Oronasal breathing may adversely impact obstructive sleep apnea (OSA) patients either by increasing upper airway collapsibility or by influencing continuous positive airway pressure (CPAP) treatment outcomes. Predicting a preferential breathing route would be helpful to guide CPAP interface prescription. We hypothesized that anthropometric measurements but not self-reported oronasal breathing are predictors of objectively measured oronasal breathing. Seventeen OSA patients and nine healthy subjects underwent overnight polysomnography with an oronasal mask with two sealed compartments attached to independent pneumotacographs. Subjects answered questionnaires about nasal symptoms and perceived breathing route. Oronasal breathing was more common (P = <0.001) among OSA patients than controls while awake (62 ± 44 vs. 5 ± 6%) and during sleep (59 ± 39 vs. 25 ± 21%, respectively). Oronasal breathing was associated with OSA severity (P = 0.009), age (P = 0.005), body mass index (P = 0.044), and neck circumference (P = 0.004). There was no agreement between objective measurement and self-reported breathing route among OSA patients while awake (κ = -0.12) and asleep (κ = -0.02). The breathing route remained unchanged after 92% of obstructive apneas. These results suggest that oronasal breathing is more common among OSA patients than controls during both wakefulness and sleep and is associated with OSA severity and anthropometric measures. Self-reporting is not a reliable predictor of oronasal breathing and should not be considered an indication for oronasal CPAP.NEW & NOTEWORTHY Continuous positive airway pressure (CPAP) interface choice for obstructive sleep apnea (OSA) patients is often guided by nasal symptoms and self-reported breathing route. We showed that oronasal breathing can be predicted by anthropometric measurements and OSA severity but not by self-reported oronasal breathing. Self-reported breathing and nasal symptoms should not be considered for CPAP interface choice.

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