Assessing heterogeneous distribution of blood flow and metabolism in the heart

The literature is reviewed on methods to assess heterogeneity of blood flow , substrate uptake and oxidative end energy metabolism in the normal heart, and their interrelations. Even though the factors controlling matching on the regional level remain largely obscure, the evidence that heterogeneous blood flow partially correlates to indicators of metabolism in the normal h eart is accumulating, particularly in face of a correlation between acetate metabolism indicative of regional O-2 consumption to microsphere blood flo w. Moreover, the partial matching cannot be explained by vascular anatomica l differences from one region to the other, since, although fractal theory can partially describe the branching patterns of the coronaries, vasodilati on is similar among regions upon metabolic stimulation of the heart. It is dissimilar among regions, so that blood flow is redistributed, upon maximum vasodilation with adenosine or hypoxia, denoting regionally different maxi mum vessel diameter and flow reserve. However, regionally differing tissue composition could also contribute somewhat to regional differences in (the need for) blood flow. It is still unknown, because of technical limitations , how the foregoing measures relate to regional workload.