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Abstract
Left main coronary artery pressure-flow relationships were obtained in anesthetized dogs with the left main coronary artery perfused from a controlled pressure source. Coronary artery pressure-flow relationships that were obtained at ten different points in the cardiac cycle were readily characterized by straight lines with pressure axis intercepts significantly greater than either right or left atrial pressures. The pressure axis intercept (PZF) reached a maximum during systole and a minimum during diastole. Submaximal reactive hyperemias and maximal vasodilation with adenosine lowered PZF at all points in the cardiac cycle. Therefore, PZF is determined by both smooth muscle tone and myocardial tissue pressure.
Resistance (the inverse slope of the pressure-flow relationship) showed small increases during systole when the vasculature was maximally vasodilated. The configuration of the resistance changes over the cardiac cycle indicated that compressive forces within the myocardium do not contribute significantly to the resistance changes. When vasomotor tone was intact, the resistance changes over the cardiac cycle were small but complex. The maximum resistance occurred at end diastole while the minimum resistance occured during systole.
In a second series of experiments, autoregulation of coronary blood flow was analyzed. Autoregulation during both diastole and systole was accomplished by increases in both PZF and resistance.
The possible role of vascular compliance in pressure-flow relationships was examined with a computer model. Capacitive effects were found to have the theoretical potential to cause large errors in PZF. However, the actual magnitude of the errors was estimated to be small under conditions of intact vasomotor tone and essentially unmeasureable when the vasculature was maximally vasodilated.
