Differential effects of halothane and enflurane on end-systolic pressure-diameter relationship in anesthetized, mechanically ventilated dogs.

To clarify the difference of negative inotropic effects, we evaluated the effects of 0, 0.5, and 1 MAC halothane and enflurane on systolic performance in anesthetized, mechanically ventilated, vagotomized dogs. Left ventricular myocardial contractility was assessed by the slope of the end-systolic pressure-diameter relationship (EES), which have been reported to be independent of alterations in preload and afterload but sensitive to changes in myocardial contractility. Both anesthetics decreased heart rate and dose-dependently decreased left ventricular systolic pressure. Enflurane decreased heart rate and left ventricular systolic pressure more than an equivalent MAC of halothane. Both anesthetics increased left ventricular end-diastolic diameter without any change in % shortening of the left ventricular internal diameter. TheEES was decreased to a similar extent at both 0.5 and 1 MAC halothane. TheEES was decreased with increasing concentrations of enflurane. TheEES was significantly larger (P<0.05) with 1 MAC of halothane than with 1 MAC enflurane. These results suggest that halothane preserves myocardial contractility better than enflurane in the presence of fentanyl.