Transmural variation in autoregulation of right ventricular blood flow

We examined transmurally the right coronary autoregulatory flow response to varied perfusion pressures in 11 anesthetized, open-chest dogs. Right coronary artery flow was measured electromagnetically, and its transmural distribution was defined with 15-micron radioactive microspheres. Heart rate, mean aortic blood pressure, right ventricular systolic pressure, end-diastolic pressure, and dP/dtmax were constant. At 100 mm Hg, subepicardial flow averaged 0.48 +/- 0.04 ml/min/g, and subendocardial flow averaged 0.56 +/- 0.05 ml/min/g. In contrast to the left coronary circulation, right coronary hypotension did not cause preferential subendocardial ischemia. As right coronary perfusion pressure was decreased from 100 to 40 mm Hg in five dogs, subepicardial and subendocardial flows were reduced similarly by 35-36%. As right coronary perfusion pressure was elevated from 100 to 150 mm Hg in six dogs, right ventricular subepicardial blood flow increased by 31%, whereas subendocardial blood flow increased by 70%. Right ventricular subendocardial-to-subepicardial flow ratios averaged 1.15-1.20 for perfusion pressures of 40 to 120 mm Hg, and they increased to 1.36 +/- 0.05 at 150 mm Hg. Right coronary artery autoregulatory closed-loop gain averaged 0.47 +/- 0.06 between 70 and 100 mm Hg and was greater than zero from 40 to 120 mm Hg. Between 120 and 150 mm Hg, gain fell to -0.15 +/- 0.10. Regional gain varied from 0.59 +/- 0.10 to 0.44 +/- 0.08 in subepicardium as pressure was decreased from 100 to 40 mm Hg. Subendocardial gains were similar to subepicardial gains over this pressure range.(ABSTRACT TRUNCATED AT 250 WORDS)