Obstructive sleep apnea syndrome is responsible of endothelial dysfunction, which is a independent cardio-vascular risk factor.

Assessment of pulse wave velocity (PWV) and peripheral arterial tone (PAT) are study measurements of arterial stiffness, and are strong predictors of late cardiovascular events.

This study will compare long term evolution in arterial stiffness (PWV) and endothelial dysfunction (PAT) for patients treated by Positive Airway Pressure Therapies.

Obstructive sleep apnea (OSA) syndrome is responsible of vascular damage. Intermittent hypoxia causes oxidative stress and low-grade inflammation. By the way of increased sympathetic outflow, it's resulting endothelial dysfunction, atherosclerosis and an increase of arterial stiffness.

Finally these mechanisms are responsible of cardiovascular comorbidities: hypertension, cardiac arrhythmias or Left ventricular dysfunction. This patients presented coronary diseases or Strokes.

OSA characterized by intermittent hypoxia, is associated with atherosclerosis and vascular inflammation. Polymorphonuclear leukocytes (PMNs) are implicated in vascular inflammation by producing oxidizing radicals and proteolytic enzymes during PMN-endothelium interactions.

Reactive oxygen species (ROS) production is increased in activated cells and after attachment, PMNs release additional ROS inducing endothelial cell injury.

Continuous positive airway pressure (CPAP) is the current "gold standard" treatment for OSA, Use of CPAP restored the respiratory flow, prevents nocturnal respiratory events and daytime symptoms.

Arterial stiffness and endothelial dysfunction are linked to obstructive sleep apnea severity with a dose-effect relationship. And meta-analyse showed significant improvements in all indices of arterial stiffness after CPAP treatment in patients with OSA.

Assessment of pulse wave velocity and peripheral arterial tone are study measurements of arterial stiffness. And are strong predictors of late cardiovascular events

The investigators will compare long term evolution in arterial stiffness (PWV) and endothelial dysfunction (Peripheral arterial tone) for patients with OSA treated by Positive Airway Pressure Therapies.

Inclusion Criteria:

• Any patient with a initial visit there is 4-7 years for the VNI-SOH protocol (Réf CPP Sud-Est V: 38/2006/2)
• Male or female patient, aged 20-75 years at the initial visit there is 4 to 7 years;
• Patients with a BMI> 30kg / m2 at diagnostic;
• Patient affiliated to a social security;
• Having given its written consent to participate in the study.

Exclusion Criteria:

• Person private of liberty by judicial or administrative decision, person under legal protection measure (pregnant or nursing, patient under guardianship) Article L1121-8
• Exclusion period for further studies
• Patient died or lost sight since the initial visit there 4-7 years

Patients with sleep apnea syndrome treated by CPAP after diagnosis and followed 5-7 years, as part of a clinical research.