Ventilation Perfusion (V/Q) Matching/Mismatch

Question 1

What is each alveolus capable of?

Answer 1

Receiving CO2 & supplying O2 to the pulmonary blood capillary

Question 2

For this to be efficient, what do we need?

Answer 2

Correct proportion of alveolar airflow (ventilation) & capillary blood flow (perfusion)

Each alveolus needs equal amounts of ventilation (oxygenation) & perfusion (blood supply)

Question 3

What is any mismatch called?

Answer 3

Ventilation - perfusion inequality

Question 4

What happens when there’s ventilation - perfusion inequality? What is it due to?

Answer 4

Hypoxia- O2 deficiency at tissues

Naturally unequal due to gravity
More perfusion at bottom of lung than top
Therefore lower v/q value there

Question 5

What are the 2 extremes of v/q?

Answer 5

1) ventilated alveoli but no blood supply

2) no ventilation but adequate blood supply

Question 6

What happens when there’s ventilated alveoli but no blood supply?

Answer 6

Increase V/Q value
Known as dead space or wasted ventilation (air but no blood)
Due to pulmonary embolism (blood clot)

Question 7

What happens when there’s no ventilation but perfused alveoli?

Answer 7

Decrease V/Q value
Blood is shunted to a different area where there is no collapsed alveoli
Due to pulmonary oedema (collapsed alveoli due to fluid build up)

Question 8

What is the local homeostatic response to ventilated alveoli & not very well perfused alveoli?

Answer 8

Local bronchoconstriction
If there’s a local decrease in blood flow to lung region due to blood clot in pulmonary arteriole
Decrease ppCO2
Air diverted to better perfused areas

Question 9

What is the local homeostatic response to not ventilated alveoli & perfused alveoli?

Answer 9

Hypoxic pulmonary vasoconstriction
Decrease in alveolar pO2
Decrease in ppO2 in alveoli and nearby blood vessels
Leads to vasoconstriction-diverts blood away from poorly ventilated areas to better ventilated areas