Circadian rhythm abnormalities of wrist activity of institutionalized dependent elderly persons with dementia.

BACKGROUND The study objective was to clarify the descriptive characteristics of circadian rhythm abnormalities of wrist activity of the institutionalized elderly with dementia. METHODS We studied 82 elderly persons with dementia who were institutionalized in a long-term medical care facility. The ambulatory continuous monitoring of their wrist activity was conducted for 7 days at 1-minute intervals. The time series data were analyzed using the double-plotted chronogram, spectral analysis was performed using the fast Fourier transformation and periodogram analysis was performed as well. RESULTS The frequency of circadian rhythm abnormalities of wrist activity rhythm in elderly persons with dementia was 57.3% (47 out of 82). The abnormalities were classified into four categories: severely impaired circadian rhythm type with no boundary between day and night, free-running rhythm type, decreased circadian amplitude type, and accentuation of ultradian rhythm type. CONCLUSION This four-category classification system provides a scientific approach for studying the mechanisms of circadian activity rhythm abnormalities of elderly persons with dementia.