metastatic disease to the bone can be found 6
months to a year before it can be detected with the usual bone radiograph
...
A nuclear brain scan is used for the
diagnosis of pathologic abnormalities such as tumors, cerebrovascular aneurysms, and
hematomas
...
11 shows a gamma camera
...
Light is detected by more than one photomultiplier tube, but the relative
amounts received improve spatial resolution
...
The resulting image has spatial resolution
of about 1% of the image dimension (Mettler and Guiberteau, 1991)
...
6 Brain Imaging: Nuclear Imaging
15
Figure 7
...
7
...
The gamma rays are collected
from the patient in a manner similar to CT, but several slices can be obtained at the same
time
...
It is
possible to see anomalies not observable with conventional X rays or gamma camera
(Van Heertum and Tikofsky, 1995)
...
8 Brain Imaging: Positron Emission Tomography (PET)
Some isotopes produce positrons that react with electrons to emit two photons at 511 keV
in opposite directions
...
12(a) shows the two detectors on opposite sides of the
patient
...
Additional pairs of detectors permit faster operation
...
An advantage of PET is that all of the most
common radioisotopes used, 15O, 13N, 11C and 18F, can be compounded as metabolites
...
If a portion of the brain is active, increased
blood flow carries the isotope to it, where it shows up on the image
...
For
example, measurement of glucose-fluorodeoxyglucose (FDG) metabolism is used to
determine tumor growth
...
Figure 7
...
(c) The circular ring does not rotate but may move slightly to fill in the gaps between the
detectors
...
9 Brain Imaging: Biomagnetism
Action potentials within the brain cause ionic currents to flow through cell membranes
and between cells
...
Magnetic shielding around the
subject can remove interference from the earth’s magnetic field of 50 µT
...
The
Superconducting Quantum Interference Device (SQUID) magnetometer has a sensitivity
of 0
...
1 pT (Malmivuo and Plonsey, 1995) (NATO, 1983)
...
In fact, no electrodes are required on the scalp
...
The combination of functional information, deduced from MEG,
with structural information obtained from MRI has become almost routine in most MEG
research groups
...
10 Eye, ERG, EOG and Visual Field
7
...
1 Electroretinogram (ERG)
7
...
Measuring the electrical response of the retina to flashes of light detects
inherited retinal degenerations, congenital (existing from birth) retinal dystrophies, and
toxic retinopathies from drugs or chemicals
...
Macular disease is
the leading cause of blindness in elderly Americans today and it is also linked to smoking
...
The degeneration is caused by the partial breakdown of the insulating layer between the
retina and the choroids (the layer of blood vessels behind the retina) (Yahoo! Health,
2000)
...
Figure 7
...
An alternative to the contact lens
electrode would be to use electrodes that hook over or rest on the lower eyelid
...
The entire retina is stimulated with light and the small
voltage is amplified and recorded
...
Figure 7
...
The reference electrode is placed
on the right temple
...
14)
...
All of the cells in the
two layers give a graduated hyperpolarizing or depolarizing response to light, as
compared with the action potentials produced by the retinal ganglion cells
...
This wave has separate rod
and cone components
...
The a wave represents photorecptorial activity and the b wave represents
postphotoreceptorial activity in the second-order retinal neuronal network, but the
sources are still unclear
...
Since the rods of the eyes are the visual receptors used in dim light, recording from the
rod system requires long periods of dark adaptation and one very dim single flash
stimulus
...
To obtain cone response, intense light flashes accompanied by an intense
light background are required (Good, 1999)
...
The degeneration
starts at more peripheral parts of the retina and progressively decreases the field of vision
...
7
...
14 The normal standardized corneal electroretinogram
...
F
...
Scale 100 V/div
...
(Good, 1999)
7
...
2 Electro-oculogram (EOG)
The resting potential of the front of the retina is electropositive with respect to the back of
the retina
...
If the eye
looks left, this positive cornea makes an electrode to the left of the eye more positive than
an electrode to the right of the eye
...
Electrodes
above and below the eye can determine the vertical direction of gaze
...
This test can be used to detect retinal pigment epithelial dysfunction
(Verdon, 2000)
...
10
...
This can be assessed by visual field measurement, in which the
examinee detects the targets that stimulate the retina at varying distances from the fovea
...
Confrontation test
For this test the patient fixates their vision straight ahead on the examiner at a distance of
1 m
...
The examiner puts one hand midway between the patient
and the examiner with some fingers extended
...
The temporal and nasal fields and the superior and the inferior fields are tested
in turn
...
In kinetic perimetry, the patient detects a test object of fixed size and
illumination moved from a nonsensing area
...
An isopter, the contour line that connects the points at which an object of certain
size and certain light intensity may be recognized, represents a line on the macula lutea
that passes through the points of equal visual acuity
...
This can be
conducted with a test object of size from 1 to 50 mm on a tangent screen, which contains
concentric circles every 5° and radiating lines 15° or 22
...
This test demonstrates the peripheral isopter, the blind
spot, and various scotomas (blind spots in the visual field)
...
It encompasses the central 20° of the visual
field when held at the reading distance
...
10 Eye, ERG, EOG and Visual Field
21
central dot and indicates any irregular line section that appears blurred, wavy, curved,
discolored, or missing
...
Amsler grid testing is recommended for
patients with macular degeneration or other retinal disordrs that threaten central vision
...
7
...
4 Eye pressure
Intraocular pressure is an important indication of glaucoma, a disease that can lead to
blindness
...
It can drain out of the eye through a network of tissues between the
iris and the cornea
...
Sometimes the extra pressure causes the collapse of tiny blood vessels that
nourish the light-sensitive cells of the retina and the optic nerve fiber
...
, 1996)
...
Strictly speaking, the intraocular pressure cannot be measured unless we insert a
cannula into the eye
...
Two methods are used to measure ocular tension
...
Indentation
tonometry measures the deformation of the globe in response to a standard weight
applied to the cornea
...
15 shows the Goldmann applanation tonometer, which measures the
force required to flatten the cornea by an area of 3
...
The flattened area
is viewed with a biomicroscope through a split prism after instillation of a topical
anesthetic and fluorescein
...
The SchiØtz tonometer measures the ease with which the cornea may be indented by the
plunger of the instrument
...
A noncontact applanation tonometer measures intraocular pressure without
touching the eye
...
When a beam of light reflects from the flattened surface, a maximum
detected signal shuts off the pneumatic pulse and measures the time elapsed, which
correlates with pressure
...
The intraocular
pressure may vary with time by 6 mmHg during a day, so continuous sampling of the eye
pressure for several hours is required for adequate evaluation of glaucoma (Newell, 1996)
...
15 The Goldmann applanation tonometer
...
7
...
5 Ophthalmoscopy
Ophthalmoscopy is used to inspect the interior of the eye
...
Direct ophthalmoscopy and indirect ophthalmoscopy are the two methods used
...
The ophthalmoscope has rotating lenses on top to magnify a particular area
being viewed up to 15 times
...
The resolving power of direct ophthalmoscopy is about 70 µm
...
7
...
16, is usually performed by using a
binocular ophthalmoscope
...
An inverted image of the fundus magnified about 5 ×
is formed between the condensing lens and the ophthalmoscope
...
The entire fundus may be
examined by indirect ophthalmoscopy with pupillary dilation and sclera (the white part of
the eye) indentation
...
) Although indirect
ophthalmoscopy only has 200 µm resolving power, it is more advantageous than direct
ophthalmoscopy in that the stereoscopic image allows detection and evaluation of
minimal elevations of the sensory retina and retina pigment epithelium
...
24
Nervous System
Mirror
Examiner’s eyes
Lamp
Inverted image of
patient’s fundus
Condensing lens
Patient’s eye ball
Figure 7
...
7
...
11
...
Anatomically, it is
divided into the external ear, middle ear, and inner ear
...
The middle ear, or tympanic cavity, is an oblong cavity bridged by an
ossicular chain consisting of three small bones between the tympanic membrane and the
inner ear
...
, 1981)
...
11 Ears and Audiometry
25
The auditory portion of the ear can be physiologically divided into two partsa
sound-conducting apparatus and an electromechanical transducer (Hawke, 1990)
...
The electromechanical transducer transforms
the mechanical energy of sound into electric impulses to be transmitted by the auditory
nerves to the auditory cortex of the brain
...
11
...
Pure tone air conduction threshold testing
The audio signal passes through the outer ear, the middle ear, and the inner ear before
being further processed by the central auditory system
...
In this test, the subject responds to bursts of singlefrequency stimuli presented through calibrated earphones
...
Pure tone bone conduction threshold testing
A special vibratory transducer is placed on the mastoid process or the forehead and thus
stimulates the inner ear directly through the skull
...
If there is a difference between the air conduction and bone conduction responses,
this indicates pathology in the outer or middle ear, which may be treatable
...
Speech discrimination testing
In this test, the subject listens to lists of single-syllable speech discrimination words
presented through earphones and repeats what he or she hears
...
In contrast to the
pure tone threshold test, which addresses hearing sensitivity, this test assesses the
integrity of the entire auditory system’s ability in hearing clearly and understanding
speech communication
...
Speech reception threshold
26
Nervous System
This test uses words that are attenuated successively
...
A threshold is determined when the patient repeats
50% of the words correctly (Laszlo and Chasin, 1988)
...
A stiff middle ear
(poor ossicular chain mobility) reduces the mobility of the eardrum, causing a 220 Hz
tone to be reflected with little attenuation
...
Evoked response audiometry (see section 7
...
3)
Clicks in the ear yield electric potentials measured by an electrode at the vertex (top) of
the scalp
...
Early latency evoked potentials
(about 10 ms) are from the brain stem
...
Late latency evoked potentials (about 100 ms) evaluate
the neurological integrity of the cortical centers
...
11
...
Evidence of injury or congenital (present at
birth) malformation is usually obvious
...
This type of ear examination can also detect a rupture or puncture of the eardrum
...
A red or
swollen eardrum can indicate an ear infection
...
7
...
12
...
Here we are interested in
7
...
The primary function of skeletal muscles
is to generate force
...
Thus skeletal muscles have two
fundamental properties: They are excitable (able to respond to stimulus) and contractible
(able to produce tension) (Biewener, 1992)
...
Each muscle fiber contains hundreds to thousands of myofibrils (Figure 7
...
Each myofibril has about 1500 myosin filaments and 3000 actin filaments lying side by
side (Carlson and Wilkie, 1974)
...
18 shows the structure of a single myofibril
...
17 The components of a skeletal muscle; the myofiber is the smallest complete contractile
system
...
(from The Muscle Physiology Laboratory,
2000)
28
Nervous System
Myofibril
"Thin" actin
filament
"Thick" myosin
filament
Sarcomere
Z disk
Actin
lattice
Myosin
lattice
Anchoring
structure
Intermeshed
networks
Figure 7
...
Each myofibril contains about 1500 myosin
filaments and 3000 actin filaments in the pattern shown above
...
During muscle contraction the thin (actin) filaments slide inward past
the thick (myosin) filaments pulling the two Z disks closer together, thus shortening the sarcomere
...
(from The Muscle Physiology Laboratory, 2000)
As an action potential travels along a motor nerve to muscle fibers, it initiates an
action potential along the muscle fiber membrane, which depolarizes the muscle fiber
membrane and travels within the muscle fiber
...
This mechanism produces muscle contraction
(Jones and Round, 1990)
...
There are three types of
contraction: Isometric, or static, contraction means a muscle contracts without change in
its length
...
Eccentric contraction occurs
when the load is greater than the isometric force and elongates the contracting muscle
(Sigel, 1986)
...
12 Muscles
The length–force relation of a muscle can be measured isometrically
...
The
tension generated by the muscle at various constant lengths is measured to generate the
length–force curve (Lieber, 1992)
...
19 shows a typical length–force curve of a
skeletal muscle (Ozkaya and Nordin, 1991)
...
19 The overall force of a muscle, F, is the sum of the active force, Fa, and the passive
force, Fp
...
The passive force results from elongation of the connective muscle tissue beyond its
resting length
...
The amount of force generated by a stimulated muscle depends on how its ends
are restrained (Woledge et al
...
If neither end of a stimulated muscle is fixed, the
muscle shortens at its maximum velocity of 33 cm/s, Vmax, and no force is generated
...
A force of sufficient magnitude, F0, will
prevent the muscle from shortening and isometric contraction occurs within the muscle
...
, 1985):
(F + a)(V + b) = (F0 + a)b
(7
...
Figure 7
...
30
Nervous System
Shortening velocity
Vma
Muscle force, F/F0
F0
Figure 7
...
The force–velocity curve can be obtained experimentally with isotonic
measurement (Lieber, 1992)
...
The muscle velocity (i
...
, shortening velocity,
or lengthening velocity) is measured and plotted against the constant load
...
12
...
EMG is used to detect primary muscular disorders
along with muscular abnormalities caused by other system diseases such as nerve
dysfunction (Junge, 1992)
...
The two main types of electrodes for measuring EMG signals from muscles are
surface electrodes and inserted electrodes
...
Selection of electrode type depends on the particular
application and the convenience of use (Loeb and Gans, 1986)
...
Saline gel
or paste is placed between the electrode and the skin to improve the electric contact
...
Needle electrodes have a relatively smaller pickup area and thus are more
suitable for detecting individual motor unit potentials
...
12 Muscles
31
repositioned in the muscle after they are inserted
...
21 shows various
constructions of needle electrodes (Kimura, 1989)
...
21 Examples of needle electrodes: (a) Monopolar needle with exposed pickup tip
...
(c) Bipolar
configuration with two pickup wires in parallel with each other in a hypodermic needle
...
This can be used to detect the
activity of individual muscle fibers
...
This can be used to detect the motor unit action potential from a large
portion of the motor unit territory
...
22 shows a wire electrode
...
The distal tips of the wires are deinsulated by about 1 to 2 mm and are bent to form
staggered hooks
...
Figure 7
...
We can obtain the EMG signal simply by placing a surface electrode on the skin
enveloping the muscle or by applying an inserted electrode in the muscle
...
The drawback of this monopolar configuration is that it detects not
only the signal from the muscle of interest but also unwanted signals from around the
muscle of interest
...
A
differential amplifier amplifies the signals picked up from the two electrodes with respect
to the signal picked up by a reference electrode
...
Figure 7
...
Signal vs
...
Nu m ber o f Po in ts
Am pl i tud e
Amplitude
5
0
0
-5
-5
0
4
x 10
50
50
100
150
150
200
200
250
0
4
x 10
50
100
150
200
200
250
0
50
100
150
Number of points
200
250
0
4
x 10
5
10 0
25 0
Am pl itude
Amplitude
5
0
0
-5
-5
0
4
x 10
5
50
10 0
150
25 0
Am pl i tu de
Amplitude
5
0
0
-5
-5
0
50
10 0
150
200
25 0
Num ber of Poin ts
Figure 7
...
Wire electrodes were inserted into these tongue muscles to
take the EMG measurement
...
7
...
3 Neuromuscular performance
Nerve cells that control movement emerge from the spinal cord and brainstem
...
Neuromuscular disorder develops
when any part along the path, from the brain to the muscle, does not work properly
...
On the other hand, if the muscle
has some disease, it may not produce normal contraction in response to the action
potential from the brain
...
By applying a dc stimulus to the skin over a
nerve at various positions in the legs or arms, and recording the time of muscle twitch
due to the stimulation with an electrode on the skin over the muscle, one can calculate the
7
...
The conduction is slowed with injury to the nerve
(Ringel, 1987)
...
Abnormal
electric signals are recorded by the EMG if there is disease in the muscle
...
13 References
American Academy of Family Physicans (AAFP)
...
[Online] http://familydoctor
...
html
Basmajian, J
...
and De Luca, C
...
1985
...
5th ed
...
Bickford, L
...
The EyeCare Connection: The EyeCare Reports
...
eyecarecontacts
...
html
Biewener, A
...
(ed
...
Biomechanics-Structures and Systems: A Practical Approach
...
Campbell, N
...
, Reece, J
...
and Mitchell L
...
1999
...
5th ed
...
Carlson, F
...
and Wilkie, D
...
1974
...
Englewood Cliffs, NJ:
Prentice-Hall
...
B
...
) 1994
...
New York: Dell
...
W
...
The origin of biopotentials
...
G
...
) Medical
Instrumentation: Application and Design
...
New York: John Wiley & Sons
...
R
...
B
...
W
...
Diseases of the Ears, Nose, and
Throat
...
Early, P
...
and Sodee, D
...
1995
...
2nd ed
...
Louis : Mosby
...
2000
...
[Online]
http://www
...
com:180/bol/topic?eu=117507&sctn=18#s_top
Freund, K
...
1997
...
[Online]
http://www
...
com/amsler
...
S
...
J
...
Electroencephalography: Brain Electrical
Activity
...
G
...
) Encyclopedia of Medical Devices and
Instrumentation
...
Good, P
...
The Electroretinogram
...
eyenews
...
dir/features
...
html
Hari, R
...
V
...
Neuromagnetism: tracking the dynamics of the
brain
...
Hine, G
...
1967
...
New York: Academic
...
R
...
EEG in Clinical Practice
...
Boston: Butterworth-Heinemann
...
1989
...
New York:
Plenum Press
...
R
...
L
...
H
...
, Shields, R
...
Jr
...
J
...
Electromyography/Electroencephalography
...
34
Nervous System
Jones, D
...
and Round, J
...
1990
...
Manchester, New York: Manchester University Press
...
1992
...
3rd ed
...
Keynes, R
...
and Aidley, D
...
1991
...
2nd ed
...
Kimura, J
...
Electrodiagnosis in Diseases of Nerve and Muscle: Principles and
Practice
...
Philadelphia: Davis
...
A
...
J
...
Audiometry
...
G
...
) Encyclopedia of
Medical Devices and Instrumentation
...
Lieber, R
...
1992
...
Baltimore: Williams & Wilkins
...
E
...
1986
...
Chicago:
University of Chicago Press
...
and Plonsey, R
...
Bioelectromagnetism: Principles and Applications of
Bioelectric and Biomagnetic Fields
...
Mazziota, J
...
and Gilman, S
...
Clinical Brain Imaging: Principles and
Applications
...
A
...
Mettler, F
...
and Guiberteau, M
...
1991
...
3rd
ed
...
B
...
The Muscle Physiology Laboratory
...
Myofilament structure
...
ucsd
...
shtml
The Muscle Physiology Laboratory
...
Fiber types
...
ucsd
...
shtml
NATO Advanced Study Institute on Biomagnetism
...
Biomagnetism: An
Interdisciplinary Approach
...
Newell, F
...
1996
...
8th ed
...
Louis: Mosby Year Book
...
and Nordin, M
...
Fundamentals of Biomechanics: Equilibrium, Motion,
and Deformation
...
Ringel, S
...
1987
...
New
York: Raven Press
...
, Shields, M
...
and Krupin, T
...
) 1996
...
2nd ed
...
Louis:
Mosby
...
J
...
Mechanics of Muscle
...
New York: New York University
Press
...
P
...
Medical imaging systems
...
G
...
), Medical
Instrumentation: Application and Design
...
New York: John Wiley & Sons
...
M
...
Muscle and its Diseases: An Outline Primer of Basic Science and
Clinical Method
...
Stein, R
...
(ed
...
Nerve and Muscle: Membranes, Cells, and Systems
...
Van Heertum, R
...
and Tikofsky, R
...
(eds
...
Cerebral SPECT Imaging
...
New York: Raven Press
...
G
...
1999
...
15th ed
...
7
...
2000
...
[Online]
http://spectacle
...
edu/ucbso/vfc/
Wake Forest University Baptist Medical Center (WFUBMC)
...
EEG Laboratory
...
wfubmc
...
html
WFUBMC
...
Evoked Potential Laboratory
...
wfubmc
...
html
Webster, J
...
(ed
...
Medical Instrumentation: Application and Design
...
New
York: John Wiley & Sons
...
C
...
A
...
1985
...
London; Orlando: Academic Press
...
2000
...
[Online]
http://health
...
com/health/Diseases_and_Conditions/Disease_Feed_Data/Macul
ar_degeneration/
7
...
1
7
...
3
7
...
5
7
...
7
7
...
9
7
...
11
7
...
13
7
...
15
Calculate the magnitude and sign of the cell membrane potential at body
temperature given that the intracellular potassium concentration = 150
millimoles/L and the extracellular potassium concentration = 5 millimoles/L
...
1 shows the change of membrane potential due to an electric stimulus
...
Calculate the velocity of propagation for the action potential in Figure 7
...
Explain the origin of action potentials and how to measure them
...
Explain why and how we measure evoked potentials
...
Calculate the improvement in signal-to-noise ratio when an average response
computer averages 200 recordings
...
Describe the beam paths used in a CT scanner
...
Describe the advantages of using nuclear medicine
...
Explain the procedure and equipment
used, including the detector type, localization method, and energy selection
method
...
Explain why and how we diagnose visual system disease
...
16
7
...
18
7
...
20
7
...
Explain why and how pressure within the eyeball is measured
...
Explain why and how we diagnose auditory system disease
...
Design an experiment to determine the force–length relationship of a muscle
...
There are over
one million heart attacks per year and over 600,000 deaths, of which 300,000 die before
reaching the hospital
...
Today, most people are aware of the things they can control that prevent heart disease (diet, not smoking, exercise, blood pressure, etc
...
Early detection and treatment of the disease continue to be key areas of emphasis in the medical
community
...
New diagnostic techniques have been developed and old ones improved, providing
added sensitivity and specificity
...
It is very important for biomedical engineers to understand the basic principles
of medical instruments
...
The human heart and blood vessels are a transportation system that delivers essential materials to all cells of the body and carries away the waste products of metabolism
...
The two chambers on the
right side of the heart send deoxygenated blood to the lungs via the pulmonary arteries
(pulmonary circulation)
...
Here, there is an exchange
of nutrients, waste products and dissolved gases
...
Hormones are also transported by
the cardiovascular system
...
1 Cardiac Anatomy and Physiology
2
Heart and Circulation
Figure 8
...
The heart, about the size of a
clenched fist, is located in the thoracic (chest) cavity between the sternum (breastbone)
and the vertebrae (backbone)
...
The upper chambers, the atria,
receive blood returning to the heart and transfer it to the lower chambers, the ventricles,
which pump the blood from the heart
...
2 shows a simplified circulatory system
...
The blood entering the right atrium has returned from the
body tissues, where O2 has been extracted from it and CO2 has been added to it by the
cells of the body
...
Thus, the
right side of the heart pumps blood into the pulmonary circulation
...
This highly oxygenated blood returning to the left atrium
subsequently flows into the left ventricle, the pumping chamber that propels the blood to
all body systems except the lungs; that is the left side of the heart pumps blood into the
systemic circulation
...
Figure 8
...
RA is the right atrium, RV is the right ventricle; LA is the
left atrium, and LV is the left ventricle
...
8
...
1
...
2)
...
The valves are positioned so that they open and close passively due
to pressure differences, similar to a one-way door
...
Deoxygenated
blood
Oxygenated
blood
Upper body
Right
atrium
Lung
Right
ventricle
Left
atrium
Left
ventricle
Lower body
Figure 8
...
The blood is delivered from the right ventricle to the
lung
...
Deoxygenated blood from the body flows back to the
right atrium and the cycle repeats
...
1)
...
If the rising ventricular pressure did
not force the AV valves to close as the ventricles contracted to empty, much of the blood
would inefficiently be forced back into the atria and veins instead of being pumped into
the arteries
...
Likewise, the left AV valve, which consists of two leaflets, is
often called the bicuspid valve or, alternatively, the mitral valve
...
They are also known as semilunar
valves because they are composed of three leaflets, each resembling a shallow half-moon
shaped pocket
...
e
...
The valves close when the ventricles relax and ventricular pressures
fall below the aortic and pulmonary artery pressures
...
The semilunar valves are prevented from swinging back into the ventricles by
the anatomical structure and positioning of the cusps (Sherwood, 2001)
...
1
...
The ventricles contract during systole
...
In an average human at rest, the
entire cardiac cycle takes about 0
...
Heart rate is
the number of heartbeats per minute
...
Figure 8
...
2
...
8
...
3 In the top figure, the electrocardiogram (ECG) initiates the cardiac cycle
...
5) are also shown
...
During diastole, the pressure in the left ventricle is low and less than that of the
arteries
...
The blood from the left atrium flows into the left
ventricle
...
1
...
The ventricles contract, which increases the pressure and closes the mitral valve
...
The blood continues to flow from the left ventricle into the aorta as long as the ventricular pressure is greater than the arterial pressure, as shown in Figure 8
...
However, if the
venticular pressure is much greater than the aortic pressure, there is a problem with the
valve and it may be stenotic (narrow)
...
Table 8
...
6
Heart and Circulation
Table 8
...
Event
Characteristics
Duration at 75
bpm (0
...
Semilunar valves close
...
AV valves open
...
Ventricular filling
...
Semilunar valves open
...
0
...
1 s
0
...
Reflection of the systolic pulse from the distal aorta distorts the aortic
contour and creates two systolic shoulders
...
That from an older person with decreased aortic compliance
has a reflected wave, which causes a more peaked pulse and higher pressure (hypertension) (O’Rourke, 1995)
...
They rely on sensing electrodes
placed on the skin surface, which measure the electric frequency of the heart, or the electrocardiogram (section 8
...
2)
...
8
...
3 Cardiac excitation and control
Figure 8
...
It is composed of specialized muscle tissue that combines characteristics of both muscle and nerve (see Chapter 7)
...
This tissue is selfexcitable, and can contract without any signal from the nervous system
...
The impulse spreads rapidly, and the two
atria contract simultaneously
...
At the bottom of the wall separating the two atria is
another patch of nodal tissue, the atrioventricular (AV) node
...
When the wave of excitation
reaches the AV node, it is delayed for about 0
...
After this delay, the signal to
contract is conducted to the apex of the ventricles along the bundle of His, and the wave
of excitation then spreads upward through the ventricular walls via the Purkinje fibers
(Davies et al
...
8
...
More sophisticated diagnoses
can be performed by studies of the electrocardiogram, the echocardiogram, the stress test,
Holter monitoring, and angiography
...
8
...
2
...
Electrodes are generally made from
metal
...
, 1999)
...
The reaction is Ag + Cl– → AgCl + e–
...
The gel
also allows for good contact between the skin–electrode interface
...
4 shows a
disposable surface electrode
...
(1981) discuss several techniques used to
manufacture Ag/AgCl electrodes
...
Figure 8
...
A typical surface electrode used for ECG recording is
made of Ag/AgCl
...
Motion artifacts (error caused by movement of the electrodes) contribute a large
error to signals from surface electrodes
...
This can be minimized by abrading the skin
with sandpaper, which short circuits the voltage
...
Other types of electrodes, such as microelectrodes, are discussed in Chapter 7
...
2
...
Voltage drop across the resistive tissue can be detected by electrodes placed on
the skin and recorded as an electrocardiogram (ECG, sometimes called EKG)
...
3
shows components of an electrocardiogram (P, Q, R, S, and T waves)
...
5)
...
From Figure 8
...
The T wave is due to repolarization (re-establishing the electric potential) of the ventricles
...
The downslope of the T wave is referred to as the vulnerable period
...
Fibrillation is an irregular contraction of cardiac muscle, which results in an ineffective propulsion of blood
...
This puts the entire myocardium in a
refractory state in which no impulse can occur
...
Direct current
defibrillation shock has been found to be more effective than alternating current shock
(Berne, 1981)
...
2 Cardiac Biopotentials
I
aVR
V1
9
V4
(d)
I
aVR
V1
V4
(e)
I
aVR
V1
V4
(f)
Figure 8
...
(a) The normal ECG
...
(c) acute inferior myocardial infarction (lack of
blood flow to heart muscle, which causes tissue to die), in which the S–T sement is depressed
...
(e) ventricular
tachycardia (faster than normal heart rate) with clear AV dissociation
...
The ECG recording instrument is called an electrocardiograph
...
6
shows the block diagram of a typical electrocardiograph
...
The input signals are amplified
and converted from analog signals to digital signals before being processed by a microprocessor
...
Clinicians can view the results on the screen of a microcomputer or print a hard
copy of the ECG signals for further analysis
...
An electrocardiograph provides the physician with valuable
information on various physical characteristics of the heart, the extent and progress of
damage incurred by the heart, and the influence of drugs on the patient
...
6 Block diagram of an electrocardiograph
...
Physicians usually attach several
electrodes on the chest of the patients as well
...
The differential amplifier rejects ground-referred interference
...
7 shows
an ECG amplifier with a dc-coupled instrumentation amplifier, which has a gain of 25
...
Chapter 2 provides more information on the differential amplifier
...
7 A circuit of an ECG amplifier
...
(From Webster, J
...
(ed
...
Medical instrumentation: application and design, 3rd ed
...
)
8
...
The buffer amplifier offers a very high input
impedance and unity gain
...
2
...
12-lead ECG
The electric potential generated by the heart appears throughout the surface of the body
...
Different pairs of electrodes at different locations generally yield different results because of
the spatial dependence of the electric field of the heart (Neuman, 1998b)
...
6)
...
By selecting different pairs of electrodes, we can obtain
ECGs that have different shapes
...
A pair of electrodes, or combination of
several electrodes through a resistive network that gives an equivalent pair, is referred to
as a lead
...
Figure 8
...
The three leads shown are lead I, right
arm (RA) to left arm (LA); lead II, right arm (RA) to left leg (LL); and lead III, LA to LL
...
1)
12
Heart and Circulation
LA
RA
LL
Figure 8
...
Lead I is from RA to LA, lead II is from RA to LL, and lead III is
from LA to LL
...
These leads are based on signals obtained from
more than one pair of electrodes
...
The three different unipolar leads are positive
electrodes placed on the right arm, augmented right (aVR), the left arm, augmented left
(aVL), and the left foot, augmented foot (aVF)
...
Physicians place an electrode at various
anatomically defined positions on the chest wall (Neuman, 1998b)
...
05 to 150 Hz
...
In these cases, only one lead, usually lead II, is monitored on a display
...
To avoid motion artifacts and muscle noise the frequency response is
reduced to 0
...
Ambulatory (Holter) monitor
8
...
The monitor records the
heart’s activity through electrodes placed on the chest of a patient
...
The recording provides a doctor with important information about
the heart and its rhythm and can help identify the cause of such normally encountered
symptoms as chest pain, palpitations (abnormally rapid pulsation in the heart), or dizziness
...
Holter introduced his portable electrocardiograph to the medical community
...
The first devices had to be worn in a backpack, and despite their large size and
weight, could only review the heart along one axis
...
The electrodes are applied to the chest
...
After the electrodes are securely attached to the chest, the excess wire is
taped to the skin to prevent accidental disconnection
...
The recorder is then tested
and a battery inserted into the device
...
Two types of Holter monitors are generally used
...
This system is composed of three components: a monitor with a cassette tape,
which records the ECG signals, a PC scanning device that scans at 60 times real time and
uses a data-reduction processor, and a printer
...
When the monitoring session is finished,
the cassette tape is put into the data-reduction processor and data are digitally stored on
the hard drive of the PC
...
These
reports are in two or three channel format depending upon the instrumentation
...
The second type of monitor is the digital solid state system
...
In some cases, a PC is used
to visualize the information on a screen
...
In a tape-based system, the
computer performs the function of digitizing, storage and analysis
...
They produce a two- or three-channel report depending upon
the instrument and are generally more expensive than individual tape-based monitors
because of their capabilities
...
As the patient recovers, the doctor may feel
comfortable with the patient moving around but may want to maintain ECG monitoring
...
With a telemetry system, a nurse attaches the patient leads to the patient in the same way
as for the bedside monitor
...
The transmitter, which resembles a portable radio, is small enough for the patient to carry
...
Manufacturers may transmit the information using frequency
modulation (FM), amplitude modulation (AM) or even pulse code modulation (PCM)
depending upon design
...
The receiver then removes the RF signal from the patient’s ECG
and sends the resulting signal to the monitor for analysis
...
In the ECG telemetry system, the receiver alarms on high and low ECG
limits the user can adjust, or possibly some arrhythmia conditions (Reinhard and Fowler,
1987)
...
It is done to screen patients
for heart disease and help predict or unmask potential coronary problems
...
The technician first abrades the
skin and applies stress electrodes to the patient’s chest
...
The exercise protocol (there are numerous protocols, which gradually
increase both speed and elevation of the treadmill) is started
...
S–T
segment depression may indicate cardiac ischemia due to coronary arterial occlusion
...
It is important to continue
monitoring the patient’s ECG, heart rate, and blood pressure during recovery, because
some problems are uncovered during that phase
...
2
...
Electrograms are measured by introducing a catheter electrode into the veins
...
We can use electrograms to study abnormal heart rhythms under controlled situations to
diagnose the specific problem with the heart’s electric system
...
2 Cardiac Biopotentials
15
obtain information on the propagation of excitation from the SA node to the ventricles
with the catheter
...
One example is patients with refractory arrhythmias of the upper chamber who need complete interruption
of the AV conduction pathway
...
The catheters are placed at different locations, such as the SA node, the AV node, and in the ventricle
...
They are then heated and destroyed with RF
energy
...
However, the risk is quite small and the electrophysiology study is relatively safe
...
8
...
The sensors used are designed so that the application of pressure modifies the electric properties of some component by stretching or otherwise deforming it
...
Strain gages are very important in biomedical instrumentation design
...
3
...
Section
8
...
2 describes a catheter that is widely used for invasive measurements of cardiovascular
variables
...
9 shows a typical system for measuring cardiac pressures
...
A syringe temporarily inflates a balloon to guide
the catheter into the pulmonary artery
...
16
Heart and Circulation
Pressure port
Catheter
Figure 8
...
A system for cardiac pressure and flow measurement
...
An external strain gage pressure sensor is also
shown
...
L
...
System for calculating compliance and cardiac hemodynamic parameters, US Patent, 5,423,323
...
3
...
1
...
11
...
Older pressure sensors had unbonded strain gage wires mounted under stress between a
frame and movable armature so that preload was greater than any expected external compressive load
...
Thus blood
pressure caused diaphragm movement, which caused resistance change, which caused a
voltage change
...
The strain gage electric resistance changes
with diaphragm deformation, which responds to pressure applied
...
These then form the four
arms of a resistance bridge
...
However, if the temperature changes, all four resistances change by the same percentage and this does not change
the output from the resistance bridge
...
3 Cardiac Pressures
17
8
...
2 Catheter
In the cardiac catheterization laboratory, catheters are inserted into the chambers of the
heart to measure pressures, flows, and oxygen saturation to determine if valve replacement is required
...
A catheter is a flexible tube for insertion into a narrow opening such as the
blood vessels, so that fluids may be introduced or removed
...
9 shows a Swan–
Ganz catheter
...
In 1929, at the age of 25, he
passed a 65 cm catheter through one of his left antecubital veins, guiding it by fluoroscopy until it entered his right atrium
...
Catheters are inserted through sheaths (the layers of connective tissue that envelop structures such as nerves, arteries, tendon, and muscle) into the arteries and the
veins of the body then pass up to the heart
...
Two approaches may be used to apply a catheter to the heart
...
The direct brachial approach may have advantages in a very obese patient, in whom the percutaneous femoral technique may be technically difficult and
bleeding hard to control after catheter removal
...
The percutaneous femoral approach has its own
set of advantages
...
Cardiac pressures are usually measured by one of several ways
...
The sensor is outside the body
...
With the catheter-tip sensor, the elastic unit is placed in a blood vessel, thus the
elastic member is in direct contact with the blood
...
8
...
The maintenance of blood flow commensurate with the metabolic needs of the body is a fundamental
requirement of human life
...
The quantity of blood delivered to the systemic cir-
18
Heart and Circulation
culation per unit time is termed the cardiac output, generally expressed in liters/minute
(L/min)
...
Most investigators use total body surface area as the standardizing variable
...
Table 8
...
Table 8
...
The data presented in this table are the average values of a
group of subjects
...
67 (±0
...
9 (±2
...
2)
The ejection fraction is defined as
Ejection fraction =
Stroke volume
End - diastolic volume
(8
...
End-systolic volume is the volume of blood remaining in the ventricle at the end of
systole when ejection is complete
...
The average resting heart rate of human is about 70 beats/min
...
6 L/min
...
Heavy exercise increases both HR and SV, and CO can increase to as high as 25 L/min
...
4
...
4)
8
...
Cv is the venous concentration of O2 (L/L)
...
The rate of inhalation or exhalation of gas is measured using
the spirometer as discussed in Chapter 9
...
The blood-O2 analyzer is used to find the concentrations of O2 in blood
...
Its accuracy when carefully performed
is approximately ±5%
...
For that reason, rapid changes in the circulation during exercise or other events cannot be studied by this technique
...
1 A patient’s O2 concentration, meaused in the pulmonary artery, is 0
...
The O2 concentration measured in the patient’s aorta is 0
...
A spirometer is used to
obtain the patient’s O2 consumption rate 0
...
Calculate the patient’s cardiac
output
...
19 L/L, Cv
= 0
...
250 L/min
...
(8
...
250 L/min
=
= 3
...
19 L/L − 0
...
4
...
A bolus of 10
mL, 0
...
The drop in temperature in the arterial circulation is usually measured using a
thermistor attached to a catheter in the pulmonary artery
...
The nurse inserts a thermodilution pulmonary artery catheter, also
known as the Swan–Ganz catheter, as shown in Figure 8
...
This catheter has a small balloon that once inflated naturally floats toward the heart to the pulmonary artery
...
10 The relationship of the temperature gradient and time
...
D
...
, Westenskow, D
...
and Johnson, R
...
Method and apparatus for producing thermodilution
cardiac output measurements utilizing a neural network, US Patent, 5,579,778
...
5)
0
where Q is the heat injected in joules, ρb is the density of the blood in kg/m3, cb is the
specific heat of the blood in J/(kg⋅K), and ∆Tb is the temperature gradient function as
shown in Figure 8
...
The area under the temperature versus time curve is inversely proportional to the blood flow or cardiac output
...
If cardiac output is reduced, the bolus
takes longer to pass through the heart
...
2 Given the following data: blood density = 1060 kg/m3, heat capacity of the
blood = 3640 J/(kg⋅K), amount of heat injected = 1
...
10 is 1
...
From Eq
...
5), the cardiac output can be computed as
8
...
25 J
3
1060 kg/m × 3640 J/(kg ⋅ °C) × (1
...
21
(8
...
Also, the lower temperature
bolus can be rapidly warmed to body temperature
...
It is more difficult to calculate
the size of the temperature perturbation than it is to measure the quantity of injected dye,
however
...
The cold saline left at the
end of the injection can further cool the blood
...
8
...
3 Dye dilution
The principle of this technique is similar to that of thermodilution
...
The dye passes through the heart, and is mixed with blood
...
Arterial blood is drawn off through another catheter by
a motorized syringe and passes at a constant rate through an optical densitometer
...
The most commonly
used dye is indocyanine green, which has low toxicity and does not remain in the blood
stream for extended periods of time
...
8
...
4 Radionuclide angiography
External detectors are used to record activity from short-lived radiopharmaceuticals
...
There are two classes of radionuclides:
1
...
This technique is excellent for measuring the extent of myocardial
ischemia and is highly specific for the diagnosis of coronary artery disease (Marwick
1995)
...
Single photon emission computerized tomography (SPECT), which is a
method based on radionuclides such as 99mTc
...
Diagnostic accuracy and adjunctive assessment of ventricular function make SPECT the currently favored stress imaging radioisotope technique ( Merz
1997)
...
22
Heart and Circulation
8
...
5 Echocardiography
Sound of frequencies greater than 20 kHz, the highest frequency that a human ear is able
to detect, are called ultrasound
...
This technique is noninvasive
...
Echocardiography can measure the size of the heart, functions of the heart, the blood flow
through the heart (when combined with the Doppler technique), and the movement of the
heart wall
...
Structural abnormalities of
the heart wall, valves, and the blood vessels going in and out of the heart can be detected
by this technique as well
...
6 to 2
...
The sound
waves are both emitted and received by the same sensor
...
Motion mode, or M-mode,
echocardiograms are generated by means of a single ultrasonic beam traversing cardiac
structures with definable anatomic shapes (chamber walls, interventricular septum) or
characteristic motions (cardiac valves)
...
Advances in echocardiographic equipment including real-time
cross-sectional scanning (two-dimensional echocardiography), Doppler echocardiography,
and contrast echocardiography have broadened the role of echocardiography in the diagnosis of a variety of cardiac diseases
...
The beam passes
through the right ventricle, interventricular septum, left ventricular cavity, posterior left
ventricular wall, pericardium and lung
...
11 shows that these structures are portrayed on the ordinate and time is displayed on the abscissa
...
By
proper positioning of the sensor all four cardiac valves, both ventricles, and the left
atrium can be visualized (Bom, 1977)
...
However, because it lacks spatial geometry, most potential information from using many cardiac
cross-sections is unavailable (Cikes and Ernst, 1983)
...
4 Cardiac Output
23
Figure 8
...
The arrows on the right image indicates the position of the ultrasound beam from which the
M-mode recording was made
...
of Tennessee
...
M-Mode
Echocardiography [Online] http://www
...
utk
...
html)
Two-dimensional echocardiography (2-D echo)
M-mode echocardiography provides extremely useful information about cardiac structures, but cannot depict lateral motion (motion perpendicular to the ultrasonic beam)
...
Images recorded in 2-D echo are displayed on videotape
...
12)
...
Table 8
...
24
Heart and Circulation
(a)
(b)
Figure 8
...
TV = tricuspid valve, AML = anterior mitral leaflet
...
1992
...
gasnet
...
html)
(c)
8
...
2 Relative advantages of echocardiographic examination techniques
...
8
...
When the ultrasonic wave is reflected by a moving object, the frequency of the
reflected beam is shifted
...
Doppler studies can measure the transvalvular pressure gradient in patients with aortic, pulmonic, tricuspid, and mitral stenosis
...
Contrast echocardiography
Contrast echocardiography is based on the fact that the injection of almost any liquid
through a small catheter produces a cloud of echoes on the M-mode echocardiogram
...
The microbubbles are too large to pass through the capillaries and yield a cloud of echos
...
We measure the cardiac output by tracing
the intravascular bubbles with a high degree of sensitivity by ultrasound (Meltzer and
Roelandt, 1982)
...
4
...
,
1996)
...
It can
also diagnose the characteristics of the cardiac muscle
...
MRI offers excellent anatomical detail of the cardiovascular system, particularly in
congenial heart disease and in diseases of the aorta (Underwood, 1992)
...
5 Cardiac Sounds
26
Heart and Circulation
Cardiac sounds shown in Figure 8
...
Table 8
...
The
first heart sound is low-pitched, soft, and relatively long
...
The opening of the valves does not produce any sound
...
The first heart sound signals the onset of systole
...
It is associated with the
closure of the semilunar valves that occurs at the onset of ventricular relaxation as the left
and right ventricular pressures fall below the aortic and pulmonary artery pressures, respectively
...
Murmurs are vibrations caused by turbulence in the blood moving rapidly through the heart
...
4 lists the types of murmurs and what they represent
...
3 The heart sounds
...
Sound
Origin
1st sound
2nd sound
3rd sound
4th sound
Closure of mitral and tricuspid valves
Closure of aortic and pulmonary valves
Rapid ventricular filling in early diastole
Ventricular filling due to atrial contraction
Table 8
...
For example, if the physician hears the 1st heart sound, a swishing
sound, and then the 2nd heart sound, the patient likely suffers from AV valve insufficiency
...
Thus,
blood must be forced through the constricted opening at tremendous velocity, resulting in
turbulence that produces an abnormal whistling sound similar to the sound produced
when you force air rapidly through narrowed lips to whistle
...
Turbulence is produced when blood flows backward through the insufficient valve and collides with blood moving in the opposite direction, creating a swishing or gurgling murmur (Sherwood, 2001)
...
8
...
1 Stethoscopes
8
...
High-frequency sounds, or murmurs, are easier to hear with the diaphragm
...
Murmurs arise from turbulent blood flow and are characterized by their timing,
quality, and intensity
...
Figure 8
...
Adapted from Mohrin, C
...
, 1995
...
US Patent, 5,389,747
...
13 shows a diagram of a stethoscope which incorporates both the bell
and diaphragm modes into the same chestpiece
...
13) adjust their openings
...
If there
is no through opening, it is in the diaphragm mode
...
8
...
2 Microphones
Microphones in use today are either crystal microphones (piezoelectric effect) or dynamic microphones (Faraday’s principle) (Peura and Webster, 1998)
...
They are very useful if one is interested in detecting surface vibrations of an object, such as the heart sound
...
Microphones turn an acoustical pressure into a voltage
...
7)
where k is the piezoelectric constant in C/N, K is the proportionality constant in C/m, and
x is the deflecting distance of the piezoelectric sensor
...
14 illustrates a charge amplifier
...
8)
where t1 is the integrating time and i is the current flowing through the capacitor, C
...
15 shows the time constant τ is
τ = RC
Hence it only passes frequencies higher than the corner frequency fc = 1/(2πRC)
...
9)
8
...
14 The piezoelectric sensor generates charge, which is transferred to the capacitor, C, by
the charge amplifier
...
Figure 8
...
30
Heart and Circulation
8
...
A number of diagnostic techniques have been developed to help the clinician determine with a good degree of accuracy whether myocardial viability is present or absent in dyssynergic (failure of muscle
coordination) regions of the heart
...
These methods depend on the demonstration of myocardial perfusion (presence
of oxygen and nutrients), myocardial metabolism, or a response to a stimulus
...
8
...
1 PET
Positron emission tomography uses isotopes that emit photons 180° apart (i
...
in opposite
directions)
...
This technique
has the distinct advantage of allowing for the assessment of both myocardial perfusion
and metabolism
...
Under normal circumstances, the myocardium uses fatty acids for its metabolism
...
A high ratio of regional glucose utilization to myocardial flow has been
found to be a reliable sign of severely ischemic but viable muscle
...
This probably relates to the improved imaging
resolution of PET and to its added benefit of also assessing metabolism
...
The disadvantages of PET are its high cost and nonportability
...
6
...
Although a heavy metal capable of causing typical heavy metal poisoning at high doses,
doses of 5,000 to 10,000 times less than that associated with clinical poisoning can be
employed for myocardial imaging
...
Thallium-201 imaging of the myocardium is one of the more difficult nuclear
medicine procedures from the standpoint of technique
...
6 Myocardial Viability
31
to obtain high-quality images
...
, 1978)
...
6
...
4
...
8
...
Arteries carry blood
away from the heart to organs throughout the body
...
Capillaries form networks of
microscopic vessels that infiltrate each tissue
...
At the downstream end, capillaries rejoin to form venules, and these small vessels converge into veins
...
Notice that arteries and veins are distinguished by the direction in which they carry blood, not by the quality of the blood they
contain
...
However, all arteries do carry blood from the heart to capillaries, and only veins
return blood to the heart from capillaries
...
The size of the capillary is 10 µm in diameter
...
Peripheral vascular diseases are a group of distinct diseases or syndromes involving the arterial, venous, or lymphatic system (Strandness et al
...
The major
vascular disease is coronary artery disease, which kills more than a million people every
year, and afflicts more than 5 million others with disabling symptoms
...
These tests enable us to diagnose and follow the course of arteriosclerosis (abnormal
condition of an artery) much more accurately than was possible in the past
...
A promising new development is Duplex scanning (section 8
...
1) of the peripheral arteries, combining Doppler spectral
analysis of blood flow with B-mode ultrasound imaging
...
Venography remains the standard for the diagnosis of deep venous thrombosis
(blood clots), but does have significant limitations
...
Likewise, invasive
techniques have become useful in the long-term evaluation of treated and untreated peripheral vascular disease
...
Direct arteriography has also seen new developments with the advent
of digital subtraction angiography
...
By combining digital subtraction techniques with direct arterial angiography, patients at high risk of renal failure can be studied safely while combined arterial systems such as abdominal and carotid vessels can be simultaneously studied in patients with normal renal function
...
However, it
appears unlikely that it will replace ultrasound and contrast arteriography
...
8 Blood Flow
Physical factors that influence blood flow are pressure and resistance
...
The flow in peripheral blood vessels is measured as an aid in the diagnosis
of peripheral vascular disease
...
F can be calculated from
F = ∆P/R, (mL/min)
...
10)
Pressure, P, is usually measured in mmHg and R is the resistance
...
11)
where L = length, η = viscosity, r = radius
...
(8
...
Since the right atrial pressure is about zero, ∆P = MABP
...
Fung (1997) provides further information on the
biomechanics of the blood vessels
...
The continuous wave (CW) and pulsed varieties each have their advocates,
the former being easier to use while the latter affords more precise flow interrogation
...
Recordings made with the zerocrossing detector are adequate to some extent for real-time frequency spectrum analyzers
...
Increased velocity and disturbances in
8
...
Measurement of volume flow requires knowledge of the cross-sectional
area of the vessel (which can be obtained from the B-mode image) and the mean of the
velocity profile
...
Laser Doppler methods are applicable only to the cutaneous tissues and are difficult to quantify
...
The use of magnetic resonance
imaging (MRI) to measure blood flow, though promising, is in its infancy
...
The
transcutaneous electromagetic flowmeter seems to have little merit
...
At present isotope clearance is
employed only for special clinical studies or for research work
...
8
...
4
...
Applying a similar approach, we can determine the blood flow
...
8
...
It can measure pulsatile flow
...
Figure 8
...
If the magnetic field, the direction of motion and the induced voltage are mutually at right angles (orthogonal), then
e = Blu
(8
...
34
Heart and Circulation
+
B
B
l
N
S
e
−
u
Figure 8
...
Small-size probes can be made using an iron-cored electromagnet to increase the
signal strength
...
The electrodes make contact with the outer wall of the
blood vessel
...
The induced voltage is small compared to surface potentials generated
at the electrodes
...
Thus dc excitation is not used commercially
...
The surface potentials at the electrodes are removed by capacitive coupling
...
The induced current cannot be separated from the desired signal at the electrodes
...
8
...
The outside diameter of the vessel is constrained to be the
same as the internal diameter of the probe, so the volume flow through it can be calculated
...
Most blood vessels display laminar
flow—flow is greatest in the center of the vessel and slowest near the walls
...
Alterations in the velocity profile across the vessel therefore alter the measured
mean velocity, giving rise to error
...
8
...
3 Ultrasonic flowmeter
Ultrasonic flowmetry is a commonly used technique for measuring blood velocity in the
peripheral arteries
...
A piezoelectric sensor is used to convert
from electric to acoustic signals (see section 8
...
2)
...
17 shows a system for blood
flow measurement using an ultrasonic flowmeter
...
14)
where f0 is the fundamental frequency of an ultrasonic wave from the source, traveling at
velocity c through the blood
...
The factor of 2 occurs because the Doppler shift arises both on absorption of the
sound by the moving blood particles and between the transmitting blood cell and the receiving transducer
...
17 Ultrasonic flowmeter
...
The RF (radio frequency) amplifier amplifies the received signal and the carrier frequency, then AF (audio frequency) signal is produced by
a detector
...
A
...
1996
...
US Patent, 5,505,204
...
The crystal on the tip sends and receives ultrasound waves
...
The returning signal is transmitted, in real time, to the display device
...
When the sample area
is constant, the peak velocity is accurately tracked in the center of the artery and the key
parameters remain relatively positionally insensitive and reliable
...
8
...
4 Laser Doppler flowmeter
The Doppler ultrasonic flowmeter can assess blood flow from the Doppler shift that
sound waves experience when they travel through a large blood vessel
...
In contrast, this is possible if laser light is used instead of sound (Shep-
8
...
Light is capable of measuring the velocities of red blood cells
even at the relatively slow speeds with which they move through capillaries
...
The spectral purity of the laser makes it practical to
detect the slight frequency shifts produced by the interactions between photons and moving red blood cells
...
18 shows the principle of Laser-Doppler measurement
...
Light that intercepts the moving red blood cells is Doppler-shifted
...
A laser-Doppler catheter velocimeter can be used to measure intravascular blood
flow velocity
...
However, catheters disturb the flow of blood in their
neighborhood, and because light is multiply scattered in passing through the blood, combining the high spatial and temporal resolution of laser-Doppler velocimetry with catheter
delivery is not straightforward
...
The major advantage of the laser-Doppler flowmeter is the ability to measure
blood flow in regions other than the limbs
...
Not only can the laser-Doppler flowmeter be used to examine variations in blood flow
through the cardiac cycle, but also, on a somewhat longer time scale, slower rhythms can
be observed
...
18 Laser-Doppler flowmetry
...
8
...
The systolic and
diastolic pressures not only provide those maximum and minimum values that are an important aspect of the pulsations, but also permit a rough estimate of mean pressure in
large arteries
...
Mean blood
flow is essentially the same at all cross sections of the arterial tree, in the total population
of peripheral arterioles as in the ascending aorta
...
The decrement in pressure per unit length of the system, or
vascular resistance, is greatest in the microcirculation
...
The degree of
circulatory impairment is usually reflected by the relative or absolute reduction in resting
pressure
...
Unfortunately, pressure measurements are not always reliable
...
9
...
19 shows a sphygmomanometer, which indirectly measures blood pressure
...
A hand
or electric pump and a pressure gage are used
...
8
...
19 The sphygmomanometer detects arterial opening and closing that occurs between systolic and diastolic pressures
...
The occlusive cuff is pumped up
to about 180 mmHg, then bled off at about 3 mmHg/s
...
20)
...
When the cuff pressure decreases below about 80 mmHg, the artery
remains open the entire cycle
...
A piezoelectric sensor placed within the cuff replaces the stethoscope for automatic detection
...
20 The pressure of the cuff occludes the blood vessel
...
40
Heart and Circulation
There are several automatic noninvasive blood pressure monitoring devices
available commercially
...
The signal from the microphone is then
passed to a filter
...
Pressure in the cuff is sometimes measured with a mercury manometer, eliminating the
need for calibration
...
When the artery changes blood
volume under the cuff, this changes air volume within the cuff, which changes pressure
within the cuff
...
Alternatively a
pressure sensor (piezoelectric sensor) can detect these fluctuations in an automatic instrument
...
Figure 8
...
So is the point
where cuff-pressure oscillations start to increase
...
Am is the maximal oscillation amplitude, which signals mean pressure
...
21 Top: Cuff pressure with superimposed Korotkoff sounds, which appear between systolic and diastolic pressures
...
From Geddes, L
...
Cardiovascular
devices and their applications
...
1984
...
9
...
9 Blood Pressure
41
Arterial and venous blood pressure can be measured by inserting a catheter into the blood
vessel and maneuvering it until the end is at the site at which the blood pressure is to be
measured
...
2)
...
A catheter can be inserted into the artery inside a needle as
well
...
Although accurate, these methods are very invasive
...
9
...
A linear array of pressure sensors is pressed against the radial
artery so that at least one sensor is directly over the lumen
...
By selecting
the maximal peak-to-peak pressure reading from all sensors, the arterial pressure is determined in the same way as for the applanation tomometer (section 7
...
4)
...
(1997) compared the Colin Pilot 9200 tonometric blood pressure measurements with intra-arterial blood pressure measurements
...
24 ± 8
...
26 ± 8
...
8
...
The difference between the pressures inside
and outside the vesselthe transmural pressureis one of the factors that controls the
radius
...
The distribution of the blood volume among different parts of the system is determined by the relation between local pressure and vascular distensibility
...
In contrast, a large part of the blood volume resides in the veins,
even though their pressure is low, because they are readily distended
...
15)
where ∆d is the diameter change and dD is the diastolic diameter (Nakatani et al
...
42
Heart and Circulation
8
...
1 Intravascular ultrasound
Intravascular ultrasound provides both in vitro and in vivo two-dimensional visualization
of arteries in real time
...
22 shows that a rotating ultrasonic transducer illuminates
the walls
...
Ultrasonic
beam
Rotating
Ultrasonic
catheter
transducer
Blood
Arterial
wall
Figure 8
...
A rotating ultrasonic transducer is
attached at its tip and illuminates the walls
...
10
...
Because arteries do not show up well on ordinary X rays, angiograms utilize a contrast agent containing iodine, which is injected
into the arteries to make them visible on radiographs
...
Once
the catheter is in place, contrast agent, or dye is injected through the catheter into the arteries and a series of X rays taken
...
In digital subtraction angiography (DSA), a first image is taken without contrast
agent
...
The two images are digitized,
then subtracted, yielding no image in all regions without contrast agent
...
8
...
11 Vessel Volume Flow
43
One application of vessel volume flow measurement is the prediction of stenosis of both
common and internal carotid arteries by monitoring common carotid blood flow
...
Vessel volume flow measurements may also be
applied in the diagnosis and treatment of vascular malformations
...
Moreover, volume flow measurements provide a quantitative way both of assessing blood
steals (deviation of normal flow) and of evaluating the effectiveness of embolization
(mass of foreign matter in the blood vessel) therapy
...
8
...
1 Flow visualization
Continuous-wave or pulsed-Doppler flow-mapping devices produces a static image on an
oscilloscope screen that corresponds to a projection of the lumen of the vessel underlying
the probe
...
Although B-mode ultrasonic scanning allows large
vessels, such as the abdominal aorta, to be visualized, it is inappropriate for the routine
study of smaller vessels
...
0 mm
...
The two technologies are complementary
...
One instrument superimposes a real-time, color-coded Doppler
flow-map on a real-time B-mode image, thus incorporating the advantages of both modalities
...
8
...
2 Ultrasonic sonography
To estimate the volume flow rate of blood through an artery, pulsed Doppler ultrasound
measures the velocity of the blood at 16 or more discrete locations across the vessel diameter
...
Other techniques, such as
color M-mode, directly measure the one-dimensional velocity profile and are also used
...
Subsequently, the
44
Heart and Circulation
volume flow rate can be determined by integrating the two-dimensional velocity profile
over the vessel lumen area
...
8
...
3 Video microscopy
With the developments in video and in computer technology over the past two decades,
we are now able to see structures that are very fine, movements that were too fast too be
seen, and images that were too dim or too noisy to be seen
...
It also utilizes advances in image-processing (Inoué, 1986)
...
8
...
and Levy, M
...
Cardiovascular Physiology
...
St
...
Bom, N
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) 1977
...
The Hague: Martin Nijhoff Medical Division
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...
Burch, G
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...
6th ed
...
Cikes, I
...
1983
...
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...
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Two-dimensional Echocardiography
...
Cohn, P
...
1982
...
Boston: Little, Brown
...
2000
...
vet
...
edu/m-mode
...
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Heart
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Forestieri, S
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and Spratt, R
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US Patent,
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New York: Springer-Verlag
...
and Baim, D
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Angiography and Intervention, 4th ed
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Huang, S
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Futura
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...
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Systolic and Diastolic Function of the Heart
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Inoué, S
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...
8
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130 (6): 1196-202
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(eds
...
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...
Merz, C
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and Berman, P
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Mohrin, C
...
1995
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US Patent, 5,389,747
...
R
...
A flow zeugmatographic interlace for NMR imaging in humans
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Nakatani, S
...
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US Patent, 5,284,151
...
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Orth, J
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US Patent, 5,423,323
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...
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...
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New York: John Wiley &
Sons
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5,505,204
...
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...
html
Reinhard, C
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and Fowler, K
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US patent,
4,658,831
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W
...
J
...
(eds
...
Thallium−201 Myocardial Imaging
...
Shepherd, A
...
and Öberg, P
...
), 1990
...
Boston:
Kluwer Academic Publishers
...
2001
...
4th ed
...
Strandness, D
...
, Didisheim, P
...
W
...
T
...
) 1986
...
Orlando: Grune & Stratton
...
, Kato, T
...
, 1981
...
US Patent,
4,270,543
...
, Tamura, T
...
1997
...
Boca Raton FL: CRC Press
...
J
...
) 1993
...
Englewood Cliffs NJ:
Prentice Hall
...
1992
...
In J
...
Ernst (eds
...
Dordrecht:
Kluwer Academic
...
G
...
Measurement of flow and volume of blood
...
G
...
)
Medical Instrumentation: Application and Design
...
New York: John Wiley &
Sons
...
A
...
B
...
J
...
and Alpert, B
...
1997
...
Blood Press
...
2 (4): 185–8
...
13 Problems
8
...
2
8
...
4
8
...
6
8
...
8
8
...
10
Sketch the anatomy of the heart chambers and valves and show the direction of
blood flow
...
Describe the relation between the arterial pressure and the left ventricular pressure during a cardiac cycle
...
Draw a typical ECG waveform, label all waves, and explain what is happening
within the heart muscle during each wave
...
An ECG has a scalar magnitude of 0
...
2 mV onlead III, calculate the scalar magnitude of lead II
...
Use the Fick method to calculate the cardiac output (in mL/min) of a patient
whose arterial concentration of O2 is 0
...
13 L/L, and the O2 consumption is 0
...
Calculate the cardiac output using the thermodilution method from the following
data:
8
...
12
8
...
14
t1
∫ | ∆T
0
b
| dt = 3 s ⋅ °C , Q = 1250 J, ρb = 1060 kg/m3, and cb = 3640
J/(kg·K)
...
A Doppler-ultrasonic blood flowmeter has a carrier frequency of 7
...
The velocity of the sound is 1500 m/s and the audio
frequency is 12
...
Calculate the blood velocity
...
An artery has a diameter of 3 mm
...
0028 Pa⋅s at
37 °C, and the mean arterial blood pressure is 90 mmHg at one end and 0 mmHg
8
...
15
8
...
17
8
...
19
8
...
21
8
...
Calculate the blood flow rate in mL/min, assuming that the
length of the artery equals 0
...
Sketch an electromagnetic flowmeter and explain its principle of operation
...
Draw the block diagram for and describe the automatic indirect auscultatory
peripheral blood pressure measurement system
...
Show all pneumatic connections between parts
...
Describe the measurement cycle
...
Explain how
the signal processing identifies significant pressures
...
Explain why and how we measure vessel pressure using arterial tonometry
...
Explain why and how we measure vessel volume flow
...
Each
of these organs has its own properties and functions: the lungs help us respire, the
kidneys help clean the blood, bone supports the body, and skin protects the body
...
9
...
To sustain life, the
human body needs oxygen, which is utilized in cells with other essential nutrients during
the metabolic oxidation process
...
The hemoglobin in the blood is the dominant transport mechanism by which oxygen is
brought to cells
...
The most important function of the lungs is to
supply tissue with adequate oxygen and to remove excess carbon dioxide
...
There are two ways of producing the pressure difference
necessary for inspiratory flow: (1) the alveolar pressure can be reduced below
atmospheric
...
This is called positive pressure breathing
...
This further lowers intrathoracic pressure, which normally is
less than atmospheric pressure and hence, the air at atmospheric pressure flows through
the nose, mouth and trachea to the lungs
...
Tests performed to
determine parameters of system efficiency are called Pulmonary Function Tests (PFTs)
(Feinberg, 1986)
...
For example, finding a
1
2
Lung, Kidney, Bone and Skin
decreased lung volume reveals restriction, but not the cause of it
...
9
...
Pulmonary volumes have been divided according to
physiological limits (Petrini, 1988)
...
Total Lung Capacity (TLC) is the largest volume to which the subject’s lung can
be voluntarily expanded
...
Residual Volume (RV) is the smallest volume to which the subject can slowly
deflate his or her lung
...
Functional Residual Capacity (FRC) is the resting lung volume achieved at the
end of normal expiration
...
4
...
All of the lung capacities are based on these four parameters (Eqs
...
1) to (9
...
IRV is the inspiratory reserve volume
...
Inspiratory capacity (IC) = IRV + TV
(9
...
2)
Vital capacity (VC) = IC + ERV
(9
...
4)
In dealing with volumes of gases, the conditions under which the values are
reported must be well defined and carefully controlled because gases undergo large
changes under different thermodynamic conditions
...
1, have led to the development of specific tests to
quantify the status of the pulmonary system
...
1 The spirometer measures lung capacities and lung volumes
...
9
...
1 Measurement of pulmonary volume
The measurement of changes in the lung volume have been approached in two different
ways
...
This is
referred to as spirometry
...
Spirometer
The spirometer was one of the early instruments used for estimating respiratory volumes
...
The tests performed by the spirometer can be classified into
two major groups: single-breath tests and multiple-breath tests
...
Maximal Voluntary Ventilation (MVV) is measured in the category of
multiple-breath tests (Feinberg, 1986)
...
This seal is often water
...
This motion can be observed on a calibrated
scale or a rotating drum (kymograph) as shown in Figure 9
...
9
...
2 In the water sealed spirometer, expired CO2 is removed in the soda-lime cannister
...
As the gas moves into and out of the spirometer, the pressure of the gas
in the spirometer changes, causing the bell to move
...
For rebreathing experiments, most
spirometer systems have a chemical absorber (soda lime) to prevent build up of carbon
dioxide
...
5)
where P is the pressure of the ideal gas, R is the universal gas constant, T is the absolute
temperature, ρ is the mole density, which for a well-mixed compartment equals the ratio
of moles of gas N in the compartment to the compartment volume V
...
They should be linear, have stability (no drift), low inertia, low resistance, and no
hysteresis
...
1, from which impared vital capacity can indicate disease
...
The expired CO2 is
absorbed by the soda lime cannister
...
The average slope of
the spirometer output yields the O2 consumption vs
...
The soda lime cannister adds pneumatic resistance, so is removed when
measuring maximal voluntary ventilation
...
Forced expiratory volume (FEV) measures airway restriction
...
A normal subject can exhale 83% of
vital capacity in 1 s whereas a subject with restricted airways takes longer
...
This device is a
volumetric displacement box into which the patient is placed
...
When the outlet connection is attached to a spirometer,
pneumotachometer, or respiratory function computer, a wide variety of measurements
can be easily made
...
Figure 9
...
7
9
...
3 The total body plethysmograph measures lung volume with the shutter closed and the
airway resistance via a pneumotachometer with the shutter open
...
A patient sits inside the plethysmograph with a pneumotachometer flow meter in his or
her mouth
...
This is
accomplished using a solenoid operated shutter to block the pneumotachometer
...
The tissues of the body are composed of liquids and solids and can be
considered incompressible when compared with the gas in the lungs
...
Also because the volume of the
plethysmograph is constant, changes in the volume of the plethysmograph are zero
...
During compression, ∆VL = –∆VB
...
As a first order
approximation, VL/VB = –∆PB/∆PL
...
The lung is
isothermal whereas the box is adiabatic
...
After
calibration, we can measure ∆PB and use it to predict ∆PL
...
6)
8
Lung, Kidney, Bone and Skin
where Q is the flow measured by the pneumotachometer
...
We can calculate the fixed impedance from Eq
...
8)
...
Because the arteries have a regular cylindrical shape, we can calculate their
longitudinal change in impedance
...
The derivation is based on three
assumptions: the expansion of vessels is uniform (this may not be the case in diseased
vessels), the resistivity of the blood does not change, and lines of current are parallel to
the arteries (Webster, 1998)
...
Zb =
ρbL
∆A
(9
...
4 A model for two electrode impedance plethysmography for cylindrical vessels
...
8)
If the assumptions are valid, the above equation shows that we can calculate ∆V
from ρb and other quantities that are easily measured
...
In respiratory impedance plethysmography, respiration is
electrically monitored by measuring changes in chest impedance
...
2 Pulmonary Volume
9
of the thoracic cavity changes with breathing movements and can be sensed in order to
monitor ventilatory activity
...
A 100 kHz
impedance measurement between electrodes on each side of the chest yields a waveform
that follows ventilation
...
As resistivity increases in response to
increased air in the chest, the impedance of the chest increases
...
Inductance plethysmography
Respiratory inductive plethysmography continuously monitors the motions of the chest
wall that are associated with changes in thoracic volume
...
It is
excited by a low-level radio-frequency signal
...
An output is obtained proportional to
the local cross-sectional area of the segment of the chest wall that is encircled by the loop,
after demodulation
...
Their sum is a more accurate estimate of lung volume that
that obtained from a single loop
...
9
...
Measurement of the variables associated with the
movement of this gas is very important
...
Convective flow occurs as a result of a difference in pressure between two points
...
9
...
1 Measurement of pulmonary flow
Pneumotachometer
The most commonly used instrument for measurement of flow is the pneumotachometer
...
It is based on the pneumatic equivalent of Ohm’s law:
10
Lung, Kidney, Bone and Skin
Q(flow) =
∆P (difference in pressure)
R (fixed resistance of pneumotachometer)
(9
...
Flowresistance pneumotachometers are easy to use and can distinguish the direction of
alternating flows
...
Even though other flow resistance elements are
incorporated in pneumotachometers, the most common are either one or more fine mesh
screens placed perpendicular to flow or a tightly packed bundle of capillary tubes or
channels with its axis parallel to flow
...
This element is mounted in a conduit of circular cross section
...
This pressure
difference is measured by a differential pressure sensor and is used as a measure of airflow through it
...
Also, as water condenses, the concentration of the gas mixture
changes
...
This can be done using various techniques
...
Also, the screen of the pneumotachometer can
be heated by passing a current through it, heated wires can be placed inside or heating
tape or other electric heat source can be wrapped around any conduit that carries expired
gas (Primiano, 1998)
...
5 A pneumotachometer measures flow from a pressure drop ∆P across resistance
elements such as (a) a fine mesh screen or (b) capillary tubes or channels
...
4 Pulmonary Diffusion
9
...
The equation is
–Vg = DL(PAg – Pcg)
(9
...
DL is the diffusing capacity in mL/(min⋅mmHg) and includes the
parameters of the surface area of gas transfer, the thickness of the membrane across
which the gas is transferred, and the properties of the gas such as the molecular weight
and solubility
...
Carbon dioxide diffuses across the alveolar membrane much more easily than
oxygen, so a diffusion defect affects oxygen transfer first
...
But obtaining the PaO2 requires a sample of arterial blood
...
In addition, it also has affinity for hemoglobin at low
concentrations; hence all carbon monoxide that enters the blood chemically combines
with the hemoglobin in the red blood cells
...
The subject inspires a mixture of air, 0
...
The subject holds his breath at TLC for about
10 s and then forcefully exhales down to RV
...
Also, it does not require samples of
arterial blood flow
...
If a wellmixed alveolar compartment is filled with a mixture of gases containing some initial
alveolar fraction FACO, then during breath holding with the airway open, the CO
diffuses into the blood in the pulmonary capillaries, and the alveolar FACO decreases
exponentially with time (Primiano, 1998)
...
11)
9
...
Resistance to air flow is a calculated quantity instead of a directly
measured one
...
12)
A noninvasive method of measuring airway resistance is the body
plethysmograph
...
The balloon should be located such that pressure
changes due to motions of other organs competing for space in the thoracic cavity are
minimized
...
The
correspondence decreases as lung volume approaches the minimum achievable volume
(RV)
...
The use of helium instead of air can extend
the usable frequency range of these systems (Primiano, 1998)
...
6 Kidney
Kidneys are paired bean-shaped organs lying on either side of the spine in the upper part
of the abdomen
...
By means of these blood vessels, the kidneys filter about 1200 mL/min
of blood
...
The key
separation functions of the kidney are: elimination of water-soluble nitrogenous endproducts of protein metabolism, maintainence of electrolyte balance in body fluids and
elimination of excess electrolytes, contribution to the obligatory water loss and discharge
excess water in the urine, and maintenance of the acid–base balance in body fluids and
tissues
...
The kidneys also provide regulatory mechanisms for the control
of volume, osmolality, electrolyte and nonelectrolyte composition, and pH of the body
fluids and tissues
...
6 shows the general anatomy of the kidney
...
5 Pulmonary Airway Resistance
13
Ureter
Kidneys
Bladder
Urethra
Figure 9
...
9
...
7
...
Nonselective glomerular filtration is followed by
the selective re-absorption in the renal tubes
...
Likewise, all glucose, amino acids, and the small amount
of protein filtered together with most of the sodium, chloride, bicarbonate and calcium is
re-absorbed
...
Creatinine, a byproduct of phosphate metabolism in muscle, is frequently used as a
measure of GFR (Glomerular Filtration Rate) because it is freely filtered and not
reabsorbed: the quantity crossing the glomerular filter is thus same as the steady state
excretion of urine
...
14
Lung, Kidney, Bone and Skin
GFR ≈ C =
UV
P
(9
...
The normal glomerular filtration rate averages 120
mL/min, about 116 mL/min is re-absorbed, and about 4 mL/min is excreted as urine
...
8 Kidney Imaging
9
...
1 Pyelogram
The main components of the urinary tract have either a tubular or cavitational structure
and their delineation with radio-opaque medium is readily possible
...
After a fixed amount of time has
passed, the X ray is taken
...
The one shot Intravenous Pyelogram (IVP) is performed when there is suspected
or potential injury to the kidney or the ureter
...
The one shot intravenous pyelogram is
a very good way to determine this
...
In this
technique 1 mL/kg of nonionic radiocontrast agent is usually injected as a rapid
intravenous bolus
...
In a hypotensive patient, the one shot IVP may
not be helpful as there may be no secretion of the contrast due to decreased renal blood
flow
...
9 Hemodialysis
Dialysis is necessary when the GFR falls below 5 to 10% of normal
...
Chronic renal
failure is a group of conditions in which renal function is slowly eroded and from which
recovery is very unusual, while in acute renal failure recovery is within a few days or
weeks
...
Hemodialysis is
a process in which blood is continuously circulated in contact with a permeable
membrane, while a large volume of balanced electrolyte solution circulates on the other
side of the membrane
...
Three processes occur simultaneously during dialysis—osmosis, diffusion
and ultrafiltration
...
9 Hemodialysis
15
concentration of solutes to a higher concentration of solutes
...
Ultrafiltration is the bulk flow of solution brought about by hydrostatic
pressure across the semipermeable membrane
...
14)
where TMP is the Transmembrane Pressure (mmHg) and KUF is the Coefficient of
Ultrafiltration of the dialyser ((mL/h)/mmHg)
...
The negative pressure is calculated using the
formula
NP = TMP −
AP + VP
2
(9
...
The transmembrane pressure can be calculated using the formula:
TMP =
Total fluid to be removed ÷ hours on dialysis
KUF of a dialyser
(9
...
This dialyser can be a coil type, parallel plate type, or
hollow fiber type
...
The blood and the dialysate flow counter current to maximize
efficiency of solute transfer
...
7 shows a typical dialyser
...
7 Typical dialyser (a) indicating the counter current flow of the blood and the dialysate (b)
Cross-sectional view of the dialyser
...
These membranes are fabricated from three classes of biomaterials:
regenerated cellulose, modified cellulose, and synthetics
...
Cuprophan (cupramonium cellulose), cellulose acetate,
polyacrylonitrile, polymethyl methacrylate polycarbonate, and polysulphate are some
other commonly used materials to prepare dialysis membranes
...
8 shows a schematic of a hemodialysis machine (Gregory, 1988)
...
Blood clots rapidly when it comes in contact with most foreign substances
...
Heparin is the most commonly used
anticoagulation agent
...
Clean blood that comes out of the dialyser is
then injected into the patient
...
A venous bubble trap is inserted in the circuit to
make sure that the blood going back to the patient does not have an air bubble in it
...
The ultrasonic sensor monitors
any change in sound transmission and the photocell monitors any change in light
transmission
...
The pressure on the venous side is also monitored using
a pressure gage
...
9 Hemodialysis
17
Heparin infusion
Blood from
patient
Dialyser
Venous pressure gage
Pump
Air/foam detector
Blood returning to
patient
Blood leak detector
Dialysate
pressure gage
Dialysate flow
meter
Pure water
Dialysate
pump
Spent dialysate
to waste
Adjustable
constriction
Heater
Conductivity and
pH cell
Concentrate
Proportioning
pump
Figure 9
...
Proportioning pumps first mix the dialysate concentrate with water until a
desired concentration is reached
...
The dialysate is warmed by a heater to near normal body
temperature
...
The
negative pressure of the dialysate is usually generated by having the dialysate pump draw
the dialysate through the dialyser and by placing an adjustable constriction upstream of
the dialyser as shown in Figure 9
...
The pH of the dialysate must match the acid/base
balance of the patient’s blood
...
The dialysate coming out of the dialyser is then passed
through a blood leak detector to check if there has been a rupture of the membrane and if
any blood has leaked into the dialysate circuit side
...
Normally the dialysate is clear and lets light pass through
...
Any break in the transmission of the light beam triggers an alarm
...
9
...
The cavity is lined with a parietal peritoneum membrane
...
The average adult peritoneal cavity
has a surface area of 1 to 2 m2
...
During the process the peritoneal cavity is filled with dialysate through a
surgically implanted catheter
...
The diffusion continues
until an equilibrium concentration is reached between the plasma and the dialysate
...
In addition to waste removal, the kidneys maintain the body’s water level
...
Glucose can readily cross the membrane and be
absorbed by the body while water filters across the membrane into the dialysate
...
Peritoneal dialysis provides the patient with added independence
...
Unlike hemodialysis, they are not required to spend 4 to 6 h three
times per week in a clinic
...
The process is typically
performed three times a week and may take 8 to 10 h
...
Many patients
prefer an automated system that performs the dialysis while they sleep
...
9 shows
a peritoneal dialysis system
...
9 A simple schematic of a peritoneal dialysis system
...
10 Peritoneal Dialysis
19
To provide a mobile system, the control hardware, dialysate supply and spent
dialysate are commonly mounted on a wheeled stand
...
The spent
dialysate collection is positioned at the bottom of the stand for same reason
...
Traveling or portable
systems may exclusively use gravity to provide a smaller, lighter system
...
After approximately 30 min, the dialysate is
pumped out of the cavity and into a collection bag
...
The key measurement in the peritoneal dialysis process is the weight of the
fluids
...
Therefore, the amount of fluid pumped into the peritoneal cavity and the
amount of fluid removed are measured as the means of monitoring the amount of water
and waste diffused from the body fluids
...
10 shows a possible
means of measuring the fluid weight
...
10 Dialysate weight measuring circuit
...
The fluid may be suspended from a spring-loaded mechanism that varies the wiper
position
...
A change in the resistance varies the input voltage, vi, to the non-inverting
op amp circuit
...
2)
...
Acceptable resistance
values for Ri and Rf are 1 kΩ and 5 kΩ, respectively
...
The output voltage can be sent to an analog-todigital converter and then to a CPU for data storage and processing
...
As the pressure decreases, less diffusion occurs
...
It is important to understand that it is this
relationship that is used to determine the frequency with which the dialysate should be
20
Lung, Kidney, Bone and Skin
refreshed
...
9 (two volumes of fluid separated by a membrane), a relationship can be
developed to determine the rate at which the body fluid wastes or solutes diffuse across
the membrane
...
17)
where C is the concentration of solute (molecules/m3), N is the number of particles in the
solute and V is the volume of the solute
...
18)
where R is the gas constant (J/(mol·K)), T is the absolute temperature, 310 K, and ω is the
solute permeability of the peritoneal membrane (1 × 10–5 moles/(N⋅s))
...
Through some algebra and knowing Js, the surface area of the peritoneum and
the initial concentrations, the concentration in the body determined as a function of time
is
Vd
Vb
C (t ) = C o
e −αt +
V b + Vd
V b + V d
(9
...
Normally, 30 min cycles are done
...
9524Co using the values given above
...
9524) n Co
(9
...
As mentioned previously, the rate of dialysis is monitored by weighing the
dialysate and spent dialysate
...
11 Kidney Function
9
...
11
...
If the kidneys are not functioning properly, the body retains
water
...
This test
measures the amount of urine a person produces in one day
...
One other method to detect excess retention is bioelectrical impedance analysis
(BIA), which estimates total body water by passing about 800 µA at 50 kHz between
electrodes on the wrists and ankles
...
21)
where TBW is the total body water in m3, Ht is the height of the person in m, R is the
resistance in Ω, and Wt is the weight in N
...
4
...
This method is controversial
...
The National Institutes of Health (1994) concludes that there are many conditions in
critical illness for which conventional BIA is a poor measure of TBW
...
There are three basic components of total body mass: water, lean body mass (muscle) and
body fat
...
4 gives many methods of estimating body fat
...
If one of each of these methods
are used to obtain an approximation for lean body mass and body fat, these can be
subtracted from the total body mass to obtain an estimate of the extracellular water
...
12 Bones and Joints
Bones can last for centuries and in some cases for millions of years
...
Because of the importance of bone to proper functioning of the body, a number of
medical specialists such as the dentist, orthopedic surgeon and radiologist are concerned
with the health of bone
...
Nature has
solved these problems extremely well by varying the shapes of the various bones in the
skeleton and the type of bone tissue of which they are made
...
g
...
Bone consists of
22
Lung, Kidney, Bone and Skin
two different types of materials plus water
...
Either of the components may be removed from the bone,
and in each case the remainder, composed of only collagen or bone mineral, looks like
the original bone
...
When collagen is removed from the bone, the bone mineral
remainder is very fragile and can be crushed with the fingers
...
9
...
1 Bone mineral density
The strength of the bone depends to a large extent on the mass of bone mineral present
...
Up to a few
years ago osteoporosis was difficult to detect until a patient appeared with a broken hip or
a crushed vertebra
...
Thus bone
mineral is very important and commonly measured to detect bone diseases such as
osteoporosis
...
The most commonly used technique for noninvasively measuring bone mineral content in
the bone is dichromatic or dual photon absorptiometry (DPA)
...
But there are some major problems with using an
ordinary X ray: the usual X-ray beam has many different bands of energy, and the
absorption of X rays by calcium varies rapidly with energy in this range of energies; the
relatively large beam contains much scattered radiation when it reaches the film; the film
is a poor tool for making quantitative measurements since it is nonlinear with respect to
both the amount and the energy of X rays
...
Figure 9
...
Tests are frequently made in the spine, hip, and
forearm but can be done on the entire body
...
12 Bones and Joints
23
Scintillation
detector
Dual beam
Soft tissue
Bone
X-ray dual beam
radiation source
Figure 9
...
Hologic (2000) improves clinical bone densitometry by integrating bone mineral
density (BMD) with Instant Vertebral Assessment (IVA)
...
A different instrument measures the speed of sound
(SOS, in m/s) and broadband ultrasonic attenuation (BUA, in dB/MHz) of an ultrasound
beam passed through the heel, and combines these results to obtain the Quantitative
Ultrasound Index (QUI)
...
9
...
2 Stress and strain
Tensile loads
When forces are applied to any solid object, the object is deformed from its original
dimensions
...
The relative
deformations created at any point are referred to as strains at that point
...
When bone is subjected to
forces, these stresses and strains are introduced throughout the structure and can vary in a
very complex manner (Ashman, 1991)
...
11(a) shows a cylindrical bar of length L and a constant cross-sectional
area A subject to a pure tensile force F
...
This situation can be described by an equation that describes the stretching of a
spring (Hooke’s law):
F = kx
(9
...
Force
σc = Ultimate
tensile strength
Fult = Failure
load
F
∆L
Fy = Yield
Force, F
Stress, σ
σy = Yield load strength
L
AE/L = Stiffness
E = Elastic
modulus
A, E
Deflection, ∆L
Strain, ε
(a)
(b)
Figure 9
...
The analogous relation for stretching of the cylinder is
∆L =
FL
AE
(9
...
Tensile, or uniaxial, strain, ε, can be calculated using the formula
ε=
∆L
L
(9
...
25)
9
...
Figure 9
...
This is followed by a nonlinear
region where yielding and internal damage occurs, often involving irreversible
rearrangement of the structure
...
The load at which yielding occurs is referred to as the yield
load, Fy
...
This
curve describes the behavior of the structure since the curve differs for a different crosssectional area or different length
...
In the stress–strain curve, the
material yields at a stress level known as the yield strength and fractures at a stress level
known as the fracture strength or the ultimate tensile strength
...
The above quantities can be measured using any of the displacement type
sensors (e
...
strain gage, LVDT (Linear Variable Differential Transformer), capacitive,
and piezoelectric sensors)
...
Shear Loads
When forces are applied parallel to a surface or along the edge of an object, the object
deforms in a way shown in Figure 9
...
The sides of the object perpendicular to the
forces stretch and shear stresses and strains result
...
12 Shear stress τ, causes shear strain γ
...
26)
Shear stress, τ, can be calculated using the formula
τ =
F
τ = F/A
A
(9
...
The shear modulus, G, can be calculated using τ and γ using the relationship:
G=
τ
γ
(9
...
9
...
3 Strain gage
The strain gage is a variable resistance sensor whose electric resistance is
R=
ρl
A
(9
...
An increase in length causes an increase in resistance
...
30)
where µ is Poisson’s ratio, which can be expressed as
µ=−
∆D D
∆L L
(9
...
Poisson’s ratio is the ratio between
the lateral strain and axial strain
...
Figure 9
...
As long as the strain remains well below the elastic limit of the strain
gage resistance, there is a wide range within which the increase in resistance is linearly
proportional to the increase in length
...
12 Bones and Joints
R2
R1
R3
27
R4
vi
Rx
vo
Figure 9
...
vi is the applied voltage with the bottom terminal grounded
...
Potentiometer Rx balances the bridge
...
1
...
The types of strain gages are dictated by their construction
...
The wire’s resistance changes because of changes in the diameter,
length and resistivity
...
Integrated strain gages may be formed from impurities diffused into a silicon diaphragm,
which forms a rugged pressure sensor (Peura and Webster, 1998)
...
9
...
4 LVDT
A transformer is a device used to transfer electric energy from one circuit to another
...
A linear variable
differential transformer (LVDT) is composed of a primary coil and two secondary coils
connected in series opposition, as shown in Figure 9
...
The ac excitation is typically 5 V
at 3 kHz
...
When the alloy is symmetrically placed, the
two secondary voltages are equal and the output signal is zero
...
The LVDT is useful in determining the strain
on tendons and ligaments (Woo and Young, 1991)
...
14 In a linear variable differential transformer, displacement of the high permeability
magnetic alloy changes the output voltage
...
Figure 9
...
It consists of one fixed and one moving head with attachments to grip the test
specimen
...
Then using Eqs
...
24) and (9
...
9
...
15 The uniaxial tension test measures force versus elongation
...
12
...
, 1990)
...
, 1990)
...
The VDA system
tracks the reference lines and yields strain versus time
...
07
...
Proteoglycans are important components of the extracellular matrix of articular
cartilage and other soft tissues
...
7
...
The angle of the cone α is 0
...
The
shear rate γ = ω/α, where ω is the rotational speed of the plate (rad/s)
...
Another viscometer is the Ostwald capillary
viscometer, which calculates the coefficient of viscosity η from the pressure gradient
dp/dL, the volume rate of flow Q, and the tube radius R using the equation η =
[πR4/(8Q)](dp/dL) (Fung, 1981)
...
30
Lung, Kidney, Bone and Skin
9
...
6 Joint friction
Diarthrodial (synovial) joints have a large motion between the opposing bones
...
The resistance to motion between two bodies in contact is given by frictional force
F = µW, where µ is the coefficient of friction and W is the applied load (Black, 1988)
...
Lubrication of bone joints is an important factor in determining coefficient of
friction
...
The synovial fluid is the lubricating fluid that is used by
the joints
...
The viscosity of synovial fluid decreases
under the large shear stresses found in the joint
...
Here a normal hip joint from a fresh cadaver is mounted upside
down with heavy weights pressing the head of femur into the socket
...
The whole unit acts like a pendulum
with the joint serving as the pivot
...
It can be concluded that fat in the cartilage helps
to reduce the coefficient of friction
...
Figure 9
...
9
...
16 Decay of oscillation amplitude in the pendulum device permits calculation of the
coefficient of friction of a joint
...
For polymeric materials,
the volume V = kPX produced by wear during sliding against metallic or ceramic
countersurfaces is proportional to the applied load P and the total sliding distance X
...
9
...
7 Bone position
Bone position is important for calculating the loading forces that act on it
...
Calculating forces for other bones, such as the femur, is relatively easy
...
A goniometer is an electric potentiometer that can be attached to a joint to
measure its angle of rotation
...
Human joint and gross body motions can be measured by simple protractor type
goniometers, electrogoniometers, exoskeletal linkage devices, interrupted light or normal
and high speed photography, television-computer, X-ray or cineradiographic techniques,
sonic digitizers, photo-optical technique, and accelerometers (Engin, 1990)
...
12
...
If the strain is
maintained, the potentials rapidly decay to a very low value, called the offset potential
...
9
...
It absorbs sunlight, softens blows, insulates from heat and cold, retains fluid
within the body and keeps foreign organisms and extraneous chemicals out of it
...
It also acts as the body’s radiator
and as such is the most significant element in the thermoregulation system
...
13
...
In the absence of profuse sweating, the TWL is predominantly controlled
by the diffusion of water vapor in the stratum corneum caused by the difference in vapor
concentration between the inside and outside surfaces
...
TWL can be measured using the direct measurement technique or the
indirect measurement technique
...
The indirect measurement technique relies on establishing a
boundary air layer over skin of known geometry
...
Flow hygrometry
In flow hygrometry, the flux of water vapor out of a fixed area of skin is determined by
measuring the increase in water vapor concentration in the flowing gas stream
...
TWL can be calculated using the formula:
TWL =
K ×V × R
A
(9
...
13 Skin
33
where K is the instrument constant, V is the increase in the sensor output, R is the gas
flow rate and A the skin area isolated by the measuring chamber
...
There are numerous possible sources of error in the flow
hygrometry system, which include uncertainty in the gas flow rate, uncertainty in the
actual area of skin exposed to flowing gas, absorption of water vapor in tubing
connecting the skin chamber with the sensor, and leaks in the seal of the chamber to the
skin site
...
In this method, transfer of water vapor to the sensor is by convection, which
normally requires gas tanks or pumps, valves, and tubing in addition to the sensor and the
skin chamber
...
Figure 9
...
Meter
Gas
source
Humidity sensor
Flow rate = R
Skin
Figure 9
...
Closed cup method
In the closed cup method, the humidity sensor is sealed into one end of a cylinder of
known length
...
18(a)
...
The application of diffusion principles to the water vapor in the volume of trapped air
predicts this behavior and shows that the TWL is directly proportional to the slope of the
transient linear portion of the detector output curve shown in Figure 9
...
The TWL is
found from:
TWL = K × l ×
dv
dt
(9
...
The closed chamber method
34
Lung, Kidney, Bone and Skin
does not permit recordings of continuous TWL because when the air inside the chamber
is saturated, skin evaporation ceases
...
18 The closed cup hygrometer: (a) configuration of measuring cup, (b) typical sensor
output curve
...
19(a) shows the open cup hygrometer
...
As in the closed cup method, the cylindrical chamber defines a volume
of undisturbed air in which the transfer of water vapor is controlled by diffusion in air
...
In this condition the rate of flow can be
calculated, according to the principles of diffusion, from the product of diffusion
coefficient of water vapor in the air and the concentration gradient
...
19(a) the sensor is mounted at a distance l from the end of the cylinder
where the humidity is determined by the room condition
...
The equation for TWL
measurement with the open cup method is then:
TWL =
(V − V0 ) × K × D
l
(9
...
Air movement and humidity are
the greatest drawbacks of this method
...
35
9
...
19 The open cup hygrometer: (a) configuration of measurement cylinder, (b) typical
sensor output curve
In the flow hygrometry method, the investigator has the option of selecting the
water content of the sweep gas within the limits of the humidity sensor
...
9
...
2 Color
Among the physical skin parameters, color is important in clinical dermatology
...
First, he frequently
bases his first-view diagnosis or elaboration of differential diagnosis to a considerable
amount on specific colors of the skin lesions themselves
...
Finally, the intensity of color may provide useful
information about the severity of a pathological process, and changes in color to normal
tell the dermatologist if the treatment works
...
Because
color perception is a subjective sensory and neurophysiological process, the evaluation of
color is highly observer dependent
...
In order to measure color objectively, color-measuring devices have been
developed instead of having it judged by subjective observers
...
Colors may be described by their hue (color position in the color wheel),
lightness (called value) and saturation (called chroma)
...
36
Lung, Kidney, Bone and Skin
Dermaspectrometer and Erythema meter
The instruments used to measure the variations in the color of skin are the
Dermaspectrometer and the Erythema meter
...
In inflammation, cutaneous vessels are dilated and blood
flow is increased
...
Changes in
skin redness affect the absorption of green light, but affect less that of red light
...
Erythema index = log10
( Intensity of reflected red light)
(Intensity of reflected green light)
(9
...
38)
The DermaSpectrometer emits green and red light (568 and 655 nm) from an
LED source
...
Figure 9
...
A microprocessor calculates the erythema and the melanin index, which is
then displayed
...
13 Skin
37
Green
Red
Green
Red
Epidermis
Superficial vascular
plexus
Dermis
Subcutis
Deep vascular plexus
Figure 9
...
Chromameter and Micro Color
The Chromameter and Micro Color are another pair of instruments based on the same
working principle as the DermaSpectrometer and Erythema meter
...
This refers both to the color of lighting and the angle under which
the light hits the object
...
Selective lighting results in limited color information; e
...
, a red
object would appear black when perceived under a green lamp
...
In order to compensate for variation in illumination,
part of the emitted Xe light is sent to a set of color sensors, whereas the rest illuminates
the object (dual beam system, Figure 9
...
The color sensors analyze the illuminating
light, and through a microprocessor, the light reflected from the object is adjusted for
variations in the illuminating light
...
In the
Chromameter, only the light remitted at 0° to the axis of the instrument (90° to the object
surface) is collected for color measurement (d/0 measurement principle, Figure 9
...
The reflected light is transferred to three photodiodes
...
These photodiodes simulate the human eye with its three blue,
green, and red sensitive cones in the central fovea
...
Reflected light
Sensor
Sensors
Light
Emitted light
Object
(a)
Object
(b)
Figure 9
...
9
...
B
...
Experimental techniques
...
C
...
) Bone Mechanics
...
Berardesca, E
...
, Wilhem, K
...
and Maibach, H
...
1995
...
Boca Raton FL: CRC Press
...
and McGlothlin, J
...
1996
...
New York: Marcel Dekker
...
1988
...
Bronzino, J
...
(ed
...
The Biomedical Engineering Handbook
...
Boca Raton
FL: CRC Press
...
R
...
G
...
Medical Physics
...
Cohen, S
...
1981
...
Boca Raton FL: CRC Press
...
1990
...
In V
...
Mow, A
...
L
...
Woo (eds
...
Vol
...
New York: Springer-Verlag
...
and Hastings, G
...
1984
...
1: Fundamentals, Vol
...
Boca Raton FL: CRC Press
...
14 References
39
Engin, A
...
1990
...
In V
...
Mow, A
...
L
...
Woo (eds
...
Vol
...
New York:
Springer-Verlag
...
N
...
Applied Clinical Engineering
...
Fung, Y
...
1993
...
2nd ed
...
Gregory, M
...
1988
...
In J
...
Webster (ed
...
Encyclopedia of
Medical Devices and Instrumentation
...
Hobbie, R
...
1997
...
3rd ed
...
2000
...
[Online] http://www
...
com/
Kryger, M
...
1994
...
In M
...
Kryger, T
...
C
...
) Principles and Practices of Sleep Medicine, 2nd ed
...
B
...
Markolf, K
...
, Gorek, J
...
, Kabo, J
...
, Shapiro, M
...
and Finerman, G
...
M
...
New insights into load bearing functions of the anteriaor cruiate ligament
...
C
...
Ratcliffe and S
...
-Y
...
) Biomechanics of Diarthrodial Joints
...
I
...
Marks, R
...
A
...
) 1981
...
Boston: MTP Press
Ltd
...
2000
...
[Online] http://www
...
com/
Mow, V
...
and Hayes, W
...
1991
...
New York: Raven
Press
...
C
...
J
...
Friction, lubrication, and wear of diathrodial
joints
...
C
...
C
...
) Basic Orthopaedic Biomechanics
...
National Institutes of Health
...
Bioelectrical impedance analysis in body composition
measurement, Technology Assessment Conference Statement
...
1–
35
...
1989
...
IEEE Eng
...
Biol
...
Petrini, M
...
1988
...
In J
...
Webster (ed
...
New York: John Wiley and Sons
...
A
...
G
...
Basic sensors and principles
...
G
...
)
Medical Instrumentation: Application and Design
...
New York: John Wiley
and Sons
...
P
...
Measurements of the respiratory system
...
G
...
)
Medical Instrumentation: Application and Design
...
New York: John Wiley
and Sons
...
H
...
E
...
An inexpensive portable monitor for
measuring evaporative water loss
...
Phys
...
Meas
...
Webster, J
...
1988
...
New York:
John Wiley and Sons
...
G
...
Measurement of flow and volume of blood
...
G
...
Medical Instrumentation: Application and Design
...
New York: John Wiley
and Sons
...
L
...
, Weiss, J
...
and MacKenna, D
...
1990
...
In V
...
Mow, A
...
L
...
Woo (eds
...
Vol
...
New York:
Springer-Verlag
...
L
...
and Young, E
...
1991
...
In V
...
Mow and W
...
Hayes (eds
...
New York:
Raven Press
...
B
...
C
...
Viscometric properties of proteoglycan solutions at
physiological concentrations
...
C
...
Ratcliffe and S
...
-Y
...
)
Biomechanics of Diarthrodial Joints
...
I
...
9
...
1
9
...
3
9
...
5
9
...
7
9
...
9
9
...
11
Sketch a spirometer output
...
Label and describe lung volumes that it cannot measure
...
You notice that a
10 kΩ from the wiper to ground causes loading error
...
You wish to measure lung volume using a body plethysmograph
...
Describe (1) sensor type and location, (2) system and method for
calibration, (3) procedure for measurement, (4) results of measurement, (5)
equation, and (6) any corrections required
...
The box pressure changes by 10 Pa
...
State any approximations
...
Given resistivity of the thorax is 300 Ω·cm
...
Describe the importance of measuring pulmonary air-flow
...
Explain any one of them
...
Label axes and significant quantities
...
The urine
flow is 4 mL/min
...
Calculate the
glomerular filtration rate
...
Explain its importance in diagnosing kidney disease
...
Describe safety devices required for hemodialysis
...
15 Problems
9
...
13
9
...
15
9
...
17
9
...
Total fluid to
be removed is 2810 mL and hours on the dialysis is 4 h
...
The arterial pressure and venous pressure are 130 mmHg and 100
mmHg respectively
...
List and describe different sensors that can
be used for this measurement
...
26 cm is tested in a uniaxial tension test
...
After applying a force of 1000 N
the length is changed to 31
...
Calculate the stress and strain generated in the
specimen
...
Describe arthrotripsometers, what they measure and their operating principle
...
Explain the importance of measuring water loss
...
Explain how skin color is important to a dermatologist
...
10
...
These four parameters are somewhat related
because they all deal with energy
...
It is
defined as the vibratory motion of its component particles
...
Temperature is a measure of the tendency of a
body to transfer heat from or to other bodies
...
Body fat is energy
related in that it is part of the heat storage process
...
We further discuss clinical temperature
measurement techniques and common devices
...
We compare various techniques
among these measurements as well
...
In each section, we explain why and how to measure these physical
parameters
...
1
Regulation of Body Temperature
Body temperature is regulated by a well-designed control system
...
6 °C for a healthy person
...
When speaking of the body
temperature, we usually mean the temperature in the interior—the core temperature
...
Temperature is an indicator of the health of a person
...
This temperature is an important
factor when discussing heat loss through sweating (evaporation) from the skin
...
It is analogous to room
temperature control (Milsum, 1966)
...
The thermostat
controls the furnace or air-conditioner (actuator) to increase or decrease the room
temperature to the preset temperature
...
During this process,
temperatures from sensors inside the thermostat and from the ambient air are fed back to
the thermostat to speed up the response and allow fine control of room temperature
...
1 shows a block diagram of body thermoregulation
...
1,
the hypothalamus in the brain is the temperature-regulating center for the body
...
The heat loss control is located in the anterior hypothalamus, which
contains more warm-sensitive neurons than cold-sensitive ones
...
It is clear that the set-point
temperature for a healthy person is 37 °C
...
However, low skin
temperature and the presence of substances released from toxic bacterial cell membranes,
such as lipopolysaccharide toxins, cause the critical set-point temperature to rise
...
This change of the set-point level acts as a unit step input to the body
temperature control system, which is considered a first-order system
...
10
...
1 The human temperature regulation system can increase or decrease body temperature
...
This part of the hypothalamus acts like a thermostat controller
in room temperature regulation
...
Sweating is the main mechanism by
which the body causes heat loss via water evaporation
...
Vasodilation is
handled through the autonomic nervous system
...
In turn, it decreases body temperature
...
They are: skin vasoconstriction, shivering, and increased
thyroxine secretion
...
Shivering is a reaction of skeletal
muscles to call for an increase in heat production of the body
...
The primary motor center for
shivering is located at the posterior hypothalamus (dorsomedial portion)
...
However, the increase of
thyroxine secretion is a long-term process of heat production increase through the
4
Body Temperature, Heat, Fat, and Movement
endocrine system
...
Thyroxine is the hormone
secreted by the thyroid gland to increase the rate of tissue metabolism
...
It is usually an efficient way to maintain
our body temperature
...
10
...
We measure temperature with
thermometers
...
This is
done by detecting a change in the physical property of a sensor
...
The thermometer
uses these materials as sensors to measure temperature
...
The
measured temperature varies from site to site, ranging from the oral temperature, which is
lower than the core temperature by about 0
...
These temperature
measurements need patient cooperation and are affected by the presence of food, drink,
and physical activity
...
Theoretically, temperature measurement taken near the tympanic membrane not only is
close to the core temperature (proximate to the hypothalamus), but also is not affected by
interfering factors
...
The measured temperature is still lower than the core temperature by about 0
...
It
all depends on how close the measurement is made to the tympanic membrane
...
10
...
1 Surface temperature measurement
Radiation from the skin surface is the main mechanism of heat loss from the body
...
The relationship between the energy emitted from the skin surface and the skin surface
temperature forms the basis of surface temperature measurement
...
It is a good indicator for bone fractures and inflammation
...
Medical thermography is a technique to scan the
skin surface and map its thermal distribution
...
2 Clinical Temperature Measurement
5
diagnosis tumors and breast cancers
...
Liquid crystal thermometer
Liquid crystal thermometers are made of chemical compounds with the property of
reflecting light within a range of temperature (26 to 40 °C)
...
They are constructed by impregnating Mylar
strips with encapsulated liquid crystals
...
Liquid crystal thermometers are easy to use, inexpensive, and
disposable but less precise than other thermometers (see next section)
...
2 °C to 0
...
10
...
2 Core temperature measurement
While surface temperature measurement is used by physicians as a diagnostic tool for
specific diseases, core temperature measurement is a rather routine method used in
hospitals, clinics, or even at home
...
High and lasting fever
above 41 °C can cause damage to the brain and other internal organs that are vital to
human life
...
Temperature measurement varies from site to site
...
This section discusses
basic principles, advantages, and disadvantages of different types of thermometers for
core temperature measurements
...
It is based on the principle of
volume expansion
...
The result of the change can be read on a calibrated scale
...
Its accuracy varies widely depending on how well
the expansion of mercury is calibrated
...
The cool mercury pulls down the temperature of the tongue
...
It is affected by how
well the probe and tissue surface are coupled
...
Other disadvantages are a potential damage to mucosal tissues when
measured orally or rectally, and possible mercury intoxication due to the broken glass
...
The
accuracy of the mercury thermometer is usually manufacturer-dependent
...
Because their sensor mass is smaller and they use electronic circuits, their
response time is faster than that of mercury thermometers
...
Thermistors are thermally sensitive resistors with either negative
(NTC) or positive (PTC) temperature coefficients
...
Figure 10
...
They are composed of
dissimilar materials with temperature-dependent electrical resistance, such as oxides of
nickel, manganese, or cobalt metal, to enhance their temperature sensitivity
...
3
10
1
← β = 3500 K
← β = 4000 K
R/R25°C
10
← β = 3000 K
−1
10
−3
10
−50
0
50
100
Temperature (°C)
150
200
Figure 10
...
The resistance–temperature curve shown in Figure 10
...
(10
...
The resistance of the thermistor at temperature T in degrees kelvin (K) is given as
10
...
1)
where β is the characteristic temperature of the material, R0 is the resistance at T0 = 298
K
...
The temperature coefficient, or sensitivity, α, can be defined by differentiating
Eq
...
1), which yields
β
dR
α = RT T = − 2
...
2)
dT
T
where α is temperature dependent and exhibits the nonlinearity of thermistors
...
4%/K
...
g
...
Bare wires have a
rapid response time
...
Wires enclosed in an insulator have the slowest response time
...
It develops an electric potential, which can be measured when we place a
voltmeter between open ends as shown in Figure 10
...
In 1823, Seebeck first reported
this phenomenon, called the Seebeck effect
...
3 shows the measuring principle of
a J type thermocouple
...
3)
where C1 and C2 are constants that depend on the thermocouple pair with T in kelvins
...
(10
...
The sensitivity or thermoelectric power of the thermocouple is the derivative of Eq
...
3)
with respect to T1 is
α=
dV
dT1
...
4)
For example, the sensitivity for the copper–constantan thermocouple is 45 µV/°C at
20 °C (Cobbold, 1974)
...
8
Body Temperature, Heat, Fat, and Movement
Voltmeter
Copper
Copper
Constantan
Cold junction, T2
(Reference)
T1 , Hot junction
(Measuring probe)
Figure 10
...
Electronic thermometers use thermistors or thermocouples as sensors to measure
temperature in the mouth, rectum, or axilla (armpit)
...
Microprocessor-based electronic thermometers
use either the steady-state or predictive method to improve the response time for
temperature measurement to less than 1 min
...
Once it is in the steady state, the display shows the temperature of the
sensor In contrast, a thermometer of the predictive type measures the temperature based
on a manufacturer's algorithm that is developed from several experiments of the rate of
rise in temperature to estimate the final temperature (Bair and Davies, 1995)
...
4
shows a simplified block diagram for an electronic thermometer
...
4 An electronic thermometer uses a thermistor sensor probe
...
Their disadvantages are similar to those of mercury
thermometers, such as mucosal damage and cross–infection if not carefully handled
...
2 Clinical Temperature Measurement
9
disposable probe cover is used to prevent cross-infection
...
Infrared thermometer
A basic infrared thermometer (IRT) design includes four parts: a waveguide (tube) to
collect the energy emitted by the target, a sensor to convert the energy to an electric
signal, an emissivity adjustment to match IRT calibration to the emitting characteristics
of the object being measured, and a sensor temperature compensation circuit to ensure
that temperature variations within the IRT are not transferred to the final output
...
5 shows a block diagram of an infrared thermometer
...
The collection of infrared radiation is enhanced by a waveguide, which
improves reflection of the infrared radiation onto the sensor when the shutter opens
...
The microprocessor handles emissivity
adjustment and temperature compensation, and calculates the patient (target) temperature
according to Eq
...
5):
Tb =
[χ (N
T
− N T0 ) + T04
4
]
(10
...
(
)
N T = Aσε a Tb4 − Ta4 ,
(10
...
67 ×
10–8 W/m2·K4), εa the emissivity of surroundings (sensor), Tb the body temperature,
and Ta the sensor temperature (Ta and Tb are both in kelvins)
...
Shutter
switch
Digital
display
Figure 10
...
The ambient sensor that monitors the sensor temperature (Ta), is a thermistor
...
The pyroelectric sensor, like the
piezoelectric sensor does not respond to steady inputs and in response to a step input
yields a high-pass first order output of the form e-t/τ
...
Its accuracy and resolution are about ±0
...
The
main advantages of the infrared thermometer are that it only contacts the ear canal and
not the eardrum (i
...
less infection), ease of use, and fast response
...
However, inaccurate
measurements occur when patients have curved ear canals or the cerumen (ear wax)
obstructs the tympanic membrane
...
3 Measurement of Body Heat: Calorimetry
Calorimetry is the measurement of heat given off by a subject
...
Indirect calorimetry measures respiratory gas
exchange to infer the amount of heat production
...
Calorimetry provides the basis for the
science of nutrition
...
Calorimetry is also a powerful research tool for energy balance
and thermal physiology studies
...
In this section, we will deal with the principles and applications of direct and
indirect calorimetry
...
3 Measurement of Body Heat: Calorimetry
10
...
1
11
Direct calorimetry
Direct calorimetry has been used on animals and in humans for energy and thermal
regulation studies
...
They are usually classified under one of four principles of operation: gradient
layer calorimeter, air–flow calorimeter, water flow calorimeter, and compensating heater
calorimeter
...
The air–flow
calorimeter is popular in studies of energy expenditure for humans and animals
...
The
compensating heater calorimeter is commonly used in experiments for small animals
...
Gradient layer calorimeter
Gradient layer calorimeters are isothermal calorimeters
...
As sensible (i
...
nonevaporative) heat from the subject
passes through the thin layer of insulating material to the heat sink (metal wall or water
jacket), the temperature gradient across the layer of insulation is sensed by a network of
thermocouples (e
...
copper–constantan)
...
These thermocouples are used to detect the temperatures of the
inner and outer surfaces
...
The main
objective of the gradient layer calorimeter design is to prevent any sensible heat loss from
convecting out of the chamber by heating up the ventilating air
...
It includes
the control of the ventilation and cooling system and instrumentation for the temperature
measurement for a huge chamber
...
McLean and Tobin (1987) provide a detailed description of how to design and
construct a gradient layer calorimeter
...
The
response time of the measurement to a unit change of heat output (i
...
when a person is
first placed inside) is 80% of the change is recorded within 3 min and 90% within 10 min
but the full response takes nearly an hour
...
7)
(10
...
9)
(10
...
11)
where VC, VT, and VE are measured voltages from the chamber, thermocouples, and
D
D
evaporative heat, respectively; Q N and QE are the rates of nonevaporative and
C
evaporative heat production in the chamber; QC is the rate of nonevaporative heat
D is the rate of heat leakage through any gaps in the
convection out of the chamber; QL
D
heat-sensitive layer; V and νD are chamber and evaporative heat measuring air flow rates;
kc, ke, and kt are constants (sensitivities); ∆p is a term due to unequal sensitivities or
unequal sampling rates; during the calibration, as performed with the chamber controlled
at 25 °C and the evaporative heat measuring unit at 10 °C, the desired value k = kc = ke
D
D
V /νD = kt V = 46
...
The advantages of the gradient layer calorimeter are accuracy and fast response;
however, they are expensive and not transportable
...
6 shows that they are
complicated in design and construction
...
3 Measurement of Body Heat: Calorimetry
13
Insulation layer
Constantan
Metal wall
Cooling tubes
Copper
Thermocouple
connection
Figure 10
...
Ventilating system and measurements not shown
...
Heat loss from the subject is carried away from the chamber
by air–flow
...
An important objective for the design of an air–flow
calorimeter is to prevent any water condensation on the surface of the chamber
...
7 shows the principle of an air–flow calorimeter
...
The heat loss from the
subject is transferred to the ventilating air, whose temperature is measured at the inlet and
the outlet of the chamber
...
12)
14
Body Temperature, Heat, Fat, and Movement
Thermometer
Air out
T2
Air in
Thermometer
Insulated chamber
(polyurethane)
T1
Figure 10
...
The advantages of the air–flow calorimeter are simplicity of construction and
fast response to heat change (7 to 20 min)
...
Water flow calorimeter
A water flow calorimeter is a heat-sink calorimeter
...
The removal
rate of heat is estimated from the flow rate and temperature rise of the coolant (water)
...
8 shows a suit calorimeter, which is a typical water flow calorimeter
...
Their suit calorimeter
consists of a water-cooled undergarment, insulating outer garments, a controlled heater
and the cooling machinery for the water loop, and the related devices for control and data
handling
...
Each 20% of the total of small tubes (a total length of 80 m with an inner
diameter of 1
...
The circulating water is pumped, at 1
...
The subject's heat loss to the water ( Q w ) is estimated from the mass flow rate
( m ), specific heat (cw) and temperature difference between water outlet (T2) and inlet
(T1)
...
(10
...
The advantages of the water flow calorimeter
are its fast response (30 s) and it is fully transportable
...
One main disadvantage reported
by Webb (1985) is that the heat loss from the subject occurs by conduction, from skin to
the cooled tubing
...
10
...
8 The water flow calorimeter measures the inlet and outlet water temperature
...
The heater is needed to protect against heat
loss to the environment
...
9 shows that when the subject's heat is added to the
chamber, the heater needs less power to maintain the constant temperature of the chamber
...
The advantages
of this type of calorimeter lie in its speed of response (on the order of 1 min) and
lightweight construction
...
Thermostat
Feedback control
AC
Power
source
Power
meter
Heater
Figure 10
...
16
Body Temperature, Heat, Fat, and Movement
10
...
2 Indirect calorimetry
Indirect calorimetry estimates heat production by quantitative measurements of the
oxidative processes of substrates, especially the measurement of the rates of oxygen
D
D
consumption ( VO 2 ) and carbon dioxide production ( VCO 2 )
...
We discuss three commonly used methods of indirect calorimetry in
this section: open-circuit systems, closed-circuit systems, and the double-labeled water
method
...
Most ambulatory, laboratory, and bedside uses for
the estimation of energy expenditure are based on measurements of respiratory gas
exchange
...
The apparatus that collects gas includes a mouthpiece with a nose clip, a ventilated
hood or bed canopy, or a whole body chamber
...
Because the whole body chamber is also a
closed-circuit system but conducted in a confined environment, we consider it as one of
the closed-circuit systems
...
In general, the whole
body chamber system is used for physiological research over long periods of time (24 h
or longer)
...
A detailed review of techniques for the
measurement of human energy expenditure and commercially available product
information are given by Murgatroyd et al
...
(1995)
...
This
D
calculation of VO 2 includes a correction for change in barometric pressure, temperature,
and relative humidity of the inspired air for adjustment of the volume to standard
temperature, pressure, and dry air condition (STPD: 0 °C, 760 mmHg, dry)
...
941) + VCO 2 (1
...
13)
D
D
where VO 2 and VCO 2 are expressed in L/min, and 1440 = the number of minutes in a
day
...
3% of the total calories arise from protein metabolism
...
17)) in g/min is added to
the bracket of Eq
...
13) to account for protein correction of energy expenditure
...
3 Measurement of Body Heat: Calorimetry
17
D
carbon dioxide ( FICO 2 , FECO 2 ), and inspired and expired minute ventilation ( VI ,
D
D
VE )
...
14)
D
and VCO 2 by a similar equation:
D
D
D
VCO 2 = V E (FECO 2 ) − V I (FICO 2 )
...
15)
D
D
However, it is technically difficult to measure the difference between VI and VE
...
e
...
Then VI is
obtained by the equation
FEN 2 D
D
VI =
VE
FIN 2
(10
...
If only N2, O2, and CO2 are analyzed, VI can be obtained by
D 1 − FEO 2 − FECO 2 V
D
VI =
E
1 − FIO 2 − FICO 2
(10
...
Substituting Eq
...
17) into Eq
...
14), the formula for VO 2 becomes
(FIO 2 − FEO 2 − FIO 2 FECO 2 − FICO 2 FEO 2 )
VO 2 =
× VE
1 − FIO 2 − FICO 2
or
(1 − FEO 2 − FECO 2 )× FIO 2
− FEO 2 × V E
VO 2 =
1 − FIO 2
(10
...
03% in most situations
...
In general VI and VE are of similar
magnitude but not equal; the same is true for FIO2 and FEO2
...
6 (see below)
...
(10
...
D
D
D
If we assume VI is equal to VE , there will be significant errors in VO 2 measurement, for
example in a patient whose respiratory rate is 10 breaths per minute at a 1000 mL tidal
18
Body Temperature, Heat, Fat, and Movement
D
D
volume ( VT ) and whose VO 2 is 250 mL/min
...
7
...
5 mL per breath of CO2
...
6) assuming that
75 mL
...
When RQ reaches 1
...
Measurement of VCO 2 is
much simpler
...
03%)
...
(10
...
0
...
10
...
At the end of the mixing chamber, a small sample is
drawn by a vacuum pump through O2 and CO2 sensors that measure FEO2 and FECO2
...
A volume transducer is used to measure minute
D
ventilation ( VE )
...
From
Inspired
gas source
O2
Switch
CO2
Computer
control
Pressure
transducer
Vacuum
pump
Thermistor
Exhaust
Patient
Expired gas
from patient
Flow
transducer
Mixing chamber
Figure 10
...
When measuring respiratory exchange gas, there are two broadly used methods:
the air may be directly expired through a mask or mouthpiece as mentioned above or it
may be drawn from a hood or canopy enclosing the subject's head
...
It needs a pump to draw constant air over a subject's
10
...
The process of VO 2 and
VCO 2 measurements is the same as before
...
Consequently this demands that the analyzers be
more precise and free of drift
...
, PO Box 900, FIN-00031, Helsinki, Finland) and
Vmax29n (SensorMedics Corp
...
It is
suitable for use with a mechanical ventilator or a canopy for patients of all ages
...
, 1990)
...
11), the expired gases enter the mixing chamber, from
which gas is sampled and analyzed to determine FEO2 and FECO2
...
VCO 2 is then calculated as
(
D
VCO 2 = Q F * CO 2
)
(10
...
The respiratory
quotient (RQ) is then calculated using the Haldane transformation
...
21)
D
where FIO2 is the O2 concentration from the inspired limb of the ventilator
...
RQ
(10
...
11 A dilution system used by Deltatrac uses mechanical ventilation
...
A microprocessor controls the sampling of gases
...
O2 measurements occur by alternately sampling the difference between
inspired and expired O2 (FIO2 – FEO2) and the measurement of FIO2
...
They also showed a different calculation procedure
V 2
D
D
for canopy measurement of VO 2 and VCO 2 in spontaneously breathing patients
...
The breath-by-breath technique was originally designed for
V 2
exercise testing and has been adapted for use with a mechanical ventilator
...
Gas samples are collected on a
breath-by-breath basis and are averaged over a preset time to obtain mixed expired values
(Branson et al
...
Furthermore, bedside mixing chamber systems can be modified
and used for ambulatory and field studies by dispensing with the CO2 analyzer to
simplify the procedure
...
Closed-circuit system
10
...
They use the volumetric loss and replenishing techniques to
D
measure VO 2
...
The latter measures the amount of oxygen needed to keep the
spirometer full
...
2) full of 100% O2, and a CO2
D
D
analyzer (Figure 10
...
Closed-circuit systems allow VO 2 and VCO 2 measurements
during mechanical ventilation and during spontaneously breathing ventilation with a
mouthpiece plus nose-clip or facemask
...
Samples of the
expired gas are analyzed to obtain FECO2 before passing through the soda lime scrubber
...
The volume change in the
spirometer as a function of time is used to calculate the rate of O2 consumption
...
During mechanical ventilation, the bellows in Figure
10
...
From ventilator
Bellows
Spirometer
Patient
CO2
Scrubber As oxygen
supply and
analyzer
Mixing
chamber
Sample
gas
CO2 analyzer
Figure 10
...
The spirometer is used as
an oxygen supply and the volume change as a function of time in the spirometer is used to calculate
the rate of oxygen consumption
...
In the whole body chamber the subject is kept in a sealed chamber that is
ventilated with a constant, measured supply of fresh air
...
Samples of well-mixed air are drawn from the chamber for continuous
analysis
...
McLean and
Tobin (1987) stated that the Atwater and Benedict respiration chamber represents one of
the earliest designs of this type of calorimeter
...
12
...
This external circuit includes one CO2 absorber, two moisture absorbers, a
spirometer, and an oxygen supply
...
The pressure drop in the system, caused by the uptake of oxygen by the subject and
the absorption of any expired CO2, is detected by the spirometer
...
This then releases a valve on the
oxygen inlet line
...
A meter is used to measure the
delivery of oxygen
...
The whole body chamber offers fast response, accuracy and precision and
allows comparative measurements during sleep, at rest, before and after meals, and
during controlled periods of exercise
...
In their review of techniques for the measurement of human energy expenditure,
Murgatroyd et al
...
They further reported that an accuracy of 1
...
Although the whole body indirect calorimeters provide fast response, accuracy and
precision of measurement, satisfactory results are only obtained with careful chamber
design and construction, and by the choice of the best possible instrumentation
...
Current design of the closed-circuit
volumetric replenishment indirect calorimeter employs an ultrasonic transducer to
monitor the volume level of a bellows that is used as an oxygen reservoir
...
The VO 2 is calculated by
multiplication of the pulse volume by the number of pulses per minute
...
Measurement of VO 2 made by this
technique has been found to be quite accurate
...
99) between
D
measured and actual VO 2 has been reported by several authors (Branson et al
...
, 1989)
...
6
...
(1995)
...
, 1955)
...
3 Measurement of Body Heat: Calorimetry
23
stable isotopes: deuterium (2H) and oxygen 18 (18O)
...
It
also has considerable appeal for field studies to estimate the energy cost of activities and
thermogenesis by subtracting the basal metabolic rate from the total energy expenditure
...
The body is in steady state; i
...
the volume of total body water pool remains
constant over time
...
The turnover rates of water and carbon dioxide are constants over time
...
The volume of labeled water distribution is only equal to total body water
...
The isotopes are lost only as water and carbon dioxide
...
Losses of labeled water and carbon dioxide in urine and exhaled carbon dioxide
have the same level of enrichment as in body water
...
The background levels of the isotopes remain constant
...
13 Principle of the doubly labeled water method
...
Figure 10
...
After a subject drinks a dose of
DLW, the deuterium mixes with the body water pool and the 18O mixes with both water
24
Body Temperature, Heat, Fat, and Movement
and bicarbonate pools
...
The formula for this calculation is:
W
rCO 2 = VCO 2 = × (k18 − k 2 )× 22
...
23)
where r (in L/h) is the production rate, W is the size of total body water in mol and k18
and k2 are fractional disappearance rates for 18O and 2H, respectively
...
The factor 2 in the denominator of Eq
...
23) is the molar proportion of
oxygen in carbon dioxide in relation to water
...
(1955) modified
Eq
...
23) by including the fractional factor: f1 (0
...
99) for H2 gas/H218O liquid, and f3 (1
...
Eq
...
23)
becomes
or
W
f −f D
D
rCO 2 = VCO 2 =
(k18 − k 2 ) − 2 1 m × 22
...
4
624
2
...
24)
D
where m is the rate of water loss as vapor in g/h
...
A number of crossvalidation studies have been performed by comparison with gas exchange analysis and
the whole body chamber under resting condition as well as during sustained heavy
exercise (see reviews in Ritz and Coward, 1995; Mclean and Tobin, 1987; Prentice et al
...
Results showed that the doubly labeled water method
is a suitable technique for assessing energy expenditure in free-living circumstances with
an accuracy of ±5%
...
Advantages of the doubly labeled water method are that it is
noninvasive (oral dosing), nonintrusive (urine sampling), and suitable for noncompliant
subjects and field studies
...
4
...
Nevertheless, the high cost for the expense of 18O-enriched water and technical
complexity are disadvantages of the doubly labeled water method
...
In-depth
knowledge of the assumptions of the doubly labeled water technique is required to apply
it to various physiological and pathological situations
...
5 Measurement of Body Movement
10
...
It is used in a wide
variety of fields, including human biology, medicine, sports science, and nutrition
...
Body fat mass is defined as pure fat—triglyceride fat in the body
...
Fat free mass (FFM) is defined as lean body mass plus nonfat components of
adipose tissue
...
The chemical composition of
the fat-free body is assumed to be relatively constant
...
1 g/cm3 at 37 °C (Behnke et al
...
2%, Pace and Rathburn, 1945)
...
9 g/cm3 at 37 °C (Mendez et al
...
All body fat methods
use either this two–component model or a further division of the fat and fat-free weight
into four compartments: water, protein, bone mineral, and fat (Brozek et al
...
The
various body fat measurement techniques may be further divided into two categories
...
Examples of indirect methods that will be discussed here are anthropometry and
bioelectrical impedance analysis (BIA)
...
10
...
1 Direct measurement of body fat
Direct measurement techniques of body fat such as densitometry (underwater weighing)
and deuterium oxide dilution are commonly used as reference methods for measuring
percent body fat
...
DPA/DEXA is another direct measuring technique that has
yet to be tested as a reference method
...
Consequently, it is not practical for field studies
...
In contrast, the deuterium oxide dilution method is applicable for a
variety of groups
...
Deuterium oxide dilution
The use of the deuterium oxide dilution technique to measure body water to predict FFM
uses the fact that fat is mainly anhydrous and water is a relatively constant component
25
26
Body Temperature, Heat, Fat, and Movement
(73
...
It is based on the assumption that the isotope has the same distribution
volume as water, is exchanged by the body in a manner similar to water, and is nontoxic
in the amount used
...
Then the amount of
the labeled water in saliva, urine, or plasma is determined after an equilibrium period (3
to 4 h)
...
25)
where C1V1 is the amount of the isotope given, and C2 is the final concentration of the
isotope in saliva, urine, or plasma and V2 is the volume of TBW
...
15
...
12), and filter-fixed infrared absorptiometry
...
Lukaski (1987) reported that a 10 g dose of deuterium oxide (99
...
Some investigators have given an
oral dose of deuterium oxide of 1 g/kg body weight (Mendez et al
...
For adult white individuals (Wellen et al
...
04 and 0
...
V2
FFMTBW (kg ) =
(10
...
04 × 0
...
27)
where FFMTBW is FFM derived from TBW (V2), weight is the subject's body weight,
and %BFTBW is the derived percent body fat from FFMTBW
...
732) in Eq
...
26) should
be adjusted to maintain an accurate estimation of %BFTBW
...
In general, the accuracy
associated with measuring body fat by the TBW method is about 3% to 4% (Lukaski,
1987)
...
This method is often used as the reference method for
evaluating new indirect methods such as bioelectrical impedance analysis
...
4 Measurement of Body Fat
27
assumes that the human body has two distinct compartments: fat mass and fat free mass
(Siri, 1961; Brozek et al
...
The measurement of body density is accomplished by
measuring body volume (according to Archimedes' principle) and body weight (by the
difference between the subject's weight in air and weight in water)
...
In a human subject, the apparent volume of the subject is determined by
correcting for the volume in the lung and the density of the water using the water
temperature at the time of the measurement
...
The tare
weight for the chair and water temperature are measured before the experiment
...
While remaining under water, the subjects exhale completely and hold their
breath
...
Underwater weight is
recorded 10 times for each subject and the mean of the three highest weights is used
...
The body density (BD) is expressed in g/cm3 and is calculated from
Eq
...
28) (Guo et al
...
28)
Wa − (W w − T )
− RV
Dw
where Wa = weight in air in grams, Ww = weight in water in grams, Dw = density of
water in g/cm3 at actual water temperature, RV = residual lung volume in cm3, and T =
tare weight in g
...
, 1963)
...
95
– 4
...
29)
%BF =
4
...
412
BD
(10
...
(10
...
30) give results within 1%
body fat if the body density is within 1
...
03 and that Siri's equation yields higher
values than the Brozek’s equation for subjects with more than 30% body fat
...
In general,
the error is greater in populations with lower bone mineral content (children, women, and
old people) and populations with high bone mineral content (athletes)
...
Dual photon absorptiometry (DPA) / dual energy X-ray absorptiometry (DEXA)
Another technique for direct measurement of body fat is dual photon absorptiometry or
dual energy X-ray absorptiometry
...
Photon aborptiometry was first
introduced by Cameron and his colleagues (1962, 1963) to measure bone mineral content
(BMC) in the limbs with a single isotope (Iodine-125 at 27
...
6 keV)
...
9)
...
Mazess and his
colleagues (Mazess et al
...
g
...
This method has
been applied to measure BMC in the axial skeleton (e
...
vertebrae) with the isotopes
Americium-241 (241Am, 59,6 keV) and Cesium-137 (137Cs, 662keV) by Roos and
Skoldborn (1974)
...
The mass attenuation
coefficients for bone mineral and soft tissues are constant and are not affected by the
amount of bone and soft tissues along the path of the photon beam
...
The basic equations for DPA are as follows (Sorenson et al
...
31)
N
ln 0 H
N
H
= µ sH M s + µ bH M b,
(10
...
By solving Eqs
...
31) and (10
...
4 Measurement of Body Fat
N 0H
N 0L
R ln
N − ln N
H
L
Mb =
(Rµ bH − µ bL )
29
(10
...
Based on the same basic equations, DEXA uses a constant voltage
X-ray generator and k-edge filters (made of cerium) to separate the X-ray beam into two
energy levels, or a switching-pulse system that rapidly alternates the constant voltage Xray generator to produce two beams with high and low energy simultaneously
...
, Fort Atkinson, WI) and Lunar DPX series (Lunar Radiation Corp
...
An example of the latter type of densitonometer is the Hologic QDR-1000 series
(Hologic, Inc
...
In recent years, DEXA has become the main stream in the
densitometer industry
...
Most of the current commercially available densitometers usually include a
scanning and examination table, X-ray system (scanner and scintillation detector), a
computer system with additional software to control and calculate BMC and body
composition, and positioning or calibration accessories
...
, 1990)
...
Typical transverse scan image
area is around 60 cm × 200 cm
...
The %BF can be
derived from the R value through application of a regression equation of %BF and the R
value resulting from the calibration phantom provided by the manufacturer
...
These calculations
are usually processed by the software provided by the manufacturer
...
In general, the precision error for the
percent body fat is within approximately 2% (Lukaski, 1987; Mazess et al
...
The advantages of DPA/DEXA include portability, capability of
measuring total body or regional composition of bone mineral and body fat, high
reproducibility (3 to 5%), and less dependence on the technician's skills and experience
...
Radiation exposure of DPA/DEXA is between 2 and 10 mrem
...
4
...
These techniques are suitable for population studies where individual distinction is less
critical
...
Anthropometry is a rapid and inexpensive way to evaluate
nutritional status for a population in a field study, but it requires a skilled technician and
30
Body Temperature, Heat, Fat, and Movement
anthropometrist to achieve accurate measurement
...
In general, both techniques are less likely to be useful for
prediction of change in body composition
...
It includes measurement of body
circumferences, skinfolds, weight, stature, etc
...
It is based on two assumptions: the
subcutaneous adipose tissue represents a fairly constant proportion of the total body fat
and the selected measurement sites represent the average thickness of subcutaneous
adipose tissue (Lukaski, 1987)
...
Skinfold thickness can be measured using special devices such as the Lange caliper
(Lange and Brozek, 1961, see Figure 10
...
The main uses for skinfold thickness are to estimate
body fat (percent body fat, or %BF) and the anatomical distribution of fat tissue for
population surveys
...
Shoulder
Triceps
skinfold
Lange
caliper
a
b
Figure 10
...
(b)
Illustration of an example of skinfold measurement, triceps skinfold taken on the midline posterior
surface of the arm over the triceps muscle
...
A distance of at least 1 cm should be maintained
between the fingers and the caliper arms to prevent any interference from the pressure of
the fingers
...
4 Measurement of Body Fat
31
perpendicular to the longitudinal axis of the skinfold (see Fig
...
14(b))
...
The sequence of
measurements is repeated three times to reduce intrameasurer bias
...
, 1988)
...
These equations are generally valid
for adult Caucasian populations, but overestimate body fat in elderly individuals
...
(1980) published equations for
estimating body density in adult men, Eq
...
34), and women, Eq
...
35), aged 20 to 50
years
...
1093800 − 0
...
0000016 ( X 1)2 − 0
...
34)
BD = 1
...
0009929 ( X 2 ) + 0
...
0001392 ( X 3)
(10
...
Correlation coefficients (r) for Eqs
...
34) and (10
...
905 and 0
...
These body densities can subsequently be used for percent body fat estimation with Eq
...
27)
...
However, the accuracy and reliability
of skinfold thickness measurement depends on the skill of the measurer, interaction
between the measurer and the subject, and the characteristic of the subject
...
In
addition, body fat of edematous (excess fluid in the tissues) patients is often
overestimated and very obese subjects cannot fit in the standard calipers
...
It is also based on the two-compartment model
(in parallel) as mentioned earlier
...
2%) in the body; it represents the main path of conduction for the
applied current
...
Therefore, the impedance of
the body is controlled by fat free mass
...
Prediction equations are often generated
using BIA values to estimate fat free mass
...
36)
where Z is the impedance in ohms (Ω), ρ is the resistivity in Ω⋅cm, L is the conductor
length in cm, and V is the volume in cm3
...
Current injector electrodes are placed in
the middle of the dorsal surfaces of the right metacarpal–phalangeal (hand) and
metatarsal–phalangeal (foot) joints, respectively
...
Measurements of body resistance
and reactance are made on ipsilateral and contralateral sides of the body (as shown in
Figure 10
...
The lowest value of resistance for each subject is used to predict fat free
mass (FFM)
...
(1969) first used four surface electrodes (tetrapolar) for the
study of TBW
...
They introduced 100 µA of ac current at 100 kHz in 20 healthy
subjects and 34 patients whose TBW were measured with the isotope dilution method
(see section 10
...
1) and showed that (stature)2/Z was the best predictor of TBW
...
92 and 0
...
Lukaski et al
...
They used a
current source of 800 µA at 50 kHz (RJL Systems, Detroit, MI)
...
95) and FFM (r = 0
...
Kushner and Schoeller
(1986) cross-validated the prediction of TBW with BIA by generating a prediction
equation from a sample of 40 nonobese adults and applying it to 18 obese patients
...
96)
...
(1985) also
confirmed the significant role of (stature)2/Z as a predictor of FFM (r = 0
...
9 to 54
...
Because fat free mass includes virtually all
water in the body, the formula that is used to predict TBW via BIA is often used to
estimate FFM
...
37)
where C1 and C2 are regression coefficients of the independent variables Stature2/R in
cm2/Ω and Weight in kg, respectively
...
These constants vary with different sample groups
...
38)
10
...
Segal et al
...
(1989) have
suggested that prediction of FFM can be enhanced by the use of gender and fatness
specific equations
...
15 In resistance measurement on the ipsilateral side of the body current flows through
one arm, the trunk, and one leg
...
) are often equipped with multiple frequency function and
specialized software
...
Theoretically
TBW is modeled as a parallel R–C circuit with the cell membrane as a capacitor to
separate intracellular and extracellular fluids
...
Therefore, at low frequency the impedance can be used to estimate
ECW
...
93) and
TBW was best estimated by resistance measured at 100 kHz (r = 0
...
Regression
coefficients (C1, C2, and C3) estimated from his study for TBW and ECW were 0
...
133, 2
...
177, 0
...
0, respectively
...
(1991) also confirmed the
significant role of resistance measured at 5 kHz and 100 kHz for prediction of ECW (r =
0
...
95) in 36 healthy males
...
455, 0
...
43 and 0
...
112, –
6
...
They cross-validated on two randomly selected subsets (18 each) and
showed that the prediction equations were reproducible and valid
...
In addition, multifrequency BIA can differentiate extracellular water (ECW)
and total body water (TBW)
...
10
...
It is useful for improving performance of motor
34
Body Temperature, Heat, Fat, and Movement
skills (such as skating) and providing efficient methods of using the body in daily life
skills (e
...
, walking and running)
...
Many methods are available, ranging from simple visual observation to
complicated computerized systems
...
A kinematic analysis system varies
from simple and subjective visual observation to more expensive and complicated video
or optoelectronic systems that can provide objective, quantitative data of threedimensional motion of selected points on the body
...
In this section, we discuss working
principles and applications for goniometers, accelerometers, and video and optoelectronic
kinematic analysis systems
...
(1995), Whittle (1996), Winter (1990), and Medved (2001)
...
5
...
The goniometer (see Figure 10
...
Traditionally, a goniometer uses a
resistance potentiometer to convert changes in rotation to an electric output proportional
to the positions of two attachment arms
...
Multiaxial measurements of the joint are possible with two or three potentiometers
mounted orthogonally in different planes
...
However, to ensure accurate
measurements, fixation to the body with cuffs around the soft tissues must be performed
carefully to prevent off-axis problems (Chao, 1980)
...
A triaxial parallelogram electrogoniometer (see Figure 10
...
, 1986)
...
They deform when they
are stretched or compressed and the electric output is proportional to the change in joint
rotation
...
3
...
10
...
16 (a) A goniometer attached to the shank and thigh to measure knee rotation
...
Vout is the output voltage that is proportional to the angle of knee rotation
...
Accelerometers
Accelerometers are instruments that measure acceleration
...
17
...
A strain gage accelerometer consists of strain gages
(wires) bonded to a cantilevered mass and a base to which the cantilever beam is attached
...
The strain in the wires changes their resistances
...
11
...
The resulting electric output is proportional to the
acceleration of the mass
...
Instead of using strain sensitive wire, it uses piezoresistive
strain elements as sensors
...
The
piezoelectric sensor converts the force produced by the acceleration to an electric charge
or voltage (see Eq
...
7) and section 8
...
2 for the working principle and its charge
amplifier)
...
Two- or threedimensional measurements are possible with several accelerometers grouped together
orthogonally
...
Some
practical limitations prevent widespread use of the accelerometer in body motion analysis:
necessity to exclude the effect of the field of gravity from true kinematic acceleration,
difficulty in extracting the rotational acceleration, and low frequency noise caused by the
baseline drift in the measurement output
...
17 Vertical acceleration of the accelerometer frame bends the cantilever beam because
the seismic mass remains at rest
...
E is the
supply voltage
...
5
...
Gait
can be measured by video recorder
...
18 shows that a video or optoelectronic
kinematic analysis system consists of active or passive markers placed at selected skin
surface locations on bony landmarks, sensors that track markers' positions, and a
computer system to control the timing for active marker display and signal processing of
markers' tracings
...
A computerized analysis system often yields graphic displays that can provide
information on joint positions, joint angles, segment angles, velocity, and acceleration as
a function of time
...
18 An example of a gait analysis setup includes a four-camera kinematic system, two
force platforms, and an electromyogram (EMG) telemetry system
...
5 Measurement of Body Movement
37
There are many commercially available video or optoelectronic kinematic
analysis systems (Walton, 1990)
...
For examples, Vicon (Oxford
Metrics Ltd
...
, Southfield, MI), OPTOTRACK (Northern Digital Inc
...
, Leics, UK) are optoelectronic systems
with active (infrared emitting diode) markers
...
In order
to achieve real-time tracking of markers in 3-D, problems of real-time 2-D tracking with
marker identity maintained and 2-D-to-3-D transformations in real time have to be solved
...
They all depend on how many
video cameras and markers they use and how often they sample the data
...
They are suitable for sports studies or whenever large and fast
movements are to be recorded because the subject is not hampered by attached wires and
battery packs carried on belts as active markers
...
The IRLEDs are often arranged in sequence and pulsed at different times (only
one at a time) by a control unit
...
2
...
They are often synchronized by the camera
control and interface unit to collect data with analog devices such as force plates, and
EMG for movement kinetics
...
They use
photodetectors to focus the pulsed infrared signals from body markers from associated
body landmarks
...
For m markers and n cameras, the DLT method determines the
3-D spatial coordinates of a marker from the 2-D coordinates of the marker, i (i = 1, … ,
m) on camera j, (j = 1, … , n) by
x ij =
y ij =
A j xi + B j yi + C j z i + D j
I j xi + J j yi + K j z i + 1
E j xi + F j yi + G j z i + H j
I j xi + J j yi + K j z i + 1
where for a given marker i:
xij = x coordinate of marker i on camera j,
yij = y coordinate of marker i on camera j,
xi = x coordinate of marker i in 3-D space,
yi = y coordinate of marker i in 3-D space,
(10
...
40)
38
Body Temperature, Heat, Fat, and Movement
zi = z coordinate of marker i in 3-D space,
Aj to Kj = coefficients in the transformation of marker i
...
18 shows an example of a gait analysis laboratory, including a four–
camera kinematic system, two force platforms, and an electromyogram (EMG) telemetry
system
...
(1995) and Walton (1990)
...
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...
7 Problems
10
...
2
10
...
4
10
...
6
10
...
8
10
...
10
10
...
Design a circuit that converts the resistance change of a thermistor to a voltage,
and then amplifies it to measure temperature
...
Design a circuit that uses an electronic cold junction and thermocouple, then
amplifies it to measure temperature
...
Compare direct and indirect calorimetry
...
Figure 10
...
Sketch an expanded
gradient layer calorimeter that includes ventilation
...
Give a symbol for the output of each sensor
...
7) through (10
...
The oxygen consumption is 0
...
The carbon dioxide production is 0
...
Calculate the energy expenditure
...
Define %BF and explain its purpose
...
42
10
...
13
10
...
15
10
...
Draw the circuit for a resistance potentiometer goniometer with an amplifier
with a gain of 2
Draw the circuit for a 4-arm piezoresistive strain gage accelerometer and
amplifier
...
You want to analyze human locomotion; list the devices you need and explain
why
Title: solution Bioinstrumentation Webster
Description: best grade with this solution book the solution is very clear
Description: best grade with this solution book the solution is very clear