AEMCA Practice Exam

What type of V/Q mismatch would be observed in a person standing upright in the apex of the lung?

1. High V/Q mismatch due to increased blood circulation

2. Low V/Q mismatch due to decreased air turbulence

3. High V/Q mismatch due to increased air turbulence and decreased blood circulation

4. Normal V/Q mismatch due to balanced ventilation and perfusion

The correct answer is: High V/Q mismatch due to increased air turbulence and decreased blood circulation

The correct answer highlights the physiological principles of ventilation-perfusion (V/Q) matching within the lungs. In the upright position, the apex of the lung experiences a high V/Q ratio. This occurs because the ventilation is relatively well maintained while the perfusion—the flow of blood—is significantly reduced due to gravity. In this region, there is less blood available for gas exchange, which leads to a condition where the amount of air available for each unit of blood is high, thus indicating a high V/Q mismatch. The reason this scenario doesn't correspond to the other options lies in the dynamics of ventilation and perfusion. In the option that indicates low V/Q mismatch, the situation would imply a balance where ventilation and perfusion are similarly low, which is not the case in the apex. The mention of increased air turbulence in the answer that includes decreased blood circulation can be somewhat misleading, as turbulence pertains more to airflow dynamics than to the proportional relationship of air and blood flow, yet it encapsulates the concept that ventilation remains but perfusion is diminished in the apex. Normal V/Q would not apply here either, as the conditions at the apex are distinctly non-normal with respect to the ratio of ventilation to perfusion. Hence, the details surrounding the blood flow dynamics