Measurement of Left Ventricular Output

Abstract

A method permitting accurate measurement of instantaneous cardiac output in intact animals is described. It is based upon a reliable device for injecting a known constant flow (Fi) of indicator (T-1824), of known concentration (Ci), into the ascending aorta. Simultaneously, the concentration of the indicator in blood (Co) is continuously sampled dlstally with a cuvette oximeter. Total blood flow (Ft) is obtained from the relationship; [image] The reliability of the method was tested with a model providing wide ranges of flow and velocity (S.D. = [plus or minus] 1.06%, [gamma] = 0.99). The mixing problem was studied and mixing proved to be complete. In dogs this method, Fick, classic dye dilution, saline pulse and the pulse pressure methods were compared. Measured flows ranged from 0.7 - 15 1/ minutes. The comparison of these measurements with those obtained by the Fick method showed a random variation (S.D. = [plus or minus] 11%). The classic dye dilution determinations, obtained between 2 determinations by the reported method at 5-7 minute intervals, were compared when blood pressure, pulse pressure, and respiration were similar, and were found to give a systematically higher output. Simultaneous samples from multiple arterial sites showed identical dye concentrations indicating complete mixing. Since the overall reliability of this method appears high, variations in measured flow are assumed to be physiological.