Myogenic and flow-dependent control mechanisms in the coronary microcirculation.

We have recently gained evidence that segmental coronary microvascular diameters, and therefore resistances, are controlled by myogenic and endothelial responses to pressure and flow. Furthermore, intact heart studies are demonstrating that these mechanisms may interact importantly with the metabolic mechanisms primarily governing coronary blood flow. Further studies utilizing measurement of segmental coronary microvascular diameters in isolated microvessels and in the beating heart may elucidate the nature of these interactions. Clinical studies may determine whether reversal of endothelial impairment in the diseased coronary microcirculation contributes to autoregulatory vasodilation, increases resting myocardial perfusion, and increases the threshold for myocardial ischemia during exercise.