lung zone


lung zone

A hypothetical region of the lung defined by the relationship between the degree of alveolar ventilation and pulmonary blood flow (perfusion). Three lung zones have been identified: I, ventilation exceeds perfusion; II, ventilation and perfusion are equal; and III, perfusion exceeds ventilation. Zone I is found in the upper lung field, where gravity impedes perfusion, and zone III in the inferior portion of the lung, where gravity assists perfusion. See also: zone