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12 CHAPTER FOUR SLEEP DISTURBANCE AND AVIATION NOISE Most noise-exposed populations especially in the vicinity of closely associated with awakenings than long-term noise airports cite sleep disturbance as a common complaint. Pro- exposures (Fidell et al. 1995). These findings do not resemble tection of a particular sleep period is necessary for overall those of laboratory studies of noise-induced sleep interference, quality of life. Sleep may be quite sensitive to environmental but agree with the results of other field studies. Importantly, factors, especially noise, because external stimuli are still the study also concludes the relationship observed processed by the sleeper's sensory functions, although there may be no conscious perception of their presence. . . . between noise metrics and behavioral awakening responses suggest instead that noise induced awakening may be usefully viewed as an event-detection process. Put another way, an awak- The large amount of research published during the last ening can be viewed as the outcome of a de facto decision that a 30 years has produced considerable variability and often con- change of sufficient import has occurred in the short-term noise troversial results. For example, in establishing the effect of environment to warrant a decision to awaken (Fidell et al. 1995). aviation noise on health, the absence of one internationally accepted exposure-effect or dose-response relationship is This is an important observation that leads to suspicion of largely the result of a lack of one obvious "best choice" any assumption about the independence of noise events made research methodology, as well as to the complex interactions in the pursuit of estimating total awakenings. of many factors that influence sleep disturbance, including the differences of the noise source and the context of the In 1989, a comprehensive database representing 25 years living environment. Current exposure-response relationships of both laboratory and field research on noise-induced sleep use either awakenings or body movements to describe sleep disturbance was the basis for an interim curve to predict the disturbance. percent of exposed individuals awakened as a function of in- door A-weighted SEL (Finegold et al. 1992). This curve was Several studies suggest that either sound exposure level adopted by FICON in 1992. Since publication of the FICON (SEL) or maximum noise level (Lmax) are better predictors of report (Federal Interagency Committee on Noise 1992), sub- sleep disturbance than long-term weighted averages [equiv- stantial field research in the area of sleep disturbance has been alent sound level (Leq)], day-evening-night average noise completed. The data from these studies show a consistent pat- levels (Lden), community noise equivalent level (CNEL), tern, with considerably less percent of the exposed population DNL, or equivalent noise level for night (Lnight). A survey of expected to be behaviorally awakened than laboratory studies the literature also shows large differences between results had demonstrated. As a result, the Federal Interagency Com- from numerous laboratory studies and those from epidemio- mittee on Aviation Noise (FICAN) published a new recom- logical or experimental studies made in real, in-home situa- mendation in 1997. Interestingly, the FICAN curve does not tions. The landmark study by Ollerhead et al. (1992) clearly represent a best fit of the study data, but rather is constructed identified a difference between laboratory and in-home to represent the out boundary of the data (FICAN 1997). studies of sleep disturbance, with the in-home data showing it takes considerably more noise to awaken people than data In summary, although the most common metrics for collected in the laboratory studies, and that the agreement assessing the impacts of DNL, Lden, or CNEL already contain between actimetrically determined arousals and electro- a 10-dB penalty for night-time noises, there are circumstances encephalogram (EEG)-measured arousals were very good where a separate analysis of the impacts of night-time trans- (Ollerhead et al 1992). It summarized by stating that "once portation noise is warranted. There are, however, different asleep, very few people living near airports are at risk of any definitions of sleep disturbance and different ways to measure substantial sleep disturbance resulting from aircraft noise, it, different exposure metrics that can be used, and consistent even at the highest event noise levels." differences in the results of laboratory versus field studies. At the present time, very little is known about how, why, and how Later studies by Horne et al. (1994) document a landmark often people are awakened during the night, although it is in-home field study that demonstrated dose-response curves generally acknowledged that the "meaning of the sound" to based on laboratory data greatly overestimated the actual the individual, such as a child crying, is a strong predictor of awakening rates for aircraft noise events. In 1995, Fidell found awakening. Although different models can estimate various that SELs of individual noise intrusions were much more metrics, there is substantial controversy associated with how to
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13 apply and interpret these studies. Current research has focused over-interpretation of the data. This is contrasted with recent on measuring in-home sleep disturbance using techniques not efforts to estimate the population that will be awakened by available in 1985. In-home sleep disturbance studies clearly aircraft noise around airports. Research may not yet have suf- demonstrate that it requires more noise to cause awakenings ficient specificity to estimate the population awakened for a than was previously theorized based on laboratory sleep specific airport environment or the difference in population disturbance studies. Recent studies have cautioned about the awakened for a given change in an airport environment.