Role of Heme-oxygenase (HO) and Nitric Oxide (NO) Pathway in Patients With Obstructive Sleep Apnea (OSA) and Pulmonary Hypertension (PH)

Research design: This is a controled prospective study.

Methodology:

Patients with newly diagnosed and untreated OSA with total apnea-hypopnea index (AHI) >5/h, and control (AHI<5/h) will be recruited from the Long Beach VA sleep center. Controls are subjects without OSA or other sleep disorders and no sign of pulmonary hypertension based on echo. The investigators also measure pulmonary artery pressure by 2D Echo and exclude patient with any sign of left heart dysfunction. PH will be defined as RVSP > 35 mmHg or mean PA pressure>25 mmHg. The investigators will recruit subjects with and without PH and OSA in three separate groups:

1. group one : OSA+ PH,
2. group two: normal individual with no OSA and no PH,
3. group three: OSA with no PH Pulmonary function test will be done to exclude patients with underlying lung disease.

The inclusion criteria is: Age >20, AHI >5, AHI <5 (as control), RVSP > 35 mmHg OR Mean PA pressure>25 mmHg, RVSP < 35 mmHg OR Mean PA pressure < 25 mmHg (as control).

Subjects will be excluded if they had known peripheral vascular disease, liver disease, hemolytic anemia, inflammatory disease, active infection, or if they were pregnant, on therapy for OSA, on chronic steroid treatment, or younger than 20 years of age, patients with left heart failure (systolic or diastolic), patients are on PH medications including sildenafil, active smokers, COPD and asthma, active infection or inflammatory disease and collagen vascular disease.

Nocturnal polysomnography will be performed and scored according to the American Academy of Sleep Medicine.

Exhaled Carbon monoxide (CO) will be measured with a calibrated fuel cell type electrochemical device with sensor sensitivity of 1 ppm. The mean of three reproducible measurements will be recorded and corrected for ambient CO.

Exhaled Nitric Oxide (NO) will be measured. At each testing session, at least three flow-regulated FENO measurements will be performed.

The investigators will repeat 2D Echo and measurements of above factors after 3 months of CPAP treatment. The investigators also check patient's compliance with the treatment by downloading data off of their CPAP device.

Each subject will be informed of the experimental procedures, which is approved by the Human Investigation Committee of the VA-Long Beach.

Finding:

The investigators hypothesize that HO pathway causing perturbation of pulmonary endothelial function by inhibition of nitric oxide.

Clinical significance:

OSA is associated with PH, but exact mechanism is not well known. In the past, I have shown that increased endogenous CO in the setting of elevated NO concentration is associated with endothelial dysfunction in patient with OSA. Therefore, the investigators sought to investigate the roles of HO and NO pathways in patients with OSA associated with PH.

Impact/significance:

It addresses a fundamental gap in our understanding of how OSA results in increase the pulmonary artery pressure and if substantiated, will provide the basis for the design and testing of new approaches to prevention and treatment of OSA.