Nighttime variability in wrist actigraphy.
ABSTRACT Wrist actigraphy measures sleep activity and circadian rhythm. This study examined nighttime variability in Actiwatch parameters in a sample of breast cancer survivors (BCSs) to determine a minimum number of nights needed to obtain an accurate picture of objective sleep. A descriptive, quantitative, and repeated measures design was used. Consenting participants wore an actigraph and completed a sleep diary across 7 nights. There were no significant differences in wake after sleep onset (WASO), total sleep time (TST), sleep latency, or sleep disturbances across nights of week (Monday to Sunday) or monitoring nights (1st to 7th). Sleep efficiency was significantly better at Night 6 compared with Night 7. The coefficients of variation (CVs) for WASO ranged from 46% to 86%, TST 23%-34%, sleep latency 154%-246%, sleep efficiency 12%-22%, and sleep disturbances 33%-41%. Although the CVs indicated high variability across women, there was little internight variability in WASO or TST during across 7 nights of sleep. This suggests that in BCSs, Actiwatch data could be collected and evaluated from any single night for an accurate measure of usual sleep.
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ABSTRACT: According to the two-process model of sleep regulation, the timing and structure of sleep are determined by the interaction of a homeostatic and a circadian process. The original qualitative model was elaborated to quantitative versions that included the ultradian dynamics of sleep in relation to the non-REM-REM sleep cycle. The time course of EEG slow-wave activity, the major marker of non-REM sleep homeostasis, as well as daytime alertness were simulated successfully for a considerable number of experimental protocols. They include sleep after partial sleep deprivation and daytime napping, sleep in habitual short and long sleepers, and alertness in a forced desynchrony protocol or during an extended photoperiod. Simulations revealed that internal desynchronization can be obtained for different shapes of the thresholds. New developments include the analysis of the waking EEG to delineate homeostatic and circadian processes, studies of REM sleep homeostasis, and recent evidence for local, use-dependent sleep processes. Moreover, nonlinear interactions between homeostatic and circadian processes were identified. In the past two decades, models have contributed considerably to conceptualizing and analyzing the major processes underlying sleep regulation, and they are likely to play an important role in future advances in the field.Journal of Biological Rhythms 01/2000; 14(6):557-68. · 2.93 Impact Factor