To determine the impact of the CPAP route (oronasal vs oral) in patients diagnosed with moderate-severe OSA using CPAP with oronasal mask on CPAP level, residual AHI, and peak flow. In addition, the impact of position (lateral vs supine position) will be evaluated during PSG.

Application of Continuous Positive Upper Airway Pressure (CPAP) during sleep using nasal mask is the gold standard treatment for Obstructive Sleep Apnea (OSA). In clinical practice, many patients with OSA are considered mouth breathers and use an oronasal mask. However, CPAP delivered by the mouth violates the principal of CPAP use to treat OSA. This study is part of a line of research over the last decade that started with the observation of a patient that CPAP delivered by an oronasal mask failed to splint the airway open and to abolish OSA . We showed subsequently in acute studies during induced-sleep that oronasal CPAP only works when the patient breathes predominantly through the nose. These observations prompted our group to lead one workshop on the importance of mask selection. One meta-analysis from our group confirmed that oronasal CPAP is associated with a higher CPAP level, higher residual AHI, and poorer adherence than nasal CPAP. Despite all this evidence the investigators intrigued by the clinical observation that oronasal masks remains common and several patients on clinical practice are well adapted to oronasal CPAP. In this study, 20 patients with OSA well adapted to the oronasal mask will be recruited. The patients will be invited to be submitted to 2 independent CPAP titration sleep studies using a customized oronasal mask with a sealed and independent nasal and oral compartments coupled to 2 pneumotachographs. One CPAP titration will be with the nasal and oral routes open and one CPAP titration with only the oral compartment opened. Our hypotheses are that obstruction of nasal compartment during CPAP titration causuing mouth breathing will result in higher CPAP and higher residual apnea-hypopnea index. Patients with OSA under treatment with oronasal CPAP will undergo CPAP titration polysomnography on 2 different nights. In one night the patient will sleep with the oral and nasal compartments opened and in another night interposed by at least seven days, the patient with sleep with only the oral compartment opened. The order of the 2 sleep studies will be randomized. Thus, researchers will assess the impact of the airway (oral vs oronasal) on titrated CPAP level, residual AHI, and sleep efficiency in supine and lateral recumbency. In addition, the preferred airway during the oronasal mask will be analyzed. At the end of the study a nasal mask will be offered to all patients.

Inclusion Criteria:

• Diagnosis of moderate or severe OSA in treatment with CPAP in an oronasal mask
• 18 Years to 85 Years (Adult, Older Adult) (Adult, Older Adult)

Exclusion Criteria:

• Other sleep disturbance (insomnia, parasomnias, narcolepsy, central sleep apnea).
• Uncontrolled clinical disease (diabetes, kidney or heart failure, recent stroke or coronary failure and recent postoperative period, oxygen dependent COPD).
• Patients adapted to other types of masks.

Patients with diagnosis moderate or severe OSA in treatment with CPAP in an Oronasal Mask