PHYS Ventilation Perfusion & Gas Exchange - Week 1

Question 1

Barometric pressure is

Answer 1

760mmHg (20% O2 & 80% CO2).

Question 2

O2 driving pressure is

Answer 2

60mmHg

Question 3

CO2 driving pressure is

Answer 3

6mmHg

Question 4

Decreased barometric pressure is observed where and what is the effect on O2 diffusion.

Answer 4

High altitudes. Decreased pressure gradient to drive O2 diffusion.

Question 5

Increased barometric pressure is observed where and what is the effect on O2 diffusion.

Answer 5

Hyperbaric chamber/diving underwater. Increased pressure gradient to drive O2 diffusion.

Question 6

Where is the partial pressure of CO2 greatest?

Answer 6

Systemic venous circulation &/ capillaries.

Question 7

5 factors which affect gas diffusion in the lungs

Answer 7

1. Partial gas pressure
2. Area of lungs available for diffusion
3. Thickness of alveoli epithelium
4. Diffusion constant of the gas
5. V/Q matching

Question 8

Clinical causes of reduced lung SA

Answer 8

Emphysema (alveoli wall damage -> rupture -> larger air space, instead of many smaller ones -> reduces SA).

Question 9

Clinical causes of thickened alveolar membranes

Answer 9

Fibrosis & oedema.

Question 10

Ideal V/Q ratio

Answer 10

1. Normal V/Q = 0.8.

Question 11

Clinical causes of V/Q < 0.8

Answer 11

Pneumonia, asthma (reduced ventilation - shunting).

Question 12

Clinical causes of V/Q > 0.8

Answer 12

Pulmonary embolism (reduced perfusion - dead space).

Question 13

Indirect gas diffusion measurement techniques.

Answer 13

Pulse oximeter & arterial blood sample gas analysis & V/Q lung scan.

Question 14

Direct gas diffusion measurement techniques.

Answer 14

TLCO/DLCO test.

Question 15

Factor affecting V/Q ratio:

Answer 15

Posture (gravity increases perfusion at base of lung).