CPAP for High Blood Pressure While Lying Down

Inclusion Criteria: * Male and female subjects, age 40-80 years, with autonomic failure including pure autonomic failure, multiple system atrophy and Parkinson disease. * Neurogenic orthostatic hypotension, defined as a ≥20-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. * Nocturnal supine hypertension (nighttime systolic blood pressure ≥140 mmHg) during the overnight screening for supine hypertension. * Patients who are willing and able to provide informed consent Exclusion Criteria: * Patients with history of recent facial trauma or surgery or intolerance to CPAP or to the CPAP mask. * Patients who cannot tolerate the medication withdrawal, defined as those who are unable to stand for at least one minute or those with sustained supine blood pressure ≥180/110 mmHg after the medication withdrawal period. * Bedridden patients or those who are unable to stand due to motor impairment or severe orthostatic hypotension. * Smokers, patients who are pregnant, or have clinically unstable coronary artery disease, or major cardiovascular or neurological event in the past 6 months; heart failure; and other factors which in the investigator's opinion would prevent the subject from completing the protocol including clinically significant abnormalities in clinical or laboratory testing.