During the later stages of BPD, functional lung volume is reduced primarily due to:

• A. Gas trapping with hyperinflation
• B. Atelectasis
• C. Worsening ventilation-perfusion matching
• D. Pulmonary edema

Answer: (A)

In the later stages of BPD, the dominant issue is chronic small-airway obstruction with inflammation and fibrosis that leads to air trapping. Expiration becomes inefficient, so air stays trapped in the lungs and parts of the lung become overinflated (hyperinflation). This trapping reduces the amount of fresh air that can fill the lungs on the next breath and diminishes the functional portion of the lung that can participate in gas exchange, effectively lowering usable functional lung volume.

Atelectasis would suggest collapse and reduced volume from airless regions, which is less characteristic of the late-BPD pattern. Worsening ventilation-perfusion matching explains hypoxemia and perfusion issues rather than a primary change in lung volume. Pulmonary edema would acutely add fluid and also mainly affect diffusion and oxygenation, not the chronic pattern of air trapping and hyperinflation seen in late BPD.