CORONARY PRESSURE-FLOW AUTOREGULATION PROTECTS MYOCARDIUM FROM PRESSURE-INDUCED CHANGES IN OXYGEN-CONSUMPTION

Pressure-flow autoregulation minimizes changes in coronary blood flow (CBF) when coronary perfusion pressure (CPP) is altered. This investigation determined if autoregulation also minimizes CPP-induced changes in coronary vascular volume (CW) and CW-dependent changes in myocardial oxygen consumption (MVo(2)). In 11 anesthetized dogs, the left anterior descending coronary artery was cannulated, and responses to 20-mmHg changes in CPP were examined over a range of CPP from 60 to 180 mmHg. Changes in CPP had no significant effect on systemic hemodynamics or on left ventricular end-diastolic segment length, end-systolic segment length, or percent segment shortening. In hearts with effective pressure-flow autoregulation [closed-loop gain (GC) > 0.4], CW increased 0.06%/mmHg change in CPP. For the same hearts, MVo(2), increased 0.04%immHg change in CPP. In hearts with ineffective autoregulation (GC < 0.4), CW increased 0.97%/ mmHg (P < 0.001 vs. autoregulating hearts), and MVo(2), increased 0.41%/mmHg(P < 0.001 vs. autoregulating hearts). MVo, and CW were correlated (r = 0.69, P < 0.0001) independently of autoregulatory capability, but only when autoregulation was poor and capacitance was elevated did CPP significantly affect MVO(2). We conclude that pressure-flow autoregulation protects myocardium from CPP-induced changes in CW, which in turn produces changes in oxygen consumption.