What are common gas exchange abnormalities in COPD?

• A. Hypertension and edema due to left heart failure
• B. Alkalosis due to rapid breathing
• C. Hypoxemia and hypercapnia due to V/Q mismatch
• D. Hyperoxemia and hypocapnia due to hyperventilation

Answer: (C)

The key idea is that COPD disrupts gas exchange mainly through ventilation-perfusion (V/Q) mismatch. In COPD, airway obstruction and structural changes (such as emphysema with loss of alveolar walls and chronic bronchitis with mucus plugging) create regions where blood passes through the lungs but ventilation is reduced, and other areas where ventilation is relatively better but perfusion is altered. This mismatch lowers the amount of oxygen that gets into the blood and impairs the removal of carbon dioxide, yielding both hypoxemia and hypercapnia. The loss of alveolar surface area also decreases diffusion capacity, making oxygenation even worse. Over time, these changes explain the characteristic gas exchange pattern in COPD.

Alkalosis from rapid breathing would indicate excessive ventilation with CO2 loss, which isn’t the typical pattern in COPD. Hyperoxemia and hypocapnia from hyperventilation likewise don’t fit the common COPD picture, where CO2 retention is more typical. Hypertension and edema from left heart failure involve the heart and fluid status rather than the primary gas exchange abnormality seen in COPD.