Pulmonary vascular volume, resistance and compliance in man. Circulation

V ARIATIONS in the volume of blood in the pulmonary vessels have been assumed to play a role in the physiology of the lesser circulation since the time of William Harvey,' but few measurements of the human pulmo-nary blood volume in vivo are available. This volume is an important variable in the hemo-dynamics of the pulmonary eirculation be-cause of the relationships between volume, pressure, and flow to be expected in an elastic system, which require that all 3 of these para-meters be measured in order to interpret changes in any one of them. In 19 patients with a variety of cardiac and pulmonary abnormalities we have made such measurements in the course of diagnostic catheterization of right and left heart cham-bers. The dye-dilution method was employed to measure cardiac output and mean transit time from pulmonary artery to left atrium, giving the data needed for calculation of pul-monary blood volume by the Stewart-Hamil-ton method.2 The results provide more direct measure-ments of pulmonary blood volume than have previously been available, and also give an estimate of relative vascular compliance. One limitation of the method is that it measures the characteristics of the entire pulmonary vascular bed, with no indication of the differ-ences in volume, compliance, and resistance that exist among the arterial, arteriolar, capil-lary, and venous parts of the bed.3 In spite of this limitation significant relationships be-tween volume, flow, resistance, and compliance were found