USMLE (United States Medical Licensing Examination) Step 1 Practice Exam 2025 - Free USMLE Step 1 Practice Questions and Study Guide

Patients with emphysema often have a "barrel-chested" appearance due to dynamic air trapping. This refers to the inability to fully exhale all of the air in the lungs, causing the chest to remain in an expanded position. This happens as a result of damaged alveoli and decreased elastic recoil in the lungs, making it difficult for air to be released from the lungs during exhalation. Increased tidal volume (B) is not an appropriate explanation as it refers to the amount of air taken in during normal breathing. Reduced airway resistance (C) would not result in a barrel-chested appearance. Decreased TLC (D) refers to decreased total lung capacity and though it is associated with emphysema, it does not fully explain the "barrel-chested" appearance. Therefore, the best explanation for this appearance is the dynamic air trapping (A) seen in patients with emphysema.