Study on the Effects of Infra- and Low Frequency Sound on the Sleep by EEG Recording R. Inaba, and A. Okada Department of Public Health. School of Medicine. Kanazawa University, 13-1 Takaramachi, Kanazawa, 920 Japan. Received June 30th 1988

ABSTRACT

Thisstudy wasperformedto investigate the effects ofinfra-and lowfrequencysound on sleep. Healthystudentswere periodically exposedtosound stimuli withfrequencies of10, 20,40and 63 Hz throughout their sleep while EEG was continuously recorded. The effects were evaluatedby the reaction rate and the changesofsleeppattern which consisted ofthe sleep efficiency index. numbers ofchangesin sleepstageand the proportion ofeach sleepstageto time in bed. Thereaction ratewashighestin sleepstage 1 and lowest in sleepstages 3 & 4. As concerns the exposures at soundpressure levels under 85 dB, therewereno significantdifferences in the reaction rates for thefour frequencies used. On the otherhand.for sound pressure levels over 85 dB, the reaction ratesobserved at 40 and 63 Hz were significantly higherthan thoseobservedat 10and 20 Hz. Thesleeppatternwasnot significantly affectedby exposureto the sounds used in this experiment. Introduction Recently, the effects of both infra- and low frequency sound and noise and vibration have attracted attention in Japan. The effects are headache, sleep disturbance etc, however, the effects of infra- and low frequency sound have not been clarified in detail. It is therefore important to investigate the effects of infra- and low frequency sound experimentally. The purpose of the present study is to obtain some basic information on the physiological effects of infra- and low frequency sound on sleep. Subjects and Methods The subjects were six healthy students, 20-25(average 22.8) years of age. They had no past histories of otolaryngological or mental diseases . During the experimental period, the subjects were told to avoid drink, heavy exercise, a nap or drinking especially strong coffee. . The subjects were exposed to the infra- and low frequency sound in the exposure chamber (2.1 x 2.8x 2.2 m) on the 3rd, 4th and 5th experimental nights. To generate the sounds, this chamber has 16 loudspeakers in the ceiling. Outdoor noise was completely excluded. Room temperature was regulated at 23± I "C.Twosubjects were used on the same night, and each of them slept on a mattress using a blanket and a quilt Prior to the experiment, electrodes were attached to the subjects for recording the polysomnogram. In this experiment, the polysomnogram consisted of an electroencephalogram (EEG) (C 3 and C4 to 0 1) , an electrooculogram (EOG), an electrocardiogram (ECG) and an electromyogram (EM G) of jaw. The background sound in the experimental chamber and the sound stimuli were also recorded. The polysomnogram was recorded on an EEG recorder (SANE! I A75) for 510 minutes, namely, from 10:00 at night to 6:00 in the next morning. On the 3rd, 4th and 5th nights, the sounds with frequencies of 10,20, 40 and 63 Hz at several sound pressure levels were randomly presented to the subjects for 30 seconds per 20 minutes throughout their sleep. The sound pressure levels exposed were: (a) 80,90,100 and 105dB at 10Hz; (b) 75,85,95, lOO and 105dB at 20 Hz; (c) 60, 70, 80,90,95 and 100dB at 40 Hz; and (d) 50, 60, 70, 80, 85 and 90 dB at 63 Hz. The analyses of sleep stages based on EEG was done

Journal of Low Frequency Noise and Vibration Vol. 7 No.1 1988

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INFRASOUND & SLEEP

according to the criteria proposed by Rechtschaffen and Kales (1). Sleep efficiency index [ (Time in bed)/(Sleep period time)], number of changes in sleep stage and proportion of each sleep stage to time in bed were calculated according to the method of Williams et al (2).The second night was used as the control night according to the principle proposed by Agnew et al (3). The criteria used in this experiment regarding the positive reaction to the exposure to infra- and low frequency sound were as follows; (a) change to a lighter sleep stage in case of non- REM sleep; (b) change to non-REM sleep in case of REM sleep; and (c) occurrence of body movement. In order to judge this point, sleep stages for one minute before and after the start of sound exposure were compared to each other. Statistical significance was tested by Student's and Welch's ttest and X2 test. Results and Discussion Figure 1 shows the reaction rate after exposure to infra- and low frequency sound at each sleep stage. The reaction rate was the highest at sleep stage 1 (S1) and the lowest at sleep stage 3-4(S3 &4).The reaction rate at sleep stage REM (8REM) was almost the same as that at sleep stage 2 (S2). The reaction rate at 81 was significantly higher than those at 82, 83 &4and 8REM (p,

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Effects of infra- and low frequency sound on the sleep efficiency index. Th e 2nd night is a control nigh t. Each value represents the mean ± one standard deviation.

17

INFRASOUND & SLEEP

In addition to the effects ofthe exposure to infra- and low frequency sounds, the effects of infra- and low frequency sound on the sleep pattern were also investigated. This method has been used frequently for evaluating the effect of noise on sleep (4-7). In this study , we used the sleep efficiency index, the number ofchanges in sleep stage and the proportion of each sleep stage to total sleep period time as the indices of sleep pattern . Figure 3 shows the effects of infra- and low frequency sound on the sleep efficiency index. There were no significant differences between the exposed nights (3rd, 4th and 5th night) and the control night (2nd night). Figure 4 shows the effects of infra- and low frequency sound on the numbers of changes in sleep stage. There were no significant differences between the exposed nights and the control night.

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Effects of infra- and low frequency sound on the numbers of changes in sleep stage. The 2nd night is a control night. Each value represents the mean ± one standard deviation.

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Changes of the proportion of each sleep stage to time in bed after exposure to infra- and low frequency sound. The second night is a control night. Each value represents the mean ± one standard deviation

18

INFRASOUNO & SLEEP

Figure 5 shows the changes of the proportion of each sleep stage to time in bed, after exposure to infra- and low frequency sound. There were no significant differences between the exposed nights and the control night These results suggest that the sleep pattern is little affected by the exposure to infra- and low frequency sound. As concerns the effects of infra- and low frequency sound on the sleep efficiency index, Fecci et al (8) reported that the sleep efficiency index was increased by exposure to sound. Nagai (9) reported that a relationship between sleep disturbance and the shaking and rattling of house fittings etc. was observed in the field study. Therefore, the exposure to infra- and low frequency sound may not have such harmful effects on the sleep. Moreover, sleep disturbance may be mainly caused by the noise which arises from the shaking and rattling of house fittings etc. caused by the infra- and low frequency sound.

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2.

Williams, R.L., Karacan, I. and Hursch, C.J. (1974) Electroencephalography (EEC) of Human Sleep; Clinical Applications. John Wiley and Sons, New York.

3.

Agnew, H.W.J., Webb, W.B. and Williams, R.L. (1966) Thefirst night effect: An EEG study of sleep. Psychophysiology, 2, 263-266.

4.

Scott, T.O. (1972) The effects of continuous, high intensity white noise on the human sleep cycle. Psychophysiology, 9, 227-232.

5.

Townsend, R.E., Johonson, L.C. and Muzet, A. (1973) Effects of long term exposure to tone pulse noise on human sleep. Psychophysiology, Vol. 10, 369376.

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Thiessen, G.J. and Lapointe, A.C. (1983) Effect ofcontinuous traffic noise on percentage ofdeep sleep, waking, and sleep latency. 1. Acoust. Soc. Am. Vol. 73,225229.

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Wilkinson, R.T. and Campbell, K.B. (1984) Effects oftraffic noise on quality of sleep: Assessment by EEG, subjective report, or performance the next day. 1. Acoust. Soc. Am., Vol. 75, 468-475.

8.

Fecci, R., Barthelemy, R., Bourgoin, J., Mathias, H., Eberle, A., Mountel, A. and Julien, G. (1971). The action ofinfrasounds on the body. Medicina del Lavoro, Vol. 62. 130-150. Nagai, N. : Process and emergence ofthe effectsofinfrasonic noise on man (1984). Report 1. Field study. 1. Wakayama Med. Soc., Vol. 35(2), 243-253.

9.

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