Effects of cardiac contraction and increased coronary sinus pressure on the coronary arterial pressure-flow relationship

Increased coronary sinus (CS) pressure and cardiac contraction impair coron ary inflow independently. However, it has not been determined how the coron ary pressure-flow relationship is strongly affected by changes in CS pressu re in the beating heart compared to the non-beating heart. The purpose of t his study was to evaluate the combined mechanical effects of cardiac contra ction and increased CS pressure. Using isolated, perfused canine hearts, co ronary perfusion pressure in the left anterior descending coronary artery ( LAD) was gradually reduced in beating and non-beating conditions. Measureme nts were obtained with and without elevation of CS pressure to determine th e mean LAD pressure-flow relationships. At normal and elevated CS pressures , the corresponding zero-flow pressures were not significantly different be tween the beating and non-beating hearts. A rightward shift of the mean cor onary perfusion pressure-coronary flow curve for the beating heart compared to the non-beating heart was observed when CS pressure was not elevated. I n contrast, the slopes for both beating and non-beating hearts were similar if the CS pressure was increased. There was a smaller increase in the mean intramyocardial pressure (IMP) at elevated CS pressures in the beating hea rt as compared to the non-beating heart. Moreover, the increase in diastoli c IMP with increased pressures in the beating heart was significantly less than that in the non-beating heart. These results indicate that cardiac con traction attenuates the inhibitory effects of increased CS pressure on coro nary inflow.