Sleep fragmentation and respiratory disturbance measures are used in the assessment of
obstructive sleep apnea (OSA) but have proved to be disappointingly poor correlates of
daytime sleepiness. This study investigates the ability of electroencephalograph (EEG) and non-EEG
sleep fragmentation indices to predict both presenting
sleepiness and the improvement in
sleepiness with subsequent
nasal continuous positive airway pressure (nCPAP)
therapy (nCPAP responsive
sleepiness). Forty-one patients (36 men, 5 women), ranging from nonsnorers to severe OSA (> 4% O2 dip rate, median 11.1, range 0.4 to 76.5), had polysomnography with microarousal scoring, computerized EEG analysis, autonomic arousal detection, and body movement analysis. All patients received a trial of nCPAP regardless of sleep study outcome. Spearman's correlation analysis showed significant and similar associations between all
sleep fragmentation indices with both pretreatment and nCPAP responsive
sleepiness. There was no deterioration in
sleepiness on nCPAP in the nonsnorers. Using stepwise multiple regression analysis, the best predictor of nCPAP responsive subjective and objective
sleepiness was body movement index, explaining 38% and 43% of the variance, respectively. Variability in EEG sleep depth, quantified from computerized EEG analysis, was the only other index to contribute to these models. Together these indices explained 44% and 51% of the subjective and objective response to nCPAP, respectively. These results suggest that
sleep fragmentation indices are useful for identifying OSA patients with
sleepiness likely to respond to nCPAP.