A comparison of middle latency auditory-evoked response in obstructive sleep apnea syndrome before and after treatment.

The ascending reticular activating system seems to be affected by nocturnal hypoxia in obstructive sleep apnea syndrome (OSAS) patients so that their vigilance level is decreased. To evaluate the change in vigilance level in OSAS patients, polysomnography, the Epworth Sleepiness Scale and middle latency auditory-evoked responses (MLR) were measured before and after treatment in seven men with OSAS (mean age 45.4 +/- 12.9 years, mean body mass index 33.3 +/- 7.6 kg/m2). After treatment there was significant improvement of nocturnal hypoxia in OSAS. Peak amplitude of P1 in MLR increased after treatment. There was also improvement of the electrical field distribution of MLR on the scalp. The results suggest that the decreased vigilance level in OSAS patients is reversible with treatment.