Which statement best describes gas exchange abnormalities in COPD due to V/Q mismatch?

• A. Hyperoxemia due to excessive ventilation
• B. Hypoxemia due to shunting only
• C. Hypocapnia due to hyperventilation
• D. Hypoxemia and hypercapnia due to V/Q mismatch

Answer: (D)

In COPD, gas exchange abnormalities mainly come from uneven ventilation and perfusion—V/Q mismatch. Some lung units are poorly ventilated but still well perfused (low V/Q), so less O2 gets transferred into the blood, causing low arterial oxygen (hypoxemia). At the same time, overall ventilation is reduced because of airway obstruction, dynamic hyperinflation, and increased dead space from emphysema, which makes it harder to eliminate CO2, leading to elevated arterial CO2 (hypercapnia). While shunting can contribute to hypoxemia in other conditions, in COPD the dominant issue is V/Q mismatch, which can produce both hypoxemia and hypercapnia. The other options describe either too much oxygen, hypoxemia from shunting only, or hypocapnia from hyperventilation, none of which fit COPD’s typical gas exchange pattern.