Hypoxemia occurring after pulmonary thromboembolism is a result of which of the following?

Hypoxemia occurs commonly after massive pulmonary thromboembolism, although normal arterial oxygen tension does not exclude the diagnosis. The most important mechanism producing hypoxemia in this setting is an increase in venous admixture caused by continued perfusion of poorly ventilated areas. Ventilation may be decreased by atelectasis or by airway constriction in response to the release of bronchoactive mediators. A fall in cardiac output that produces a low mixed venous P can increase the effect of venous O2 admixture. Increased dead-space ventilation would not be a cause of hypoxemia.