Daytime tiredness correlates with nocturnal respiratory and arousal variables in sleep apnea patients: Polysomnography and EEG mapping investigations

There is evidence that daytime tiredness is caused by apnea/hypopnea with o xygen desaturation and/or by sleep fragmentation due to arousals. The aim o f this study was to investigate objective and subjective sleep and awakenin g quality and daytime vigilance objectified by midmorning mapping of vigila nce-controlled EEG (V-EEG)- in sleep apnea patients (N: 18), as compared wi th age- and sex-matched normal controls (N: 18) as well as to correlate noc turnal respiratory distress and arousals to daytime brain function. Statist ical analyses demonstrated a deterioration in subjective and objective slee p and awakening quality in apnea patients. Midmorning V-EEG mapping in apne a patients exhibited less total power, more delta and theta, less alpha and beta activity, as well as a slower dominant frequency and centroid of the total activity compared to controls, which suggests a vigilance decrement. The Spearman rank correlation between 6 polysomnographically registered res piratory variables and 36 diurnal quantitative EEG measures demonstrated th e following: the higher the apnea, apnea-hypopnea, snoring and desaturation indices and the lower the minimum and average low oxygen saturation, the m ore pronounced was diurnal tiredness. Eleven arousal measures based on ASDA criteria showed the following significant correlations: the higher the noc turnal arousal index and the more arousals due to hypopneas, the greater wa s daytime tiredness. On the other hand, the greater the average frequency c hange during arousals and the more spontaneous arousals, the better was day time vigilance. Our findings show that, in contrast to the lengthy Multiple Sleep Latency (MSLT) and Maintenance of Wakefulness (MWT) tests which eval uate sleep pressure under resting conditions conducive to sleep,V-EEG mappi ng provides a brief objective measure of a sleep apnea patient's daytime ti redness under conditions of wakefulness more appropriate to reflect the pat ient's everyday life.