Measured at the level of large coronary arteries, coronary blood flow, CBF, is rather well adapted to the oxygen requirement of the heart muscle and rather independent of coronary pressure. This adaptation is the result of local control based on feed back between metabolism and smooth muscle tone in resistance vessels.

Understanding of the flow control system would be easier if all resistance in a microvascular network would be controlled at a single spot. However, this is not the case. Resistance is adapted in all arterial vessels smaller then 400 microns and at each diameter level with different mechanism. Mathematical models are rather useful in evaluating the interactions of the different mechanisms involved. Especially for the heart, where interactions depend on the depth in the muscle and where small vessels, other than epicardial, can hardly be observed directly. In order to arrive at a truthful anatomy of the coronary microvascular structure in the heart, we developed a 3D reconstruction technique based on an imaging cryomicrotome. Our model studies indicated that not only control of vasodilation is important but control of vasoconstriction as well. Moreover, the model studies indicate that, in engineering terms, CBF control has a low gain which allows a large margin for interaction of different mechanisms.