ventilationperfusion

Ventilation-perfusion, often abbreviated V/Q, describes the relationship between airflow into the lungs (ventilation) and blood flow through the pulmonary capillaries (perfusion). The ventilation-perfusion ratio (V/Q) is the amount of alveolar ventilation divided by the amount of pulmonary perfusion and is a key determinant of efficient gas exchange.

In healthy individuals, ventilation and perfusion are matched regionally across the lungs, but there are systematic variations due to gravity and lung architecture. Alveolar ventilation and capillary perfusion are not uniform, creating a gradient from nondependent to dependent regions. The overall average V/Q is around 0.8, supporting adequate oxygen uptake and carbon dioxide removal.

V/Q mismatch arises when ventilation and perfusion are discordant. A shunt occurs when perfusion exceeds ventilation (perfusion without ventilation), while dead space describes ventilation exceeding perfusion (ventilation without perfusion). Common clinical scenarios include airway obstruction, edema, pneumonia, or atelectasis that reduce ventilation, and pulmonary embolism or vascular disease that reduce perfusion.

Clinical assessment includes methods such as the V/Q scan, which separately evaluates ventilation and perfusion using radiotracers, and arterial blood gas analysis to detect hypoxemia. Management focuses on correcting the underlying cause of the mismatch and may involve oxygen therapy, bronchoscopy, treatment of infection or edema, or anticoagulation or thrombolysis for thromboembolic disease.