Temporal Heterogeneity of Myocardial Blood Flow in Anesthetized Dogs

Temporal variation in perfusion to small segments of the myocardium was studied in 19 opened-chest dogs. In six control dogs, three or four differently labeled 7-10 mu microspheres were injected simultaneously into the left atrium to assess the variability in measured myocardial perfusion due to the microsphere technique. In 13 other dogs, microspheres were injected four times at 5 minute intervals while various hemodynamics parameters (mean aortic pressure, peak systolic pressure, heart rate, left ventricular end-diastolic pressure, and Vmax) were stable (less than 10% variation in any one parameter). The left ventricles were divided into 96 segments, the mean weight+/- SD of each segment was 0.95+/-0.17 grams. The flow to each segment was expressed as a percent of the mean flow of the three or four measured flows to that segment, and the difference between the largest and the smallest percent of each segment was taken as a measure of the variability of flow to that segment. The average variability of segmental flow (mean +/-SD) when the three to four differently labeled microspheres were injected was 14.0+/-4.7; and the variability when differently labeled microspheres injected sequentially was 31.0+/-10.8% (P less than 0.001). Furthermore, in the sequentially injected animals the magnitude of temporal variation was similar in various subdivisions of the ventricle (layers, walls, apex to base). The mean and standard deviation of the variability of flow to the endo, mid, and epicardial layers were 28.7+/-10.2, 30.0+/-11.3 and 34.5+/-12.4%, respectively. These changes may reflect either spontaneous or local autoregulatory changes in precapillary sphincters or arterioles.