Evaluation of the microsphere-method for determination of cardiac output

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Abstract
Cardiac output [CO] was determined using radioactive microspheres, 15 .+-. 5 .mu.m in diameter. Blood flow in the ascending aorta was measured by an electromagnetic flowmeter. In 8 cats, 38 simultaneous measurements were made of CO and aortic flow. The observations correlated well (r [correlation coefficient] = 0.89), with a mean difference of 5.2%, probably corresponding to coronary blood flow. Continuous flow recordings showed no changes in aortic flow during the injections of microspheres; arterial blood pressure and heart rate remained unchanged even after 6 injections, each consisting of about 2 .times. 105 spheres/kg body wt. Tests for shunting of microspheres were performed and revealed shunt fractions in the systemic circulation of about 8%, with no significant shunting through the lungs. The microsphere method for determining CO is considered an accurate method, suitable for small and medium-sized animals.