Research on nighttime sleep disturbance due to community noise sources, particularly from exposure to aircraft noise, has been conducted for over a half decade. However, there are still no national environmental noise policies (i.e., laws and regulations) promulgated which prescribe a specific criterion for an exposure limit which is regulatory in nature. In the U.S., the new American National Standards Institute (ANSI) Noise Standard, ANSI S12.9-2008/Part 6, Quantities and Procedures for Description and Measurement of Environmental Sound - Part 6: Methods for Estimation of Awakenings Associated with Outdoor Noise Events Heard in Homes, does provide the currently recommended exposure-response relationship used in the U.S. In Europe, there has also been significant laboratory and field research on sleep disturbance, although the U.S. and European research publications often use different research methodologies, different noise metrics and different meta-analysis techniques. The current article will provide a brief overview of sleep disturbance research internationally to document the similarities and differences between the various research approaches and research results.
Keywords: Noise, aircraft noise, sleep disturbance
|How to cite this article:|
Finegold LS. Sleep disturbance due to aircraft noise exposure. Noise Health 2010;12:88-94
| Introduction|| |
Sleep disturbance is a common effect described by most noise-exposed populations and their complaints are often very strong, especially around airports. Protection of this particular rest period is necessary for a good quality of life, as day-time well being often depends on sleep quality and efficiency. Reduction or disruption of sleep is detrimental in the long term since chronic partial sleep deprivation induces marked tiredness, increases a low vigilance state, and reduces both day-time performance and the overall quality of life. Sleep appears to be quite sensitive to environmental factors, especially noise, since external stimuli are still processed by the sleeper sensory functions although there may be no conscious perception of their presence. The vast research published during the last 30 years has produced considerable variability of results and often some are quite controversial. The absence of one internationally accepted "exposure-effect" (or "dose-response") relationship is largely due to the lack of one obvious "best choice" research methodology, as well as to the complex interactions of the many factors which influence sleep disturbance. These include differences in the characteristics of the noise itself, differences in individual sensitivities, differences in attitudinal biases towards the noise source, and the context of the living environment. Current exposure-response relationships from major published meta-analyses use either "awakenings" or "body movements" to describe sleep disturbance. For brevity, this summary paper will focus predominantly on these meta-analyses, while recognizing that there are a great many individual studies published over the past decade which provide considerable sleep disturbance data using a wide variety of research techniques.
| How to Assess Sleep Disturbance|| |
Different noise metrics
Sleep disturbance from exposure to noise at night has been studied in a variety of environments, although the effects of transportation noise have been studied the most. Different indices have been used to describe various types of community noise exposure, and there is no general agreement on which should be preferred among the various integrated energy indices (LAeq, LDN, LDEN, and Lnight), statistical indices (L10, L50,…), or event indices (LAmax, Sound Exposure Level: SEL, Number of Noise Events: NNE,…). The choice of a noise metric for policy-making purposes depends on both the particular type of noise source and the particular effect being studied. Even for sleep disturbance due to transportation noise exposure such as aircraft noise, there is no single noise exposure metric or measurement approach which is generally agreed upon. At the single event level, a previous review of the publilshed sleep disturbance literature by Pearsons et al.  considers SEL, across various studies included in their meta-analysis, and concludes that this metric is a better predictor of sleep disturbance than LAmax. However, other reviews of the literature show that measures of maximum sound level are better predictors of disturbances during sleep than measures of average sound level. , The comprehensive review of the sleep disturbance research literature conducted by Michaud, et al.  According to these authors: "This literature review of recent field studies of AN-ISD finds that reliable generalization of findings to population-level effects is complicated by individual differences among subjects, methodological and analytic differences among studies, and predictive relationships that account for only a small fraction of the variance in the relationship between noise exposure and sleep disturbance. It is nonetheless apparent in the studied circumstances of residential exposure that sleep disturbance effects of nighttime aircraft noise intrusions are not dramatic on a per-event basis, and that linkages between outdoor aircraft noise exposure and sleep disturbance are tenuous". (p. 32).
The community noise guidelines published earlier by the World Health Organization  (WHO) allows the use of either LAmax or SEL, while the newer WHO report, "Night Noise Guidelines for Europe"  advocates the use of Lnight, outside for Europe, as does the European Commision (EC) "Environmental Noise Directive".  and the associated EC "Position Paper on Dose-Effects Relationships for Night Time Noise"  In the U.S., SEL is predominantly used for assessing sleep disturbance. ,, Thus, there is still no clear international consensus on this issue and further discussion is needed within the scientific community.
Different response measurement approaches
Effects of noise on sleep can be measured immediately or be evaluated afterwards, at the end of the night or during the following day. Thus, immediate effects are mainly measured by objective data recorded during sleep and they show how the sleeper is reacting to noise. After-effects are measured at the end of the night by subjective evaluation or by some objective biochemical data (such as levels of stress hormones) or by performance levels during the following day. The following list includes some of the various objective physiological, biochemical and behavioral measures used to assess the immediate effects of night time noise:
As the list shows, a variety of different research methodologies have historically been used in sleep disturbance research. For example, sleep stage change analyses were sometime made every 10, 20, 30 or 60 seconds in various published studies. The results of these studies, and especially those about the number of awakenings, sleep stage changes and sleep architecture should thus be expected to be quite different from each other, as indeed they are. Some of the most cited field studies present limited sleep disturbance indices; and the choice of measurement methods and sleep disturbance indicators is still controversial. This is particularly the case for studies using either behavioral awakening, as indicated by pushing a button when awakened,  and/or body motility (i.e., body movement as measured by an actimeter) as indicators of nocturnal awakening. ,, Pushing a button when being awakened during the night is only a rough, conservative technique to evaluate sleep disturbance, although it is an obvious indicator of awakening and should be easily understood by the public. However, changes in sleep architecture, including sleep stage changes and short-lasting awakenings as determined by electroencephalographic (EEG) recordings, are more subtle and would often be totally missed by both the button-press and the actimetry research techniques. In addition, body movements during sleep are quite normal physiological events. Only a small amount of them result in behavioral awakenings; most night-time body movements do not result in awakening. Therefore, measuring bodily movement by actimetric techniques during sleep is a relatively poor way of predicting awakenings. Although physiological indicators of awakening would ideally provide the most scientifically accurate data, usable conclusions from research using EEG and other physiological parameters, especially data from field research studies, are not yet ready for use in establishing noise exposure policies.
- Electroencephalograph (EEG) arousal responses
- Sleep stage changes
- Bodily movements using actimetric data
- Behaviorally-confirmed awakenings (e.g., a "button press" response)
- Autonomic responses
- Total waking time
Other measures made after night-time noise exposure include day-time performance and cognitive function deterioration analyses. In addition, the excretion of stress hormones in the morning urine flow can be measured to evaluate the impact of global noise exposure at night.  However, these types of measurements are quite difficult to perform in field situations and only a few studies have included them in the past.
Subjective evaluation of sleep disturbance
Recordings of objective sleep disturbance data can be too costly and too difficult to use with large samples of the population or when research funding is scarce, while subjective evaluation of sleep quality using a morning-after questionnaire is an easier and less costly way of collecting field data. Sleep disturbance can be assessed from complaints about bad sleep quality, nocturnal awakenings, often accompanied by impaired quality of the subsequent day-time period with increased tiredness, day-time sleepiness and need for compensatory resting periods. However, subjective complaints are quite different than objective (instrumental) measures. There are many factors which influence people's subjective evaluations of their own sleep quality. It has been very difficult for researchers to find a clear relationship between subjective complaints and actual noise exposure levels. In general, however, subjective self-reports of awakenings do not correlate well with more objective measures of sleep disturbance.
Laboratory versus in-home field studies
Survey of the literature shows large differences between results obtained in numerous laboratory studies and those issued from epidemiological or experimental studies made in real in-home situations. In the Pearsons et al.  meta-analysis, a comprehensive database representing over 25 years of laboratory and field research on noise-induced sleep disturbance was compiled and analyzed. The researchers firmly established the rather large differences observed between laboratory and in-home field studies with nocturnal awakenings being much greater in laboratory studies. It would certainly be the case that a certain degree of habituation occurs in people's own homes for the number of noise-induced awakenings they experience. On the other hand, modifications in sleep stage architecture (i.e., number of sleep stage changes) seem to habituate less with time, while purely autonomic responses do not habituate at all over extended periods of time. Effects on the endocrine and immune systems are more difficult to establish through both laboratory and field studies, and further research is clearly needed in these areas, especially because it is more difficult to extract the exact part due to the just noise exposure.
| Current Exposure-Response Relationships for Sleep Disturbance|| |
European union research
In July 2002 the European Commission (EC) published the "EU Directive on the Assessment and Management of Environmental Noise" (END).  This document specifies Lnight as the indicator for sleep disturbance, although a required response measure for sleep disturbance has not yet been selected. As part of developing the END, the European Commission contracted The Netherlands Organization for Applied Scientific Research (TNO) to derive exposure-response relationships between Lnight and sleep disturbance for transportation noise, which are expected to be included in a future Annex to the END. ,, TNO recognized that outdoor night-time noise exposure at the most exposed facade of a dwelling (Lnight) is not the only acoustical factor that influences sleep disturbance. Therefore attention is being given to the role of other factors, notably the actual noise exposure at the faηade of the bedroom, and the difference between outdoor and indoor noise levels (sound insulation) of bedrooms. There is also concern about whether using only a metric which describes the whole night exposure, such as Lnight, is sufficient or whether an individual event metric is also needed. As an alternative approach, Vallet  has argued for a supplementary indicator, Lmax, to be used in addition to Lnight.
In a recent review of nine published studies on awakening by noise by Passchier-Vermeer,  it was found that there were several different definitions of "awakening". In that review, however, all awakening data were collected on behavioral awakening; namely, awakenings that were followed by an action such as pressing a button. The number of awakenings defined in this manner is much smaller than the number of sleep stage changes which lead to EEG-patterns similar to wakefulness. Data were included for rail traffic noise, ambient (probably road) noise, civil aviation noise and military aviation noise. However, data for civil aviation noise, from seven studies comprising 174,000 aircraft noise events experienced by over 1,000 subjects, were sufficient to derive the following dose-effect relation:
Percentage of noise-induced awakenings =
-0.564 + 1.909*10 -4 *(SELinside) 2 (1)
Where SELinside is the sound exposure level of an aircraft noise event inside the bedrooms
With this relation, it was possible to calculate the expected number of noise-induced awakenings for an individual Lnight. This approach requires that all single contributions over the year to this Lnight be known. Alternatively, if a future situation has to be estimated (for which the exact data are available) a worst case scenario can be calculated. [Figure 1] represents the results of this worst case approach (with SEL converted to Lnight) showing the maximum number of awakenings, n max, that may be expected at typiceal levels of exposure. ,,
n max = 0.3504*10 (Lnight-35.2)/10 (2)
The European Commission position paper on night-time noise  also points out: "It should be noted that, on average, 600 spontaneous awakenings are reported per year. This also explains why so many more awakenings are reported than can be attributed directly to aircraft noise. At 55 Lnight, nearly 100 overflights per night with SEL,inside = 58.8, or one per five minutes are possible. It is therefore very likely that an overflight coincides with a spontaneous awakening.
Relationships between night-time noise and motility
In the TNO analysis, relationships were developed between noise-induced increase in motility (m) or noise-induced increase in onset of motility (k) in the 15-second interval following the maximum noise level of an overflight, using indoor exposure levels (Lmax* or SEL*). Although the TNO reports contain several versions of the derived exposure-response relationships, for simplicity, only one is presented here. [Figure 2] shows a plot of the probability of (aircraft) noise-induced motility (m) in the 15-second interval at which indoor maximum noise level occurs as a function of Lmax*, for various levels of long-term aircraft noise during sleep period (Lnight*). Other determinants of the relationships between instantaneous motility and Lmax* or SEL* are the point of time in the night, and time since sleep onset; e.g., after seven hours of sleep noise-induced motility is about 1.3 larger than in the first hour of sleep. Age has only a slight effect on noise-induced motility, with younger and older people showing a lower motility response than persons in the age range of 40 to 50 years. Discussion concerning the use of single event versus whole-night exposure indicators and whether the time of night also needs to be considered will continue for some time. In the TNO analysis, no relationship could be assessed between Lnight and self-reported sleep disturbance on the basis of the analysis of aircraft noise surveys. Thus, future use of self-reports of movement, awakenings, or other effects needs serious reconsideration because of the questionable validity of self-report data for predicting actual responses to noise events.
Sleep disturbance exposure-response relationships in the U.S.
Pearsons et al.  compiled an early comprehensive database representing over 25 years of laboratory and field research on noise-induced sleep disturbance. This database was the basis for an interim curve recommended by Finegold et al.  to predict the percent of exposed individuals awakened as a function of indoor A-weighted Sound Exposure Level (ASEL). This curve was adopted by the U.S. Federal Interagency Committee on Noise  as an "interim" sleep disturbance exposure-response relationship with the caveat that additional research was needed. Since the publication of the FICON report, a series of additional field studies were conducted in the U.S. to further investigate noise induced sleep disturbance from transportation noise sources, primarily aircraft noise, in various residential settings. Based on this series of field studies, BBN Laboratories developed the exposure-response relationship shown in [Figure 3],  For several methodological reasons, however, the BBN Laboratories meta-analysis was redone by Finegold and Elias  with several changes in the technical approach. The results of this meta-analysis are shown in [Figure 4].
An interesting new approach to predicting sleep disturbance from Harris, Harris, Miller and Hansen  has been incorporated into the latest U.S. ANSI Standard on sleep disturbance  . A summary of this new approach is reproduced here as provided by Nick Miller of HMMH, Inc. 
"From the early 1990's many researchers have conducted studies which investigated the effects of noise form aircraft operations on subjects sleeping in their own bedrohoms (as opposed to sleeping in laboratories). Invariably, these studies produce a dose-response relationship that relates the percent of awakenings (or increased motility, or change in sleep stage, or other measure of sleep disturbance) to a physical metric of an aircraft noise event's (ANE) sound level. Such a dose-response relationship, usually a single curve, though a useful summary presentation of the results, is difficult to apply to real-world situations at airports. Recently, Anderson and Miller used the underlying data from studies conducted by Fidell at three airports (Castle Air Force Base, Los Angeles International, and Denver International) to develop a practical application of sleep awakening results.
The application relies on two fundamental concepts. First, dose-response data can be used to convert a full night of ANE to a probability of awakening at least once during the night. This conversion is based on the principal that the probability of awakening from a single ANE when subtracted from unity becomes the probability of not awakening from that single ANE. For a series of single events, the probability of not awakening from any of them is the product of all the individual probabilities of not awakening. Thus if the probability of not awakening from one event is 0.9 and the probability of not awakening from a second event is 0.8, then the probability of not awakening from either is 0.9 times 0.8 or 0.72. In this manner the probability of sleeping all night through any number of events may be computed and when this probability is subtracted from unity, the result is the probability of awakening at least once.
The second concept is the use of logistic regression to produce a probability function from several predictor variables. The dose-response relations that had been published by various researchers were generally averages across all subjects, across all nights and all times of night. Using the raw, subject-by-subject, event-by-event data of the Fidell studies, a logistic analysis was developed that retained not only the time of night of each ANE, but the individual responses of the sleep subjects. The result is a method that derives the probability of awakening once during the night based on the probability of awakening from single events developed by the logistic regression. The method uses time of night of each ANE and sensitivity to awakening to yield the number of people or the percent of the population awakened at least once by night-time aircraft operations. The method can use common output from existing aircraft noise prediction computer programs such as the Federal Aviation Administration's Integrate Noise Model. Results may be plotted as contours of awakening."
| Comparison of Various Exposure-Response Relationships for Sleep Disturbance|| |
[Figure 5] presents a recent summary description of various published exposure-response meta-analyses for sleep disturbance.
| Exposure Criteria for Sleep Disturbance|| |
In a review paper on noise and health, Mouret and Vallet  conclude that increasing the number of noises at night would increase the probability of being awakened and that if this number is increasing, it is necessary to reduce the individual noise levels. Analyzing the effects of nocturnal aircraft noises around Paris-Charles-de-Gaulle airport, they reported that in order to avoid 90% of the awakenings there should be no more than 15 to 20 noises per night, with a maximum individual event level of 48 dB(A) (Lmax). The French Airport Noise Control Authority has proposed a threshold of 85 dB LAeq (1sec) as the maximum noise level measured on the ground from aircraft flying over residential areas at night. According to the average sound attenuation value of 35 dB (A) applicable in these well-defined areas by established techniques, the residual value of individual peak levels should not exceed 50 dB (A) inside the bedrooms.
The WHO  has stated: "Considering the scientific evidence on the thresholds of night noise exposure indicated by Lnight,outside as defined in the Environmental Noise Directive (2002/49/EC), an Lnight, outside of 40 dB should be the target of the night noise guideline (NNG) to protect the public, including the most vulnerable groups such as children, the chronically ill and the elderly. Lnight,outside value of 55 dB is recommended as an interim target for the countries where the NNG cannot be achieved in the short term for various reasons, and where policy-makers choose to adopt a stepwise approach. These guidelines are applicable to the Member States of the European Region, and may be considered as an extension to, as well as an update of, the previous WHO Guidelines for community noise (1999)" (p. VI). These guideline values, however, do not take into account the practicality of achieving these goals. According to an earlier WHO report, "…the evaluation of (noise) control options must take into account technical, financial, social, health and environmental factors." and "Cost-benefit relationships as well as the cost-effectiveness of the control measures must be considered in the context of the social and financial situation of each country 
| Summary|| |
Although the most common metrics to assess the impacts of community noise, Day-Night Average Sound Level (DNL) and Day-Evening-Night Average Sound Level (DENL) already contain a 10-dB penalty for night-time noises, there are circumstances where a separate analysis of the impacts of night-time transportation noise is warranted. There are, however, different definitions of sleep disturbance and different ways to measure it, different exposure metrics that can be used, and consistent differences in the results of laboratory versus field studies. At present, very little is known about how, why, and how often people are awakened during the night, although it is generally acknowledged that the "meaning of the sound" to the individual, such as a child crying, is a strong predictor of awakening. Very little is also known about the long-term, cumulative effects of intermittent sleep disturbance, such as from aircraft noise exposure. This article briefly discusses the various approaches used in sleep disturbance research and presented currently available information to describe the exposure-response relationships between transportation noises and sleep disturbance. It also briefly discusses the issue of noise exposure criteria for sleep disturbance and how to use existing criteria in community noise management. Very little is known about community noise sources other than transportation sources. However, it is believed that enough is known about transportation noise for government agencies to develop adequate noise policies including both noise regulations and noise guidelines as part of a broader environmental noise management program.
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Lawrence S Finegold
Finegold and So, Consultants, 1167 Bournemouth Court, Centerville, OH 45459
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]