Alteration in upper airway dilator muscle coactivation during sleep: comparison of patients with obstructive sleep apnea and healthy subjects

In patients with obstructive sleep apnea (OSA), substantial increases in genioglossus (GG) activity during hypopneas/apneas usually fail to restore normal airflow. We have previously suggested that sleep-induced alteration in tongue muscle coordination may explain this finding, as retractor muscle coactivation was reduced during sleep compared with wakefulness. The present study was undertaken to evaluate whether these alterations in dilator muscle activation during sleep play a role in the pathogenesis of OSA and whether coactivation of additional peripharyngeal muscles (non-GG muscles: styloglossus, geniohyoid, sternohyoid, and sternocleidomastoid) is also impaired during sleep. We compared GG and non-GG muscle electromyographic (EMG) activity in 8 patients with OSA and 12 healthy subjects during wakefulness while breathing through inspiratory resistors with the activity observed during sleep toward the end of flow limitation, before arousal, at equivalent esophageal pressures. During wakefulness, resistive breathing triggered increases in both GG and non-GG muscle activity. During sleep, flow limitation was associated with increases in GG-EMG that reached, on average, >2-fold the level observed while awake. In contrast, EMGs of the non-GG muscles, recorded simultaneously, reached, on average, only similar to 2/3 the wakefulness level. We conclude that during sleep GG activity may increase to levels that substantially exceed those sufficient to prevent pharyngeal collapse during wakefulness, whereas other peripharyngeal muscles do not coactivate during sleep in both patients with OSA and healthy subjects. We speculate that upper airway muscle dyssynchrony during sleep may explain why GG-EMG activation fails to alleviate flow limitation and stabilize airway patency during sleep. NEW & NOTEWORTHY Pharyngeal obstruction during sleep may trigger genioglossus activity to levels substantially exceeding those observed during wakefulness, without ameliorating flow limitation. In contrast, other peripharyngeal muscles exhibit a much lower activity during sleep in both patients with obstructive sleep apnea and healthy subjects. Coordinated muscular synergy stabilizes the pharynx despite relatively low activity while awake, yet even higher genioglossal activity allows the pharynx to obstruct when simultaneous activity of other dilator muscles is inadequate during sleep.