Use of radioactive microspheres to assess distribution of cardiac output in rabbits

Abstract

A method is described for assessing the relative distributions of cardiac output in unanesthetized rabbits, and its accuracy and repro-ducibility was examined. Under general anesthesia, polyvinyl catheters were passed into the left ventricle and a peripheral artery and vein. After recovery, a small amount of 50-[mu]-diam microspheres labeled with selected gamma emitting nuclides was injected into the left ventricle. Total cardiac output was calculated from dye-dilution curves inscribed just before the injection of microspheres. Absolute blood flows to various organs and tissues were determined by relating percentage distribution of the microspheres to the cardiac output. Microsphere injection produced no measurable circulatory disturbance. Standard deviation of flows obtained with injection of microspheres with different nuclide labels was about 10%; the flow estimates were subject only to random error. No preferential streaming to any circulation was evident and recirculation of microspheres was minimal. The results of regional flow measurements are reported in 6 anesthetized and 20 unanesthetized rabbits and they are compared to the regional flows in other species.