Mouth breathing during oronasal CPAP may compromise treatment efficacy
Oronasal continuous positive airway pressure (CPAP) functions less effectively in mouth breathers and when positive pressure is transmitted through the mouth, a study has found.
Researchers monitored 13 obstructive sleep apnoea (OSA) patients, who were well adapted to oronasal CPAP, using full polysomnography, pharyngeal pressure catheter and nasoendoscope. In sleep, patients received low doses of midazolam via an oronasal mask with sealed nasal and oral compartments.
CPAP was titrated during oronasal and nasal routes, then decreased to generate stable flow limitation and abruptly switched to the alternate route. Pressure transmission to the oral cavity was blocked using a tape sealing the mouth.
Best titrated CPAP was markedly better in oronasal than nasal route (p=0.005), and patients who breathed through their mouths >25 percent (n=5) failed to achieve stable breathing during oronasal CPAP.
During stable flow limitation, oronasal route was associated with lower inspiratory peak flow, higher driving pressure, higher upper airway inspiratory resistance, and retropalatal and retroglossal area as compared with nasal route (p<0.05 for all comparisons). Differences were seen even among patients with no oral flow, but it disappeared when a tape sealing the mouth was used (n=6).
Another study has reported that open-mouth breathing significantly narrows the retropalatal and retroglossal areas, lengthens the pharynx, and shortens the mandible and hyoid bone. These changes are said to contribute to the understanding of the increase in OSA severity and low adherence to nasal CPAP therapy in mouth breathers. [Laryngoscope 2007;117:1102-1106]