GENIOHYOID MUSCLE-ACTIVITY IN NORMAL MEN DURING WAKEFULNESS AND SLEEP

Reduction in the activity of upper airway 'dilator' muscles during sleep may allow the pharyngeal airway to collapse in some individuals. However, quantitative studies concerning the effect of sleep on specific upper airway muscles that may influence pharyngeal patency are sparse and inconclusive. We studied seven normal men (mean age 27, range 22-37 yr) during a single nocturnal sleep study and recorded sleep staging parameters, ventilation, and geniohyoid muscle electromyogram (EMGgh) during nasal breathing throughout the night. Anatomic landmarks for placement of intramuscular geniohyoid recording electrodes were determined from a cadaver study. These landmarks were used in percutaneous placement of wire electrodes, and raw and moving-time-averaged EMGgh activities were recorded. Sleep stage was determined using standard criteria. Stable periods of wakefulness and non-rapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep were selected for analysis. The EMGgh exhibited phasic inspiratory activity during wakefulness and sleep in all subjects. In six of seven subjects, mean and peak inspiratory EMGgh activities were significant (P < 0.05) reduced during stages 2 and 3/4 NREM sleep and REM sleep compared with wakefulness. This reduction of EMGgh activity was shown to result from a sleep-related decline in the level of tonic muscle activity. Phasic inspiratory EMGgh activity during all stages of sleep was not significantly different from that during wakefulness. Of interest, tonic, phasic, and peak EMGgh activities were not significantly reduced during REM sleep compared with any other sleep stage in any subject. In addition, the slope of onset of phasic EMGgh activity was not different during stage 2 NREM and REM sleep compared with wakefulness in these subjects. These data indicate that 1) human geniohyoid muscles have a predictable anatomic location in normal-weight cadaver specimens, 2) the geniohyoid muscles exhibit phasic inspiratory activity during wakefulness and sleep, 3) sleep-related decrements in peak inspiratory EMGgh activity due to a reduction in the tonic activity component were observed in six of seven normal men, 4) no measure of EMGgh activity was further reduced during REM sleep compared with other stages of sleep, and 5) the slope of phasic inspiratory EMGgh activation was not significantly altered during sleep in normal men.