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. 20 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 supine, breathing quietly via nose, then switched to oral breathing for ~5 min/route, 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 OSA participants was inversely correlated to 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.
Burke et al. (Sun,) studied this question.