THE EFFECT OF SLEEP ON REFLEX GENIOGLOSSUS MUSCLE ACTIVATION BY STIMULI OF NEGATIVE AIRWAY PRESSURE IN HUMANS

1. The present study was designed to determine the effect of sleep on reflex pharyngeal dilator muscle activation by stimuli of negative air way pressure in human subjects. 2. Intra-oral bipolar surface electrod es were used to record genioglossus electromyogram (EMG) responses to 500 ms duration pressure stimuli of 0 and - 25 cmH(2)O applied, via a face-mask, in four normal subjects. Stimuli were applied during early inspiration in wakefulness and in periods of non-rapid-eye-movement (n on-REM) sleep, defined by electroencephalographic (EEG) criteria. 3. T he rectified and integrated EMG responses to repeated interventions we re bin averaged for the 0 and - 25 cmH(2)O stimuli applied in wakefuln ess and sleep. Response latency was defined as the time when the EMG a ctivity significantly increased above prestimulus levels. Response mag nitude was quantified as the Ln ratio of the EMG activity for an 80 ms post-stimulus period to an 80 ms prestimulus period; data from after the subject's voluntary reaction time for tongue protrusion (range, 15 0-230 ms) were not analysed. 4. Application of the -25cmH(2)O stimuli caused genioglossus muscle activation in wakefulness and sleep, but in all subjects response magnitude was reduced in sleep (mean decrease, 81%; range, 52-82 %; P = 0.011, Student's paired t test). In addition, response latency was increased in sleep in each subject (mean latency awake, 38 ms; range, 30-50 ms; mean latency asleep, 75 ms; range, 40- 110 ms; P = 0.072, Student's paired t test). 5. Application of the - 2 5 cmH,O stimuli caused arousal from sleep on 90 % of occasions, but in all cases the reflex genioglossus muscle responses (maximum latency, 10 ms) always preceded any sign of EEG arousal (mean time to arousal, 643 ms; range, 424-760 ms). 6. These results show that non-REM sleep a ttenuates reflex genioglossus muscle activation 3 by stimuli of negati ve airway pressure. Attenuation of this reflex by sleep may impair the ability of the upper airway to defend itself from suction collapse by negative pressures generated during inspiration; this may have implic ations for the pathogenesis of obstructive sleep apnoea.