Effect of Alterations of Coronary Blood Flow on the Oxygen Consumption of the Nonworking Heart

Abstract

The effect of varying CBF and myocardial O 2 delivery on MV O O2 was studied in 23 experiments. In 14 of the experiments an isolated dog heart was perfused, while in the others the heart of a dog, whose systemic circulation was maintained on cardiopulmonary bypass, was studied. The ventricles were kept empty, developed no pressure and performed no external work, while their temperature was held constant. CBF and myocardial O 2 delivery were controlled by pumping blood into the coronary arteries, total coronary venous return was collected from the right side of the heart and MV O O2 , was calculated during a steady state by the Fick principle. Myocardial anoxia was avoided by maintaining the coronary venous O 2 content above 4 vol % and myocardial O 2 extraction below 78%. A comparison of MV O O2 at two levels of CBF (and O 2 delivery) was made in 42 instances, and in 32 of them 11 MV increased substantially as CBF was elevated, or vice versa. The ten exceptions all occurred when O 2 delivery greatly exceeded MV O O2 with O 2 extraction ratios below 35%. The fundamental mechanisms responsible for these findings are not clear, but a number of possible explanations are discussed.

Cerebral Blood Flow in Coarctation of the Aorta

“…We have no evidence on this point. Available data indicate that if the rate of perfusion of blood through the coronary circuit is increased artificially, the myocardial oxygen consumption may be increased (9)(10)(11)(12)(13). The mechanism of this increase in myocardial oxygen consumption dependent upon increased blood flow is not known, and the relation, if any, to the present discussion is not clear.…”

“…Since the cerebral circulation is in the portion of the body where the mean arterial blood pressure is elevated, it appeared worthwhile to study a larger group of subjects to see whether the cerebral vascular resistance adapted itself to this increase in pressure or whether the reported increase in cerebral blood flow (8) was consistent in a larger group. Furthermore, information concerning the relation of the rate of blood perfusion to oxygen consumption is needed for the brain, since it is reported that under certain conditions when coronary blood flow is increased through mechanical means in the isolated or partially isolated preparation, the myocardial oxygen consumption is also increased (9)(10)(11)(12)(13). Hence under certain conditions that are apparently unrelated to hypoxia, coronary blood flow may control myocardial oxygen consumption (9)(10)(11).…”

“…Furthermore, information concerning the relation of the rate of blood perfusion to oxygen consumption is needed for the brain, since it is reported that under certain conditions when coronary blood flow is increased through mechanical means in the isolated or partially isolated preparation, the myocardial oxygen consumption is also increased (9)(10)(11)(12)(13). Hence under certain conditions that are apparently unrelated to hypoxia, coronary blood flow may control myocardial oxygen consumption (9)(10)(11).…”

Effect of Alterations of Coronary Blood Flow the Oxygen Consumption of the Working Heart

“…The methods employed for inducing anesthesia and for instituting cardiopulmonary bypass have been described. 1 The experimental dogs weighed between 13.6 and 20.5 kg, and averaged 16.5 kg. Both vagus nerves were sectioned in the neck.…”

“…• The finding that the oxygen consumption of the empty, nonworking heart could be influenced by the rate of coronary blood flow 1 was at variance with the concept that myocardial oxygen consumption is determined primarily by the mechanical activity of the heart. 2 " 5 Furthermore, the results of these studies in the nonworking heart were not in accord with the preliminary results of experiments in the isolated supported heart made available to us by Dr. S. J. Sarnoff.…”