Basic and Clinical Sciences (BCSE) Practice Exam

Which of the following factors could lead to a decrease in physiological dead space?

1. Increased alveolar perfusion

2. Increased airway resistance

3. Decreased tidal volume

4. Increased pulmonary vascular resistance

The correct answer is: Increased alveolar perfusion

A decrease in physiological dead space can occur with increased alveolar perfusion. Physiological dead space refers to the volume of air that does not participate in gas exchange because it is either ventilated but not perfused (anatomical dead space) or because the alveoli are being ventilated but lack sufficient blood flow (physiological dead space). When alveolar perfusion increases, more blood flows to the areas of the lungs that are being ventilated, enhancing the efficiency of gas exchange. This leads to a reduction in the proportion of ventilated air that does not contribute to effective gas exchange, thereby decreasing the physiological dead space. The other factors listed do not contribute to or result in a decrease in physiological dead space. Increased airway resistance can lead to inefficient ventilation and may contribute to an increase in dead space. Decreased tidal volume reduces the amount of air exchanged, which is not favorable for gas exchange. Increased pulmonary vascular resistance can limit perfusion to the alveoli, potentially increasing dead space instead of decreasing it. Therefore, increased alveolar perfusion is the correct factor that effectively lowers physiological dead space.