Response of the intact canine left ventricle to increased afterload and increased coronary perfusion pressure in the presence of coronary flow autoregulation

Background-Increased left ventricular (LV) contractile force or oxygen cons umption has been documented with increased coronary arterial pressure (CAP) and flow (Gregg phenomenon). We investigated whether the increase in contr actile force with increased LV afterload might be mediated by the concomita nt increase in CAP when coronary autoregulation is intact. Methods and Results-The LV of 6 autonomically blocked open-chest dogs was p erfused through the left main coronary artery by a cannula with a side gate to the aortic root. With the gate open, CAP increased from 77+/-20 to 93+/ -20 mm I-Ig (P<0.05) with aortic constriction (AC). With the gate closed, C AP was maintained at a constant level of 100 mmHg. A small reduction in the slope of the preload recruitable stroke work (PRSW) relationship was obser ved with AC, but this response was not altered by the coronary perfusion ga te position. The end-systolic pressure-volume (ESPV) relationship shifted u pward significantly with AC (P<0.001), but this shift was not greater with open-gate perfusion than with closed-gate perfusion. Furthermore, with coro nary autoregulation intact, wide changes in CAP (between 60 and 180 mm Hg, n=5) did not alter either the PRSW or ESPV relationship. In contrast, when autoregulation was abolished with intracoronary adenosine (n=6), both index es of contractility increased progressively with increased CAP. Conclusions The concomitant increase in CAP with increased afterload in the intact canine LV does not contribute to the afterload-induced increase in contractile force. Coronary perfusion pressure per se does not influence LV contractile function. Coronary perfusion pressure influences contractility only when coronary flow changes.