Upper Airway Muscle Activation Is Augmented in Patients with Obstructive Sleep Apnea Compared with That in Normal Subjects

Although phasic electromyographic (EMG) activity of upper airway muscles in patients with obstructive sleep apnea (OSA) decreases at apnea onset, the presence of phasic activity in normal subjects has not been studied and compared with that in patients. We consequently compared the percentage of total sleep time in which phasic activity of the genioglossal EMG activity was present in 8 adult patients with OSA and 3 control groups without OSA, one consisting of 6 young, normal subjects, one matched for age, and one matched for age and obesity. From wakefulness to sleep, genioglossal EMG phasic activity time increased in patients but not in control subjects. Patients with OSA had more phasic genioglossal group EMG activity during non-REM sleep than did control subjects. At apnea onset, phasic EMG activity decreased in patients but remained greater than zero. In many control subjects, phasic activity was not detected, yet their pharyngeal airway remained patent. We conclude that phasic genioglossal group EMG activity occurs more frequently during sleep in patients with OSA than in control subjects, suggesting that it is a compensatory mechanism that occurs when patency of the pharyngeal airway is precarious.