The Multiple Sleep Latency Test by Carskadon and Dement (1977) recorded the sleep latency lying down and is recommended for the investigation of daytime sleepiness in OSAS patients in the ICSD-2. The MSLT is based on the assumption that a strong physiological sleepiness can reduce the sleep latency (Arand et al. 2005).
For a long time the MSLT has been considered a gold standard for the investigation of daytime sleepiness (Carskadon et al. 1986). The MSLT (as well as the Maintenance of Wakefulness Test (MWT)) is often used to determine the alertness with expert's investigations, e.g. to assess the driving ability (Poceta et al. 1992). Five times a day electrophysiological recordings (C3/A2, C4/A1, EOG, EMG) are performed in 2-hour intervals. The first time of measurement should be from 1.5 to 3 hours after waking. The patient lies in a darkened room and is asked to fall asleep. During the test procedure, the patient is monitored with a video recording.
A pathological fall asleep exists, when the medium sleep latency is < 5 minutes (Richardson et al. 1982). The gray area is between 5-10 minutes and > 10-20 minutes is a normal finding. But are also divergent standard values of 5-8 minutes; thereby establishing of normal values is equivalent to a kind of "rule of thumb" (Guilleminault et al. 1994, van den Hoed et al. 1981, Johns 2000). Although the MSLT perform and should be evaluated strictly according to objective criteria and standardized, it seems to have low implementation objectivity, because the results of individual tests vary greatly (Danker-Hopfe et al. 2006). As other reasons for the inconsistent individual test results Thorpy (1992) describes the different day times and measuring times and not objectified sleep deprivation and sedative or stimulating effects of drugs. In spite of these influences, however satisfactory test-retest reliabilities of rtt = .65 to .97 (van den Hoed et al. 1981, Zwyghuizen-Doorenbos et al. 1998) have been found. Another problem of MSLT is the limited external generalization of daytime sleepiness in everyday situations (Johns 1994). The assumption that the MSLT describe daytime sleepiness - as reflection of everyday life - Johns (2000) keeps being wrong. As a predictor of MSLT is therefore not own, regardless how strict standards and criteria were met. In considering of the relationship between ESS and MSLT are unsatisfactory correlation of r = .27 (p <.001) or on those that are not significant (Mitler et al 1998.). Reasons for the inconsistent correlations are different: Either there are satisfactory (significant) correlations when all patients fell asleep in all MSLT times or when the patients rarely slept or not fell asleep (Chua et al. 1998).
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