Primary objectives: evaluate the efficacy of noninvasive ventilation (NIV) treatment versus continuous positive airway pressure (CPAP) and life style modification treatment in Obesity Hypoventilation Syndrome (OHS), with PCO2 (first phase) and days of hospitalization (second phase) analyzed as a primary variables and percentage of dropouts for medical reasons and mortality as operative variables. As secondary variables: Measure functional and clinical improvement during sleep and wakefulness, quality of life, echocardiography and the incidence and blood pressure and evolution of cardiovascular events. Objectives secondaries:role of apneogenic sleep events on molecular inflammation, endothelial damage and the genesis of diurnal hypercapnia. Methods:prospective, randomized controlled trial. Patients with OHS will be divided initially into two groups based on their apnea-hypopnea index (AHI) score, >=30 and < 30, using conventional polysomnography. The AHI >=30 group will be randomized to CPAP, NIV or life style modification treatments. The AHI <=30 groups will be randomized to NIV or life style modification treatments. Treatment efficacy at the medium- and long-term will be analyzed by comparing groups. The role of apneic events and leptin in the genesis of daytime alveolar hypoventilation will be analyzed by comparing the daytime PCO2/AHI coefficient between responders and non-responders to CPAP treatment, and the evolution of leptin levels in the four branches of the study. The role of apneic events in metabolic and biochemical alterations and endothelial dysfunction will be analyzed by comparing basal and post-treatment levels of related substances between groups, with and without significant AHI.

The AHI >=30 group will be analyzed to CPAP, NIV or life style modification treatments for two mouths.Once an evaluation is done during this period, the life style modification treatment will be randomized with the NIV/CPAP treatment for a continuation of three years.

Inclusion Criteria:

• Age between 15 and 80 years old.
• Absence of moderate or severe chronic obstructive pulmonary disease (COPD).
• Absence of neuromuscular, chest wall or metabolic disease which cause daytime hypercapnia.
• Absence of narcolepsy or restless legs syndrome
• Exceed correctly treatment of at least 30 minutes with CPAP/NIV at wakefulness.

Exclusion Criteria:

• Psychophysical incapacity to answer questionnaires.
• Patients who are not able to be evaluated by means of quality of life questionnaires for suffering restrictive chronic disease previously diagnosed (neoplasy, chronic pain of any origin, renal failure, severe chronic obstructive pulmonary disease and any other restrictive chronic disease).
• Subjects with important chronic nasal obstruction that prevents from using CPAP/NIV.
• Informed consent not obtained.