Abbreviation: V/Q mismatch
An imbalance between the total lung ventilation (airflow; V) and total lung perfusion (blood flow; Q). V/Q mismatch is an indicator of gas exchange and is the most common cause of hypoxemia. Normal V/Q ratio is 0.8 (since lung bases are better ventilated and perfused than the apices). Decreased ventilation (e.g., in pneumonia, atelectasis) decreases the V/Q ratio. Decreased perfusion (e.g., in pulmonary embolism) increases the V/Q ratio.