Anesthesiology
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The effects of 1.5, 2.0, and 2.5 MAC halothane (N = 8) and isoflurane (N = 6) upon systolic performance and isovolumic relaxation were evaluated in open chest dogs. Left ventricular internal volume was determined using piezoelectric crystals. Left ventricular end-systolic pressure-volume points were determined for a series of normal sinus beats during transient venae caval occlusions. ⋯ There were no differences in T or its load-dependency between drug groups. These results indicate that both anesthetics evoke load-independent negative inotropic effects. Systolic ejection fraction is maintained during isoflurane anesthesia by decreased systemic vascular resistance and less pronounced negative inotropic effects than equivalent MAC halothane.(ABSTRACT TRUNCATED AT 250 WORDS)