3. Alveolar Gas Exchange

Question 1

How does one calculate minute alveolar ventilation?

Answer 1

Subtract dead space from tidal volume then multiply by frequency

Question 2

How much O2 and CO2 is exchanged every minute (under normal resting conditions)?

Answer 2

250 ml O2
200 ml CO2

Diffusion of each gas is independent of each other.

Question 3

How is distance variable during alveolar gas exchange?

Answer 3

Distance between capillary and alveolus can increase, such as deposition of collagen in interstitial space.

Question 4

Which is more soluble in water, O2 or CO2?

Answer 4

CO2

About 20x greater

Question 5

How does exercise effect the amount of time a RBC is in the capillary? How does this effect gas exchange?

Answer 5

It lessens the amount of time the RBC is in a pulmonary capillary. In those with lung disease, this might not be enough time to fully diffuse O2 into the RBC.

Question 6

What is the diffusion capacity of the lung for oxygen?

Answer 6

21 ml O2/min/mm Hg

This is calculated using the average gradient along alveolar capillary.

Question 7

How does one calculate the diffusion capacity of the lung for oxygen?

Answer 7

Using CO because it binds to Hb so avidly it doesn’t dissolve in plasma. Then use correction factor:

DL(O2) = 1.23 x DL(CO)

Question 8

What is LaPlace’s Law?

Answer 8

Pressure = 2T/r

T = tension
r = radius

Question 9

What is surfactant’s effect on surface tension in small alveoli?

Answer 9

It reduces surface tension (T) so they do not collapse.

Question 10

Which surfactant protein is most important for maintaining surface tension?

Answer 10

SPB