CAPNOSOH study is a single-center study conducted at Toulouse University Hospital, aiming to estimate the prevalence of obese and apneic subjects maintaining nocturnal hypoventilation under continuous positive airway pressure (CPAP).

Obstructive sleep apnea hypopnea syndrome (OSAS) is highly prevalent in the global population (1 in 10 people worldwide according to Inserm), particularly in relation to the increase in the prevalence of obesity. The standard treatment for this pathology is continuous positive airway pressure (CPAP) which most often allows, when properly applied and adjusted, the normalization of symptoms and the apnea-hypopnea index (AHI). In addition to OSAHS, some obese subjects are at risk of presenting hypoventilation obesity syndrome (OHS) defined by the presence of obesity (body mass index [BMI] > 30 kg/m2) associated with diurnal hypoventilation. (PaCO2 > 45 mmHg) in the absence of other respiratory pathology. Identifying patients with OS is often difficult but essential, as early as possible.

Transcutaneous capnography, when properly performed and interpreted, is a much more informative tool than nocturnal oximetry, and could therefore allow better screening for these patients. It is an examination increasingly used in pulmonology departments/sleep centers.

The CAPNOSOH study is a single-center study conducted at Toulouse University Hospital, aiming to estimate the prevalence of obese and apneic subjects maintaining nocturnal hypoventilation under continuous positive airway pressure (CPAP). The study hypothesis is based on the limited data present in the literature. This is preliminary work for a multicenter study aimed at determining the impact of nocturnal hypoventilation without daytime hypercapnia on the quality of life and morbidity and mortality of patients.

We estimate that between 10 to 20% of obese subjects on CPAP hypoventilate at night.

Inclusion criteria:

• Obese patients (Body Mass Index > 30 kg/m2)
• Fitted by one of the following providers: ASTEN, Vitalaire, Orkyn, ISIS, RespiO2, BASTIDE for > 3 months with compliance of more than 4 consecutive hours per night in average during 3 months
• "Good quality" criteria for continuous positive airway pressure (CPAP) treatment: compliance > 4 consecutive hours per night, unintentional leaks < limit defined by the manufacturer, residual AHI < 10/h
• Aged 18 to 80
• Affiliated or beneficiaries of the social security system or equivalent
• Having given written informed consent
• Able to understand instructions and information given

Exclusion criteria :

• Patient under legal protection measure
• Non-compliant patients
• Pregnant or breast-feeding women (assessed on questioning)