The Determination of Cardiac Output by the Dilution Method without Arterial Sampling

Abstract

The selection of an external site for a radioisotope determination of cardiac output is discussed with respect to satisfying the analytical conditions of the Stewart-Hamilton dilution equation. Examples of both single-chamber and multichamber recording are illustrated, along with a discussion of the difficulties of curve calibration and extrapola. tion from multiple sites. The development of a method independent of critical placement or patient variability is described.A LTHOUGH earlier determinations of 14A cardiac output in this laboratory 1-3 by the radioisotope dilution method were performed by isolating the flow from a specific artery, such sampling is not required by the general formulation of the method. Since the obviation of the arterial puncture would considerably simplify this measurement clinically, studies have been extended 4-to determine cardiac output by focusing a gamma ray detector externally over the region of the cardiac chambers or great vessels. We have been concerned since 1951 with the selection of a site that could be observed externally with sufficient reliability for this technic to be accepted as a routine clinical measurement. Many sites of arterial flow may be chosen for quantitation of a dilution curve of cardiac output; therefore, the problem has resolved to a selection of such sites and technics that will not be critically affected by variations in patients.It is the object of the following investigation to examine the choice of the external site From the

Studies of Cardiac Output and Pulmonary Blood Volume

“…in 1954 (3). Com parative m easurem ents have been carried out using this m ethod, Fick's method and the arterial sam pling method, and the results of the three techniques of cardiac output determ in ation have been found to he well com parable (4)(5)(6)(7)(8)(9)(10)(11)(12). Diverging results have also been obtained, the results of the precordial iso tope dilution technique being considered inconsistent and un reliable in com parison to the arterial sam pling m ethod (13).…”

Reliability of first-pass radionuclide determination of cardiac output in the upright position at rest and during exercise

“…Firstpass radionuclide cardiography determines the forward blood flow through the cardiac chambers with the aid of the tracer dilution principle (Shipley etal. 1953;MacIntyre et al 1958;Donato 1973). A method using the gamma camera for recording of technetium-99m transit curves has been described and evaluated recently (Glass 1986;Kelb~ek et al 1987Kelb~ek et al , 1989a.…”

Special Article: Factors Modifying the Contours of Indicator-Dilution Curves

“…MacTntyre and colleagues 17 have critically reviewed the assumptions and technical problems inherent; in the application of surfacescanning methods. They stressed the importance of scanning mainly from one side of I he heart so that the contribution of the other chambers would not appreciably distort the final extrapolation; also, because of the inherent uncertainty of the character of the extrapolated line, they pointed out the desirability of having the directly measured area as large as possible in order to minimize errors arising from the extrapolated area.…”