Transmission of Oral Pressure Compromises Oronasal CPAP Efficacy in the Treatment of OSA.

BACKGROUND: An oronasal mask is frequently used to treat OSA. In contrast to nasal CPAP, the effectiveness of oronasal CPAP varies by unknown mechanisms. We hypothesized that oral breathing and pressure transmission through the mouth compromises oronasal CPAP efficacy.

METHODS: Thirteen patients with OSA, well adapted to oronasal CPAP, were monitored by full polysomnography, pharyngeal pressure catheter, and nasoendoscope. Patients slept with low doses of midazolam, using an oronasal mask with sealed nasal and oral compartments. CPAP was titrated during administration by the oronasal and nasal routes, and was then reduced to induce stable flow limitation and abruptly switched to the alternate route. In addition, tape sealing the mouth was used to block pressure transmission to the oral cavity.

RESULTS: Best titrated CPAP was significantly higher by the oronasal route rather than the nasal route (P = .005), and patients with > 25% oral breathing (n = 5) failed to achieve stable breathing during oronasal CPAP. During stable flow limitation, inspiratory peak flow was lower, driving pressure was higher, upper airway inspiratory resistance was higher, and retropalatal and retroglossal area were smaller by the oronasal rather than nasal route (P < .05 for all comparisons). Differences were observed even among patients with no oral flow and were abolished when tape sealing the mouth was used (n = 6).

CONCLUSIONS: Oral breathing and transmission of positive pressure through the mouth compromise oronasal CPAP.