Coronary flow by left atrial and left ventricular microsphere injection in the rat

Previous studies have reported significantly higher variability in coronary blood flow (CBF) measurements obtained by microsphere injection into the left ventricle (LV) as compared with microsphere injection into the left atrium (LA) of the rat. Questions have arisen concerning whether or not some of the variability may have been due to successive rather than simultaneous injections at the two sites, thereby giving measurements at different cardiovascular states. To address this question, we measured cardiac output (CO) and CBF as well as other systemic organ blood flows by employing simultaneous injection of two different sets of radiolabeled microspheres into the left atrium and left ventricle of semiconscious rats. Using this technique, CBF values (ml.min-1.g-1) of 5.45 +/- 0.43 and 5.24 +/- 0.46 for LA and LV injection sites, respectively, were measured (all values reported as means +/- SE). CO values (ml/min) of 67.5 +/- 3.5 for LA and 67.6 +/- 3.4 for LV were obtained. Paired left atrial and left ventricular measurements of CBF, CO, and other systemic organ blood flows using tracer microsphere methodology were not significantly different. All variabilities in these measurements by LA and LV injection were not significantly different. Our procedure did not significantly alter physiological parameters such as heart rate, mean arterial pressure, hematocrit, or blood gases. These findings indicate that, in our rat model, measurements made by LV microsphere injection are not only adequate for determining systemic blood flow at distal beds but provide coronary blood flow data with variability not significantly different from that of left atrial injection.