Reproducibility of Results obtained with Indicator-Dilution Technique for Estimating Cardiac Output in Man

The reproducibility of the indicator-dilution estimation of cardiac output was assessed by evaluating pairs of indicator-dilution curves recorded simultaneously from normal subjects and patients by two similar linear densitometers. Measurement error was defined by comparison of 90 simultaneous measurements obtained from the same needle; two standard deviations of the difference equaled 430 ml./min. (6 per cent of the mean cardiac output). A much larger variation resulted when 159 simultaneous cardiac output determinations, sampling from the brachial and femoral arteries, were compared (two standard deviations of the difference equaled 1,200 ml./min. or 20 per cent of the mean cardiac output). Intermediate values were obtained in a comparison of 29 simultaneous measurements from the radial and brachial arteries of the same arm. The larger deviations between the simultaneous measurements from different arteries suggested nonuniform distribution of dye. The discrepancies between the paired cardiac output determinations were larger and more frequent when peripheral blood flow alterations were produced. However, the nature of dye-distribution abnormalities and the mechanisms whereby peripheral arterial flow influence the dye-dilution cardiac output measurement were not evident.