Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Respiratory physiology
The respiratory system
2 zones as we know:
 Respiratory site of gas exchange between air and blood
...
Ventilation (breathing)
2
...
Oxygen utilization- cell respiration
External respiration ventilation and exchange of gas (oxygen and carbon dioxide) between the air and blood
Internal respiration gas exchange between tissue and oxygen utilization by the tissue
Ventilation:
 Is a mechanical process that moves air into and out of the lungs
o Oxygen diffuses from air to bloodbecause conc of oxygen in lungs is higher than in the blood
 Carbon dioxide diffuses from blood to airbecause conc of CO2 is more in the tissues than in the lungs
...
hence providing large surface area for diffusion of gases
The diffusion rate is further increased
...
Type 1 alveolar cells
Comprises of 95 to 97% of the total surface area of the lung, gas exchange is primarily occured here
...
Hence diffusion
distance is least
...
3um1/100th of human hair
2
...




The great tensile strength of alveolar wall is due to the fused basement membranes composed of type 4
collagen proteins
...

 The inspired air when reaches the respiratory zone its temperature is 37 C and it is saturated with water vapor
as it flows over warm, wet mucous membranes that line the respiratory airways
This ensures that a constant internal body temperature is maintained and the lung tissue is protected from
desiccation
...
This thickened, stiff
tissue makes it more difficult for your lungs to work properly
...
Diaphragm : a dome-shaped sheet of striated muscle, the divides the anterior of the body cavity into two
parts
2
...
Thoracic cavity : present above the diaphragm, consist of heart, large blood vessels, trachea, esophagus and
thymus in the central region and is filled with right left lungs
4
...
Pleural membranes: has two layers parietal (inside) and visceral pleura (surface of the lungs)
The lungs normally fill the thoracic cavity so that the visceral pleura covering each lung is pushed against the parietal
pleura lining against thoracic wall
Hence under normal condition little or no air between the visceral and parietal pleura
6
...


Tracheotomy
A tracheotomy is a surgical procedure in which an incision is made in the front of the neck and a breathing tube is
placed into the trachea, also called the windpipe
...

 Trachea becomes occluded through inflammation, excessive secretion , trauma, or aspiration of the foreign
object

Tracheostomy
A tracheostomy is a medical procedure — either temporary or permanent — that involves creating an opening in the
neck in order to place a tube into a person's windpipe
...
This allows air to enter the lungs
...

 The air enters lung during inspiration because the atmospheric pressure is greater than the intrapulmonary or
intraalveolar pressure
 Since the atmospheric pressure cant change so the intrapul pressure has to fall below the former to cause
inspiration
 Hence the pressure below that of the atmosphere is called subatmospheric pressure or negative pressure
 Whereas expiration occurs when the intrapul pressure is greater than the atmospheric pressure and hence is
positive atmospheric pressure
Intrapleural pressure (IP)
It is simply the pressure in the pleural cavity  outside the lungs
Explanation:
 When the lung tries to collapse creating that elastic tension, the thoracic walls try to expand the lung countering
the effect of the lungs
...
Intrapleural pressure is normally lower than the intrapulmonary pressure during both inspiration and
expiration
Transpulmonary pressure:
Also called transmural pressure
o It is the difference between the intrapulmonary pressure and the intrapleural pressure
o Thus is the pressure difference across the wall of the lung
o Because the pressure within the lungs(intrapul) > outside the lung(intrapleural pres) = keeps the lungs against
the chest wall
o Hence the result: the changes int eh lungs parallels with the changes the thoracic volume during inspiration and
expiration

Boyle’s law:
Pressure (P) α 1/Volume (V)
How is it applied here?

 An increase in lung volume during inspiration decreases intrapulmonary pressure to subatmospheric levels air
goes in (inspiration)
 Decrease in lung volume during expiration increases intrapul pressure more than subatmospheric levelsair
goes out(expiration)

Physical properties of lungs
What are required?
Compliance lungs must be able to expand when stretched during inspiration
Elasticity lungs must get smaller when tension is released during expiration
Surface tensionaids the tendency to get smaller; it’s the force that acts within the alveoli

Compliance:
 The lungs are very distensible (stretchable)
 It refers to the ease with which the lungs can expand under pressure
Lung compliance: is defined as change in lung volume per change in the transpulmonary pressure expressed
symbolically as ∆V/∆P
The transpulmonary pressure in other words cause greater or lesser expansion depends on compliance of lungs
Compliance of lungs is reduced by factors:
 That produce resistance to distension
Eg: if lung is filled with concrete and when a condition called pulmonary fibrosis
Pulmonary fibrosis:
Infiltration of lung tissue with connective tissue proteins
Def: lung disease that occurs when lung tissue becomes damaged and scarred
...

It decreases lung compliance

Elasticity:
Refers to the tendency of a structure to return to its initial size after being distended
Lungs contains: high content of elastin proteins, hence they are elastic and resist distension
Normal: lungs stuck to the chest wall  always in the state of elastic tension
Elastic tension: increases during inspiration when the lung are stretched and is reduced by elastic recoil during
expiration

Clinical application: pneumothorax, atelectasis
1
...
Atelectasis:
 Is a complete or partial collapse of the entire lung or area (lobe) of the lung
...

 Also it occurs as a result of elastic recoil
The difference between them?
If it is a total collapse, it is called pneumothorax
...


Surface tension:
The force that act to resist distension include  elastic resistance and surface tension
o It is the tension or force exerted by fluid in the alveoli
Lungs secret and absorb fluid by two antagonistic processes leaving a thing fluid film on the alveolar surface
Fluid absorption driven through osmosis by active transport of Na+
Fluid secretionactive transport of Cl- out of the alveolar epithelial cells
Cystic fibrosis transmembrane regulator or CFTR:
People with this have genetic defect in one Cl- carriers
Result: an imbalance in fluid absorption and secretion
Airway fluid becomes excessively viscous (due to lower water content) and difficult to clear
Law of laplace:
Laplace's law states that the pressure inside an inflated elastic container with a curved surface
...
g
...

Laplace, the pressure created is directly proportional to the surface tension and inversely proportional to the radius of
the alveolus
Hence: pressure α surface tension
Pressure α radius of alveolus

Surfactant and respiratory distress syndrome:
Surfactant: substances that reduce surface tension
Eg : alveolar fluid
o It is secreted by type 2 alveolar cells and consists of phsopholipids primary phosphatidylcholine and
phosphatidylglycerol and hydrophobic surfactant proteins
o When surfactant is scattered between the water molecules at the water-air interface reduces the hydrogen
bonds between the water moleculesreduces surface tension
o Hence due to this pulmonary surfactant the surface tension of the alveoli is neglible
o The surfactant secreted by type 2 cells is removed by alveolar macrophages
During expiration:
 The surfactant lowers the surface tension helping the alveoli get smaller
 It gets more conc in the alveoli hence it prevents alveoli from collapsing during expiration
 Surfactant follows the Laplace law
 Even after a forceful expiration, the alveoli remain open and a residual volume if air remains in the lungs
 it never leaves the lungs and prevents collapsing of lungs
 Less surface tension is required to inflate alveoli at next inspiration
Fetal life, RDS, ARDS
Surfactant production begins in the late fetal life
If premature babies are born with lungs without surfactants have alveoli collapsed RDS respiratory distress syndrome
Since a full term pregnancy lasts 37 to 42 weeks, RDS occurs in 60% of babies born less than 28 weeks and 30% at 28 to
30 weeks and 5% of babies born after 34 weeks
How can it be assessed?
 By analysis of amniotic fluid

 Treatment: the mothers can be given exogenous corticosteroids to accelerate the maturation of the fetus’s
lungs
ARDS: acute respiratory distress syndrome
Here inflammation causes increased capillary and alveolar permeability that leads to the accumulation of protein-rich
fluid in the lungs
...

 Because the newborn must overcome the great surface tension forces in order to inflate its partially collapsed
alveoli
...
Inspiration : inhalation
2
...
External intercostal muscles
2
...

 Its fibers are oriented similar to that of internal intercostals
 Also called as parasternal intercostals

Unforced or silent inspiration:
 Primarily results from the contraction of the dome-shaped diaphragm
 It lowers and flattens when it contracts
 Thoracic volume increases in the vertical direction
 Inspiration is aided by contraction of the parasternal and external intercostals raises the ribs and increases
the thoracic volume laterally
 Muscles involved in forced inspiration are : scalene, pectoralis minor and in extreme cases
sternocleidomastoid muscles
 Contraction of these muscles elevates the ribs in anterioposterior direction
 Same time the upper rib cage is stabilized
 Increase in thoracic volume = decreases intrapul pressure due to the contraction of the muscles inspiration
Quite expiration
o It is a passive process
o After inspiration the lungs and thorax recoil as a result of elastic tensionrespiratory muscles relax
o Decreased lung volume = increased pressure in the alveoli air pushes out
o Forced expiration: internal intercostal muscles contract and depress the rib cage
o Along the abdominal muscles
...


Pulmonary function tests
1
...
Lung capacity : it is equal to the sum of two or more lung volumes
2
...
Vital capacity (VIP): the max amount of air that can be forcefully exhaled after a max inhalation
 VITAL CAPACITY = inspiratory reserve volume + tidal volume + expiratory reserve volume
4
...

6
...

8
...


 This air remains in the lungs because the alveoli and bronchiole normally do not collapse
 Why? larger airways are noncollapsible
Expiratory reserve volume: it is the additional air left in the lungs after an unforced expiration
Functional residual capacity(VIP): the sum of the residual volume and expiratory reserve volume
 During quite breathing tidal volume ends at functional residual capacity, from here the tidal volume
inspiration begins
Forced expiratory volume: measures how much air a person can exhale during a forced breath
Total minute volume: tidal volume at rest × no of breathes per min
...
Restrictive
2
...


Pulmonary disorders
Dyspnea: shortness of breathe
o It can occur also when ventilation is normal
o But it can’t occur when total minute volume is very high as in exercise
Asthma:
 It is an obstructive respiratory disorder
 Symptoms: dsypnea, wheezing and obstructive air flow in the bronchioles that occurs in the episodes or attacks
 The obstruction is caused due to inflammation, mucous secretion and bronchoconstriction
 Esp : inflammation is the characteristic of asthma and contributes to increased airway responsiveness to agents
that promote bronchiolar constriction
 Further bronchoconstriction increases airway resistance and makes breathing difficult
 The increased airway resistance may be provoked by:
1
...
by breathing cold, dry air
3
...
aspirin (minor asthmatics)
Allergic asthma:
 chronic inflammatory disorder of the airways
 also called atopic asthma, and is the most common type of asthma
 the allergen (inducer of asthma)activates helper T lymphocytes to release a variety of cytokines interleukin-4,
interleukin-9 and interleukin-13
 this all leads to the production of IgE antibodies and pulmonary eosinophilia (high eosinophil count)
 since eosinophilia is a hallmark of asthma, they release a variety of cytokines that contribute to asthma
 mast cells are abundant in asthmatic lungs and found in :
Normal locations: lamina propria
Abnormal location: epithelium and smooth muscles of the airways
o when exposed to the same allergen the allergen bonds to IgE on the surface of the mast cells and basophiles
Causing these cells to release chemicals like: histamine, leukotrienes and prostaglandins
Some other stimulate bronchioconstriction and mucus secretion of asthma
o treatment of asthma :
1
...
Singulair: drugs like these block the action of leukotriene and suppress the inflammatory response
3
...

hence the drug terbutaline is developed considering this difference and works by selectively stimulating
the beta2 adrenergic receptors and causing bronchodialtion without affecting the heart
Emphysema:
o It is a chronic progressive condition which is an obstructive lung disorder

o
o
o
o
o

o

The alveolar tissue is destroyed resulting in a few but larger alveoli
Result: reduction in surface area for gas exchange
Important part: since alveoli exert a lateral tension of the bronchiolar walls to keep them open, the loss of alveoli
causes reduced ability of the bronchioles to remain open during expiration
...
9feet which is not
attainable in a device
...

21% of 760mmHg 159mmHg
Same like that with Nitrogen 78% of 760 = 593mmHg
P (dry atm) = PN2 + PO2 + PCO2 = 720mHg

Calculation of PO2
o Increasing altitude = total atm pressure and partial pressure decreases
1) Eg: Denver has 619 mmHg and the PO2 is reduced to 619*0
...
g
...
3 ml of O 2 is
dissolved in the plasma and 19
...
3ml) affect the PO2 measurement, RBC removal won’t make a difference

Significance of blood PO2 and PCO2 measurements:
Since we consider only the plasma for the PO2 measure, the total oxygen content of the whole blood is not provided
though
...

It is normally 97%
But if we intake 100% oxygen, it doesn’t affect this
...

Pulmonary veins: they take blood from lungs to tissue (oxygenated)
 It has PO2 of 100mmHg and PCO2 of 40mmhg
What do we see?  The arterial blood value is constant and is clinically hence significant because it reflects lung
function
Why is the arterial blood considered and not the venous?
Because the venous blood values are far more variable like during exercise the PO2 values are much lower and PCO2
is much higher than at rest
...


Clinical: pulse oximeter:
 Commonly used in hospitals to measure oxyhemoglobin saturation
 Used: clips on the finger or pinna and gives reading of oxygen saturation an pulse rate within the short time
helpful in emergency medicine and during anesthesia
 Has 2 light emitting diodes with different wavelength(red and infrared range)
 Oxyhemoglobin and deoxyhemoglibin absord this light differently and determine the conc
...
5L per minute
Rate of blood flow in pulmonary circulation = same in systemic circulation
Hence the,
1) Blood flow α 1/vascular resistance
2) blood flow α pressure difference between two ends of the vessels
 eg: mean arterial pressure is 90 to100 mmHg - pressure of the right atrium is 0 mmHg
Hence the driving pressure in the pulmonary circulation: 100mmHg
Now read carefully:
1
...
vascular resistance in the pulmonary circulation = 1/10 th of the systemic VR
Therefore, pulmonary circulation:
 low-resistance,
 low-pressure pathway,
 less filtration pressure
 protection against pulmonary edema
Pulmonary edema:
Dangerous condition in which the excessive fluid enters the interstitial spaces of the lungs and then the alveoli
Hampering ventilation and gas exchange
It occurs when there is pulmonary hypertension, produced by left ventricular heart failure

Disorders caused by high partial pressures of gases
Consider surface atm as 1atm and then start adding 1 atm after every 10m or 33feet

Oxygen toxicity:
o
o
o
o

more than 1 or 2 atm (100%) pressure can safely by tolerated for few hour
oxygen toxicity may develop rapidly when the PO2 rises above about 2
...
But if the decompression occurs too rapidly it can form bubbles and
these cause the problem
...
(rapid depression at high altitude)

Clinical application: hyperbaric oxygen therapy:



Here the patient is given 100% oxygen at 2 to 3 atm for a varying amount of time
Used to treat CO poisoning, decompression sickness, severe traumatic injury and infections that could lead to
gas gangrene



1
...

3
...
3ml O2/100ml blood raises to 6ml O2/100ml (according to henrys law)
this helps killing anaerobic bacteria that cause gangrene
promotes wound healing
reduces the size of the gas bubbles (in decompression sickness)
quickly eliminates carbon monoxide from the body
important point: it was used to treat premature infants for RDS but stopped due to the fibrotic deterioration of
the retina resulting to blindness

Regulation of breathing:
The respiratory rhythm is generated by a loose aggregation of neurons in the ventrolateral region of the medulla
oblongata, which forms the rhythmicity center for the control of automatic breathing

---