Nasal obstruction and male gender contribute to the persistence of mouth opening during sleep in CPAP‐treated obstructive sleep apnoea

BACKGROUND AND OBJECTIVE: During continuous positive airway pressure (CPAP) treatment, some patients with obstructive sleep apnoea syndrome (OSAS) require an oronasal mask (ONM) to prevent excessive mouth leakage. Factors contributing to sleep-related mouth opening under CPAP treatment remain known. We compared mouth opening during sleep in patients treated with CPAP by nasal mask (NM) versus ONM. METHODS: Cross-sectional prospective study: patients treated with CPAP for at least 4 months underwent a sleep recording using a type 4 monitoring device (Brizzy-Nomics) that records mouth opening via a magnetometric distance meter. Clinical assessment included anthropometry, smoking status and the Mallampati score. Nasal obstruction was assessed by the Nasal Obstruction Symptom Evaluation questionnaire. RESULTS: Thirty-eight patients were included, 34 analysed (22 men; age = 57.4 (53; 62) years; body mass index = 32.6 (29.1; 35.2) kg/m(2) ; median (25th; 75th)). Twenty-seven patients were treated with NM and seven with ONM. Patients with ONM were more often active smokers and trended to have greater nasal obstruction and lower forced expiratory volume in 1 s. They also exhibited a greater mouth opening during sleep (median (25th;75th) = 13.0 (11.0; 15.0) vs 6.0 (5.0; 10.0) mm, P < 0.001) and a higher oxygen desaturation index (9.5 (6.2; 15.5) vs 2.9 (1.0; 6.1) events/h, P = 0.009). In multivariate analysis, male gender and nasal obstruction were independently associated with mouth opening under ONM CPAP treatment. CONCLUSIONS: After several months of CPAP treatment, some patients using ONM persist in keeping their mouths open at night. Nasal obstruction and male gender contribute to this phenomenon.