pathophylung_lec1 by cannan

8/2/2019 PathoPhyLUNG_Lec1 by Cannan

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PathoPhy LUNG Lec1

3 Gas exchange processes

1) Ventilation

2) Perfusion

3) Diffusion

- Ventilation, the filling with the lung and bronchi with fresh air must be properly

match with perfusion for proper gas exchange.

- So Ventilation/Perfusion ratio is change, subject may have problem with gas

exchange.

1) Ventilation- Tidal volume(volume of fresh air which we use to filled our lung during every

quiet inspiration) = 500 ml.

- The Minute ration of breathing is 12. This means minutes ventilation is about 6L

- We use to represent minutes ventilation

- The minutes ventilation has 2 component:

Part of this component is use to filled airway, and not use for gases

exchange.

The rest features, small brochiole, alveoli, are use for gases exchange

- Within this 500 ml, which enter our respiratory system, during every average

inspiration:

150 ml ~ Anatomy Dead Space: air that is use to filled airway (not use for

gas exchange)

350 ml ~ Alveolar Ventilation : air reach alveoli (use for gas exchange)

- Part of Tidal Volume, which is not used for gases exchange, is called Dead Space/wasting ventilation. There are 2 type of Dead Space, Anatomy and Physiology.

As this dead space is relate to anatomy of our respiratory system, so air

that goes toward alveoli first, must pass through trachea and we call this

Anatomy Dead Space. http://en.wikipedia.org/wiki/Dead_space

Physiological Dead Space is equal to the Anatomy Dead Space +

Alveolar Dead Space.

-> Alveolar dead space is the area in the alveoli that does get air to be

exchanged, but there is not enough blood flowing through the capillaries

for exchange to be effective. It is normally veery small (less than 5ml) in

healthy people. It can increase dramatically in some Lung Disease.- Alveolar Ventilation:

means part of fresh air which is use in Gases exchange

alveolar ventilation, the part of fresh air reach Alveoli, this is true in

physiology sense.

Inpathology, alveoli is properly fed with fresh air, BUT, they had NO

Perfusion. In this case, they also form Dead Space and not use for gas

exchange.

Within 6 L , 400ml is use for gases exchange. A= 4 L

- Always ventilation at the bottom of the lung are much more higher then the top

of the lung due to its property.
http://en.wikipedia.org/wiki/Dead_spacehttp://en.wikipedia.org/wiki/Dead_space


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- At the end of Expiration, Alveoli at the top of the lung are little bit expanded

compare to bottom.

- Curve of compliance:

It is defined: V / P

[Voluem changes which occurs when pressure ischange of 1 unit]

- so if Alveoli at the bottom which are totally close, with littlelow pressure, we change the pressure in the region of one unit,volume expand much more in comparison with the same effectat the top.

- Due to gravity, alvioli at the top initially, are little bit expanded in compare to

bottom. [imagine in ventilation, 2 ballones: 1st which is totally collapse

initially are easy to fill. The the 2nd ballone are already slightly expanded, and

it would be harder for us to expanded it more due to its already posses

pressure]

EXTRA READDING!!!!!!!!!!!!!!!!!!!!

Lung volumes

From Wikipedia, the free encyclopedia

Lung Volumes

Lung volumes refer to physical differences in lung volume, while

lung capacities represent different combinations of lung volumes,usually in relation to respiration and exhalation.
http://upload.wikimedia.org/wikipedia/en/6/6a/LungVolume.jpg


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The average pair of human lungs can hold about 6 liters of air, butonly a small amount of this capacity is used during normal breathing.

Breathing mechanism in mammals is called "tidal breathing". Tidalbreathing means that air goes into the lungs the same way that it

comes out.

Factors affecting lung volume

Several factors affect lung volumes, some that can be controlled andsome that can not. These factors include:

Larger volumes Smaller volumes

males females

taller people shorter people

non-smokers smokers

athletes non-athletes

people living at high altitudes people living at low altitudes

A person who is born and lives at sea level will develop a slightlysmaller lung capacity than a person who spends their life at a highaltitude. This is because the atmosphere is less dense at higheraltitude, and therefore, the same volume of air contains fewermolecules of all gases, including oxygen. In response to higheraltitude, the body's diffusing capacity increases in order to be able toprocess more air.

When someone living at or near sea level travels to locations at highaltitudes (eg. the Andes, Denver, Colorado, Tibet, the Himalayas, etc.)s/he can develop a condition called altitude sickness because theirlungs cannot respirate sufficiently in the thinner air.

Measurement and values

These values vary with the age and height of the person; the valuesthat follow are for a 70 kg (154 lb), average-sized adult male:


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Measurement Value Calculation Description

Total lung capacity(TLC)

= 6.0 L = IRV + TV + ERV +RV

The volume of gas contained in the lung at the end of

maximal inspiration. The total volume of the lung (i.e.:the volume of air in the lungs after maximum

inspiration).

Vital capacity (VC) = 4.6 L = IRV + TV + ERV

The amount of air that can be forced out of the lungs

after a maximal inspiration. Emphasis on

completeness of expiration. The maximum volume of

air that can be voluntarily moved in and out of the

respiratory system.

Forced vital capacity

(FVC)= 4.8 L measured

The amount of air that can be maximally forced out of

the lungs after a maximal inspiration. Emphasis on

speed.

Tidal volume (TV) = 500 mL measured

The amount of air breathed in or out during normal

respiration. The volume of air an individual is

normally breathing in and out.

Residual volume (RV) = 1.2 L measuredThe amount of air left in the lungs after a maximalexhalation. The amount of air that is always in the

lungs and can never be expired (i.e.: the amount of air

that stays in the lungs after maximum expiration).

Expiratory reserve

volume (ERV)= 1.2 L measured

The amount of additional air that can be breathed out

after the end expiratory level of normal breathing. (At

the end of a normal breath, the lungs contain the

residual volume plus the expiratory reserve volume, or

around 2.4 litres. If one then goes on and exhales as

much as possible, only the residual volume of 1.2litres remains).

Inspiratory reserve

volume (IRV)= 3.6 L

measured IRV=VC-

(TV+ERV)

The additional air that can be inhaled after a normal

tidal breath in. The maximum volume of air that can

be inspired in addition to the tidal volume.

Functional residual

capacity (FRC)= 2.4 L = ERV + RV

The amount of air left in the lungs after a tidal breath

out. The amount of air that stays in the lungs during

normal breathing.


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Inspiratory capacity

(IC)= 4.1 L = TV + IRV

The volume that can be inhaled after a tidal breathe-

out.

Anatomical dead space = 150 mL measured

The volume of the conducting airways. Measured withFowler method.

Anatomical dead space is the gas in the conducting

areas of the respiratory system, such as the mouth and

trachea, where the air doesn't come to the alveoli of

the lungs.

Physiologic dead

volume= 155 mL The anatomic dead space plus the alveolar dead space.

The tidal volume, vital capacity, inspiratory capacityand expiratoryreserve volume can be measured directly with a spirometer.Determination of the residual volume can be done by radiographicplanemetry, body plethysmography, closed circuit dilution andnitrogen washout.

These are the basic elements of a ventilatorypulmonary functiontest. The results (in particular FEV1/FVC and FRC) can be used todistinguish between restrictive and obstructive pulmonary diseases:

Type Examples Description FEV1/FVC

restrictive

diseases

pulmonary

fibrosisvolumes are decreased often in a normal range (0.8 - 1.0)

obstructive

diseases

asthma or

COPD

volumes are essentially

normal but flow rates are

impeded

often low (Asthma can reduce the

ratio to 0.6, Emphysema can

reduce the ratio to 0.3 - 0.4)

2)Perfusion- Q = pulmonary capillary blood flow. Often referred to as "perfusion".

- Minute perfusion Q 5L -> this is actual cardiac output of right ventricle.

-> this is also the same as cardiao output of left ventricle.

- When we compare perfusion again with at the top of the lung with the perfusion atthe bottome, Perfusion is also Higher at the bottom due to gravity!!
http://en.wikipedia.org/wiki/Spirometerhttp://en.wikipedia.org/wiki/Body_plethysmographyhttp://en.wikipedia.org/wiki/Pulmonary_function_testhttp://en.wikipedia.org/wiki/Pulmonary_function_testhttp://en.wikipedia.org/wiki/Spirometerhttp://en.wikipedia.org/wiki/Body_plethysmographyhttp://en.wikipedia.org/wiki/Pulmonary_function_testhttp://en.wikipedia.org/wiki/Pulmonary_function_test


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- Ventilation & Perfusion ratio:

in perfect situation in the alvioli, Ventilatino/ perfusion = 1

this situation shows our alveoli has just enough fresh air for oxygenation

of blood which perfuses our alveoli.

However, the mean alveoli Ventilation / Perfusion ration = 0.8* This mean our lung act as a whole are little bit under ventilated

* If think about minute ventilation~6L, 4L reaches area of gases

exchange, so minute alveolar ventilation ~ 4L. Minute Perfusion ~ 5 L.

* Mean Ventilation / Perfusion = 4/ 5

( / V QA ) = 0.8

= a little more air is necessary for

oxygenation of blood in 100%.

Ventilation / Perfusion ratio lower than 1 means that blood is not oxidized

in 100% in physiology.

In physiology, 1% up to 3 % of blood is not properly oxygenized, and wecalled it Venous Admixture.

Venous Admixture refers to venous blood which is actually added to

proper venous (not oxygenated blood is added to arterial blood).

Venous Admixture INCREASES during AGING.

Venous Admixture is related to the problem of peroper matching

ventilation perfusion.

Both Ventilation & Perfusion are higher at the bottom of lung then top.

* Ventilation/Perfusion RATIO is higher at the top of the lung then the

bottom of lung.

* if only compare ventilation or perfusion (not their ratio) it is higher at the

bottom of the lung.

* Why Ventilation/Perfusion RATIO is higher? Because both ventilation

and perfusion changes according to location of lung BUT not

proportionally.


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* The graph shows that ventilation is higher at the bottom and decreases

when moving upward to the top of the lung.

* Blood flow also higher at the bottom in comparison to the top.

* However, Blood flow changes much more in comparison to ventilation,

so Ventilaion / Perfusion ratio is low at the bottom and Increases when

moving toward top of the lung. So the Ratio is Very HIGH at the top.* In Physiology, at the bottom of the lung, the Ratio = 0.5 [lowest value]

* In Physiology, at the top of the lung, the Ratio = 3.3 [Highest value]

* These values means that:

> always we talk about gases exchange, we must

talk about ventilation unit (conpose of Alveoli

& Capillary).

> When ventilation perfusion is low ~0.5,it

meaning much blood come to the unit in

comparison to the fresh air. blood leaving

this unit is not properly ventilated.

> unit at the top of lung ~3.3. Mean lot of freshair in comparison with blood coming to the

unit. the blood leaving the unit is properly oxygenized.

Venous Admixture has 2 component:

* 1st is related to period with low ventilation / perfusion ration

> related to the alveoli at the bottom

> when we breath deeper, we can improve ventilation so the ventilation

perfusion ration is better. The blood is better oxygenized

* 2nd component is Anatomy Shunt .

> Blood has no contact with the fresh air.

> Alveoli is not ventilated (or No ventilation = 0)> Alveoli is perfuse, but with no fresh air / V QA = 0

(Ventilation / perfusion = 0)

> This type of shunt is also called Alveolar Shunt, and we dont have this

type of shunt In physiology.

* Anatomy Shunt is different,

- 1st component of anatomy shunt:

> This is blood pump by Left Ventricle (Oxygenized blood) goes back to

left heart without oxygenation.

> in bronchial circulation, bronchial artery transport nutrient & O2 to

bronchi, part of them have direct contact with pulmonary system. So

the blood is drained from bronchi, directly to Left Ventricle.

> if this blood is not oxygenized, it form Anatomy Shunt.

- 2nd component of anatomy shunt:

> it is form by part of circulation of the heart. We have so called,

Thebesian Veins, which drained blood from Myocardium directly to

the Left Heart.

> This Thebesian Veins is not oxygenized, so form Anatomy Shunt.

Anatomy shunt is less important when in comparison with this blood

coming from the bottom of our lung.

Gfdac


8/13

/ V QA = 1 (perfect situation)

/ V QA = 0 (Alveolar Shunt)

/ V QA < 1 (is called Venous Admixture)

Alveolar shunt is a special form of Venous Admixture

Remember in physiology, we dont have blood that is shunting EXCEPT

Anatomy Shunt.

We may have Alveoli which are Ventilated, BUT not Perfused. Eg.

Capillary are obstruct by thrombus, / V QA = ( Q = 0). The air enter this unit is not use

for gases exchange and form Alveolar Dead Space (Alveolar Wasting Ventilation).

Summary:

Venous Admixture ( / )V QA = 0 . If

ventilation of an alveolus was

stopped but flow allowed tocontinue, the PO2 and PCO2 of the

alveolar air and end capillary

blood would approachE that ofmixed venous blood.

Alveolar Dead Space ( / )V QA = . If ventilation to an alveolus was continued while blood

flow was halted, the PO2 and PCO2 of the alveolar air and end capillary blood would

approached that of inspired air.


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EXTRA READDING !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

In respiratory physiology, the ventilation/perfusion ratio (or V/Q

ratio) is a measurement used to the efficiency and adequacy of thematching of two variables:

"V" - ventilation - the air which reaches the lungs

"Q" -perfusion - the blood which reaches the lungs

A normal value is approximately 0.8.

Because the lung is centered vertically around the heart, part of thelung is superior to the heart, and part is inferior. This has a majorimpact on the V/Q ratio:

apex of lung - higher

base of lung - lower

The V/Q ratio can be measured with a ventilation/perfusion scan.

An area with no ventilation (and thus a V/Q of zero) is termed "deadspace" An area with no perfusion (and thus a V/Q of infinitiy) istermed Shunt (medical)|shunt]]

http://en.wikipedia.org/wiki/Ventilation/perfusion_ratio

Normal V (ventilation) is 4 L of air per minute. Normal Q (perfusion) is 5L of blood per minute.

o So Normal V/Q ratio is 4/5 or 0.8.

When the V/Q is higher than 0.8, it means ventilation exceeds

perfusion.

When the V/Q is < 0.8, there is a VQ mismatch caused by poor

ventilation.

http://www.rnceus.com/abgs/abgvq.html

EXTRA READDING!!!!!!!!!!!!!!!!!

SHUNTS AND VENOUS ADMIXTURE

Shunt is an overused word in pulmonary physiology and often means differentthings to different people.

In its simplest definition, a shunt occurs whenever one thing bypasses another. In

the lungs, a shuntcan be thought of as an extreme form of venous admixture, i.e.,a mixing of totally unventilated, unoxygenated blood with ventilated, oxygenatedblood.*
http://en.wikipedia.org/wiki/Ventilation/perfusion_ratiohttp://www.rnceus.com/abgs/abgvq.htmlhttp://en.wikipedia.org/wiki/Ventilation/perfusion_ratiohttp://www.rnceus.com/abgs/abgvq.html


10/13

Venous admixture can occur in one of three situations, only two of which aretraditionally called "shunt."

1. An anatomic shuntoccurs when blood bypasses the lungs through an anatomicchannel, such as from the right to the left ventricle through a ventricular septaldefect or from a branch of the pulmonary artery directly to a pulmonary vein.

2. Aphysiologic shuntoccurs when a portion of the cardiac output goes through theregular pulmonary vasculature without coming into any contact with alveolar air.There is no abnormal connection between the blood vessels; rather, there is asevere redistribution of pulmonary blood flow. Physiologic shunting is often seen inconditions such as pulmonary edema, pneumonia, and lobar atelectasis.

3. Low ventilationperfusion ratiosoccur when there is relatively more blood in thepulmonary capillary than can be fully oxygenated by the alveolar air. Althoughblood flow is to some extent redistributed, the blood is still exposed to somealveolar air. Low V/Q ratios account for most cases of hypoxemia seen clinically.

In terms of its effect on oxygenation, a physiologic shunt is not different from ananatomic shunt. In both, some unoxygenated blood bypasses the alveoli and mixeswith oxygenated blood. Although both types of shunt represent venous admixture,they differ in one important aspect from venous admixture that occurs from low V/Qratios. Since shunted blood contacts no air, increasing the fraction of inspiredoxygen (FIO2) will not improve oxygenation (except by adding more dissolvedoxygen to the normally oxygenated blood). In contrast, oxygenation of the bloodfrom low V/Q areas will definitely be improved by increasing FIO2 because blood inlow V/Q units is in contact with some air. Increasing the FIO2 should eventuallydenitrogenate the alveolar air in the low V/Q units and completely oxygenate theblood that serves these units; 100% oxygen should accomplish this exchangecompletely.

Administration of 100% oxygen was recommended in the past to determinewhether hypoxemia was from low V/Q areas or from a shunt. It is now known that100% oxygen can cause shunting by converting areas of low V/Q to 0 V/Q. Thisconversion happens when the pure oxygen in the poorly ventilated alveoli is fullyabsorbed by the capillary blood and the alveoli collapse. Wellventilated alveoli(normal or high V/Q) are anatomically larger, and their collapse is less likely. Even if100% oxygen gave an accurate measure of the percent shunt, the calculation wouldnot ordinarily affect therapy. (Shunts and their calculation are discussed further inChapter 11.)

http://www.lakesidepress.com/pulmonary/books/physiology/chap5_3.htm

3) Diffusion- It is passive transport (without energy)

- it is related to special amount of special gases which is transported

- it is related to the Pressure difference of the gas in 2 compartment.

- Diffusability: how easy gases pass through barrier and the structure of the gas.

- 3rd parameter is related to the Area of gases exchange. Eg alveoli is destroyed, area

is lower, and subject will have problem with gas exchange.

- In physiology, 2 gases are exchange, O2 & CO2.

- pressure of CO2 in venous blood coming to the lung is 46mmHg. PvCO2=46mmHg- pressure of O2 in venous blood is 40 mmHg. PvO2 = 40 mmHg.
http://www.lakesidepress.com/pulmonary/books/physiology/chap5_3.htmhttp://www.lakesidepress.com/pulmonary/books/physiology/chap5_3.htm


11/13

- Partial Pressure of O2 in Alveolar = 100 mmHg PAO2 = 100mmHg

-mean atmosphere pressure of gases at sea level = 760 mmHg.

only 21% of atmosphere gases are O2

the rest consist other gases

760 x 21% = 160 mmHg

= O2 pressure in atmosphere at sea level- when air enter our respiratory system, Eg upper respiratory part, Mosture is added to the air.

- This 21% is called Fraction of Oxygen in Inspired air (FIO2): FIO2 = 0.21

- when we want to know O2 pressure in inspired air:

Barometric Pressure 47(moisture which is added to the air)

FIO2~21%

Pressure in Inspired Air(PIO2) = (PB-47) x FIO2

At sea level & breath with Normal air:

(PIO2) =(760 47) x 0.21

= 150 mmHg

= Partial pressure of O2 in air which enter the alveoli due gas exchange, fresh air is coming from outside into alveoli, CO 2 also

coming to alveoli from the capillary.

More CO2 coming , less O2 in the alveoli PIO2 is lower by the pressure of

CO2 coming to the alveoli from the capillary.

Partial Pressure of O2 in the alveoli:

(PAO2) = PIO2 - ( )8.02

=quotientyrespiratorR

PCO

= 150 -8.0

40

= 100 mmHg = mean O2 in the alveoli

the mean of O2 in venous blood is 40 mmHg.

Initially, pressure difference of O2when diffused start is 60 mmHg

NOTE:

* Respiratory Quotient is some how related to Metabolic Quotient (the % of

CO2 which is exchange for O2 at the tissue level).

* So when diet is changed, eg. Highly diet, This quotientbecause less CO2is produced.

* when at Hard CO2 diet, more is produce & quotient is* The mean in Physiology of this R = 0.8

end point of diffusion through the IDEAL

alveoli unit is 100 mmHg.

Alveoli form open compartment with the air,

so little bit lower O2 is compensated by the air from outside

constantly.

In Reality, the end point of diffusion through

the REAL LIFE alveoli unit is slightly LOWER due to Venous

Admixture.

- If we want to know if our lung properly transfer O2, we can calculate a special parameter.

Ratio of O2

&CO2

which are exchange

every respiratory

cycle:

200[CO2

]/250[O2

]=

0.8


12/13

- This parameter is called: Alveolar-Arterial Pressure Gradient for the Oxygen.

- The Proper name is: Alveolar-Arterial Pressure Difference for the Oxygen.

- P(A-a)O2 = PAO2 PaO2 = 5 15 mmHg (increase during Aging!! Eg, up to 30 mmHg)

- Alveolar-Arterial pressure Difference always exist due to Venous Admixture.

-- now we combine all equation that we discuss so far and calculate PAO2:

PAO2 = PIO2- ( )8.02


PCO

= (PB-47) x FIO2 - ( )8.02


PCO

= (equation 2)

- in this equation, partial pressure of CO2 (PCO2) is the most important determinant of O2pressure in the alveoli.

- At sea level, PB ~ Constant (but in High Altitude, PB will change ).

- in Normal Air: FIO2 ~ 0.21 (this value changes when subject is breathing with AirSupplement Eg. 40% Oxygen or 100% pure Oxygen)

- Conclusion: PIO2 = 150 mmHg(more or less constant under the following condition

* at sea level

* breathing under atmosphere air)

- Inatmosphere, PCO2 = 0 CO2 does not enter alveoli with fresh air.

- CO2 enter alveoli from the blood.

- In alveoli, mean PACO2 = 40 mmHg

- In venous blood, meanPvCO2 = 46 mmHg

- so pressure difference between alveoli & Venous blood for CO2:P(A-V)CO2 = 6 mmHg (very

low)- PAO2 = 100 mmHg ; PVO2 = 40 mmHg ; P(A-V)O2 = 60 mmHg

- although Pressure difference of CO2 between Alveoli & Vein is 10 times lower then the

Pressure difference of O2 between Alveoli & Vein, CO2 still diffuse much easier in

comparison with O2.through the alveolar blood barrier. CO2 diffusability is much higher

(20 times higher)!!!

- This is why subject my have Hypoxemia WITHOUT Hypercapmia!!! due to High

diffusibility of CO2!!!

- Hypoxia = low oxygen in the tissue

- Hypoxemia = low oxygen in the blood

Hypoxia(low O2 in tissue) may be present WITHOUT Hypoxemia (low O2 in Blood) !!!! think about Heart, ischemic heart disease refer to Hypoxia in the heart (low O2 inMyocardium).

99% subject with ischemic heart disease have NORMAL O2 in blood!!! Hypoxia(low O2 in tissue) may be present in subject WITH Hypoxemia (low O2 in Blood)

!!!!

this is callHypoxemic Hypoxia subject may have low O2 in tissue, blood which is coming is not properlyoxygenized.

But subject may have Normal oxygenized Hemoglobin and still he may haveHypoxia. This is calledAnemic Hypoxia Eg in anemia, ParteryO2 = normal~high as a

compensated feature, BUT, Hypoxia may be present due to LOW Haemoglobine, as in this

case, the unit of blood transport less O2.


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Subject may have so call Circulatory Hypoxia.This is problem with O2 in the tissuein subject with ABNORMAL circulation Eg Heart Failure. Problem with proper blood flow

We may haveHistotoxic Hypoxia. In this case, circulatory system is ok, normal levelof haemoglobin with normal level of O2 in blood, BUT tissue are not able to utilize the O2Eg

Cyanid Poison

- Hypoxia MAY NOT be relate to problem in Respiratory system- Hypoxemia is ALWAYS relate to the problem in Respiratory system.

- due to equation PAO2 = PIO2- ( )8.02


PCO:

Hypercapmia (CO2) ALWAYS exist WITH Hypoxemia (O2 in Blood )!!!

when breathing in normal air at sea level, it is 100% O2 in alveoli, and the

end point of diffusion is also 100% O2 in the blood

subject has high CO2, it lowers O2 in alveoli, eg 60 %, and the end point of

diffusion is also 60 % O2 in the blood.

- Hypoxemia(O2) MAY be present WITHOUT Hypercapemia (CO2)!!!

pathophylung_lec1 by cannan

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