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

What characteristic is typically seen in obstructive lung capacity?

1. Reduced TLC

2. Increased FEV1/FVC ratio

3. Loss of elastic recoil

4. Normal or increased FEV1

The correct answer is: Loss of elastic recoil

Obstructive lung capacity is typically associated with a loss of elastic recoil. This is due to airway inflammation and constriction, causing difficulty in expelling air from the lungs. The other options, reduced TLC, increased FEV1/FVC ratio, and normal or increased FEV1, are usually seen in restrictive lung diseases. TLC (total lung capacity) is often decreased in restrictive diseases, whereas FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) are typically decreased. In contrast, in obstructive lung diseases, these lung volumes can be normal or increased, but the ability to exhale air is impaired due to narrowed airways. Therefore, the correct answer is C, as a loss of elastic recoil is a defining characteristic of obstructive lung diseases.