Respiratory system: closing capacity: practice question

Try it

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Closing capacity rises with age and can exceed FRC supine, so dependent airways close during tidal breathing

Closing capacity is the lung volume at which small dependent airways begin to close. It increases with age, and FRC falls when supine and under anaesthesia. When closing capacity exceeds FRC, alveoli in the dependent zones are perfused but poorly ventilated during tidal breathing, so V/Q mismatch and hypoxaemia result.

Option by option

• A. Closing capacity rises with age and can exceed FRC supine, so dependent airways close during tidal breathing (correct)

  Closing capacity above FRC leads to airway closure and V/Q mismatch in dependent lung.

• B. FRC rises when supine, which increases the dead space fraction and impairs gas exchange

  FRC falls, not rises, in the supine position because the abdominal contents push up the diaphragm.

• C. Residual volume falls with age, so airways remain open at lower volumes

  Residual volume increases with age as airways close earlier.

• D. Closing capacity falls with age, so more gas is trapped in dependent airways

  Closing capacity rises, not falls, with age, and it is the closure rather than the capacity itself that traps gas.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Physiology questions