Cardiac Output Distribution in Rats Measured by Injection of Radioactive Microspheres via Cardiac Puncture

A modification of the microsphere method for the measurement of the cardiac output distribution in small experimental animals is described. The method is suitable for use in both anesthetized and unanesthetized animals. Radioactive microspheres are injected into the left ventricle by cardiac puncture through the closed thorax, which eliminates the need for the cannulation of the left ventricle. The results obtained by this modified method in rats agree with those based on the injection of microspheres through the left ventricular cannula. The described method is suitable for the detection of changes in cardiac output distribution as demonstrated by comparing the results in anesthetized and unanesthetized animals. The cardiac output distribution measured by the microsphere method differs significantly from that based on the rubidium method. The main feature is the fact that the rubidium method tends to overestimate the fractional blood flow to organs with two systems of capillary bed.