Studies of the effects of hypothermia on regional myocardial blood flow and metabolism during cardiopulmonary bypass. I. The adequately perfused beating, fibrillating, and arrested heart.

The effects of hypothermia (32 degrees, 28 degrees, and 22 degrees C.) on left ventricular flow distribution (microspheres) and oxygen uptake in adequately perfused, beating, empty, fibrillating, and arrested hearts were studied. Minute left ventricular oxygen uptake fell progressively as myocardial temperature was reduced under all conditions. In beating hearts, however, left ventricular oxygen uptake per beat increased significantly due to the inotropic effect of hypothermia and diastolic compliance fell. Cold fibrillating hearts consumed slightly less oxygen per minute than beating hearts at comparable temperatures as fibrillation became less forceful with hypothermia. Myocardial wall tension, however, was always higher in fibrillating than beating hearts at each level of hypothermia. The lowest myocardial oxygen requirements were always found in arrested hearts (70 to 80 per cent less than either beating empty or fibrillating hearts) at any myocardial temperature. Left ventricular coronary flow remained distributed evenly across the beating heart at all myocardial temperatures and in fibrillating hearts at 28 degrees, and 22 degrees C. Left ventricular flow became redistributed toward the subendocardium in fibrillating hearts at 37 degreegs and 32 degrees C. and in arrested hearts at all myocardial temperatures.