Continuous positive airway pressure (CPAP) is considered the gold standard treatment for patients with moderate to severe obstructive sleep apnea (OSA).

Nasal and oronasal masks are often used interchangeably and are generally believed to be equally effective; the choice of interface for OSA therapy remains largely based on clinical judgement and patients preference. However, there is increasing evidence that CPAP delivered by an oronasal mask may be less effective, requires more pressure and are worse tolerated than nasal mask. Patients with OSA on oronasal mask are also less adherent to CPAP.

Some authors have suggested that in some subjects, the CPAP was not effective when an oronasal mask was used. Moreover when pressures are increased to overcome the obstruction, a paradoxical obstruction may take place.

Specific mechanisms explaining upper-airway obstruction events remain unclear and it is not known how many patients exhibit this behavior.

This observational retrospective study is designed to compare a group of patients with obstructive sleep apnea with persistent obstructive events using oronasal masks during CPAP, that were fully recovered with the shift to nasal one with the same or also lower pressure, versus a control group of patients who did not report obstruction with oronasal masks. Aim of the study was to find differences in term of clinical, anatomical and physiological characteristics between these two groups.

Continuous positive airway pressure (CPAP) is considered the gold standard treatment for patients with moderate to severe obstructive sleep apnea (OSA).

The treatment of OSA with CPAP was first proposed by Sullivan et al and traditionally delivered using a nasal mask because the pressure applied through the nose would be transmitted as a pneumatic splint to the back of the upper airway and would push them anteriorly.

However patients with OSA frequently present nasal obstruction and leakage of air from the mouth, and different mask interfaces have been developed, including the oronasal mask that may be used to deliver CPAP.

Nasal and oronasal masks are often used interchangeably and are generally believed to be equally effective; the choice of interface for OSA therapy remains largely based on clinical judgement and patients preference .

In our clinical practice, CPAP titration is started adapting the patient to a nasal mask but an oronasal can be selected if a patient reports inability to breathe through their nose, severe nasal obstruction, leakage of air from the mouth or from other part of the face due to anatomical variation.

However, there is increasing evidence that CPAP delivered by an oronasal mask may be less effective, requires more pressure and are worse tolerated than nasal mask.

Patients with OSA on oronasal mask are also less adherent to CPAP. One recent randomised trial and a preliminary report suggest that subjects with sleep apnea treated with CPAP showed a significantly lower residual AHI when subjects wore a nasal mask rather than a oronasal mask.

Similarly, a recent prospective observational cohort study suggested that the use of a facial mask was associated with higher CPAP pressure requirements than both nasal masks and nasal pillows.

Some authors have suggested that in some subjects, the CPAP was not effective when an oronasal mask was used. Moreover when pressures are increased to overcome the obstruction, a paradoxical obstruction may take place.

These findings have been called "the Starling paradox effect", according to which the pressure that opens the pharynx can also lead to pharyngeal collapse when applied orally.

In these difficult-to-titrate patients the specific mechanisms explaining upper-airway obstruction events remain unclear and it is not known how many patients exhibit this behavior.

This observational retrospective study is designed to compare a group of patients with obstructive sleep apnea with persistent obstructive events using oronasal masks during CPAP, that were fully recovered with the shift to nasal one with the same or also lower pressure, versus a control group of patients who did not report obstruction with oronasal masks.

Aim of the study was to find differences in term of clinical, anatomical and physiological characteristics between these two groups.

Inclusion Criteria:

• confirmed diagnosis of OSA and use of CPAP treatment
• age> or equal to 18 years old
• sign of informed consent

Exclusion Criteria:

• none

In this observational retrospetive study were selected patients affected by OSA treated with CPAP. From this population were selected patients using oronasal mask with complete recovery of OSA (AHI<5) during CPAP treatment (control group) and patients shifted to nasal mask due to persistent of obstructive events (AHI>5) during the initial treatment with oronasal mask.