ADAPTIVE RESPONSES OF CORONARY CIRCULATION AND MYOCARDIUM TO CHRONIC REDUCTION IN PERFUSION-PRESSURE AND FLOW

We tested the hypothesis that chronic reduction in perfusion pressure and flow in the coronary circulation induces a state of myocardial ''h ibernation'' characterized not only by a steady-state reduction in myo cardial O-2 consumption (MVo(2)) but also by evidence of persistent di lator reserve of the distal vasculature. Biochemical and morphological changes in the coronary vasculature were also assessed. Experiments w ere conducted in swine with an extraluminal coronary stenosis placed 4 -32 wk before study. Stenosis reduced lumen diameter by similar to 80% at the time of final experimentation. Baseline, regional myocardial b lood flow distal to the stenosis in both endocardial and epicardial la yers was reduced vs. that of the normal zone. Vasodilator reserve pers isted in both endocardial and epicardial layers of the stenosis zone. Flow increased in each layer in response to adenosine plus phenylephri ne and failed to decline despite a marked reduction in perfusion press ure in response to adenosine alone. Regional MVO(2) at baseline was re duced vs. historical controls without coronary stenosis. Protein synth esis rate in coronary vessels of the stenosis zone was reduced vs. tha t of the normal zone. Morphological responses of stenosis zone vessel walls were heterogeneous. Smaller microvessels exhibited mild hypertro phy of their walls, whereas walls of larger microvessels tended to atr ophy. Thus chronic reduction in perfusion pressure and flow induces a state of myocardial hibernation characterized by a steady-state reduct ion in MVO(2) in association with persistent dilator capacity. Biochem ical and morphological changes occur in microvessel walls and may cont ribute to observed physiological responses.