Interaction between contraction and coronary flow: Theory

Abstract

Heart contraction affects coronary perfusion in two experimentally distinguishable ways; the time averaged flow through the myocardium is reduced, depending on the depth in the heart muscle, and the flow is pulsatile. The relation between these two phenomena is not trivial and is hard to study because of technical difficulties. Up to now almost all experimental studies on the transmural distribution of flow during contraction were hampered by the fact that flow measurements are time averaged rather than instantaneous. On the other hand, information on the pulsatile nature of coronary flow is obtained from measurements on epicardial arteries or veins and hence provide a time varying flow signal per unit muscle mass which is the space average of the pulsatile flow over the different layers. As long as we are unable to measure time varying flow at different depths within the myocardium, the relation between space dependent time averaged flow and time dependent space averaged flow has to be determined by predictive models. These models postulate a mechanism for the effect of contraction on the coronary vasculature, resulting in mathematical predictions of, amongst others, coronary arterial or venous pressure-flow relations and microsphere distribution.