CPAP oronasal masks collapse the airway more than nasal masks
Oronasal masks have an adverse effect on airway anatomy and function compared to nasal masks.
Higher pressures required by masks covering both the nose and mouth cause the airway to collapse more than with nasal masks, significantly increasing airway resistance and reducing CPAP effectiveness. And mouth versus nasal breathing is deleterious across the board.
A study recently published in the journal Chest, Oronasal vs Nasal Masks, The Impact of Mask Type on CPAP Requirement, Pharyngeal Critical Closing Pressure (Pcrit), and Upper Airway Cross-sectional Areas in Patients With OSA, reveals a big difference between the oronasal masks that cover both the nose and mouth and nasal masks that cover only the nose.
The authors note:
“OSA [obstructive sleep apnea] is a common sleep disorder associated with long-term health consequences.1 CPAP therapy remains the gold standard treatment for patients with OSA. CPAP [continuous positive airway pressure] is highly effective and works by pneumatically splinting the upper airway2 during sleep. However, CPAP is often poorly tolerated3,4 because of patient characteristics, disease severity, psychological factors, side effects, and the type of mask used (ie, nasal vs oronasal masks). Nasal masks are recommended for patients referred for CPAP treatment,5 but oronasal masks are still frequently used in clinical practice despite the common difficulty of maintaining a good fit or seal. As such, oronasal masks are often associated with a higher CPAP level, higher residual apnea-hypopnea index (AHI), and poorer adherence than nasal masks,6 according to a meta-analysis of both randomized and nonrandomized controlled trials. However, the physiological mechanisms underlying the differences in mask performance are currently unknown.”
Moreover…
Imaging techniques (ie, cine-MRI or endoscopy) during wake or drug-induced sleep have found that CPAP applied via oronasal masks can lead to the posterior displacement of the tongue and an increase in upper airway resistance.7,8 The increase in upper airway resistance may increase the collapsibility of the airway, explaining the need for higher optimal CPAP with an oronasal mask. However, to date, no study has successfully quantified how these different CPAP interfaces alter an individual’s airway collapsibility during natural sleep.
So they used cine-MRI (MRI ‘video’) plus digital manometry (pressure measurement) and a MRI-compatible respiratory effort sensor to investigate investigate the dynamic changes within the upper airway with CPAP therapy during sleep and wake, using the two most common commercial oronasal and nasal CPAP mask types rather than specialized research masks.
Airway collapse with oronasal masks
Higher CPAP pressures with oronasal masks are a clear factor:
“The current study demonstrated that oronasal masks require higher therapeutic CPAP levels and that this increase in CPAP requirement was strongly associated with increased airway collapsibility (higher Pcrit)…During nasal breathing, the oronasal mask was associated with smaller retroglossal and retropalatal cross-sectional area than the nasal mask.”
They suggest that having to increase the CPAP pressure setting can be a surrogate marker for airway collapse:
“Taken together, these data provide further evidence that a patient’s therapeutic CPAP level may be a reasonable surrogate marker of airway collapsibility19 and that oronasal masks cause measurable anatomical compromise that may offset some degree of CPAP efficacy.”
Additionally, the oronasal mask straps may push the mandible backward, further constricting the airway:
“The tightening of the oronasal mask straps may push the mandible posteriorly20 #0166EF. Accordingly, we found that the cross-sectional area of the retroglossal/retropalatal region when using an oronasal mask was slightly reduced compared with the nasal mask at low pressures (ie, 4 cm H2O).”
Breath through the nose, not the mouth
And, importantly, they observed the significant difference between mouth and nose breathing as observed in other contexts:
“Another possible mechanism is the route of breathing (ie, whether patients are breathing nasally or orally). Studies using a specialized dual compartment (nasal/oral) oronasal mask interface in which PAP delivery was switched between the nasal or the oronasal (both) compartments without changing the interface found a +2- to 3-cm H2O difference in therapeutic CPAP levels.8,21 These analyses further show that patients with a greater percentage of oral breathing (relative to nasal breathing) required greater pressures to induce stable breathing with oronasal PAP.”
Mouth taping can help, even without obstructive sleep apnea:
“More recently, Madeiro et al21 have shown increased airway resistance during oronasal PAP delivery. This increase in airway resistance could be eliminated by application of tape to the mouth to prevent mouth breathing, mouth opening, or transmission of pressure to the oral cavity. More broadly, mouth opening during the application of nasal CPAP increases collapsibility (Pclose) by a magnitude similar to that found in the current study (approximately +2 cm H2O).23 Moreover, oral breathing has been shown to increase airway resistance during sleep in non-OSA patients.24…the available evidence would suggest that the oronasal masks are associated with more mouth opening/breathing, which in turn increases the airway resistance/collapsibility and therefore drives the higher therapeutic CPAP requirement.”
