Vascular volumes of the pulmonary circulation in intact dogs

Abstract

Pulmonary arterial blood volume (Vpa), pulmonary capillary blood volume (Vc), pulmonary venous blood volume (Vpv), mean pulmonary arterial pressure, mean left atrial pressure and pulmonary blood flow were measured in anesthetized dogs at functional residual capacity, and changes in vascular volumes were produced by administration of serotonin (5-hydroxytryptamine) or angiotensin II. Pulmonary blood flow and pulmonary blood volume (PBV) were determined with a double-indicator dilution technique. Mean pulmonary arterial transit time, measured by injecting ether into the pulmonary artery and recording its evolution from the capillaries in a body plethysmograph, was multiplied by pulmonary blood flow to obtain Vpa. A rebreathing technique was used to measure diffusing capacity for CO at low and high O2 concentrations from which Vc was calculated. Vpv was obtained by subtracting the sum of Vpa and Vc from PBV. Mean Vpa comprised 26% (64 .+-. 33 (SD) ml), Vc 22% (48 .+-. 21 (SD) ml), and Vpv 52% (120 .+-. 69 (SD) ml) of PBV (232 .+-. 92 (SD) ml). I.v. infusion of serotonin (5 .mu.g/min) produced a slight decrease in Vpa, but not changes in Vc and Vpv. Infusion of angiotensin II (20-40 .mu.g/min) resulted in increases of Vpa, Vc and Vpv. At functional residual capacity the distribution of the vascular volumes in the intact pulmonary circulation depends on the vascular pressures. At the drug concentrations used in these studies, the magnitude of the observed changes in vascular volumes in relation to the vascular pressures suggests a direct effect on pulmonary vasomotor tone of serotonin but not of angiotensin II.