Influence of wakefulness on pharyngeal airway muscle activity

Introduction: Whether loss of wakefulness itself can influence pharyngeal dilator muscle activity and responsiveness is currently unknown. We, therefore, assess the isolated impact of sleep on upper airway muscle activity after minimizing respiratory/mechanical inputs. Methods: Ten healthy subjects were studied. Genioglossus (GG), tensor palatini (TP), and diaphragm (DIA) electromyography (EMG), ventilation, and sleep- wake status were recorded. Non-invasive positive pressure ventilation was applied. Expiratory pressure was adjusted to yield the lowest genioglossal EMG thereby minimizing airway negative pressure (mechanoreceptor) effects. Inspiratory pressure, respiratory rate, and inspiratory time were adjusted until the subjects ceased spontaneous ventilation, thereby minimizing central respiratory input. We evaluated muscle activity during wakefulness, wake-sleep transitions, stable non rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep in the supine position. Results: In transitions from wakefulness to sleep, we observed significant decrements in both average GG and TP EMG (1.6 (0.3) to 1.3 (0.4) % of maximal GGEMG; 4.3 (2.3) to 3.7 (2.1) % of maximal TPEMG; respectively). Compared with sleep onset, the activity of TP during stable NREM sleep and REM sleep demonstrated further decreases (3.7 (2.1) vs. 3.0 (2.0) vs. 3.0 (2.0) % of maximal EMG). However GGEMG was only further reduced during REM sleep (1.3 (0.4) vs. 1.1 (0.4) vs. 1.0 (0.3) % of maximal EMG). Conclusion: This study suggests that wakefulness per se, independent of respiratory/mechanical stimuli, can influence pharyngeal dilator muscle activity.