Norepinephrine Infusion for Orthostatic Hypertension

Background: - Orthostatic hypotension is a fall in blood pressure when standing up. Normally, a reflex action of the automatic nervous system makes blood vessels tighten when people stand up. The nervous system releases the chemical norepinephrine, which tightens blood vessels and keeps blood pressure in check. In orthostatic hypotension, the nervous system does not release enough norepinephrine when a person stands up, which can cause fainting or falling. Researchers are interested in determining whether norepinephrine given as a drug by vein can help maintain blood pressure during changes in body position. Objectives: - To determine whether intravenous norepinephrine can maintain blood pressure in people with orthostatic hypotension. Eligibility: - Individuals at least 18 years of age who have been diagnosed with orthostatic hypotension related to Parkinson's disease or pure autonomic failure. Design: * This study will require a 2-day inpatient admission to the NIH Clinical Center. The first day will involve laboratory evaluation and the second day will involve testing with norepinephrine. The second day requires an overnight stay. * Participants will be screened with a medical history and physical examination, blood samples, and an electrocardiogram or echocardiogram. * Participants who are on medications may be asked to taper or discontinue one or more medications for the purposes of this study. Participants may not take aspirin or any drugs that slow blood clotting for 7 days before study participation. * Day 1: Participants will have a clear liquid breakfast, and will have a 1-hour baseline tilt table test to monitor blood flow, skin temperature, sweating, and blood pressure. Body temperature and breathing will also be monitored. * Day 2: Participants will have a clear liquid breakfast, and will have a 2-hour tilt table test. Initial blood pressure readings will be taken, and an intravenous line will be placed. Participants will then receive norepinephrine or saline, followed by additional position changes of the tilt table to measure blood pressure differences before returning to the starting position. After about 10 minutes, the tilt table testing and infusion will be repeated with the other drug (saline or norepinephrine). * Participants will be discharged 24 hours after the testing is complete.