• Shane A Landry, Dwayne L Mann, Richard Beare, Richard McIntyre, Caroline Beatty, Luke D J Thomson, Jinny Collet, Simon A Joosten, Garun S Hamilton, and Bradley A Edwards.
• Department of Physiology, Biomedical Discovery Institute, Monash University, Melbourne, VIC, Australia. Electronic address: shane.landry@monash.edu.
• Chest. 2023 Sep 1; 164 (3): 747756747-756.

BackgroundCPAP delivered via an oronasal mask is associated with lower adherence, higher residual apnea-hypopnea index (AHI), and increased CPAP therapeutic pressure compared with nasal masks. However, the mechanisms underlying the increased pressure requirements are not well understood.Research QuestionHow do oronasal masks affect upper airway anatomy and collapsibility?Study Design And MethodsFourteen patients with OSA underwent a sleep study with both a nasal and oronasal mask, each for one-half of the night (order randomized). CPAP was manually titrated to determine therapeutic pressure. Upper airway collapsibility was assessed using the pharyngeal critical closing pressure (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 4 cm H2O and at the nasal and oronasal therapeutic pressures.ResultsThe oronasal mask was associated with higher therapeutic pressure requirements (ΔM ± SEM; +2.6 ± 0.5; P < .001) and higher Pcrit (+2.4 ± 0.5 cm H2O; P = .001) compared with the nasal mask. The change in therapeutic pressure between masks was strongly correlated with the change in Pcrit (r2 = 0.73; P = .003). Increasing CPAP increased both the retroglossal and retropalatal airway dimensions across both masks. After controlling for pressure and breath phase, the retropalatal cross-sectional area was moderately larger when using a nasal vs an oronasal mask (+17.2 mm2; 95% CI, 6.2-28.2, P < .001) while nasal breathing.InterpretationOronasal masks are associated with a more collapsible airway than nasal masks, which likely contributes to the need for a higher therapeutic pressure.Copyright © 2023 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.

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