How do oronasal masks affect upper airway anatomy and collapsibility? 

YARMOUTH, Maine – Oronasal masks are associated with a more collapsible airway than nasal masks, which likely contributes to the need for a higher therapeutic pressure, according to a new study published in the journal Chest. CPAP therapy delivered via an oronasal mask is associated with lower adherence, higher residual AHI and increased pressure compared to nasal masks; however, the mechanisms underlying the increased pressure requirements are not well understood. Researchers found oronasal masks were associated with higher therapeutic pressure requirements (ΔM±SEM; +2.6±0.5, p<0.001) and higher Pcrit (+2.4±0.5cmH2O, p=0.001) compared to nasal masks. The change in therapeutic pressure between masks was strongly correlated with the change in Pcrit (r2=0.73, p=0.003). Increasing pressure increased both the retroglossal and retro-palatal airway dimensions across both masks. After controlling for pressure and breath-phase, the retropalatal cross-sectional area was moderately larger when using a nasal versus an oronasal mask (+17.2mm2, CI95%: 6.2–28.2, p<0.001) while nasal breathing. To conduct the study, researchers had 14 OSA patients undergo a sleep study with both a nasal and oronasal mask, each for half the night (order randomized). CPAP was manually titrated to determine therapeutic pressure. Upper airway collapsibility was assessed using the Pcrit technique. Cine MRI was done to dynamically assess the cross-sectional area of the retroglossal and retropalatal airway throughout the respiratory cycle with each mask interface. Scans were repeated at 4cmH2O and at the nasal and oronasal therapeutic pressures.