In previous studies, indicator-dilution curves obtained by videodensitometry of contrast two-dimensional echocardiograms have shown close correlation with measurements of blood flow in vitro. In this study the technique was extended and contrast indicator-dilution curves obtained in vivo were correlated with simultaneous cardiac output measurements determined by thermodilution in eight dogs. Two-dimensional echocardiograms of the left ventricle were performed with the transducer on the myocardium during left atrial-pulmonary vein injection of 10 cc of a 1 x 10-4 concentration of 30 μ diameter microballoons. A total of 148 injections were performed at 37 levels of cardiac output (1.70 to 7.90 liters/min) induced by alterations of left ventricular preload, isoproterenol and propranolol. Indicator-dilution curves were obtained from recordings of the analog signal of a linear videodensitometer focused on the left ventricle. Linear regression analysis between total area of the indicator-dilution curves and cardiac output yielded correlation coefficients (r) of 0.77 to 0.96 (mean 0.90) for individual dogs, and 0.65 for all cardiac output determinations in all dogs. Analysis of indicator-dilution curve area by the forward triangle-exponential decay method yielded enhanced individual coefficients of 0.90 to 0.97 (mean 0.94) with cardiac output and 0.61 for the group of animals. It is concluded that echographic indicator-dilution curves obtained from uniform size microballoons and videodensitometry may be obtained in vivo and correlate with cardiac output measurements.
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