THE PULMONARY BLOOD VOLUME IN MAN *

The measurement of blood volume in the pulmo-nary vascular bed during life became theoretically feasible with the introduction of indicator dilution methods by Stewart (1) and Hamilton, Moore, Kinsman and Spurling (2). The principles and formulas set forth by these investigators have since undergone extensive scrutiny by theoretical anal-ysis, in circulation models, and in vivo. As a result of these studies, there exists now general agreement that the introduction of an indicator substance into the central circulation, either di-rectly or by peripheral venous injection, and downstream recording of its concentration change with time during the first transit permits the determination of three important circulatory pa-rameters: 1) the cardiac output, 2) the mean transit time from injection to sampling site, and 3) by multiplication of cardiac output and mean transit time, the circulating volume of blood be-tween injection and sampling sites, including all temporally equidistant points in the vascular bed. Practically speaking, then, the measurement of pulmonary blood volume in vivo requires deter-mination of the mean transit time of an indicator from the pulmonary artery to the left atrium to-gether with cardiac output. The development of right and left heart catheter-ization has made the pulmonary artery and left atrium accessible as injection and sampling sites in man. Injection of an indicator through