In obese and pregnant individuals, what happens to functional residual capacity and why?

• A. Increases due to diaphragmatic relief
• B. No change
• C. FRC reduces to near tidal volume
• D. Greatly reduces due to abdominal contents pressing on the lungs

Answer: (D)

Functional residual capacity is the volume remaining in the lungs after a normal exhalation. In obese and pregnant individuals, FRC is markedly reduced because the abdominal contents push the diaphragm upward—pregnancy raises the uterus, and obesity adds intra-abdominal fat. This upward displacement shortens the vertical dimension of the chest, lowers the baseline lung volume, and promotes early airway closure in the dependent regions. The result is a greatly diminished FRC, which means less oxygen reserve during periods of apnea or sedation.