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 elastance (Elv) rather than LV pressure (Plv) appears to be the major factor responsible for systolic coronary flow reduction, although effects of both have been demonstrated. However, normal perfusion in the presence of intact autoregulation in the heart in situ may modify these effects. To investigate the systolic coronary flow (Qsyst) responses to changes in end-systolic Elv and in systolic Plv in the intact coronary bed, we studied 7 anesthetized dogs. Dogs were vagotomized, paced and instrumented with Doppler flow probes. Elv, obtained from micromanometer- and conductance-catheters, was changed by dobutamine infusion (10 micrograms/kg/min) and characterized by its slope (Ees) and volume position at 15 kPa (V15). Plv was changed stepwise by volume loading. Correction for metabolism induced changes in Qmean was made. Thus, we found that dobutamine increased Ees by 44% (p < 0.0001), decreased V15 by 43% (p < 0.0001), and reduced corrected Qsyst significantly (p < 0.001) from 22.8 to 13.8 ml/min, while Plv (9.5-19.5 kPa) did not affect corrected Qsyst (p > 0.5). We conclude that systolic coronary flow reduction is related to both elastance parameters, Ees and V15, and not to Plv in the normally perfused canine heart in situ.