Reduced oxygen and blood flow demands in the chronically sympathectomized heart

Using an anesthetized, open-chest preparation, seven 3-week sympathectomized (CS) and eight 3-week sham operated (SO) dog hearts were studied. Circumflex blood flow per 100-g heart (CBF), left ventricular oxygen extraction [(a-v)O2], maximal dP/dt, and tension-time index (TTI) were measured at constant heart rate while aortic pressure (AoP) was changed by aortic constriction or hemorrhage. Left ventricular myocardial oxygen consumption (MVO2) was calculated from (a-v)O2 and CBF. The MVO2, CBF, (a-v)O2, and maximal dP/dt were related to TTI at each level of AoP by regression analyses. Over a wide range of TTI, MVO2 and CBF in CS were only about 50% of those in SO; (a-v)O2 was not different between the groups. These data indicate that the chronically sympathectomized heart operates at reduced oxygen and blood flow demands. Also, since (a-v)O2 and the regression of CBF on MVO2 were not different between the two groups, the data suggest that the reduced CBF in CS was secondary to a metabolic vasocontriction resulting from the reduced MVO2. Analyses of maximal dP/dt did not indicate that the reduced MVO2 in CS was as a result of reduced contractility.