American Board of Internal Medicine (ABIM) Certification Practice Exam

High V/Q or (V/Q = infinity) refers to which type of physiology?

1. Shunt physiology

2. Dead space physiology

3. Normal ventilation

4. Type 2 respiratory failure

The correct answer is: Dead space physiology

High ventilation to perfusion ratio (V/Q) or V/Q = infinity indicates dead space physiology. In this scenario, ventilation continues without corresponding blood flow (perfusion) to the areas of the lung being ventilated. This can occur in conditions such as pulmonary embolism, where a blockage in the pulmonary arteries prevents blood from reaching alveoli, causing some areas of the lung to be well ventilated but poorly perfused. Understanding dead space is essential because it highlights how ventilation can occur without effective gas exchange, which is a key aspect of respiratory function. In contrast to shunt physiology, where blood bypasses ventilated areas leading to low oxygen levels due to unoxygenated blood entering the systemic circulation, dead space represents a mismatch favoring ventilation without blood flow, resulting in wasted ventilation. Thus, recognizing V/Q abnormalities, such as high V/Q, is crucial in diagnosing and managing respiratory disorders effectively.