Cardiac Conduction System

(From West JB, Dollery CT, Naimark A. Distribution of blood flow in isolated lung: relation to vascular and alveolar pressures. J Appl Physiol. 1964;19:713-718, with permission.)

The lung is divided into three pulmonary blood flow zones reflecting the impact of alveolar pressure (PA), pulmonary artery pressure (Ppa), and pulmonary venous pressure (Ppv) on the caliber of pulmonary blood vessels.