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An actigraph (ZAK company) is a small device that can be worn on the wrist like a watch. We carried out a study to compare sleep efficiency and total sleep time as determined by actigraphy and polysomnography. The number of body movements per minute is a density function. The integrated function shows a virtually constant gradient in the wake state and a different constant gradient during sleep. The body movement density function per hour provides a useful threshold for correctly differentiating between wake and sleep states. This threshold is defined as the minimum between the two maxima of the bimodal logarithmic body movement density distribution. In the second step we computed a rank scale of the different gradients and approximated the integrated function for every scale element using linear graphs. The points of intersection of the straight lines define the time points for sleep onset and end of sleep. Sleep efficiency is given by SE = 100 (TST-sleep interruption time)/TST. Total sleep time is the interval between sleep onset and end of sleep. Actigraphy is a suitable semi-objective method for estimating sleep efficiency and total sleep time, and--for cost reasons--should be used for screening before approaching a sleep laboratory. Actigraphy carried out over several days shows only small differences in comparison with polysomnography. The estimation of parameters is more accurate the longer the patient wears the actigraph, and a minimum of five days is recommended. Spectral analysis of the intregrated body movement density provides important information for detecting subclinical sleep disorders.

Untersuchung des Ruhe-Aktivitäts-Zyklus des Menschen. - Analysis of the Rest-activity Cycle in Man