Effect of halothane, enflurane and isoflurane on the end-systolic pressure-length relationship

Myocardial contractility was measured using the end-systolic pressure-length (ESPL) relationship in dogs subjected to increasing concentrations of halothane (0.5-2 per cent), enflurane (0.77-2.6 per cent) or isoflurane (0.70-2.13 per cent), combined with an infusion 7 micrograms X kg-1 X min-1 of fentanyl, after induction of anaesthesia with 15 mg X kg-1 thiopentone. The relationship between the concentrations of the different drugs and contractility (ESPL) can best be described by ESPL = a + b/(MAC fraction) where "a" is a constant and "b" is the slope of the curve relating ESPL to MAC. At 1.0 MAC values, the ESPL for halothane (69.04 +/- 25.83 mmHg X mm-1) did not differ from that of isoflurane (63.19 +/- 17.36 mmHg X mm-1). However, the myocardial contractility during 1.0 MAC halothane and isoflurane anaesthesia was better preserved than that of enflurane (38.66 +/- 9.73 mmHg X mm-1: p less than 0.01, p less than 0.05 respectively).