A novel EEG index for evaluating the sleep quality in patients with obstructive sleep apnea-hypopnea syndrome

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is a highly prevalent sleep disorder characterized by recurrent episodes of oxygen desaturation during sleep, decreased sleep quality, and excessive daytime sleepiness. A basic method of evaluating sleep quality is polysomnography (PSG) where sleep stages are identified from the electroencephalogram (EEG), electrooculogram and chin electromyogram. The implementation of PSG is limited to sleep laboratories because this test is rather complicated to perform and quite time-consuming to analysis, requiring skilled technicians. Development of simple alternative methods to PSG could enable sleep tests to be performed at home. Our study aimed to identify simple measures for evaluating the sleep quality. We focused on a simple index, entropy, which is derived from power spectrum of EEG signals throughout the night, and reflects the dynamics of EEG signals, and examined whether the entropy of EEG reflects the sleep quality of OSAHS. The EEG signals for the analysis of EEG entropy were recorded from the temple area. The EEG entropy was compared with the sleep quality by traditional approaches of EEG from PSG in 58 OSAHS patients and 8 healthy volunteers. The EEG entropy in each subject showed the negative values and fluctuated during sleep. There was a significant correlation between the EEG entropy and the sleep quality (r = 0.626, p < 0.001); namely, the amplitude of the fluctuation was increased with the increase in the sleep quality. We therefore propose that the EEG entropy could be useful for evaluating the sleep quality of OSAHS.