Residual volume during pregnancy does what?

• A. Increases
• B. Decreases
• C. Remains unchanged
• D. Varies with activity

Answer: (B)

During pregnancy, the diaphragm is pushed upward by the enlarging uterus, and the chest wall becomes stiffer. This mechanical shift changes how air is stored in the lungs at the end of expiration. With the lungs operating from a higher baseline volume and expiratory forces being less able to trap air, the amount of air left in the lungs after a full exhale decreases. At the same time, tidal volume increases to meet the higher metabolic demands, but the end-expiratory air—the residual volume—still falls. So, residual volume tends to decrease as pregnancy progresses.