STUDIES OF THE PULMONARY CIRCULATION IN MAN AT REST. NORMAL VARIATIONS AND THE INTERRELATIONS BETWEEN INCREASED PULMONARY BLOOD FLOW, ELEVATED PULMONARY ARTERIAL PRESSURE, AND HIGH PULMONARY “CAPILLARY” PRESSURES 1

Abstract

Pulmonary hemodynamics was studied in normal individuals at rest and the response of the pulmonary vasculature to large pulmonary blood flows, high pulmonary arterial pressures, and elevated pulmonary "capillary" pressures was analyzed. In 8 normal patients at rest but not in a basal state, the avg. mean pulmonary artery pressure was 15 mm. Hg, the avg. mean pulmonary "capillary" pressure was 9 mm. Hg, the avg. gradient of pressure between the 2 was 6 mm. Hg, and the avg. arteriolar resistance was 67 dynes/sec./cm.-5. The avg. work of the right ventricle against pressure or more properly the pulmonary peripheral work was 0.89 kg. m./min./sq. m. body surface. The relation of large pulmonary blood flows to the pressure gradient from pulmonary artery to pulmonary "capillaries" was studied at rest in patients with uncomplicated patent ductus arteriosus and atrial septal defect. The gradient of pressure across the lung widened when the pulmonary blood flow exceeded approx. 10 liters/min./sq. m. of body surface. In 3 patients with Eisenmenger''s complex with pulmonary arterial pressures which were essentially aortic in magnitude, the resistance to blood flow offered by the pulmonary arterioles was of the same order of magnitude as that in the systemic circuit. Elevated pulmonary "capillary" pressures were consistently found in patients with mitral stenosis and left ventricular failure. When the pulmonary "capillary" pressure rose to values of about 25 mm. Hg, the pressure in the pulmonary artery rose proportionately, the pulmonary artery-pulmonary "capillary" pressure gradient and the pulmonary arteriolar resistance remained normal. With pulmonary "capillary" pressures in excess of 25 mm. Hg (the approx. osmotic pressure of plasma), pressure in the pulmonary artery rose disproportionately, the PA-"PC" pressure gradient widened, and the pulmonary arteriolar resistance increased on occasion to 20 or more times the normal value.