Respiratory System MCAT Practice Question
A 62-year-old man with a 3-year history of idiopathic pulmonary fibrosis presents with progressive dyspnea on exertion. Pulmonary function testing shows a forced vital capacity (FVC) of 58% predicted and a diffusion capacity (DLCO) of 42% predicted. High-resolution CT scan demonstrates bilateral lower lobe predominant reticular opacities with traction bronchiectasis. Histopathology confirms usual interstitial pneumonia (UIP) pattern with extensive collagen deposition and myofibroblast proliferation. Which of the following best explains the mechanism by which collagen accumulation contributes to this patient's dyspnea?
Answer choices
- ACollagen deposition increases alveolar surface area available for gas exchange, but impairs oxygen diffusion due to increased barrier thickness
- BCollagen decreases lung compliance by increasing elastic recoil, requiring greater inspiratory pressure to achieve a given tidal volume
- CCollagen accumulation increases dynamic airway resistance during expiration, trapping air and increasing total work of breathing
- DCollagen deposition decreases lung compliance by reducing tissue distensibility, thereby increasing the pressure gradient required for ventilation and overall work of breathingCorrect answer
- ECollagen primarily affects the viscous properties of pleural fluid, increasing frictional resistance during inspiration but not expiration
- FCollagen impairs mucociliary clearance mechanisms, leading to increased airway obstruction and airflow limitation
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