Hemodynamic Mechanisms of Abdominal Compression in the Treatment of Orthostatic Hypotension in Autonomic Failure

Inclusion Criteria: * Male and female patients, * between 18-80 yrs., * with neurogenic orthostatic hypotension associated with primary autonomic failure (Parkinson Disease, Multiple System Atrophy and Pure Autonomic Failure). Orthostatic hypotension will be defined as ≥20 mmHg decrease in systolic BP or ≥10 mmHg of diastolic BP within 3 minutes on standing associated with impaired autonomic reflexes determined by autonomic testing in the absence of other identifiable causes (Freeman et al., 2011). * Patients able and willing to provide informed consent. Exclusion Criteria: * Pregnancy. * Significant cardiac, renal or hepatic illness, or with contraindications to administration of pressor agents or external abdominal compression will be excluded. * Clinically unstable coronary artery disease, or major cardiovascular or neurological event in the past 6 months, and; other factors which in the investigator's opinion would prevent the subject from completing the protocol including clinically significant abnormalities in clinical, mental or laboratory testing