Myocardial blood flow and oxygen consumption after aortic cross-clamping

Abstract

The effect of four repetitive periods of 10 min global ischemia, followed by 15 min of reperfusion on myocardial blood flow and oxygen consumption at 34°C (group N) and 25°C (group H) were studied in comparison with that of 60 min continuous ischemia combined with multidose St. Thomas Cardioplegia (group C) in dogs on cardiopulmonary bypass (CPB). Two groups, in which a protocol comparable to the groups N and H, respectively, but without repetitive periods of ischemia was followed, served as control. In all groups a hyperemic response was observed after release of aortic cross-clamping (AC). Myocardial blood flow was not diminished at the end of CPB as compared to the values at the start of CPB. We conclude that the no-reflow phenomenon did not occur after these procedures of intermittent or continuous AC. Immediately following release of AC the arterial-coronary sinus difference of oxygen content reached a peak value in groups N and H indicating rapid replenishment of the low tissue oxygen content. These peak values appeared to be much smaller after cardioplegia. After 10 min of reperfusion a significant lower oxygen consumption was observed at 25°C (0.2 μmole·g −1·min −1 O 2) as compared to 34°C (1.5 μmole· g −1·min −1 O 2). This difference cannot be explained by temperature alone because oxygen consumption did not decrease below 0.5 μmole·g −1·min −1 in the control group of dogs put on CPB at 25°C. Based on the findings of myocardial blood flow and oxygen consumption the conclusion is drawn that the heart tolerates well the periods of ischemia and reperfusion, as used in the present protocols mimicking the procedures routinely applied during aorta-coronary bypass surgery.