Predictive Factors of Obesity-hypoventilation Syndrome (OHS) Among Obese Subjects- ETUDE COHYPOB -

Inclusion criteria: * Obese volunteer Subject (BMI\> 30 kg/m2) * Adults of either sex * Social security affiliation * Written informed consent Exclusion criteria: * Confirmed OHS at baseline defined by a daytime hypercapnia with PaCO2\> 45mmHg * Any cause of chronic respiratory failure other than obesity such as COPD, chest deformation, phrenic nerve paralysis, pulmonary fibrosis, neuromuscular disease, a history of mutilating thoracic surgery ... * Obstructive ventilatory defect with FEV1/ FVC \<70% post-bronchodilator * Long term oxygen therapy, noninvasive ventilation, continuous positive airway pressure * Any serious illness involving life-threatening within 3 years after inclusion * Drug or alcohol abuse * Pregnancy