Nocturnal polysomnographic correlates of daytime sleepiness.

The relations of nighttime polysomnographic sleep variables with daytime sleepiness scores on the Epworth Sleepiness Scale were assessed in a retrospective chart review of 38 patients referred to a sleep clinic. Of the variables assessed, only slow wave sleep was statistically significantly correlated with daytime sleepiness, regardless of whether the analysis was based on absolute minutes of slow wave sleep or percentage of total sleep time spent in slow wave sleep. Stepwise linear regression suggested that other polysomnographic variables did not provide additional predictive value beyond the two indices of slow wave sleep. Apparently, reduced quantity of slow wave sleep was weakly but significantly related to increased daytime sleepiness among these sleep-clinic patients.