Ventilation Perfusion Mismatch

Question 1

What is the ventilation / perfusion (V/Q) ratio throughout the lung?

Answer 1

1

Question 2

What is normal partial pressure of oxygen in alveolus?

Answer 2

13.3kPa

Question 3

What is normal partial pressure of carbon dioxide in alveolus?

Answer 3

5.3kPa

Question 4

What happens if V/Q is less than 1?

Answer 4

Higher pCO2
Lower pO2

New steady state established

Question 5

What can cause a V/Q ratio less than 1?

Answer 5

Asthma (not uniform)

COPD (not uniform)

Pneumonia (acute inflammatory exudate in affected alveoli)

RDS in newborn (some alveoli not expanded)

Pulmonary oedema (fluid in alveoli)

V/Q mismatch is the commonest mechanism causing hypoxia.