V/Q Mismatch: Distribution of Ventilation through the Lung (PK5)

Question 1

Where in the the lung is the more negative pleural pressure and why?

Answer 1

• Apex
• Gravity pulls the lung away from the pleura (at the base it pulls it into pleura), so there is greater retraction

Question 2

What are the apex and base Ppl?

Answer 2

• A = -1kPa
• B = -0.25kPa

Question 3

Where is ventilation greater in the lung and why?

Answer 3

• Base
• Looking at sigmoidal graph, dropping Ppl by given amount causes a greater increase in base volume
• Because apex alveoli are already more inflated due to more negative resting Ppl and reaching elastic limit

Question 4

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

Answer 4

2.5x