Habituation of sleep to road traffic noise by Actiwatch

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The habituation of sleep to road traffic noise was evaluated by body movement using wrist accerelometer and also sleep polygraphy.Subjects were four 21-year old students and they slept for 17 nights independently in a sleep laboratory. From fifth to 14th nights, road traffic noise was exposed all-night long. From fifth to 17th night, consecutive experiments were conducted. The daily life is not limited. They usually go to bed at 22 o'clock and gets up around seven o'clock in the next morning. ACTIWATCH【encircledR】 was installed in the wrist of their recessive arms. The sampling frequency was 32Hz and sensitivity was 0.05G, counting for one minute as a unit. The number of body movement was calculated by the summation in the number of active electricity. If the count is 40 or over, we judged it as awakening. Though under 40, n(e-2)×0.04+n(e-1)×0.2+n(e)+n(e+1)×0.2+n(e+2)×0.04 exceeds 40, then we judged it as awakening. By this algorithm, the agreement between ACTIWATCH【encircledR】 and sleep polygraph was 87% on average by calculating 18 nights.There was no trend in activity of mental muscle. Sleep latency in subject A in the last three days increased rapidly. Body movement % for all-night long decreased significantly in subject B. There was a significant relationship between body movement % and activity of mental muscle by sleep polygraphy.A significant increase of body movement in MT was recognized in subjects B, C, D. A significant increase of body movement in REM was recognized in subjects A, B, D. The latter fact is not logical because of drop in muscle tonus. There was a significant decrease of body movement in slow wave sleep in subject D.Body movement by accerelometer seems to be a good indicator for monitoring the effect of noise on sleep from the point of simplicity. As some individual differences are existed, much more cases are needed to check the validity using sleep polygraphy.