1. From the Departments of Anesthesiology (A.P., X.G., C.Z.), Surgery (A.P., X.G., C.Z.), and Physiology (A.P., X.G., S.B., B.J.P., M.F., W.M.C., C.Z.), Louisiana State University Health Sciences Center, New Orleans. Current address for C.Z.: Veterinary Physiology & Pharmacology, Texas A&M University, College Station.