Main objective:

To describe clinical and functional characteristics of the obese hypoventilating patient; to study the relation between the obesity-hypoventilation syndrome (OHS) and the obstructive sleep apnea hypopnea syndrome (OSAHS). In the second stage of the study, to assess patient response to non-invasive mechanical ventilation (NIV) and continuous positive airway pressure (CPAP), and to identify predictors of unfavourable response to treatment.

Methodology:

• Patients: Patients with obesity degree I-III, with pCO2 awake and at rest > 45 mmHg, with no underlying pulmonary or neuromuscular lung disease; two control groups, one of non-hypoventilating obese patients and the other of obese patients with OSAHS, will also be studied over the same period.
• Design: Prospective observational study. In the first stage anthropometric, clinical, functional and metabolic data will be recorded for the obese hypoventilating patients and the two control groups (obese patients without respiratory pathology, and obese patients with OSAHS). In the second stage patients with OHS will be divided into two subgroups: group 1: patients with polysomnography (PSG) suggestive of hypoventilation, in whom NIV treatment will be initiated; group 2: patients with PSG suggestive of OSAHS (apnea-hypopnea index >15), who will be administered CPAP. Patients will be examined one month and three months after the start of treatment. The same measurements will be carried out as at the beginning of the study, with the exception of the polysomnographic study. Nonetheless, pulse oximetry and arterial gases will be performed on waking.

Expected Results:

Patients with OHS may be characterized and differentiated from obese patients without associated respiratory pathology on the basis of clinical, functional and metabolic data. There is a group of patients with association between OSAHS and OHS that do not respond to treatment with CPAP, and this unfavorable response can be predicted in advance.