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

What is a characteristic of Compromised airways in Obstructive Airway Diseases regarding air trapping during exercise?

1. Decreased TLC

2. Increased FEV1

3. Decreased dynamic air trapping

4. Elevated FRC

The correct answer is: Elevated FRC

In the context of obstructive airway diseases such as asthma or chronic obstructive pulmonary disease (COPD), one of the hallmark features is air trapping. During exercise, individuals with these conditions experience difficulty in exhaling effectively due to narrowed airways. This leads to a characteristic increase in functional residual capacity (FRC), which represents the volume of air remaining in the lungs after normal exhalation. As airways are compromised, not all of the air can be expelled, resulting in a larger volume of air remaining in the lungs after expiration. This ongoing retention of air contributes to the elevated FRC observed in patients with obstructive lung disease, particularly during periods of exertion when breathing rates increase but exhalation is impeded. In contrast, total lung capacity (TLC) may not necessarily decrease; rather, the distribution of air within the lung compartments is altered. Forced expiratory volume in one second (FEV1) typically falls in obstructive airway diseases, as the forced expiratory maneuver is impaired due to airway resistance. Decreased dynamic air trapping would not accurately describe the pathophysiology, as dynamic air trapping is a condition more pronounced in these diseases rather than diminished. Thus, the characteristic of elevated functional residual capacity during exercise in