V/Q matching and CO2 Transport

Question 1

What does diffusion rate depend on?

Answer 1

Surface area
Conc. gradient
Thickness of membrane
Diffusion constant (proportional to solubility of gas)

Question 2

How does exercise impact time that RBCs spend in pulmonary capillaries?

Answer 2

Usually spend 0.8s in capillaries - more than enough time for complete equilibration.
Exercise decreases time as RBCs pass through faster.

Question 3

What can cause hypoxemia?

Answer 3

Low PiO2
Hypoventilation
V/Q mismatch
Hindered diffusion (e.g. thickened alveolar/capillary interface)

Question 4

What is the normal V/Q ratio?

Answer 4

4. 2L air/5L blood/min

0. 84 - normally under ventilated and overperfused.

Question 5

How does autoregulation work to balance ventilation-perfusion coupling?

Answer 5

Changes in alveolar PaO2 cause changes in arteriole diameter

• Increase in PaO2 = dilate
• Decrease in PaO2 = constrict

Changes in alveolar PaCO2 cuase changes in bronchiole diamater

• Increase in PaCO2 = dilate
• Decrease in PaCO2 = constrict

Question 6

Describe the regional differences in Va and Q of the lungs

Answer 6

Hydrostatic pressure is greater lower part of the lungs, so there is stronger perfusion

Va/Q ratio is HIGH at apex of lung (low perfusion)
Va/Q ratio is LOw at base of lung (high perfusion)

Question 7

What can cause a high Va/Q?

Answer 7

Pulmonary embolism

Question 8

What can cause a low Va/Q?

Answer 8

Chronic bronchitis, asthma, pulmonary oedema

Question 9

Describe the difference in arterial blood and venous blood CO2 content

Answer 9

Change is small.