V/Q Mismatch: Distribution of Blood Flow (Perfusion) through the Lung (PK5)

Question 1

How much more perfusion does the base receive than the apex?

Answer 1

6x

Question 2

Pulmonary artery pressure in cmH2O

Answer 2

20cmH2O

Question 3

How much do arterial and venous pressure increase as you go up and down the lung?

Answer 3

1cmH2O for every cm travelled

Question 4

What is the constant difference between arterial and venous pressure in the lung at any level?

Answer 4

10cmH2O

Question 5

What is alveolar pressure in the lung in cmH2O?

Answer 5

0cmH2O

Question 6

3 zones of the lung based on arterial, alveolar and venous pressures (and which pressures are greater than each other)?

Answer 6

• Zone 3 (bottom) = Pa > Pv > PA
• Zone 2 (middle) = Pa > PA > Pv
• Zone 1 (top) = PA > Pa > Pv

Question 7

How do the differences in pressures allow blood flow in zone 3?

Answer 7

• Arterial + venous pressure drives blood flow
• Not much change as you move throughout zone, as difference between Pa + Pv constant

Question 8

How do the differences in pressures allow blood flow in zone 2?

Answer 8

• Arterial + alveolar pressure drives blood flow
• As you get higher blood flows decreases, as Pa drops but PA remains 0

Question 9

Why is there no blood flow in zone 1?

Answer 9

Pressure greatest is alveolar pressure, so blood won’t flow from lower Pa to higher PA

Question 10

When is zone 1 seen?

Answer 10

• Fall in arterial pressure (eg. haemorrhage)
• Rise in PA (eg. positive pressure ventilation)

Question 11

What is recruitment?

Answer 11

• At rest pulmonary arterioles are collapsed
• With rising pressure they are ‘recruited’ and available for blood flow

Question 12

In which zone does recruitment cause changes in blood flow?

Answer 12

Zone 2

Question 13

What is distension?

Answer 13

Once all vessels are open, they can then stretch/distend, increasing blood flow

Question 14

In which zone does distension cause changes in blood flow?

Answer 14

Zone 3