Distribution of coronary blood flow across the canine left ventricular free wall during reactive hyperemia

In a group of open-chest anesthetized dogs, reactive hyperemia (RH) in epi- and endocardial layers of the myocardium was quantitated by measurements of cumulative excess blood flow (CEBF) In the hyperemic period following occlusions of the left anterior descending coronary artery (LAD) for 10 to 120 s. Blood flow measurements were obtained by means of the local X3-133 washout technique. When ischemia was extended from 10 to 45 s, CEBF increased significantly and uniformly in both layers; with further extension of the ischemia to 60, 90 and 120 s, the increment in CEBF was significantly greater in the endocardial than in the epicardial layer (29, 57 and 64% greater, respectively). In accordance with the concept that CEBF is mainly controlled by metabolic factors, this result supports the hypothesis that the capacity for formation of vasodilatory "metabolites" is greater in the subendocardial tissue. Left ventricular wall was homogeneously perfused in the pre-occlusive period and during maximal vasodilation of the coronary bed. In another group of dogs, maximal vasodilation and abolishment of local autoregulation was ascertained by 30 s of occlusion of LAD. When diastole in the post-occlusion period was shortened by 33%, i.e. from about 37.5 s. min-1 to about 25.5s.min-1 by artificial pacing at 250 min-1, endocardial maximum blood flow amounted to only 43% of that of the corresponding epicardial region, which apparently was not affected by the increased heart rate.