744-4 Evidence for Downward-Shift of Coronary Pressure-Flow Relationship Following a Brief Period of Ischemia in Dogs

This study was undertaken to test whether a brief period of ischemia affects the coronary pressure-flow relationship during reduction of coronary perfusion pressure (CPP). The left anterior descending coronary artery was cannulated and perfused with blood from the left carotid artery in 40 open-chest dogs. Coronary blood flow (CBF) was measured during intracoronary administrations of papaverine and adenosine. Coronary pressure-flow relationship was assessed during transient reduction of CPP from 100 to 30 mmHg with 10 mmHg intervals. Coronary hyperemic flow due to adenosine and papaverine was attenuated at 30 min of reperfusion following 10 and 15 min of ischemia. In the group of transient 10 min ischemia, both fractional shortening (FS) and CBF returned to the pre-ischemic values at 30 and 60 min of reperfusion, however, marked decreases in CBF (35 ± 5 vs 56 ± 4 ml/100 g/ml at CPP = 60 mmHg, p l 0.01) during graded reductions in CPP were observed. Furthermore, both FS (6 ± 1 vs 14 ± 1% at CPP = 60 mmHg. p l 001) and lactate extraction ratio (–41 ± 15 vs 1 ± 6% at CPP = 60 mmHg, p l 0.05) were decreased. The endocardial vs. epicardial flow ratio was reduced relative to the control condition. The downward-shift of the coronary perfusion pressure-flow relationship and the deterioration of myocardial contractile and metabolic function during reduction of CPP were restored at 60 min of reperfusion. In contrast, in the group of transient 15 min ischemia, although both baseline FS and coronary hyperemic flow due to adenosine and papaverine remained to be at 30 and 60 min of reperfusion, the coronary perfusion pressure-flow relationship was not shifted. Conclusion Transient brief period of ischemia can reversibly affect the coronary pressure-flow relationship due to the reduced capability of vascular relaxation, however, the downward-shift of coronary pressure-flow relationship can be blunted by the reduced myocardial contractile force against the coronary resistance vessels.