1. From the Departments of Anesthesiology (Z.-D.G., S.Q., X.B., D.C.W., J.R.K., Z.J.B.) and Physiology (Y.L., Z.J.B., M.L.), Medical College of Wisconsin, Milwaukee, Wisconsin. Current affiliation: Department of Ophthalmology, Stanford University School of Medicine, Stanford, California (Z.-D.G.).