Graded Coronary Pressure Reduction in Conscious Dogs

The purpose of the present study was to examine subendocardial flow and function during graded coronary pressure reduction to determine the effect of tachycardia on the lower autoregulatory pressure limit (critical coronary pressure) in unanesthetized dogs. During atrial pacing at a rate of 200 beats/min, subendocardial flow measured by radioactive microspheres averaged 1.55±0.34 ml/min/g and remained unchanged as pressure was reduced over the autoregulatory plateau from 84±10 to 59±t 7 mm Hg. Further reductions in coronary pressure to below a critical coronary pressure of -60 mm Hg were associated with concomitant reductions in subendocardial flow and the endocardial-epicardial flow ratio during tachycardia. Although regional function remained constant over the autoregulatory plateau, there was