SYSTOLIC CORONARY FLOW REDUCTION IN THE CANINE HEART IN-SITU - EFFECTS OF LEFT-VENTRICULAR PRESSURE AND ELASTANCE

In the externally perfused coronary bed of the isolated heart, LV elas tance (E(lv)) rather than LV pressure (P-lv) appears to be the major f actor responsible for systolic coronary flow reduction, although effec ts of both have been demonstrated. However, normal perfusion in the pr esence of intact autoregulation in the heart in situ may modify these effects. To investigate the systolic coronary flow (Q(syst)) responses to changes in end-systolic E(lv) and in systolic P-lv in the intact c oronary bed, we studied 7 anesthetized dogs. Dogs were vagotomized, pa ced and instrumented with Doppler flow probes. E(lv), obtained from mi cromanometer- and conductance-catheters, was changed by dobutamine inf usion (10 mu g/kg/min) and characterized by its slope (E(es)) and volu me position at 15 kPa (V-15). P-lv was changed stepwise by volume load ing. Correction for metabolism induced changes in Q(mean) was made. Th us, we found that dobutamine increased E(es) by 44 % (p < 0.0001), dec reased V-15 by 43 % (p < 0.0001), and reduced corrected Q(syst) signif icantly (p < 0.001) from 22.8 to 13.8 ml/min, while P-lv (9.5 - 19.5 k Pa) did not affect corrected Q(syst) (p > 0.5). We conclude that systo lic coronary flow reduction is related to both elastance parameters, E (es) and V-15, and not to P-lv in the normally perfused canine heart i n situ.