The dynamics of subendocardial flow during cardiopulmonary bypass

Subendocardial flow was measured as a temperature differential between the epicardium and the subendocardium during cardiopulmonary bypass by a measured bolus of cold blood of known temperature injected into the aortic root. The probes, with 0.1 second time response, were accurately placed in the subendocardium and the subepicardium, equidistant from the nearest coronary vessel. The least change recorded was 0.015° C. Direct-current operational amplifier offset the basal temperature, which was measured by a separate probe and maintained constant by small variations from the heat exchanger. Subendocardial and subepicardial flows were recorded in 20 dogs at constant aortic root pressures in the empty, beating and the empty, fibrillating heart. The effects of varying the aortic root pressures on the subendocardial and subepicardial flow ratios were studied in the empty, beating and empty, fibrillating heart. At all pressures studied, the endocardial-epicardial ratio was significantly lower for the empty, fibrillating than for the empty, beating heart (p