Hideki Tani

Autoregulation by the right coronary artery in dogs with open chests; comparison with the left coronary artery

Experiments were conducted to study autoregulatory responses of the right and left coronary arteries in dogs with open chests. The right and left circumflex coronary artery were cannulated and perfused with blood from the femoral artery via a pressurized reservoir. The perfusion pressure was varied in steps over a wide range and coronary blood flow rates were measured. Both the right and left coronary arteries exhibited autoregulation but the pressure at the lower end of the autoregulatory range was lower in the right (39.8±9.1 mm Hg) than in the left circumflex coronary artery (57.6±14.5 mm Hg). The slope of the pressure-flow relationship in the autoregulatory range was less steep in the right than the left circumflex coronary artery. The closed-loop gain when the perfusion pressure was less than 100 mm Hg was greater in the right than in the left circumflex coronary artery. Increases in the right ventricular afterload produced by pulmonary artery constriction decreased the closed-loop gain, shifted the autoregulatory range upward and to the right, and made the slope steeper. These results indicate that more effective autoregulation is carried out by the right than the left circumflex coronary artery.

Reactive hyperaemic flow characteristics of the right coronary artery compared to the left anterior descending coronary artery in the open-chest dog

Reactive hyperaemia, the cardiovascular response to transient occlusion of a vessel, was examined and compared in the right coronary artery (RCA) and the left anterior descending coronary artery (LAD) in the same heart of an open-chest dog. First, to study the relationship between reactive hyperaemia and occlusion time in the RCA and LAD, respective flows were measured and reactive hyperaemia was induced with different occlusion times. Occlusion time required for half the maximum peak percentage reactive hyperaemic flow (%PRH), t1/2, for the RCA was approximately twice that of the LAD: 11.4±2.3 s versus 5.9±1.4 s. Maximum %PRH of the RCA was significantly greater than that of the LAD while the percentage repayment of the RCA was lower than that of the LAD. Augmentation of right ventricular oxygen consumption shortened t1/2 and increased percentage repayment significantly. Second, to determine “critical pressure”, which was defined as the perfusion pressure below which reactive hyperaemia was abolished completely, the RCA and LAD were perfused through a shunt from the carotid artery, perfusion pressure was varied in the range of 100 to 20 mmHg and reactive hyperaemia was induced. Critical pressure in the RCA was significantly lower than in the LAD: 32.2±5.7 mmHg versus 41.5±5.0 mmHg. These results suggest that the RCA has a greater flow reserve than the LAD. These results were consistent with the difference of oxygen metabolism between the right and left ventricles. The difference of oxygen metabolism between the two ventricles would, at least partly, account for these results.