Myocardial oxygen consumption and regulation of coronary blood flow during stepped relief of the left ventricle.

In 25 calves an atrio-ventriculo-aortic bypass was performed and the metabolism and the regulation of coronary blood flow during stepped assistance of the left ventricle was studied. With mean aortic blood pressure kept constant stepped decrease in left ventricular pressure from 120 to 0 mmHg diminished myocardial oxygen consumption from 7.7 to 1.9 ml O2/min X 100 g. Increasing right ventricular pressure by banding the pulmonary artery with left ventricular pressure and mean aortic pressure kept constant the oxygen uptake of the left ventricle increased about 20.7 +/- 32.% when measured by Fick's principle but remained unchanged when calculated from hemodynamic parameters of the left ventricle (-1.5 +/- 3.5%). At constant coronary perfusion pressure coronary blood flow decreased when left ventricular pressure was reduced from 120 to 100 mmHg. Further decrease in left ventricular pressure to 0 mmHg showed no effect on coronary blood flow. Increasing heart rate from 152 +/- 9 to 208 +/- 8 b.p.m. enhanced myocardial oxygen uptake of the assisted heart about 59.0 +/- 11.4% while resistance to flow decreased about 40.4 +/- 2.8%. These results show that the metabolic regulation of coronary blood flow is still acting even in the assisted left heart.