1. From the Autonomic Dysfunction Center, Divisions of Clinical Pharmacology (S.R.R., I.B., D.R.) and Cardiovascular Medicine (B.K.B.), Departments of Medicine, Pharmacology (S.R.R., I.B., D.R.), Neurology (D.R.), and Biomedical Engineering (P.A.H.), Vanderbilt University, Nashville, Tenn.