Use of Accelerometer for Quantification of Neurogenic Orthostatic Hypotension Symptoms

Inclusion Criteria: * Male and female subjects, age 40-80 years. * Possible or probable Multiple Systems Atrophy, Pure Autonomic Failure, or Parkinson's disease with neurogenic orthostatic hypotension. * 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. * Patients on treatment for neurogenic orthostatic hypotension with either midodrine or atomoxetine, who have experienced some improvement in their orthostatic symptoms, but still remain symptomatic (Orthostatic hypotension symptom assessment \[OHSA\] score of 1 to 5 while on medication). * Patients who are able to stay with their caregiver during study participation. * Able and willing to provide informed consent. Exclusion Criteria: * Bedridden, physically disabled, or unable to walk. * Patients with Orthostatic hypotension symptom assessment (OHSA) score ≥ 6, or orthostatic systolic blood pressure drop ≥ 30 mmHg on their regular treatment. * Patients taking more than one medication for the treatment of neurogenic orthostatic hypotension (concomitant use of pyridostigmine or fludrocortisone are accepted). * Pregnancy * Systemic illnesses known to produce autonomic neuropathy, including but not limited to diabetes mellitus, amyloidosis, monoclonal gammopathies, and autoimmune neuropathies. * Clinically unstable coronary artery disease (recurrent angina despite medical therapy), or major cardiovascular or neurological event in the past 6 months (myocardial infarction, stroke). * Concomitant use of anticoagulants.