Genioglossal muscle response to CO₂ stimulation during NREM sleep

Study Objectives: The objective was to evaluate the responsiveness of upper airway muscles to hypercapnia with and without intrapharyngeal negative pressure during non-rapid eye movement (NREM) sleep and wakefulness. Design: We assessed the genioglossal muscle response to CO₂ off and on continuous positive airway pressure (CPAP) (to attenuate negative pressure) during stable NREM sleep and wakefulness in the supine position. Setting: Laboratory of the Sleep Medicine Division, Brigham and Women's Hospital. Patients or Participants: Eleven normal healthy subjects. Interventions: During wakefulness and NREM sleep, we measured genioglossal electromyography (EMG) on and off CPAP at the normal eupneic level and at levels 5 and 10 mm Hg above the awake eupneic level. Measurements and Results: We observed that CO₂ could increase upper-airway muscle activity during NREM sleep and wakefulness in the supine position with and without intrapharyngeal negative pressure. The application of nasal CPAP significantly decreased genioglossal EMG at all 3 levels of PETCO² during NREM sleep (13.0 ± 4.9% vs. 4.6 ± 1.6% of maximal EMG, 14.6 ± 5.6% vs. 7.1 ± 2.3% of maximal EMG, and 17.3 ± 6.3% vs. 10.2 ± 3.1% of maximal EMG, respectively). However, the ab-sence of negative pressure in the upper airway did not significantly affect the slope of the pharyngeal airway dilator muscle response to hypercapnia during NREM sleep (0.72 ± 0.30% vs. 0.79 ± 0.27% of maximal EMG per mm Hg PCO₂, respectively, off and on CPAP). Conclusions: We conclude that both chemoreceptive and negative pressure reflex inputs to this upper airway dilator muscle are still active during stable NREM sleep.