Atelectasis is defined as...

• A. A chronic infectious disease
• B. An inflammatory condition of the pleura
• C. An accumulation of fluid in the alveoli
• D. Part or all of a lung collapses, preventing it from fully expanding

Answer: (D)

Atelectasis is the collapse or incomplete expansion of part or all of a lung, so that those airspaces cannot fill with air and participate in gas exchange. This happens when airways are blocked by mucus, secretions, or a mass, after surgery when breathing is shallow, or when external pressure compresses lung tissue. The result is reduced oxygenation and decreased breath sounds in the affected area. The definition fits this scenario best because it specifically describes collapse preventing full expansion. It isn’t a chronic infection, a pleural inflammatory condition, or merely fluid in the alveoli—that would describe other processes like infection, pleuritis, or edema, respectively.