Coronary blood flow autoregulation and flow heterogeneity in the stunned heart

We used an anesthetized swine model of regionally "stunned" myocardium to determine the effect of stunning on coronary autoregulation and blood flow heterogeneity. In 18 domestic swine, stunning was accomplished by reducing blood flow to the left anterior descending coronary artery (LAD) by approximately 75% of baseline for 15 min and restoring it to normal for 1 hour. We quantified coronary autoregulation using both the slope of coronary pressure-flow curves and an autoregulation index. We quantified blood flow heterogeneity using radioactive microspheres to determine the variability in flow (dispersion index) among forty 200 mg segments of myocardium from the center of the stunned, LAD-perfused left ventricle. Before and after stunning, we measured autoregulation, myocardial blood flow and flow heterogeneity, as well as hemodynamic indices of myocardial oxygen demand. Fifteen min of ischemia and 1 hour of reperfusion produced both a 46% reduction in mechanical function, and a 7% drop in systemic arterial pressure, but not change in heart rate or rate pressure product. Myocardial oxygen consumption was 15% reduced and myocardial blood flow 16% reduced in the stunned myocardium when measured at one hour of reperfusion. Fifteen min after reperfusion, the slope of the coronary pressure flow plots and the coronary venous oxygenation were increased whereas the autoregulation index decreased. These findings all indicate reduced autoregulation during early reperfusion. However, after one hour of reperfusion, the slope of the coronary pressure-flow relation (0.41 +/- 0.19 vs. 0.48 +/- 0.26 ml.100 g-1.min-1.mmHg-1) and the autoregulation index (0.43 +/- 0.16 vs. 0.30 +/- 0.32) were unchanged from control measurements (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)