Genioglossal muscle response to CO2 stimulation during NREM sleep

Abstract

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 absence 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.

Figure 1

Individual raw data traces from 1 subject at 3 end-tidal PCO₂ (PETCO₂) levels: basal breathing and +5 and +10 mm Hg above awake eupneic level during stable non-rapid eye movement (NREM) sleep both off and on continuous positive airway pressure (CPAP). Carbon dioxide (CO₂) can increase genioglossal muscle activity both off and on CPAP during stable NREM sleep. Note that the inspiratory increment in the PCO₂ trace at 10 mm Hg above eupnea both on and off CPAP indicates CO₂ accumulation in the inspiratory line during expiration. GGEMG refers to genioglossal electromyogram; EEG, electroencephalogram; TV, tidal volume.

Figure 2

Bar graphs show the mean (± S.E.M.) peak genioglossal electromyogram (GGEMG) response to CO₂ stimulation at 3 end-tidal PCO₂ (PETCO₂) levels during wakefulness and non-rapid eye movement (NREM) sleep both on and off continuous positive airway pressure (CPAP). CPAP significantly decreases GGEMG at all levels of PCO₂ during NREM sleep but only at the eupneic level during wakefulness. During wakefulness and NREM sleep, both on and off CPAP, the genioglossal muscle can significantly respond to CO₂ stimulation. •P < .05, off vs on CPAP; *P < .05, eupneic vs 5 mm Hg above eupneic levels; †P < .05, eupneic vs 10 mm Hg above eupneic levels; ‡P < .05, 5 mm Hg vs 10 mm Hg above eupneic levels.

Figure 3

During wakefulness, there is a trend (not significant) for continuous positive airway pressure (CPAP) to reduce the slope of peak genioglossal electromyogram (GGEMG) response to CO₂ stimulation (A). During non-rapid eye movement (NREM) sleep, on and off CPAP, the slopes of peak GGEMG response to CO₂ stimulation are parallel with CPAP shifting the curve to the left (B).

Figure 4

Both on and off continuous positive airway pressure (CPAP), non-rapid eye movement (NREM) sleep shifted the waking hypercapnic ventilatory response to the right and downward. During NREM sleep, CPAP increased the slope of the hypercapnic ventilatory response.