1. From the Departments of Neurology (A.A.A., L.D.M., M.M.W.) and Anesthesiology and Critical Care Medicine (A.A.A., P.D.H.), Johns Hopkins Medical Institutions, Baltimore, Md; National Institutes of Health (K.S.K.), Bethesda, Md; and Department of Physiology (D.H.M.), Medical College of Wisconsin, Milwaukee.