THE EFFECT OF ANESTHETICS ON CARDIO-VASCULAR INTERACTION

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We compared the effects of two volatile anesthetics, halothane and isoflurane, on ventriculo-arterial coupling using an index of Ea/Ees. Ea and Ees represent arterial effective elastance and left ventricular end-systolic elastance, and are used as indices of cardiac afterload and cardiac contractility, respectively. Halothane 2MAC significantly decreased the cardiac output, Ea, and Ees by 35%, 18%, and 39%, respectively. Isoflurane 2MAC significantly decreased the cardiac output, Ea, and Ees by 37%, 38%, and 43%, respectively. Halothane increased Ea/Ees from 0.83 to 1.22, whereas isoflurane maintained the Ees/Es at a constant level. These results suggest that mechanical efficiency is well maintained during isoflurane anesthesia because it has an equivalent effect on left ventricular contractility and arterial properties, whereas halothane can impair mechanical efficiency by depressing left ventricular contractility more than the arterial system.Our results also suggest that al-adrenoceptor stimulation is capable of reversing direct cardiac depressant effects of halothane, and that al-adrenoceptor stimulation may also be accompanied by a possible impairment of the oxygen supply-demand balance during halothane anesthesia.