1 Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tenn; Autonomic Dysfunction Center, Vanderbilt University Medical Center, Nashville, Tenn.
2 Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tenn.
3 Division of Allergy, Pulmonary, and Critical Care Medicine, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tenn.
4 Department of Neurology, Vanderbilt University Medical Center, Nashville, Tenn.
5 Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tenn; Autonomic Dysfunction Center, Vanderbilt University Medical Center, Nashville, Tenn. Electronic address: italo.biaggioni@vanderbilt.edu.