Analysis of Factors Used in Calculations Based Upon Radiocardiograms on Dogs

The radiocardiogram4 provides information on the circulation of radioactive material through the heart and lungs. Because the radiocardiograph records cardiac output with little trauma to the patient and because it offers minimal in terference with circulation, it is a potentially valuable method of studying circulation. This method, however, has not provided the desired accuracy in quantitative measurements, probably because of errors related to the geometry of the detector system. This study suggests identification of the background radio activity as one method to minimize the effect of geometry. Prinzmetal et at ( 1 ) proposed the use of an externally placed detector to determine the characteristics of circulation. Shipley (2 ) and Huff (3) with their associateS provided the basis for the present use of the radiocardiogram in making quantitative estimates of cardiac output. Huff based his calculations on equations derived from the dye-dilution principle, then compared the results with simultaneous estimations obtained by the application of the Fick Principle. Powers and Sevelius (4) have presented a different mathematical model based on mean transit time for the tagged particles. Both theories lead to similar equa tions for the calculation of cardiac output. In models of circulation, Glick (5) and others (6,7) have tested and supported the use of the radiocardiogram as the basis for estimating cardiac output. The geometry of the detector system relates the field of the detector and dis tribution of radioactive particles in the field. During radiocardiograph recording, two sets of conditions lead to different geometries of recording in a single record.