Effects of Halothane on Isometric Contractions of Isolated Heart Muscle

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Abstract
In isometric contractions of an isolated heart muscle preparation exposed to halothane (0.10, 0.40, 0.85, 1.65 and 2.35 volumes%), peak developed tension and maximum rate of tension development were reduced as much as 53% and 57%, respectively, in direct proportion to the concentration of the anesthetic. Time to peak tension and total twitch duration, were not decreased more than 6.3% by any concentration of halothane. Resting tension was affected only by the highest concentration, 2.35 volumes%, which lowered it 6.8%. Relaxation time and muscle length were not altered. Recovery from the effect of halothane was essentially complete in each instance. The results are consistent with the concept that halothane exerts its cardiac effects primarily by a direct reduction in active state intensity of heart muscle.