1 Hospital Padre Hurtado, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago de Chile, Chile.
2 Departamento de Neurologia, Pontificia Universidad Catolica de Chile, Santiago de Chile, Chile.
3 The Vanderbilt Autonomic Dysfunction Center and Division of Clinical Pharmacology, Departments of Medicine and Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.