Importance of injection site for coronary blood flow determinations by microspheres in rats

Because coronary blood flow (CBF) determinations require that blood and microspheres be uniformly mixed in the root of the aorta, we developed a technique of left-atrial (LA) catheterization in rats and compared the variability of results obtained by LA injection and left-ventricular (LV) injection as regards systemic [cardiac output (CO)], proximal (coronary), and distal (renal, cerebral) flows in anesthetized animals. CBF values averaged 410 +/- 224 and 358 +/- 99 (SD) ml.min-1.100 g-1 from LV and LA injection, respectively, or 5.7 +/- 2.9 and 4.9 +/- 1.3 (SD) %CO. The variability with LA injection was significantly lower than with LV injection as shown by the marked differences in standard deviations obtained with the two methods (224 vs. 99 ml.min-1.100 g-1 or 2.9 vs. 1.3 %CO, P greater than 0.01). In contrast, no significant difference in variability was found for either CO or more distal regional flows. These results indicate that LV injections might be adequate for systemic flow and regional flows to relatively distal beds but that accurate measurements of CBF require LA injection of microspheres.