Differential genioglossus muscle responses to changes in breathing route in awake people with and without obstructive sleep apnea

This study examined the effects of nasal and oral breathing routes on genioglossus electromyographic activity (EMG), inspiratory (nadir) epiglottic pressures, and the pressure-dependent reflex regulation of inspiratory genioglossus EMG in awake supine participants. We hypothesized that oral breathing reduces negative pharyngeal pressure swings during inspiration and, via a pressure-dependent reflex mechanism, reduces phasic inspiratory genioglossus EMG. Twenty participants with obstructive sleep apnea (OSA) and 8 people without OSA were recruited into this study. Measurements included multiunit genioglossus EMG via percutaneous bipolar electrodes, airflow via nasal pneumotach, epiglottic pressure, and end-tidal CO₂. Participants were studied while in supine position, breathing quietly via nose, then switched to oral breathing for ̴5 min/route, and then repeated the protocol. Oral breathing reduced inspiratory epiglottic negative pressures by ̴50% in all participants [OSA nasal: ̶4 ± 1.8 (SD) cmH₂O; oral: ̶1.8 ± 0.8 cmH₂O; non-OSA nasal: ̶2.4 ± 1.6 cmH₂O; oral: ̶1.1 ± 0.8 cmH₂O]. In people without OSA and a third of people with OSA, oral breathing was associated with reduced phasic inspiratory genioglossus EMG and correlated with reduced inspiratory negative epiglottic pressure swings. Unexpectedly, in the remaining two-thirds of people with OSA, phasic inspiratory EMG was maintained and/or increased with oral breathing, despite reduced inspiratory negative pharyngeal pressure swings. Remarkably, the increased inspiratory genioglossus EMG during oral breathing in these participants with OSA was inversely correlated with epiglottic pressure. The divergent responses in most people with OSA may represent a reflex adaptation to oral breathing, perhaps due, at least in part, to increased and persistent nocturnal oral breathing.