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

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Abstract
Techniques for determining cardiac output by recording the dilution curve of injected iodinated (I131) human serum albumin from precordial sites are described. It has been found essential to view predominantly either the right or left side of the heart and to make rapid deliveries of the isotope in order to secure curves from which accurate outputs can be recorded. The curves recorded externally from the right side of the heart give increased counting sensitivity and a large ratio of the measured to the extrapolated portion of the curve. Errors in counter placement too high over the inflow tract are to be avoided from right side positioning. Left sided positioning offers the advantages of a greater number of points on the descending limb of the curve for extrapolation and avoids problems of poor mixing. In a series of 26 determinations in normal patients cardiac output values calculated from simultaneously recorded precordial curves and withdrawn arterial blood showed an average agreement within [plus or minus] 8%. In a smaller series of 8 determinations on patients in heart failure, an average deviation of [plus or minus] 10% was found.