The Ventilation/Perfusion (V/Q) Ratio (PK5)

Question 1

Why does the V/Q ratio not increase linearly in the lung?

Answer 1

V̇ + Q̇ increase at different rates

Question 2

What is the mean V/Q ratio across the whole lung?

Answer 2

0.8

Question 3

Taking V/Q as 0.8, what do PAO2 and PACO2 equilibrate to?

Answer 3

• PAO2 = 13kPa
• PACO2 = 5kPa

Question 4

Taking V/Q as 0 (no ventilation), what do PAO2 and PACO2 equilibrate to?

Answer 4

• PAO2 = 5kPa
• PACO2 = 6kPa

Question 5

Taking V/Q as ∞ (no blood flow) what do PAO2 and PACO2 equilibrate to?

Answer 5

• PAO2 = 20kPa
• PACO2 = 0kPa
  (Normal air levels)

Question 6

What condition causes V/Q to be ∞ (no blood flow)?

Answer 6

Pulmonary embolism