A STUDY OF THE PULMONARY BLOOD VOLUME IN MAN BY QUANTITATIVE RADIOCARDIOGRAPHY*

Abstract

A method for obtaining pulmonary blood volume (PBV) from a double-peaked radio-cardiogram is presented. The pulmonary mean transit time is estimated as the interval from the mean time of ejection of label from the right ventricle to the peak time of counting rate resulting from label in the left heart chambers. The validity of the determination of the pulmonary mean transit time was analyzed with the aid of an electronic digital computer on a theoretical model of the central circulation, under varying conditions of flow, volume of the mixing chambers, counting efficiency of the detector, and distribution selected to represent the frequency function of the pulmonary transit times. Analysis of the mathematical model has shown the degree to which the pulmonary mean transit time, as determined, is affected by variations in the volume of the heart chambers, in the counting efficiency, and in the distribution of the pulmonary transit times. It has also been shown that PBV closely parallels the changes in stroke volume in changing states, such as during exercise, or the infusion of sodium bicarbonate or Tris. Variations in cardiac output, however, are not necessarily accompanied by changes in PBV.