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2005| July-September | Volume 7 | Issue 28
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Confounding or aggravating factors in noise-induced health effects : Air pollutants and other stressors
D Schwela, S Kephalopoulos, D Prasher
July-September 2005, 7(28):41-50
Different scientific groups have studied and continue to study the health impacts of physical and chemical agents in the environment. In most cases, every study group has considered the health effect as being solely due to the air pollutant(s) under investigation, for example air pollution without due regard for the simultaneous presence of noise pollution whereas both have an impact on the cardiovascular system. Or in the case of noise studies the contribution of solvent, asphyxiant or metal exposures has not been considered, which can have an impact on hearing impairment. One can, therefore, question the stringency of the available evidence of epidemiological studies in both fields to warrant the consideration of air pollutants as confounding or aggravating factors in studies of specific effects due to noise (and vice versa). In this paper we weigh the existing evidence on the association of noise and air pollutant exposure and associated health impacts. In forthcoming publications, the authors will consider the influence of other factors, which can confound noise studies but are currently not included in the analysis.
Hearing protector performance and standard deviation
W Williams, H Dillon
July-September 2005, 7(28):51-60
The attenuation performance of a hearing protector is used to estimate the protected exposure level of the user. The aim is to reduce the exposed level to an acceptable value. Users should expect the attenuation to fall within a reasonable range of values around a norm. However, an analysis of extensive test data indicates that there is a negative relationship between attenuation performance and the standard deviation. This result is deduced using a variation in the method of calculating a single number rating of attenuation that is more amenable to drawing statistical inferences. As performance is typically specified as a function of the mean attenuation minus one or two standard deviations from the mean to ensure that greater than 50% of the wearer population are well protected, the implication of increasing standard deviation with decreasing attenuation found in this study means that a significant number of users are, in fact, experiencing over-protection. These users may be disinclined to use their hearing protectors because of an increased feeling of acoustic isolation. This problem is exacerbated in areas with lower noise levels.
Complaint data as an index of annoyance-theoretical and methodological issues
M Maziul, RFS Job, J Vogt
July-September 2005, 7(28):17-27
Complaining constitutes one facet of all reactions to noise annoyance and is one way to cope with annoyance due to aircraft noise. In order to value and to establish the usefulness of complaint data as an index of annoyance, four questions need to be answered: * Which factors lead annoyed residents to complain about aircraft noise or related issues? * Which factors keep annoyed residents from complaining? * Are the existing ways to handle annoyance adequate and efficient (e.g. keeping track of complaints, reaction to complains, kinds of complaint services)? * Which are new ways to handle annoyance adequately and efficiently? In this paper a first attempt to answer these questions is made. Obviously, complaint data do not reflect noise annoyance in the surroundings of airports to the full extent as there are residents living in affected areas who do not complain, as well as residents living in areas with relatively low noise levels who complain. Also there is a large group of people who declare to be highly annoyed and yet, they do not lodge any complaint. Possible intervening factors are gathered that determine if an annoyed resident takes action and complains. It was found that noise levels per se are not the crucial factor for residents' decisions to complain or not to complain. Personal as well as feasibility factors play a vital role. Yet, the ongoing controversy on the relation between annoyance and complaint behavior seems not resolved yet. However, complaint behavior seems to be influenced by various aspects and complaint data consequently cannot be accepted as an accurate measure of public annoyance. Further research is required to address the preferred method of handling reaction to noise and the extent to which complaint itself helps with coping, for different groups of residents.
Combined effects of noise and gentamicin on hearing in the guinea pig
F Bombard, P Campo, R Lataye
July-September 2005, 7(28):29-39
The last ten years, the use of gentamicin has increased due to antibiotic resistance among bacterial pathogens. One of the side effects of gentamicin is its toxicity on hearing. Several authors had even pointed out synergistic effects of gentamicin and noise on hearing. It was therefore reasonable to think that the damaging effects of noise could be emphasized by a gentamicin treatment of the subjects. In order to test the applicability of the Leq8h for estimating the hazard of noise on animals treated with a non-ototoxic dose of gentamicin (40 mg/kg for 8 days), two experiments were carried out with guinea pigs. The animals were exposed to octave band noises centered at 8 kHz and treated with gentamicin either simultaneously or sequentially with regard to the noise exposure. Two noise exposures having different acoustic energy, respectively Leq8h = 85 dB and 98.8 dB SPL, were tested. The auditory function of the guinea pigs was tested by recording auditory-evoked potentials. The electrophysiological findings were completed by histological data. The gentamicin treatment tested in the current studies did not cause any auditory permanent threshold shift neither cochlear disruptions, although the treatment could be considered as approximately ten times the therapeutic dose used in human. The auditory deficit induced by the mixed exposures to noise and gentamicin did not worsen the noise effect alone in our experimental conditions. As a result, the European value recommended for noise exposure (Leq8h=85 dB) seems to be robust enough to protect gentamicin-treated workers.
The Nord-Trondelag Norway Audiometric Survey 1996-98 : Unscreened thresholds and prevalence of hearing impairment for adults > 20 years
HM Borchgrevink, K Tambs, HJ Hoffman
July-September 2005, 7(28):1-15
As supplement to a general health screening examination (HUNT-II), we conducted a pure-tone audiometry study in 1996-98 on adults (
20 years) in 17 of 23 municipalities in Nord-Trondelag, Norway, including questionnaires on occupational and leisure noise exposure, medical history, and symptoms of hearing impairment. The study aims to contribute to updated normative hearing thresholds for age and gender, while evaluating the effects of noise exposure, medical history, and familial or genetic influences on hearing. This paper presents the unscreened hearing threshold data and prevalence of hearing impairment for different age groups and by gender. Valid audiometric data were collected from 62% (n=50,723) of 82,141 unscreened invited subjects (age-range 20-101 years, mean=50.2 years, SD=17.0 years). Two ambulant audiometric teams each conducted 5 parallel self-administered, pure-tone hearing threshold examinations with the standard test frequencies 0.25-0.5-1-2-3-4-6-8kHz (manual procedure when needed). Tracking audiometers were used in dismountable booths with in-booth noise levels well within ISO criteria, except being at the criterion around 200 Hz. The data were electronically transferred to a personal computer. Test-retest correlations for 99 randomly drawn subjects examined twice were high. The mean thresholds recorded were some dB elevated from "audiometric zero" even for age group 20-24 years. As also found in other studies, this might indicate too restrictive audiometric reference thresholds. Males had slightly better hearing
0.5kHz for all age groups. Mean thresholds were poorer in males
30 years from
2kHz, with maximal gender differences of ~20dB at 3-4kHz for subjects aged 55-74 years. Weighted prevalence data averaged over 0.5-1-2-4kHz showed hearing impairment
25dB hearing threshold level of 18.8% (better ear) and 27.2% (worse ear) for the total population - for males 22.2% and 32.0%, for females 15.9% and 23.0%, respectively. Mean hearing loss
10dB at 6kHz registered for both genders even in age groups 20-24 years may be partly due to calibration artefacts, but might possibly also reflect noise-related socioacusis.
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