EEG recurrence markers and sleep quality

OBJECTIVES To show that EEG markers formed using the variable percent recurrence reliably quantified two related aspects of sleep quality, sleep depth and sleep fragmentation. As hypotheses, the depth marker would increase and the fragmentation marker decrease in patients where improved sleep quality occurred when assessed by polysomnography. METHODS The patients (N=20) had been diagnosed with obstructive sleep apnea during diagnostic polysomnography (dPSG), and had exhibited increased REM sleep (clinical indication of improved sleep quality) during subsequent polysomnography to titrate the pressure of a treatment device (cPSG). Percent recurrence was computed second-by-second from the EEG; sleep-depth and sleep-stability markers were obtained algorithmically. By assumption, the markers contained temporal information regarding the extent of deterministic (non-random) brain activity. Marker means were compared between the dPSG and the cPSG for NREM and REM sleep. RESULTS Sleep depth was greater and sleep fragmentation was less during cPSG, as hypothesized (P<0.05). The effects occurred during NREM and REM sleep, but were greater during NREM sleep (P<0.05). At least one of the predicted changes occurred in 95% of the patients. CONCLUSIONS The factors generally regarded as responsible for subjective sleep quality were objectively quantified on the basis of dynamical changes in the EEG.