[The effect of noise on sleep--changes in hypnograms of subjects exposed to repeated truck-passing sound].

The effect of traffic noise on sleep was evaluated in an experimental room using repeated recorded truck-passing sounds. The peak sound level was 55, 60 or 65 dB (A) with frequencies of three times per hour. The background noise of the exposure night was Leq 42 dB (A) and that of the control night was Leq 35 dB (A). The subjects were five students 23 to 24 years old. The sleep stage of each epoch with a 20-second duration was judged visually based on the criteria of Rechtschaffen & Kales and the data of the second night of noise-exposure and the control night were used. The sleep parameters used were total sleep time (TST), each sleep stage, % of sleep stage against TST, sleep efficiencies, sleep latency, REM latency, REM cycle, REM duration, waking from sleep, number of stage shifts, and subjective sleep judged by the OSA sleep inventory. A paired t test was used for the statistical analysis. TST, REM stage in minutes, and % of REM stage against TST of the exposure night were significantly decreased compared with those of the control night. Other objective and subjective parameters showed no changes during noise exposure. Dividing the all-night into halves, the amount and % of each sleep stage were compared between the exposure and control night. There was no change of sleep stage in the former half, but the % and amount of REM sleep in the latter half were significantly decreased as a result of the noise exposure. The decreases of REM sleep and % REM against TST, especially in the latter half of all-night sleep, were caused by the intermittent truck-passing sounds 20 to 30 times per night.