1. From the Departments of Anesthesia and Perioperative Care (A.X.H., J.P.B., A.S.A., W.L.Y.), the Center for Cerebrovascular Research (A.X.H., J.P.B., A.S.A., W.L.Y.), the Departments of Neurology (S.C.J., V.S., W.L.Y.), Epidemiology and Biostatistics (S.C.J., C.E.M.), and Neurological Surgery (W.L.Y.), University of California, San Francisco, Calif.; and the Division of Research (S.S.), Kaiser Permanente Medical Care Program, Oakland, Calif.