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

What is a consequence of decreased alveolar ventilation to tissue oxygenation?

1. Increased FEV1/FVC ratio

2. Compensatory tachypnea

3. Decreased amount of anatomic dead space

4. Significantly reduced tidal breaths

The correct answer is: Compensatory tachypnea

Decreased alveolar ventilation leads to insufficient oxygen delivery to the tissues, which can cause hypoxemia (low levels of oxygen in the blood). In response to hypoxemia, the body attempts to compensate by increasing the respiratory rate, resulting in compensatory tachypnea. This is a normal physiological response aimed at enhancing gas exchange to restore adequate oxygen levels in the bloodstream. When alveolar ventilation is compromised, the efficiency of oxygen exchange in the lungs decreases, leading to the body needing to take more breaths per minute to try to improve oxygenation. Therefore, tachypnea arises as a compensatory mechanism to counteract the effects of decreased oxygen supply to the tissues. While the other options address different aspects of respiratory physiology or may imply changes in other conditions, they do not directly relate to the immediate physiological response associated with decreased alveolar ventilation and tissue oxygenation. For instance, alterations in the FEV1/FVC ratio are more indicative of obstructive or restrictive lung disease rather than a direct consequence of decreased ventilation alone. Similarly, changes in anatomic dead space and tidal volume are not direct consequences of the hypoxemia associated with inadequate alveolar ventilation in this context.