Comparative effects of halothane, enflurane, and isoflurane at equipotent anesthetic concentrations on isolated ventricular myocardium of the ferret. I. Contractility.

Abstract

The effects of halothane, enflurane, and isoflurane on myocardial contractility were compared in papillary muscles of the right ventricle of adult male ferrets at 30 degrees C. Isotonic and isometric variables of contractility were measured before, during, and after exposure to incremental concentrations of halothane (n = 9 muscles), enflurane (n = 9 muscles), and isoflurane (n = 9 muscles), in steps of 0.25 MAC up to 1.5 MAC of halothane and of enflurane, and up to 2.0 MAC of isoflurane. Each of the three anesthetics caused a dose-dependent reversible decrease in contractility. The onset of maximal myofibrillar activation was delayed in a dose-dependent manner, and time to peak shortening of the isotonic preloaded twitch was unchanged, except for a slight decrease at greater than 1 MAC of enflurane. Isoflurane's negative inotropic effects were clearly less than those of either halothane or enflurane. Comparison of the time course of contraction and relaxation in both isometric and isotonic twitches suggests that, in addition to effects on intracellular calcium availability, these anesthetics decrease the myofibrillar responsiveness to calcium and/or the calcium sensitivity of the contractile proteins.