Pulmonary Arterial Pressure at High Pulmonary Flow *

The relationship between pulmonary arterial pressure and pulmonary blood flow has been stud-ied by a number of investigators in anesthetized animals (1), in man after pneumonectomy or uni-lateral pulmonary arterial occlusion (2, 3), and in normal man during exercise (4-7). With a few exceptions (1) these studies have agreed that doubling or trebling the pulmonary arterial flow does not produce a comparable increase of pulmo-nary arterial pressure. Sloan, Morris, Figley, and Lee (2) and Brofman (3) found in human subjects only a very slight rise of pulmonary ar-terial pressure during balloon occlusion of one main pulmonary artery branch when cardiovas-cular dynamics were normal. However, the re-lationship between pulmonary arterial pressure and pulmonary arterial blood flow at higher rates of flow has been examined by only a few investi-gators. In 1950, Cournand, Riley, Himmelstein, and Austrian (8) published studies of pulmonary blood pressure in normal physicians at rest and during exercise and in patients who had had a pneumo-nectomy with a normal remaining lung. These investigators concluded that pulmonary blood flow in man can increase to approximately three times the normal before the pulmonary arterial pressure will rise above normal limits. Lategola studied pulmonary pressure and flow relationships at high flow levels achieved by occluding 50 % or more of the pulmonary circulation in anesthetized dogs (9). Lategola also found that when pulmonary blood flow was increased to approximately 250 to 300 % above normal, the pressure rose sharply