Analysis of myocardial and total body integral extraction ratios of rubidium-86

Coronary blood flow (Q(M)) measurement with radiorubidium (Rb) assumes that Rb distributes to the myocardium in proportion to flow. This assumption is correct if the integral myocardial Rb extraction ratio (ER(M)) equals total body extraction (ER(TB)). A right-heart-bypass preparation was employed to test the hypothesis that ER(M) = ER(TB) and to examine the determinants of Rb extraction. Dogs were anesthetized with pentobarbital, and arterial, coronary venous, and total body venous Rb concentrations were continuously measured for 4 min after injection. We found that ER(M) (0.56 ± 0.01) was significantly less than ER(TB) (0.70 ± 0.01), P<0.01 (n=29) and concluded that Rb did not distribute in proportion to flow. We do not recommend this method for clinical use. ER(M) is flow dependent and ER(TB) is a function of the total cardiac output and the distribution of cardiac output. Before employing Rb in animal experiments, it is recommended that a preliminary study be performed comparing flow measured with Rb to an independent measure of blood flow.