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Bio-Medical Engineering (UNIT-I)
Introduction:
Biomedical Engineering: It is the application of Engineering principles (electronics, electrical,
computer, mechanical and others) to medicine and biology for the health care complications
(Diagnostic, monitoring, supporting and therapeutic)
...
Medical Instrumentation
2
...
Biomaterials
4
...
Medical Informatics
Age of biomedical Engineering:

Age refers to long and distinct period of history (era) of biomedical engineering, similarly age
of automobile and radio communication
...

In 1970 will be well known decade in which most of the rapid progress was made in this highly
important filed
...
Bioengineering subdivides into different areas for example,
bioelectronics and mechanics
...

One of the societies that emerged in the interface area is the association for advancement of
medical instrumentation (AAMI)
...
Engineers are
divided into clinical engineers and medical engineers
...

Medical engineer, who theory of operation, underlying physiological principles and practical,
safe clinical application of biomedical equipment
...


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Post World War-II
(1939-45)

Nuclear, Aerospace and
communication
engineering in peak state

Computer engineering in
progress & BME started
its significance

IEEE in medicine and
biology, ASME and
AAMI were formed

Recognized the need of
clinical and Medical
Engineers
...
He invented the
first practical electrocardiogram (ECG or EKG) in 1903 and received the Nobel Prize in
Medicine in 1924 for it ("for the discovery of the mechanism of the electrocardiogram
...
At that time they started to experiment for medical
use, but the results were disappointing
...
A large measure help was provided by the US
government, in particular By NASA
...
Consequently, much research and development money
went to this area
...
Awarness of need for engineers and technicians work with medical
profession developed
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1
...
Stimulus
3
...
Signal condition circuit
5
...
Recording, data processing and transmission equipment

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Control feed
back

Stimulus

Transducer

Signal
conditioning
circuit

Display

Recording, data
processing and
transmission
...
It constitutes a many
biopotentials and living organisms
...

Stimulus: In many measurements, the response to some of external stimulus is required
...

Transducer: it is defined as capable of converting one of energy to another
...
For example thermistor converts temperature to
electrical signal, strain gauge produces electrical signal by sensing the pressure
...
It amplify the given signal some extent then process the signal by removing
the noise and measure signal parameters
...

Display device: output of signal conditioning circuit must be converted into form that can be
perceived by one of man’s senses and that can be convey the information obtained by the
measurements in a meaningful way
...

Recording, data processing and transmission: It is often necessary to record the measured
information for possible later use or to transmit it from one location to another
...

Control feedback device: it is necessary or desirable to have automatic control of stimulus,
transducer or ant part of man-instrument system, a control system is incorporated
...


Physiological Systems of Human Body:
Physiology means functional activities of living organs and every organ responsible for one
activity in turn these are work together to achieve systematic activity of human body
...
We will briefly discuss the major functions of
each organ system below
...
By controlling information flow through biochemical signaling and
the flow of chemical energy through metabolism, biochemical processes give rise to the
complexity of life
...
The
chemistry of the cell also depends on the reactions of smaller molecules and ions
Nervous system– (brain, spinal cord, nerves) Control system of the body, responds to internal
and external changes, activates muscles and glands
...

Cardiovascular system– (heart, blood vessels) The heart pumps blood and blood vessels transport
it
...

Skeletal system– (bones, joints) Supports and protects the body’s organs
...
Bones also store minerals and create blood cells
...

Produces heat
...
Gaseous exchanges occur in the respiratory
system (lungs)
...

Urinary system– (kidney, ureter, urinary bladder, urethra) Eliminates nitrogenous wastes from
the body
...


Figure 4: Communication system of human body

Problems encountered in measuring a living system:
1
...
For example
neuro chemical activity of brain ,it is impossible to place transducer so we need to do the
indirect measurement
...

2
...
so these must be represented by some statistical or probability
distribution
...
Lack of knowledge of interrelationship: physiological measurements with large tolerance
are often accepted by the physician because of lack of this knowledge and the resultant
in ability to control variations
...

4
...
The result is that stimulation of one part of a given
system generally affects all other parts of the system in some way and often affects other
systems as well
...
Effect of transducer: Transducer can be considered as a device converting one form of
energy to another form
...
The physical quantity to be
measured can be position, displacement, flow, temperature, strain, velocity etc
...
Transducer block diagram is given below
...

Transduction Element: Sensor output is carried on to the transduction element which converts
the non-electrical signal to electrical signal in proportion to the input
...

Linearity: Transducer is meant to measure a physical quantity and output the electrical signal
relative to the measured quantity
...


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Repeatability: Transducer has the ability to reproduce the same output signal for the same
input physical quantity measured repeatedly that is being measured under same
environmental situations
...

High stability and reliability: Transducer measurements shows minimum error and the output
is unaffected by environmental vibrations, temperature etc
...
Artifacts: it is component or variable is observed while doing experiment, which is not
naturally present
...

7
...
For example,
resistance measurements require the flow of electric current through the tissue or blood
being measured
...

8
...
Recent
emphasis on hospital safety requires that extra caution must be taken in the design of any
measurement system to protect the patient
...
Combination of cells is called
tissues
...

Generation of the resting potential:
Cell membranes are typically permeable to only a subset of ions
...
To simplify the description of the
ionic basis of the resting membrane potential, it is most useful to consider only one ionic species
at first, and consider the others later
...
In a more formal notation,
the membrane potential is the weighted average of each contributing ion's equilibrium potential
...
In the normal case, where three
ions contribute to the membrane potential:
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Equilibrium potentials:
For most animal cells potassium ions (K+) are the most important for the
resting potential
...
Most cells have potassium-selective ion channel proteins that
remain open all the time
...
The outward movement of positively charged potassium ions is due to random
molecular motion (diffusion) and continues until enough excess negative charge accumulates
inside the cell to form a membrane potential which can balance the difference in concentration of
potassium between inside and outside the cell
...
This balance point is an equilibrium potential as the net
transmembrane flux (or current) of K+ is zero
...
It can be calculated using the Nernst equation:

where
Eeq,K+ is the equilibrium potential for potassium, measured in volts
R is the universal gas constant, equal to 8
...
15)
z is the number of elementary charges of the ion in question involved in the reaction
F is the Faraday constant, equal to 96,485 coulombs·mol−1 or J·V−1·mol−1
[K+]o is the extracellular concentration of potassium, measured in mol·m−3 or mmol·l−1
[K+]i is likewise the intracellular concentration of potassium

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Resting potential:
The resting membrane potential is not an equilibrium potential as it relies on the constant
expenditure of energy (for ionic pumps as mentioned above) for its maintenance
...
The resting
membrane potential is dominated by the ionic species in the system that has the
greatest conductance across the membrane
...
As potassium is also
the ion with the most negative equilibrium potential, usually the resting potential can be no more
negative than the potassium equilibrium potential
...

Under normal conditions, it is safe to assume that only potassium, sodium (Na+)
and chloride (Cl−) ions play large roles for the resting potential:

Action potential:
An action potential (also known as a nerve impulse or a spike) is a self-regenerating wave of
electrochemical activity that allows excitable cells (such as muscle and nerve cells) to carry a
signal over a distance
...
Action
potentials are pulse-like waves of voltage that travel along several types of cell membranes
Relatively static membrane potential of quiescent cells is called resting membrane potential (or
resting voltage), as opposed to the specific dynamic electrochemical phenomenon called action
potential and graded membrane potential
...
These channels are shut when the membrane potential is near the
(negative) resting potential of the cell, but they rapidly begin to open if the membrane increases
to a precisely defined threshold voltage, depolarizing the transmembrane potential
...
This then causes more
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channels to open, producing a greater electric current across the cell membrane, and so on
...
The rapid influx of sodium ions causes the polarity of the
plasma membrane to reverse, and the ion channels then rapidly inactivate
...
Potassium channels are then activated, and there
is an outward current of potassium ions, returning the electrochemical gradient to the resting
state
...

Propagation of action potential:
All cells in animal body tissues are electrically polarized – in other words, they maintain a
voltage difference across the cell's plasma membrane, known as the membrane potential
...
In neurons, the types of ion channels in the
membrane usually vary across different parts of the cell, giving the dendrites, axon, and cell
body different electrical properties
...
Each excitable patch
of membrane has two important levels of membrane potential: the resting potential, which is the
value the membrane potential maintains as long as nothing perturbs the cell, and a higher value
called the threshold potential
...
Synaptic inputs to a
neuron cause the membrane to depolarize or hyperpolarize

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Figure 5: Action potential

Sodium pump:
The process of active transport differs from diffusion in that molecules are transported away
from thermodynamic equilibrium; hence, energy is required
...
The maintenance of electrochemical
gradients in biologic systems is so important that it consumes perhaps 30–40% of the total
energy expenditure in a cell
...
The
pump that maintains these gradients is an ATPase that is activated by Na+ and K+ (Na+K+ATPase)
...

Clinicians can evaluate the conditions of a patient's heart from the ECG and perform further
diagnosis
...

Electrocardiography (ECG or EKG) is the recording of the electrical activity of the heart over
time via skin electrodes
...
The etymology of the word is derived from electro, because it is related to electrical
activity, cardio, Greek for heart, graph, a Greek root meaning "to write"
...
The impulses stimulate the myocardial muscle fibres to
contract and thus induce systole
...
Electrodes on different sides of the heart measure the
activity of different parts of the heart muscle
...
This display indicates the overall rhythm of the heart and weaknesses in
different parts of the heart muscle
...

In electrocardiography, the word, "lead" (rhymes with 'speed') refers to the signal that goes between two
electrodes
...


Unipolar vs
...
Bipolar leads have one positive and one
negative pole
...
Unipolar leads
have only one true pole (the positive pole)
...
In a 12-lead ECG, all leads besides the limb leads are
unipolar (aVR, aVL, aVF, V1, V2, V3, V4, V5, and V6)
...
The electrodes
that form these signals are located on the limbs—one on each arm and one on the left leg
...


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Figure 6: Electrocardiogram
P-Wave:
During normal atrial depolarization, the main electrical vector is directed from the SA node
towards the AV node, and spreads from the right atrium to the left atrium
...
Because the ventricles contain more muscle mass than the atria, the QRS complex is
larger than the P wave
...
It is usually 120 to 200 ms long
...
08 to 0
...

T-Wave:The T wave represents the repolarization (or recovery) of the ventricles
...
It is typically small, and, by definition, follows the T
wave
...


Electroencephalogram (EEG) is electrical activity along the scalp produced by the firing of
neurons within the brain
...
In neurology, the main diagnostic application of
EEG is in the case of epilepsy, as epileptic activity can create clear abnormalities on a standard
EEG study
...

EEG used to be a first-line method for the diagnosis of tumors, stroke and other focal brain
disorders, but this use has decreased with the advent of anatomical imaging techniques such as
MRI and CT
...
The positions are
determined as follows: Reference points are nasion, which is the delve at the top of the nose,
level with the eyes; and inion, which is the bony lump at the base of the skull on the midline at
the back of the head
...
Electrode locations are determined by dividing these perimeters into 10% and
20% intervals
...
The rhythmic
activity is divided into bands by frequency
...
e
...

Most of the cerebral signal observed in the scalp EEG falls in the range of 1–20 Hz (activity
below or above this range is likely to be artifactual, under standard clinical recording
techniques)
...
EMGs are usually done to see if one or more nerve roots have
been pinched by a herniated disc
...
If there has been a change in the function of the nerve, the
muscle will send off different types of electrical signals
...

A needle electrode is inserted through the skin into the muscle
...


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Figure 7: EMG Acquisition
Electroretinogram:
ERG responses are recorded with an active extracellular electrode positioned either on the
cornea, in the vitreous or at different levels inside the retina
...
An example of extracellular electrical current in the vertebrate
retina is the 'dark' current spreading from the inner segments to the outer segments of the
photoreceptors

Figure 8 : Electroretinogram(ERG)

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Evoked Potential:
An evoked potential or evoked response is an electrical potential recorded from the nervous
system of a human or other animal following presentation of a stimulus, as distinct from
spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG),
or
other electrophysiologic recording
method
...

Evoked potential amplitudes tend to be low, ranging from less than a microvolt to several
microvolts, compared to tens of microvolts for EEG, millivolts for EMG, and often close to a
volt for ECG
...
The signal is time-locked to the stimulus and most of the noise occurs randomly,
allowing the noise to be averaged out with averaging of repeated responses
...
auditory evoked potentials can be used to
diagnose learning disabilities in children, aiding in the development of tailored educational
programs for those with hearing and or cognition problems

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