The effect of total peripheral resistance on indicator-dilution curves from the central circulation of the dog.

The influence of total peripheral resistance on the dispersion of indicator particles passing through the central circulation was studied in five dogs. The standard deviation of indocyanine green indicator-dilution curves provided a measure of dispersion. The peripheral vascular resistance of the dog was altered during the experiment by the intravenous administration of sodium nitroprusside and methoxamine. We calculated the area of each curve by fitting the first portion of the curve to a random walk function and the cardiac output and the total peripheral resistance were calculated in the usual manner. The mean, standard deviation and area of each of the curves were calculated from the least squares estimate of the random walk function. The relationship of the cardiac output, mean arterial pressure, and total peripheral resistance to the mean and the standard deviation were compared in a multiple stepwise linear regression. For each dog there was a definite linear relationship between total peripheral resistance and standard deviation (p less than 0.01). These results indicate that the dispersion of particles passing through the central circulation is directly related to the total peripheral resistance.