[Effect of the first sleep night in polysomnography: classification by variable sensitivity and factorial analysis of differences between nights].

It has been known since the sixties that a habituation phenomenon is present in polysomnographic analyses of sleep, the first night including more awakenings and less Rapid Eye Movement sleep (REM) than consecutive ones. Results about Non-Rapid Eye Movement sleep (NREM) are less clear. The study presented here attempted to classify the variables in function of their sensitivity to this phenomenon by comparing inter-night and inter-subject effects in a series of ANCOVA analyses and on the other hand, to group the same variables in function of a factorial analysis on the differences between the two first nights. The study included 26 subjects with no somatic nor psychiatric disorder and was performed at their homes for four consecutive nights. The most sensitive variables were, in descending order: Ultra-Slow spectral power band, REM sleep, Sleep Efficiency Index, Delta spectral power band, number of awakenings, duration of awakenings, number of ultradian sleep cycles and Total Sleep Time. The factorial analysis showed 7 factors, grouping separately the two series of results from the spectral analysis (corresponding to visually-scored NREM and REM sleep), awakenings, sleep duration variables, variables linked to REM sleep, microarousals and deep sleep.