Quantitative Radiocardiography

Abstract

The method of quantitative radiocardiography has been applied to the study of cardiac output, right ventricular and pulmonary blood volume in cardiovascular normals, emphysematous subjects, and patients with various types of heart disease. The values of blood flow obtained by means of this technic have been compared with those measured simultaneously by the direct Fick method. A linear correlation has been demonstrated between Q_RIHSA and Q_Fick, with a regression coefficient of 1.0395 ± 0.0566, when appropriate correction has been made for the contribution of activity in the paracardiac tissues. The principle of the measurement of right ventricular rate of emptying from the fractional decay rate of the precordial counting during the passage of the indicator through the right heart has been validated. The right ventricle behaves essentially as a mixing chamber; a constant fraction of its volume is ejected with each systole. The variability of the emptying rate does not exceed the limits expected on the grounds of statistics of radioactive measurements in normal and in cardiac patients. The significance of the variability observed in emphysematous patients has been discussed. The measured ventricular rates of emptying are reproducible in repeated curves recorded after injection of RIHSA or dissolved Kr⁸⁵; are little affected by change of the position of the tip of the injecting catheter; or by small changes in the position of the collimator. The right ventricular end-diastolic and residual volumes have been found to average 221 ± 50 ml. and 128 ± 34 ml. respectively, in 18 normal subjects. The calculated pulmonary blood volume in 18 normal subjects averages 313 ± 58 ml./M.² The significance of this value and the possible extreme range of error resulting from the method have been assessed.