American Board of Internal Medicine (ABIM) Certification Practice Exam

Which term describes low V/Q or shunt physiology?

1. Hypoventilation

2. Shunt physiology

3. Dead space physiology

4. Normal ventilation

The correct answer is: Shunt physiology

Low V/Q ratio refers to a condition where there is inadequate ventilation relative to perfusion in the lungs, leading to inefficient gas exchange. This can occur in scenarios such as pulmonary edema or pneumonia, where areas of the lung receive blood flow but are not adequately ventilated, causing a level of shunting. Shunt physiology specifically describes this phenomenon, where blood bypasses ventilated parts of the lungs, leading to reduced oxygenation of the blood. The other terms do not accurately represent this concept. Hypoventilation describes a decreased rate or volume of air entering the lungs, impacting overall ventilation but not necessarily creating a shunt effect. Dead space physiology refers to areas of the lung where ventilation occurs without corresponding perfusion, resulting in wasted air that does not contribute to gas exchange. Normal ventilation simply indicates that the air is being exchanged adequately; it does not align with the low V/Q state. Thus, shunt physiology is the most appropriate term to describe the situation characterized by low V/Q ratios.