Behavior of Normal Pulmonary Circulation during Changes of Total Blood Volume in Man*

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Abstract
Hemodynamic changes induced by alterations in total "effective" blood volume were studied in 26 patients with normal pulmonary circulation. For this purpose, simultaneous right- and left-heart catheterization was carried out in each patient, while blood volume was varied by the rapid injection of a 3.5% polyvinylpyrrolidone solution, by peripheral venous blood pooling, or by both. During the infusion of polyvinylpyrrolidone, significant increases were observed in cardiac output, stroke volume, right and left ventricular stroke work, pulmonary arterial and venous (left atrial) pressures, right atrial pressure, and in the blood volume between the inferior vena cava and pulmonary artery, which included a portion of the blood in both venae cavae and their tributaries as well as in right atrium and ventricle. The same variables declined during peripheral venous blood pooling. The increase or decrease of the total effective blood volume elicited small or in significant changes in heart rate and systemic arterial pressure. Total peripheral resistance varied inversely with cardiac output. The significant changes that were noted in the average intravascular pressure in the pulmonic circuit were not paralleled by important alterations of the pulmonary blood volume, especially during the infusion of the solution containing polyvinylpyrrolidone. Low and inconsistent variations were observed in pulmonary vascular resistance. These results suggest that the pulmonary circulation behaved as a system of low distensibility. They are consistent with the view that rapid changes in total volemia are accompanied mainly by variations of the systemic venous blood volume while the pulmonary blood volume is kept within narrow limits.