Abstract
Estimation of the volume of blood pumped by the heart per unit time in health and disease is not a broadly utilized clinical procedure, not because the information it would provide is not in itself eminently useful, but because of the many practical and theoretical difficulties inherent in finding a method which is relatively simple, and yet sufficiently accurate. |This paper, which contains the results of a program of experimentation carried on in its majority in the Radioisotope Service of the Veterans Administration Hospital in Omaha, Nebraska, between June 1959 and May 1960, endeavors to cover certain more general aspects of the problem of cardiac output, as well as the specific technic subjected to critical study. It is hoped thereby that these pages may serve as a primer for anyone interested in achieving a basic understanding of the field. |In itself, the problem of determining the output of the heart is first and last one whose solution must be based on solid principles of physics: measurement is to be made of the rate of flow of a liquid through a system of containing vessels. Any method, then, of determining flow is at least potentially capable of being applied to the determination of cardiac output, as long as its use is compatible with the nature and physical arrangement of the living organism. | In the radioisotopic technic which is the subject of the current study, the principle is utilized that there exists an inverse relationship between the flow in a system and the concentration of any introduced and measurable substance integrated over the period of time that it takes the entire amount of tracer substance to pass by a given and constant observation point in the system. | This is a well-substantiated approach to any type of flow situation; its application to the study of cardiac output with the use of a radioactive isotope as the indicator substance is peculiarly a happy one in that the integration of time vs. concentration can be estimated by a counting mechanism completely external to the body. The practical implementation of this approach is a chief portion of the substance of this paper.