ALTERATIONS IN MECHANICAL PROPERTIES OF HEART MUSCLE PRODUCED BY HALOTHANE

¹ Department of Anesthesiology, Boston University School of Medicine, Boston, Massachusetts

In isolated rat left ventricular trabeculae carneae muscle preparations, halothane lowered V _max and P₀ of the force-velocity relation with no reductions in the constants a or b. Work, power and developed tension were depressed, but resting tension was not consistently affected. The extensibility of series elasticity tended to be increased. The extent of shortening of unloaded muscle and the instantaneous contractile element velocity during the latter half of the period of rising developed tension were not altered. It is concluded that, although halothane directly depresses heart muscle performance, its effects on the contractile element per se may be indirect rather than direct.