Effect of perfusion pressure distal to a coronary stenosis on transmural myocardial blood flow.

We tested the hypothesis that reductions of perfusion pressure distal to a flow-limiting coronary artery stenosis can directly impair perfusion of the subendocardial myocardium. Dogs were instrumented with an electromagnetic flowmeter probe and a variable occluder on the proximal left circumflex coronary artery. Coronary perfusion pressure was measured with a catheter distal to the occluder. Coronary autoregulation was abolished by intraarterial infusion of adenosine to produce maximal coronary vasodilation. The transmural distribution of myocardial blood flow was measured with radioactive microspheres during unimpeded arterial inflow, when the occluder was progressively narrowed to reduce distal coronary pressure to approximately 70%, 50% and 35% of the control coronary perfusion pressure, and during total coronary occlusion. Heart rate, left ventricular diastolic pressure and the fraction of coronary artery flow during systole remained constant throughout the study. Progressive reductions of coronary pe...