Individuals with obstructive sleep apnea (OSA)  who breathed through their mouths >25% of the time failed to achieve stable breathing during oronasal continuous positive airway pressure (CPAP) therapy, according to study results published in CHEST.

Researchers evaluated inspiratory peak flow, driving pressure, upper airway inspiratory resistance, and retropalatal and retroglossal areas during CPAP titration monitored by full polysomnography, pharyngeal pressure catheter, and nasoendoscopy in patients with OSA. Results from patients who breathed through their mouths >25% of the time were compared with patients who did not.

Of the 13 patients, 5 breathed through their mouths >25% of the time. During stable flow limitation, inspiratory peak flow was lower, driving pressure and upper airway inspiratory resistance were higher, and retropalatal and retroglossal areas were smaller in oronasal than in nasal route (P <.05 for all).

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Several study limitations were noted, including the small sample size, the potential for compromising the oronasal CPAP because of changes in chin position, and the inability to measure pressure at the mouth cavity. In addition, the researchers only collected data from patients in the supine position.

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“We provide evidence that oronasal breathing compromises the efficacy of oronasal CPAP,” the researchers wrote. “The widespread use of the oronasal mask is concerning, particularly because oral breathing is both the major indication and the major cause of oronasal CPAP failure.”


Madeiro F, Andrade RGS, Piccin VS, et al. Transmission of oral pressure compromises oronasal CPAP efficacy to treat obstructive sleep apnea [published June 22, 2019]. CHEST. doi:10.1016/j.chest.2019.05.024