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The authors studied the effects of sevoflurane and isoflurane on systemic hemodynamics and regional blood flow distribution (microsphere technique) in 15 rats during general anesthesia with intravenous chloralose and controlled ventilation. Inhaled anesthetics were applied to reduce mean arterial blood pressure (MAP) to 70 mm Hg (1.66 vol% sevoflurane and 0.96 vol% isoflurane) and 50 mm Hg (MAP 50; 3.95 vol% sevoflurane and 2.43 vol% isoflurane). Control recordings were obtained with intravenous chloralose only. At a MAP of 70 mm Hg, both anesthetics reduced heart rate, cardiac output, and systemic vascular resistance to a similar degree. Isoflurane decreased systemic vascular resistance markedly at a MAP of 50 mm Hg and thereby maintained cardiac output at higher levels than sevoflurane. The left ventricular rate-pressure product decreased comparably with both anesthetics. Cerebral blood flow increased dose-dependently with both inhaled anesthetics but to a greater degree with isoflurane. Total hepatic blood flow remained unchanged from control at a MAP of 70 mm Hg but decreased at a MAP of 50 mm Hg. This was due to reductions of hepatic arterial and portal venous tributaries. Renal blood flow was reduced with only the high concentrations of the anesthetics. Myocardial blood flow was reduced at all concentrations of volatile anesthetic; however, the decrease was less with isoflurane. This would indicate a more pronounced coronary vasodilation by isoflurane as the rate-pressure product, as a measure of the actual left ventricular oxygen demand, decreased by comparable degrees with both anesthetics. Our results indicate that sevoflurane and isoflurane (each approximately 0.7 MAC) have no dissimilar systemic and regional hemodynamic effects at a MAP of 70 mm Hg in this animal model. At higher concentrations (approximately 1.7 MAC), cerebral blood flow was more with isoflurane than with sevoflurane and was associated with a more pronounced vasodilation in the myocardium.