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

What is a result of impaired ventilation in pathological cases such as pneumonia or pulmonary edema?

1. Increased perfusion of bronchial arteries

2. Normal lung function

3. Enhanced gas exchange

4. Reduced tidal volumes

The correct answer is: Increased perfusion of bronchial arteries

Impaired ventilation in conditions such as pneumonia or pulmonary edema leads to a consequential adjustment in the respiratory system's hemodynamics. In these pathological states, the lungs are not able to ventilate effectively, which reduces the oxygenation of blood and can trigger various compensatory mechanisms. Increased perfusion of bronchial arteries can occur as part of a compensatory response to provide additional blood flow to the affected areas. The bronchial arteries are responsible for supplying oxygenated blood to the lung tissue. In states of impaired ventilation, the body attempts to maximize oxygen delivery by directing more blood flow towards areas that are better ventilated or need more oxygen, such as through the enhanced perfusion of bronchial arteries. While the other choices suggest outcomes that are either normal or beneficial in terms of lung function, they do not accurately reflect the consequence of impaired ventilation from conditions like pneumonia or pulmonary edema. Reduced tidal volumes would be a direct consequence of impaired ventilation, but it reflects the mechanism rather than a compensatory response like the increase in bronchial artery perfusion.