Persistent right coronary flow reserve at low perfusion pressure

To determine whether right coronary (RC) flow reserve persists at perfusion pressures below the apparent autoregulatory range, the RC artery of 18 anesthetized dogs was cannulated and perfused at controlled pressures. RC blood flow (RCBF) fell from 65.3 +/- 6.1 to 33.7 +/- 2.3 ml.min-1.100 g-1 as RC perfusion pressure (RCPP) was reduced from 80 to 40 mmHg. At 40 mmHg, intracoronary adenosine increased RCBF by 97.9 +/- 10.6 ml.min-1.100 g-1 (P less than 0.001). RCBF fell to 9.5 +/- 1.7 ml.min-1.100 g-1 at 20 mmHg, and RCBF did not significantly increase during adenosine, although RC vasodilation was observed in four dogs. Regional right ventricular (RV) blood flows at RCPP of 80 and 40 mmHg were measured by radioactive microsphere technique. Before adenosine infusion, RCBF was distributed uniformly across the RV free wall at normal and low perfusion pressures. During adenosine infusion, blood flow in both regions increased significantly, but the flow reserve was greater in the subendocardial region at both normal and reduced pressures. RV myocardial O2 consumption (MVo2) was decreased significantly at 40 mmHg, however, there was no evidence of ischemia at this pressure, since the RV lactate extraction ratio was normal (n = 8). Thus RV O2 demand fell when RC O2 supply was reduced, although a flow reserve was available. RV MVo2 was restored to normal when right coronary flow reserve was mobilized by adenosine infusion. For RCBF from 65 to 365 ml.min-1.100 g-1, RC venous O2 content rose and RV MVo2 was essentially constant.(ABSTRACT TRUNCATED AT 250 WORDS)