Pulmonary gas exchange

Question 1

Perfusion-limited exchange?

Answer 1

• gas equilibrates early along the length of the pulmonary capillary, therefore the partial pressure of the gas in the arterial blood equals that in the alveolar air
• the only way to increase diffusion of a gas is therefore to increase blood flow

Question 2

Diffusion-limited exchange?

Answer 2

• gas does not equilibrate by the time the blood has reached the end of the pulmonary capillary
• a partial pressure gradient is therefore maintained between the arterial blood and the alveolar air

Question 3

Examples of perfusion-limited exchange?

Answer 3

• Oxygen (normal conditions)
• Nitrous oxide
• Carbon dioxide

Question 4

Examples of diffusion-limited exchange?

Answer 4

• Oxygen (during strenuous exercise)
• Oxygen (lung fibrosis)
• Oxygen (emphysema)
• Carbon monoxide

Question 5

Mnemonic to remember - Examples of perfusion-limited exchange

Answer 5

CON

C arbon dioxide

O xygen (normal conditions)

N itrous Oxide

Question 6

Mnemonic to remember - Examples of diffusion-limited exchange​

Answer 6

COOO

C arbon monoxide

• *O** xygen (during strenuous exercise)
• *O** xygen (lung fibrosis)
• *O** xygen (emphysema)