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|Year : 2004 | Volume
| Issue : 22 | Page : 27--33
Disturbed sleep patterns and limitation of noise
B Griefahn1, M Spreng2,
1 Institute for Occupational Physiologie at the University of Dortmund, Germany
2 Institute for Physiology and Experimental Pathophysiology, University of Erlangen, Germany
Institute for Occupational Physiology at the University of Dortmund, Ardeystr. 67, D-44139 Dortmund, Fed. Rep.
Due to the undisputable restorative function of sleep, noise-induced sleep disturbances are regarded as the most deleterious effects of noise. They comprise alterations during bedtimes such as awakenings, sleep stage changes, body movements and after-effects such as subjectively felt decrease of sleep quality, impairment of mood and performance. The extents of these reactions depend on the information content of noise, on its acoustical parameters and are modified by individual influences and by situational conditions. Intermittent noise, that is produced by air traffic, rail traffic and by road traffic during the night is particularly disturbing and needs to be reduced. Suitable limits are suggested.
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Griefahn B, Spreng M. Disturbed sleep patterns and limitation of noise.Noise Health 2004;6:27-33
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Griefahn B, Spreng M. Disturbed sleep patterns and limitation of noise. Noise Health [serial online] 2004 [cited 2020 Nov 29 ];6:27-33
Available from: https://www.noiseandhealth.org/text.asp?2004/6/22/27/31676
Apart from its effects on hearing acuity, noise causes extraaural effects which might be subdivided into primary effects that comprise disturbances of communication, of sleep, and of autonomous functions. Their consequences, categorized as secondary effects or as aftereffects are annoyance and impaired performance. In the long run, i.e. within decades, primary and secondary effects might contribute to the genesis and accelerate the manifestation of multifactorial chronic diseases. Social surveys have repeatedly shown that annoyance is the most frequent effect of noise, where sleep disturbances are regarded as most deleterious. Particularly concerned are residents in the vicinity of large airports and those living along roads with heavy traffic and along railway tracks.
Normal sleep and its recording
Sleep is obviously an essential need, which is exhibited by all living creatures. The sleep-wake cycle is the most significant sign of the circadian rhythm, which develops during the first months of life in humans. Sleep behavior of newborn infants is irregular during the first weeks of life. A clear diurnal rhythm, where sleep occurs mainly during the night and the state awake during the day develops gradually and is completely established after about six months. A polycyclic sleep behavior with interspersed sleep episodes during daytime and repeated periods awake at night, is again resumed by aged people. Total sleep time alters dramatically during lifetime. As shown in [Figure 1], the newborn baby sleeps up to 16 hours a day, whereafter daily sleep time decreases rapidly. Young children exhibit 11 to 12 hours of sleep, school children approximately 10 hours, and adults between 7 and 8 hours, where aged people do not sleep more than 5 to 6 hours. The interindividual variability is, however, huge, where sleep times range between 2 and 12 hours, whereas the intra-individual sleep duration is rather stable. As humans need obviously less sleep than actually exhibited, some scientists separate between obligatory and facultative sleep (Horne 1988).
The polysomnography, that is the simultaneous recording of the electroencephalogram (EEG), the electrooculogram (EOG), and the electromyogram (EMG) is the only measure which reliably indicates whether a person is awake or asleep and provides informations on sleep depth. Alternative, but less precise methods are signalled awakenings (pressing a button when woken up) and body movements which are detected by actimeters.
Subjective sleep quality is assessed with short questionnaires just after getting up in the morning and the efficiency of sleep might be indicated by performance tests that are applied to measure working speed and errors.
Sleep consists of two fractions mainly, known as REM-sleep (paradoxical sleep, dream sleep) and non-REM-sleep (NREM). REM- and non-REM sleep alternate periodically, thus structuring sleep into 4 to 6 cycles of 90 to 100 minutes each. NREM sleep itself reveals systematic electroencephalographic changes within each cycle, where a decline in frequency coupled with a simultaneous rise in amplitude corresponds to a deepening of sleep which is followed by the reverse, an increase in frequency accompanied with a decrease in amplitude, i.e. a gradual flattening of sleep. The electroencephalographic pattern in REM sleep corresponds to that of the flattest sleep stage 1, but is characterized by rapid eye movements, that are registered by the electrooculogram (EOG). The maximum sleep depth attainable lessens from cycle to cycle, whereas the time spent in REM sleep increases gradually [Figure 2].
Sleep disturbances in general are objectively measurable and/or subjectively felt deviations from habitual or desired sleep behaviour. From the viewpoint of preventive medicine, sleep disturbances may be subdivided into
* sleep disturbances that are related to underlying diseases thus requiring causal therapy, and
* sleep disturbances that are caused by environmental influences thus allowing prevention by an adequate design of the environment (Griefahn 1985).
Noise-induced sleep disturbances belong to the latter category. They typically begin with a Kcomplex, i.e. a biphasic EEG wave formation, accompanied by altered autonomic functions (increase in heart rate, constricted peripheral blood vessels etc., see [Figure 3]) and by body movements. Depending on the nature and the intensity of the impinging sound, this initial reaction is followed by a more or less long lasting desychronization of cortical activity that reach from a flattening of sleep up to awakening, thereby causing more or less extended partial sleep deprivations. Autonomous responses are for instance alterations of heart rate or an increased release of stress hormones, respectively an increased excretion of their metabolites.
Sleep disturbances are by no means limited to the sleep period itself. They may instead affect mood, well-being, and performance the next day. In the long run, they are suspected to contribute to the genesis and manifestation of clinically relevant health disorders.
Referring to the WHO definition (1968) of health as 'a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity', awakenings induced by noise, consecutive impairments of mood, psychosocial well-being, and performance are clearly classified as health effects (Porter et al. 2000).
The extents of noise-induced sleep disturbances are determined by the acoustic characteristics of the impinging noises as well as by individual and situational factors.
Information content: The most pronounced influence on the reaction is undoubtedly the informational content of noise, which is not solely determined by its physical parameters, but in the first case by the experience a person has with the respective noise. As the human brain can perceive, recognize and respond adequately to intruding noises, unfamiliar as well as unpleasant noises cause larger responses than familiar or neutral noises (Strauch et al. 1976). The informational content may change in the course of time and may either become insignificant or of greater significance to the individual concerned, with the result that both habituation as well as sensitization are possible this way.
Acoustic parameters: The temporal distribution of noises has a considerable influence on the reaction. Despite the same equivalent noise level intermittent noises that are usually emitted by air traffic and by rail traffic disturb much more than rather continuous noises that are caused by high density road traffic (Eberhardt 1987, Ohrstrom and Rylander 1982). Concerning road traffic, the density decreases considerably during the night so that an intermittent noise emission is even characteristic for most streets with otherwise vivid traffic.
The frequencies of noise-induced awakenings and body movements increase with the number of noises (partly at the expense of spontaneous awakenings and movements), but the relationships are not linear, since the risk to react to an individual stimulus decreases with the total number of stimuli (Griefahn et al. 1976, Ohrstrom 1995).
Broadly scattered dose-effect interrelationships exist as a rule between the intensity of the impinging noises and the extent of acute reactions, that are registered immediately following the onset of the acoustic stimuli (such as awakenings, sleep stage changes, and body movements). The quality of sleep is progressively judged as worse, sleep latency is perceived as longer and more difficult, and fatigue is experienced as greater [Figure 4].
Individual, biorhythmic, and situational characteristics: The extents of reactions are determined by individual differences, where several personal traits might be decisive. Persons who are sensitive to noise and those with neurotic tendencies reveal stronger effects. Stronger effects are also registered in aged people whose overall time awake is scarcely longer in noisy than in quiet nights but who attribute the time awake more often to noise intrusion. Contrary to a common belief, children are much (about 10 dBA) less sensitive than adults, whereas gender has no influence on the susceptibility to noise.
Biorhythmic alterations play a significant role when it comes to noise processing. So, the thresholds of noise-induced responses are inversely related to sleep depth that alters periodically during the night (infradian rhythm) and becomes gradually flatter towards the morning (e.g. Basner et al. 2001) meaning that noise-induced awakenings are also more likely in the late than in the early night. Another important influence results from the circadian rhythm. Daytime is for instance a very unfavorable chronobiological timeframe where people sleep usually 1-2 hours less than during the night, even under comparable and optimal acoustic conditions. In the real situation, the acoustic conditions are, however, considerably worse during the day. The equivalent noise level is then 7 to 15 dB(A) above those measured during the night and characterized by a high rate of meaningful and thus particularly disturbing noises (children, telephone etc.), so that night shift workers are then much more disturbed by noise.
The environment has another decisive influence. Data pooled from 21 investigations have accordingly shown much smaller effects in the field than in the laboratory (Pearsons et al. 1995). The possible reasons are in the first place habituation (Finegold 1993) and the simultaneous influence of other acoustic and non-acoustic stimuli that modify or even mask the responses to noise.
Evaluation limits, critical noise loads
Concerning noises emitted from various sources, transportation noise leads most frequently to sleep disturbances. Though noise emission of the single vehicles and airplanes was significantly reduced within the last decades, the equivalent noise levels increased nevertheless due to a considerably larger traffic density that is expected to increase further. As compared to the year 1995, freight traffic will have increased by 80 % in the year 2010 and traffic density within cities by about 50 % and the increase will be greater during the night than during the day (European Commission 1997). The limitation of noise is therefore mandatory.
The undoubtedly best way for the protection of residents against the impact of the mainly intermittent transportation noise is the avoidance of any noise immission during the night. If this is not achievable, as far as possible awakenings are concerned, it is suggested to concentrate traffic to the less sensitive first part of the night, in particular as disturbances experienced during this period can be compensated in the following quieter part of the night (Griefahn 1977, Maschke 1992).
In case that traffic density cannot be reduced adequately in the second part of the night, it is recommended that the maximum levels are lowered within the first part of the night as compensations are no longer possible thereafter. Concerning intermittent noises, 2 models were developed, that allow the calculation of noise and number combinations that cause the same predefined admissible risk (Griefahn 1992, Spreng 2002). The physiological model proposed by Spreng (2002) refers to the admissible noise-induced release of cortisol in the normal range and its results match almost perfectly the noise and number relation determined for awakenings in the largest study ever done on the effects of aircraft noise on sleep (Basner et al. 2001). Based on this model [Figure 5] evaluation limits were derived for intermittent noise as shown in [Table 1] (Griefahn et al. 2002). These limits apply in the first case to aircraft noise, which, concerning transportation noise, annoys the most whereas railway noise annoys the least and this is true for 'Nighttime Annoyance' as well (Health Council of the Netherlands 1999).
There is some indication that the shoulder hours, especially in the evening should be respected as well. However, the database is as yet too to derive suitable limits.
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