In COPD, which lung volume parameter is typically increased due to air trapping?

• A. Forced vital capacity
• B. Total lung capacity
• C. Residual volume
• D. Diffusing capacity

Answer: (C)

Air trapping in COPD happens when expiratory airflow is blocked, especially in damaged small airways, so air cannot be fully exhaled. This causes air to remain in the lungs after a maximal exhale, increasing the amount of air left in the lungs — the residual volume. That trapped air is the direct reason RV goes up and contributes to overall hyperinflation. While total lung capacity can also rise with hyperinflation, the feature most specifically increased because of trapping is residual volume. Forced vital capacity tends to decrease due to obstruction, and diffusing capacity is usually reduced, not increased. Residual volume.