Gas Exchange

Question 1

‘What is the basal gas exchange requirement?

Answer 1

250ml O2 per minute
200ml CO2 per minute

Question 2

What is the common physiological challenge to gas exchange in health?

Answer 2

Excercise

Question 3

What is maximal exercise limited by?

Answer 3

Cardiac output

Question 4

What cells are present in the alveolar wall?

Answer 4

Epithelial cell (type 1 pneumocyte) - basal membrane
Endothelial cell

Question 5

What does gas exchange depend on?

Answer 5

Partial pressure gradient from pulmonary arteriole to pulmonary venule
Passive

Question 6

Define Fick’s Law.

Answer 6

Volume of gas diffusing across a membrane per minute is directly proportional to surface (A) of membrane, partial pressure gradient across membrane (P1 - P2) and inversely proportional to membrane thickness (T)
Vgas = D.A.(P1-P2)/T

Question 7

What is the diffusion constant proportional to?

Answer 7

Solubility/(molecular weight)^0.5 of gas

Question 8

In the liquid phase what is the amount of dissolved gas in solution proportional to?

Answer 8

Partial pressure of the gas and its solubility

Question 9

What 3 things is adequate gas exchange in lung enabled by?

Answer 9

Large SA of gas exchange membrane
Thin gas exchange membrane
Maintaining partial pressure gradient across gas exchange membrane

Question 10

What makes the lung vulnerable to oedema?

Answer 10

Thin gas exchange region

Question 11

What 2 thingscauses damage to the gas exchange membrane?

Answer 11

Destruction and loss of alveolar walls
Thickening of alveolar capillary membrane

Question 12

What causes thickening of alveolar wall?

Answer 12

Fibrotic Process

Question 13

How many ml of blood is in the capillaries at any time?

Answer 13

70ml

Question 14

How many ml of air is FRC

Answer 14

3500ml

Question 15

At rest how many ml of blood does the heart pump through the lung?

Answer 15

5L/min

Question 16

What is atmospheric O2 and CO2?

Answer 16

O2 - 21%
CO2 - 0.05%

Question 17

How can alveolar ventilation be changed?

Answer 17

Decreasing/increasing ventilation
Decreasing/increasing tidal volume

Question 18

What happens in increased alveolar ventilation (VA)?

Answer 18

Hyperventilation -> decreased CO2 in lungs = new steady state reached to compensate

Question 19

What happens in decreased VA?

Answer 19

Hypoventilation -> increased CO2 in lungs = new steady state reached

Question 20

What happens in half ventilation?

Answer 20

CO2 doubles
Rate of CO2 return remains constant

Question 21

What is the effect of changes in VA on Hb saturation?

Answer 21

Increasing - not a huge difference
Decreasing - decreases saturation by 5%

Question 22

What is the calculation for O2 uptake by blood?

Answer 22

Amount inspired - amount expired
VI.FIO2 - VE.FEO2

Question 23

What does hyperventilation cause?

Answer 23

Reduced PACO2 (hypocapnia)
Increased PAO2

Question 24

What does hypoventilation cause?

Answer 24

Increased PACO2 (hypercapnia)
Reduced PAO2

Question 25

What is the effect of acute reduced alveolar ventilation?

Answer 25

Respiratory compensation for acidosis

Question 26

What is the effect of chronic reduced alveolar ventilation?

Answer 26

Renal compensation for acidosis

Question 27

Why does blood flow have to increase during excercise?

Answer 27

Required increase rate of O2 and CO2 exchange in the alveolus to maintain normal arterial blood gases

Question 28

What happens to capillaries as CO increases>

Answer 28

Greater proportion of capillaries are recruited and perfused - increases gas exchange SA

Question 29

What do ,ore parallel pathways for blood through lungs cause?

Answer 29

Reduced velocity of flow at any given CO More time for loading of O2 into RBCs

Question 30

What prevents an increase in PACO2 and reduction in PAO2?

Answer 30

Alveolar ventilation increases - must match increased CO2 delivery and O2 removal

Question 31

In normal lung, what is oxygen uptake in maximal exercise limited by?

Answer 31

Cardiac output

Question 32

In normal lung, what limits maximal oxygen uptake?

Answer 32

Perfusion

Question 33

Do reductions in diffusion capacity impair oxygen uptake at rest?

Answer 33

No

Question 34

How do you asses info about gas exchnage membrane?

Answer 34

Examine uptake of gas that is diffusion limited - CO

Question 35

What 3 properties must a gas have to assess diffusion capacity?

Answer 35

Extremely soluble in blood Blood must not fill up during transit through lung Must have gradient always driving gas from blood