Question

Mismatch of ventilation/perfusion ratio is seen in?

• A. Apex
• B. Base
• C. Both
• D. None

Hint:

V/Q is about 3.0 at the apex and 0.6 at the base, both off the ideal 0.8.

Answer 1

The Correct Option is C

Step 1: The lung is not uniform from top to bottom. Taking alveolar ventilation near 4.2 L/min and pulmonary blood flow near 5.0 L/min, the average V/Q works out to about 0.8.

Step 2: Gravity pulls blood toward the dependent base, so perfusion increases more steeply downward than ventilation does. Consequently the apex ends up with too little blood relative to air and the base with too much blood relative to air.

Step 3: Numerically the V/Q reaches about 3.0 at the apex and falls to about 0.6 at the base. Both values sit away from the ideal 0.8, which means a mismatch exists at both poles of the lung.

Step 4: Functionally, apical gas tensions resemble inspired air with high PO2 and low PCO2, while basal gas tensions resemble pulmonary arterial blood with low PO2 and high PCO2. Because both regions are mismatched, the correct response is both.

\[\boxed{\text{Both}}\]