INFLUENCE OF SLEEP ONSET ON UPPER-AIRWAY MUSCLE-ACTIVITY IN APNEA PATIENTS VERSUS NORMAL CONTROLS

Current evidence suggests that patients with obstructive sleep apnea ( OSA) may have augmented pharyngeal dilator muscle activity during wake fulness, to compensate for deficient anatomy. However, the isolated ef fect of sleep on the activity of these muscles (comparing OSA patients with controls) has not been studied. We therefore determined waking l evels of genioglossus (GG) and tensor palatini (TP) muscle activity (% of maximum electromyographic [EMG] activity) in 10 OSA patients and e ight controls, and then assessed the impact of the first two breaths o f sleep (theta electroencephalographic [EEG] activity) following a per iod of stable wakefulness. Apnea patients demonstrated greater geniogl ossal (27.4 +/- 4.0 versus 10.7 +/- 2.1%) and tensor palatini (31.9 +/ - 6.5 versus 10.6 +/- 1.9%) EMG activity than did controls during wake fulness. This augmented muscle activity in apnea patients could be red uced to near control levels during wakefulness with the application of continuous positive airway pressure (CPAP) to the upper airway. At sl eep onset, control subjects demonstrated small but consistent decremen ts in the activity of both the TP and GG muscles. On the other hand, a pnea patients demonstrated large, significantly greater decrements in TP EMG at sleep onset than did the control subjects. The effect of sle ep on GG EMG in apnea patients was inconsistent, with most (n = 7) dem onstrating large (significantly larger than controls) decrements in ge nioglossal activity. However; three OSA patients demonstrated small in crements in GG EMG at sleep onset despite falling TP EMG and obstructi ve apnea or hypopnea. We conclude that sleep onset is associated with significantly larger decrements in TP muscle EMG activity in OSA patie nts than in controls, which may represent a loss of neuromuscular comp ensation that is present during wakefulness. However, our results for the GG muscle were more variable, and did not always support this hypo thesis.