Effect of Midodrine vs Abdominal Compression on Cardiovascular Risk Markers in Autonomic Failure Patients

The study includes up to 5 days spent in the Vanderbilt University Medical Center, at least one day of screening tests, followed by 2 study days. Screening tests include a physical examination and history, routine safety laboratory assessments, and testing of the autonomic nervous system. Medications affecting blood pressure and the autonomic nervous system such as pressor medications will be withdrawn for at least 5 half-lives before studies, except for fludrocortisone. Other medications will be held constant throughout the study. Eligible participants will then be studied on two separate days in random order: one day with midodrine combined with sham abdominal compression, and one day with abdominal compression combined with a placebo pill. On each study day, participants will be instrumented to measure blood pressure, heart rate, hemodynamic parameters, segmental impedance, and markers of cardiovascular risk. A baseline tilt table test will be performed to obtain supine and upright baseline measurements, including the assessment of orthostatic symptoms. Participants will then receive a single oral dose of placebo or midodrine, and a deflated binder will be placed around the abdomen. Thirty to sixty minutes later, a second tilt table test will be done with sham or active abdominal compression. Outcome measurements will be repeated in the supine and upright positions. At the end of the second tilt table test, the investigators may also assess splanchnic venous capacitance.