5. Blood Supply, Gas Exchange, Ventilation and Perfusion

Question 1

Where in the lungs is the greater volume change for a given change in pressure?

Answer 1

At the base

Question 2

What happens to alveolar ventilation with height from base to apex?

Answer 2

It declines

Question 3

What also declines from base to apex?

Answer 3

Compliance

Question 4

Why does compliance decline?

Answer 4

The alveoli are more inflated at the FRC, at the base the lungs are slightly compressed by the diaphragm hence the greater compliance on inspiration

Question 5

What brings about a larger change in volume at the base compared to the apex?

Answer 5

Any given change in intrapleural pressure

Question 6

What are the two circulations in the body and how do they differ?

Answer 6

Pulmonary and Systemic
Pulmonary circulation is opposite from systemic circulation in function
It delivers CO2 to the lungs and picks up O2

Question 7

Does the pulmonary vein or artery travel away from the heart?

Answer 7

Pulmonary Artery

Question 8

What does the Bronchial circulation supply?

Answer 8

Supplies nutrients and O2 to the lungs

Question 9

What does the Pulmonary circulation carry?

Answer 9

The entire cardiac output from the right ventricle

Question 10

What is the flow and pressure of the pulmonary circulation?

Answer 10

High flow, Low pressure

Question 11

Where is blood pressure higher? In the pulmonary or systemic circulation?

Answer 11

Systemic (~120mmHg)

Question 12

Which side of the heart has a greater driving force to push blood?

Answer 12

Left

Question 13

Where does gas exchange take place?

Answer 13

Between the alveoli and the blood capillaries

Question 14

What happens to oxygen as it moves from the alveoli to the pulmonary vein?

Answer 14

It moves down the concentration gradient

This is the opposite for CO2

Question 15

What do the abbreviations A,a and ṽ stand for?

Answer 15

A - Alveolar
a - Arterial blood
ṽ - Mixed venous blood (e.g pulmonary artery)

Question 16

What does PaO2 and PACO2 stand for?

Answer 16

PaO2 = partial pressure of oxygen in arterial blood
PACO2 = partial pressure of carbon dioxide in alveolar air

Question 17

What are the normal mmHg and kPa figures?

Answer 17

Insert table

Question 18

What is the rate of diffusion across the membrane directly proportional to?

Answer 18

The partial pressure gradient and to gas solubility specifically
Also to the available surface area and is inversely proportional to the thickness of the membrane

Question 19

How many times greater is the gradient between O2?

Answer 19

10x greater

Question 20

Why is the rate of diffusion more similar than expected for CO2 compared to O2?

Answer 20

CO2 is more soluble in water so can diffuse much more readily

Question 21

What happens during Emphysema?

Answer 21

Destruction of alveoli reduces surface area for gas exchange

PO2 is low (alv)

Question 22

What happens during Fibrosis?

Answer 22

Thickened alveolar membrane slows gas exchange causing loss of compliance which may decrease alveolar ventilation
O2 will be lower in the vein as the rate of diffusion is reduced

Question 23

What happens during Pulmonary edema?

Answer 23

Fluid in interstitial space increases diffusion distance/ Arterial PCO2 may be normal due to higher CO2 solubility in water

Question 24

What happens during asthma?

Answer 24

Does not alter the diffusion process but does impede ventilation
Increased airway resistance decreases airway ventilation

Question 25

What is the primary cause of emphysema?

Answer 25

Smoking

Question 26

What is the Ventilation-Perfusion Relationship like?

Answer 26

They ideally compliment each other
Perfectly matched Ventilation:Perfusion ratio = 1.0
Mismatch 1 Ventilation>Perfusion ratio > 1.0
Mismatch 2 Ventilation

Question 27

Is blood flow in the lung uniform?

Answer 27

No, most of the blood is pulled to the base of the lung

Question 28

What happens due to more blood in the base of the lung?

Answer 28

Increased pressure causes lower alveolar pressure which slightly crushes alveoli
Base: ventilation < blood flow
Apex: ventilation > blood flow

Question 29

What happens at rib 3?

Answer 29

Ventilation and perfusion are equal, however away from 3 there is a mismatch (it is more significant at the apex)

Question 30

When ventilation is decreased what happens?

Answer 30

PCO2 increases and PO2 decreases

Blood flowing past these alveoli does not get oxygenated

Question 31

What is shunt and what happens?

Answer 31

Shunt - Dilution of oxygenated blood from better ventilated areas
Blood is moved from right side of heart to left side without being properly oxygenated

Question 32

What does the poorly oxygenated blood do?

Answer 32

Dilute oxygenated blood

Question 33

What is Hypoxia?

Answer 33

Lower partial pressure of oxygen than normal

Question 34

What is alveolar dead space?

Answer 34

When there in an increase to alveolar PO2 causing pulmonary vasodilation and a decrease in alveolar PCO2 causing bronchial constriction
OPPOSITE OF SHUNT

Question 35

What is anatomical dead space?

Answer 35

air in the conducting zone of the respiratory tract unable to participate in gas exchange as walls of airways in this region (nasal cavities, trachea, bronchi and upper bronchioles) are too thick

Question 36

What is physiological dead space?

Answer 36

Alveolar DS + Anatomical DS