Effects of Midodrine and Droxidopa on Splanchnic Capacitance in Autonomic Failure

Inclusion Criteria:

* Male and female subjects, age 40-80 years with possible or probable Multiple System Atrophy, Pure Autonomic Failure, or Parkinson disease, as defined by Consensus Criteria.
* Neurogenic orthostatic hypotension defined as a ≥30-mmHg decrease in systolic blood pressure within 3 minutes of standing associated with impaired autonomic reflexes determined by autonomic testing in the absence of other identifiable causes.
* Subjects able and willing to provide informed consent.

Exclusion Criteria:

* Supine hypertension, defined as systolic blood pressure of ≥ 160 mmHg measured on two separate occasions.
* Pregnancy.
* Systemic illnesses known to produce autonomic neuropathy, including but not limited to diabetes mellitus, amyloidosis, monoclonal gammopathies, and autoimmune neuropathies.
* History of known aortic aneurisms, thoracic, abdominal or pelvic surgery in the past 6 months.
* Symptomatic abdominal or inguinal hernias.
* Severe gastroesophageal reflux.
* Recent fractures or fissures of ribs, thoracic or lumbar spine.
* Medical devices implanted on the abdominal wall or abdomen that would interfere with the abdominal compression.
* Intolerance to any increase in intraabdominal pressure.
* 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.