The Effect of Ēthrane on Cardiac Muscle Mechanics

The inotropic effect of Ēthrane on the intrinsic contractile stale of the cat papillary heart muscle was studied in terms of mechanics of contraction. Negative inotropic responses to Ēthrane were compared with those of methoxyflurane and halothane. Ēthrane caused dose-dependent decreases in maximal velocity (Vmax), peak force (Fm), power, and work during isotonic contraction, and was less depressant than halothane and methoxyflurane. A greater concentration of Ēthranc (11 mg/100 ml) was required to produce the same degree of depression (50 per cent) in myocardial power as either methoxyflurane (4 mg/100 ml) or halothane (3 mg/100 ml). Similarly, a 50 per cent reduction in Vmax required a higher concentration of Ēthrane (233 per cent more than halothane and 18 per cent more than methoxyflurane). Therefore, Ēthrane was less depressant to myocardial contractility than methoxyflurane or halothane. Probable mechanisms and significance of the change in the active state resulting from anesthetics are discussed.