USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What condition is associated with reduced pulmonary compliance?

1. Asthma

2. Surfactant deficiency

3. Diffusion-limited gas exchange

4. Pulmonary infarction

The correct answer is: Surfactant deficiency

Surfactant deficiency is associated with reduced pulmonary compliance. Surfactant is a substance that decreases surface tension within the alveoli, preventing the collapse of the lungs at the end of expiration. Without adequate surfactant, the alveoli become stiff and difficult to inflate, leading to decreased lung compliance. This results in increased effort required for breathing and decreased lung volumes. Asthma is characterized by airway inflammation, bronchoconstriction, and airway hyperresponsiveness, leading to increased airway resistance rather than reduced pulmonary compliance. Diffusion-limited gas exchange refers to the limitation of gas transfer between the alveoli and the blood due to a decreased surface area or thickness for gas exchange, which is different from reduced pulmonary compliance. Pulmonary infarction is the result of blocked blood flow to a portion of the lung, causing tissue damage and potentially compromised gas exchange, but it is not directly related to reduced pulmonary compliance.