Prospective noise induced changes to hearing among construction industry apprentices

Aims: To characterise the development of noise induced damage to hearing.

Methods: Hearing and noise exposure were prospectively monitored among a cohort of newly enrolled construction industry apprentices and a comparison group of graduate students, using standard pure tone audiometry and distortion product otoacoustic emissions (DPOAEs). A total of 328 subjects (632 ears) were monitored annually an average of 3.4 times. In parallel to these measures, noise exposure and hearing protection device (HPD) use were extensively monitored during construction work tasks. Recreational/non-occupational exposures also were queried and monitored in subgroups of subjects. Trade specific mean exposure L_eq levels, with and without accounting for the variable use of hearing protection in each trade, were calculated and used to group subjects by trade specific exposure level. Mixed effects models were used to estimate the change in hearing outcomes over time for each exposure group.

Results: Small but significant exposure related changes in DPOAEs over time were observed, especially at 4 kHz with stimulus levels (L1) between 50 and 75 dB, with less clear but similar patterns observed at 3 kHz. After controlling for covariates, the high exposure group had annual changes in 4 kHz emissions of about 0.5 dB per year. Pure tone audiometric thresholds displayed only slight trends towards increased threshold levels with increasing exposure groups. Some unexpected results were observed, including an apparent increase in DPOAEs among controls over time, and improvement in behavioural thresholds among controls at 6 kHz only.

Conclusions: Results indicate that construction apprentices in their first three years of work, with average noise exposures under 90 dBA, have measurable losses of hearing function. Despite numerous challenges in using DPOAEs for hearing surveillance in an industrial setting, they appear somewhat more sensitive to these early changes than is evident with standard pure tone audiometry.

     

Occupational noise exposure and hearing loss of workers in two plants in eastern Saudi Arabia.

OBJECTIVE: To determine the prevalence of hearing loss associated with occupational noise exposure and other risk factors. DESIGN: A cross-sectional study involving 269 exposed and 99 non-exposed subjects (non-industrial noise exposed subjects) randomly selected. Current noise exposure was estimated using both sound level meter and noise-dosimeter. Past noise exposure was estimated by interview questionnaire. Otoscopic examination and conventional frequency (0.25-8 kHz) audiometry were used to assess the hearing loss in each subject. RESULTS: 75% (202 subjects) from the exposed group were exposed to a daily Leq above the permissible level of 85 dB(A) and most (61%) of these did not and had never used any form of hearing protection. Hearing loss was found to be bilateral and symmetrical in both groups. Bivariate analysis showed a significant hearing loss in the exposed vs non-exposed subjects with a characteristic dip at 4 kHz. Thirty eight percent of exposed subjects had hearing impairment, which was an 8-fold higher rate than that found for non-exposed subjects. Multivariate analysis indicated exposure to noise was the primary, and age the secondary predictor of hearing loss. Odds of hearing impairment were lower for a small sub-group of exposed workers using hearing protection (N=19) in which logistic regression analysis showed the probability of workers adopting hearing protective devices increased with noise exposure, education, and awareness of noise control. Hearing loss was also greater amongst those who used headphones to listen to recorded cassettes. CONCLUSION: Gross occupational exposure to noise has been demonstrated to cause hearing loss and the authors believe that occupational hearing loss in Saudi Arabia is a widespread problem. Strategies of noise assessment and control are introduced which may help improve the work environment.     

甲苯与职业性噪声接触对听力损失的联合作用

目的 探讨甲苯与噪声联合接触对听力损失的影响。 方法 选择珠海市两家企业中同时接触甲苯和噪声人员78例为混合接触组,单纯接触噪声人员75例为噪声接触组,不接触职业病危害因素的办公室和后勤人员90例为对照组,进行现场甲苯浓度和噪声强度检测,对三组研究对象进行纯音测听检查,并对结果进行统计学分析。 结果 接触组各作业点甲苯浓度、噪声强度均超过国家职业接触限值。混合接触组与噪声接触组在高频段(3.0 kHz、4.0 kHz、6.0 kHz)听阈值差异有统计学意义(P均<0.05)。混合接触组与对照组比较,各频段听力差异均有统计学意义(P均<0.05)。混合接触组、噪声接触组的语频听力异常检出率(25.6%、22.7%)均高于对照组(2.2%),差异均有统计学意义(P<0.05/3);混合接触组的高频听力异常检出率(51.3%)均大于噪声组(24.0%)和对照组(7.8%),差异有统计学意义(P<0.05/3)。工龄≥ 5年者,混合接触组与噪声接触组听力损害发生率差异有统计学意义(P<0.05)。 结论 甲苯与噪声联合接触对听力损害有协同作用,应充分考虑联合接触因素的职业安全防护。     

Hearing loss in workers exposed to toluene and noise

In this study we investigated the risk of hearing loss among workers exposed to both toluene and noise. We recruited 58 workers at an adhesive materials manufacturing plant who were exposured to both toluene and noise [78.6-87.1 A-weighted decibels; dB(A)], 58 workers exposed to noise only [83.5-90.1 dB(A)], and 58 administrative clerks [67.9-72.6 dB(A)] at the same company. We interviewed participants to obtain sociodemographic and employment information and performed physical examinations, including pure-tone audiometry tests between 0.5 and 6 kHz. A contracted laboratory certified by the Council of Labor in Taiwan conducted on-site toluene and noise exposure measurements. The prevalence of hearing loss of >or=25 dB in the toluene plus noise group (86.2%) was much greater than that in the noise-only group (44.8%) and the administrative clerks (5.0%) (p<0.001). The prevalence rates were 67.2, 32.8, and 8.3% (p<0.001), respectively, when 0.5 kHz was excluded from the estimation. Multivariate logistic regression analysis showed that the toluene plus noise group had an estimated risk for hearing loss>or=25 dB, 10.9 times higher than that of the noise-only group. The risk ratio dropped to 5.8 when 0.5 kHz was excluded from the risk estimation. Hearing impairment was greater for the pure-tone frequency of 1 kHz than for that of 2 kHz. However, the mean hearing threshold was the poorest for 6 kHz, and the least effect was observed for 2 kHz. Our results suggest that toluene exacerbates hearing loss in a noisy environment, with the main impact on the lower frequencies.     

Combined effect of smoking and occupational exposure to noise on hearing loss in steel factory workers

Background: Evidence has accumulated concerning the adverse effects of smoking on hearing acuity, but it is not clear whether smoking modifies the association between exposure to noise and hearing loss.

Aims: To examine the synergistic effect of these variables on hearing.

Methods: Data used were derived from periodic health examinations for 4624 steel company workers in Japan and included audiometry testing and information on smoking habits. Occupational exposure to noise was determined based on company records. Logistic regression was used to examine the dose-response association between smoking and hearing loss. The Cochran-Mantel-Haenszel method was used to calculate the prevalence rate ratio (PRR) of hearing loss for each combination of smoking and noise exposure factors, taking non-smokers not exposed to occupational noise as a reference. The interaction between smoking and noise exposure was assessed using a synergistic index, which equals 1 when the joint effect is additive.

Results: Smoking was associated with increased odds of having high frequency hearing loss in a dose-response manner. The PRR for high frequency hearing loss among smokers exposed to occupational noise was 2.56 (95% CI 2.12 to 3.07), while the PRR for smokers not exposed to noise was 1.57 (95% CI 1.31 to 1.89) and the PRR for non-smokers exposed to noise was 1.77 (95% CI 1.36 to 2.30). The synergistic index was 1.16. Smoking was not associated with low frequency hearing loss.

Conclusions: Smoking may be a risk factor for high frequency hearing loss, and its combined effect on hearing with exposure to occupational noise is additive.

     

An epidemiological study regarding the hearing acuity of residents in the area with high level of aircraft noise: results of hearing tests conducted in the vicinity of Kadena Air Base]

Hearing tests, primary and secondary, were conducted in two communities vicinal to Kadena US Air Base in Okinawa from May 1996 to July 1998. The noise exposure expressed in WECPNL as designated by the Defense Facilities Administration Agency ranged from 85 to 95 and above. A total of 2035 subjects aged between 25 and 69 years inclusive were considered eligible for inclusion in this study and among them 137 males and 206 females underwent the primary test. Before the test, subjects were asked about hearing difficulty, tinnitus, otological anamnesis and past experience of noise exposure at work and/or hobbies. The primary test was a pure tone audiometry using the ascending method of limits with 5 dB step at 7 test frequencies of 0.5 to 8 kHz. Forty individuals who were judged to have possible noise induced hearing loss were sent to Okinawa Chubu Hospital as subjects for the secondary test. The secondary test consisted of pure tone audiometry with 1 dB step at 9 test frequencies with the addition of 3 kHz and 6 kHz to the primary test frequencies, a Short Increment Sensitivity Index (SISI), test, tympanometry and audioscan audiometry. Based on test findings 12 subjects were considered to have noise induced hearing loss. The examiners interviewed the 12 subjects again to confirm that they had not experienced habitual or repeated intense noise exposure other than aircraft noise exposure around their homes. The geographical distribution of the subject's residences showed their proximity to the airfield, which strongly suggests that the cause of hearing loss may be exposure to aircraft noise from Kadena Air Base.     

Hearing impairment among workers exposed to excessive levels of noise in ginning industries

Cotton ginning workers have a risk of hearing loss due to excessive noise levels at the workplace environment. In this study, estimates of typical sound levels prevailing at the workplace environment and its effects on hearing ability of the exposed workers were made among cotton ginning workers. Data on self-reported health status was collected by a questionnaire survey at 10 cotton ginning industries located at Jalgaon district of Maharashtra state, India. The cotton ginning workers were exposed to continuous noise levels between 89 and 106 dBA. The hearing ability of the subjects was accessed by pure tone audiometry. The results of audiometry show mild, moderate and moderately severe degree of hearing impairment among the cotton ginning workers. The data generated during the study show that hearing loss was significantly associated with period of exposure to the workplace noise (P <0.0001). The prevalence of audiometric hearing impairment defined as a threshold average greater than 25 dB hearing level was 96% for binaural low-frequency average, 97% for binaural mid frequency average and 94% for binaural high-frequency average in the cotton ginning workers. We recommend the compulsory use of personal protective equipment like ear plug by the cotton ginning workers at the workplace environment. A regular maintenance of ginning and pressing machineries will avoid the emission of excessive noise at the workplace environment of cotton gins. A regular periodic medical examination is necessary to measure the impact of workplace noise on the health of cotton ginning workers.     

The likelihood of detecting a significant hearing threshold shift among noise-exposed workers subjected to annual audiometric testing

The ability of annual audiometric surveillance to detect significant deteriorations in hearing sensitivity is examined considering the time pattern of the growth of noise-induced hearing loss. The yearly rate of change in hearing level due to the effects of noise exposure and age is computed from a mathematical model put forward in the International Standard ISO 1999 (1989). The first-order derivative of hearing level associated with noise and age was compared with different criteria of significant threshold shift (STS). The results show that the potential annual variation in hearing level at 4 kHz, the audiometric frequency most affected by noise, is always less than the minimum margin of error of audiometry under exposure to 90 dBA-8 h. At 100 dBA it nearly equals the margin of error only for the very first year of exposure and for the most sensitive individuals. The rate of change in hearing threshold at 4 kHz is less than or equal to 1 dB per year for a major portion of a population exposed to an average noise level of 90 dBA-8 h (+/- 5 dB SD). For other audiometric frequencies, or for combinations of frequencies, this rate is even lower. It is also demonstrated that, using annual hearing tests, the likelihood of measuring an STS in a noise-exposed population is very small. It would be nearly equal to the likelihood of some workers being exposed to 100 dBA-8 h or more for a first year. Such results throw doubt on the validity of audiometric surveillance as a procedure for early detection of noise-induced hearing loss. They also imply that the detection by audiometric tests of true cases of significant threshold shift due to noise is excessively expensive.     

用个体暴露评价脉冲噪声与稳态噪声所致高频听力损失的关系

目的用个体噪声暴露测量数据比较工业脉冲噪声与稳态噪声所致高频听力损失剂量反应关系的异同。方法1998至1999年,以32名接触脉冲噪声的机械制造工人和163名接触稳态噪声的纺织工人为观察对象,用噪声剂量计采集8h工作期间的噪声暴露数据,计算8h等效声级(LAeq.8h),并按等能量原理将LAeq.8h和噪声作业工龄合并为累积噪声暴露量(CNE)。用常规方法测量工人左右耳气导听阈,按GBZ492002对听阈做年龄性别校正,并诊断是否为高频听力损失。结果脉冲噪声组的CNE[(103.2±4.2)dB(A)·年]明显低于稳态噪声组[(110.6±6.0)dB(A)·年],脉冲噪声组高频听力损失患病率(68.8%)与稳态噪声组(65.0%)相似,分层分析和趋势卡方检验证实,两组CNE与高频听力损失患病率间均存在典型的剂量反应关系,差异有统计学意义;脉冲噪声100～104和105～109dB(A)·年两组的高频听力损失患病率(76.9%和90.9%)高出稳态噪声组(30.4%和50.0%)约1倍。logistic回归模型显示,脉冲噪声组CNE与高频听力损失患病率的剂量反应关系曲线与稳态噪声组相比出现曲线左移,斜率增大。结论采用个体噪声暴露数据计算时,在能量相同的情况下,脉冲噪声所致高频听力损失的危害大于稳态噪声。     

The Nord-Trøndelag Norway Audiometric Survey 1996-98: unscreened thresholds and prevalence of hearing impairment for adults > 20 years

As supplement to a general health screening examination (HUNT-II), we conducted a puretone audiometry study in 1996-98 on adults (>20 years) in 17 of 23 municipalities in Nord-Tr?ndelag, 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 0.25-0.5-1-2-3-4-6-8 kHz (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 < or =0.5 kHz for all age groups. Mean thresholds were poorer in males > or = 30 years from > or =2 kHz, with maximal gender differences of approximately 20 dB at 3-4 kHz for subjects aged 55-74 years. Weighted prevalence data averaged over 0.5-1-2-4 kHz showed hearing impairment >25 dB 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 > or =10 dB at 6 kHz 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 socio-acusis.     

Hearing status among aircraft maintenance personnel in a commercial airline company

The aim was to study subjective and objective hearing loss in a population of aircraft maintenance workers and identify predictors. A total of 327 aircraft maintenance personnel answered a self-administered work environment questionnaire (response rate 76%) and underwent audiometric test. The mean values for the hearing threshold at 3, 4, and 6 kHz for the ear with the most hearing loss were compared with a Swedish population database of persons not occupationally exposed to noise. Equivalent noise exposure during a working day was measured. Relationships between subjective and objective hearing loss and possible predictors (age, years of employment, self-reported exposure to solvents, blood pressure, and psycho-social factors) were analyzed by multiple logistic regression. At younger ages (<40 years), aircraft maintenance workers had higher hearing thresholds (1-3 dB) compared to the reference group, but such a difference was not found in older employees. Relationships were found between age and objective hearing loss, and between exposure to solvents and reported subjective hearing loss. Equivalent noise exposure during working days were 70-91 dB(A) with a maximal noise level of 119 dB(A). Aircraft maintenance workers are exposed to equivalent noise levels above the Swedish occupational standard, including some very high peak exposures. Younger employees have a higher age-matched hearing threshold level compared with a reference group. Thus, there is a need for further preventive measures.     

High-frequency (10-18 kHz) hearing thresholds: reliability, and effects of age and occupational noise exposure.

The objective was to investigate the reliability and effects of age and noise on high-frequency hearing thresholds. A cross-sectional study was used involving 187 exposed and 52 non-industrial noise-exposed subjects selected randomly from noise-exposed and non-industrial noise-exposed subjects, respectively. Each subject was tested with both conventional-frequency (0.25-8 kHz) and high-frequency (10-18 kHz) audiometry. Test-retest results showed that high-frequency audiometry (HFA) was as reliable as the conventional procedure. Although the inter-subject variation was large, the intra-subject variation was small, indicating that HFA can be used more reliably than the conventional procedure to monitor individual cases over time. Both the hearing threshold at high frequencies and the upper frequency limit deteriorated as a function of age and frequency. The exposed subjects had significantly higher hearing thresholds than the non-exposed subjects at all the high frequencies tested, the difference between the two groups being greatest at 14 kHz. Multivariate analysis indicated that age was the primary predictor and noise exposure the secondary predictor of hearing thresholds in a high frequency range (10-18 kHz). In contrast, multivariate analysis indicated the reverse order-noise exposure as the primary predictor, then age-for a conventional frequency range (0.25-8 kHz). The results of this study suggest that HFA might be used as an early indicator for noise-induced hearing loss and acoustic trauma rather than audiometry at a conventional frequency (4 kHz), particularly for younger groups.     

Predictors of hearing threshold levels and distortion product otoacoustic emissions among noise exposed young adults

Aim: To examine the relations between noise exposure and other risk factors with hearing function as measured by audiometric thresholds and distortion product otoacoustic emissions.

Methods: A total of 456 subjects were studied (393 apprentices in construction trades and 63 graduate students). Hearing and peripheral auditory function were quantified using standard, automated threshold audiometry, tympanometry, and distortion product otoacoustic emissions (DPOAEs). The analysis addressed relations of noise exposure history and other risk factors with hearing threshold levels (HTLs) and DPOAEs at the baseline test for the cohort.

Results: The cohort had a mean age of 27 (7) years. The construction apprentices reported more noise exposure than students in both their occupational and non-occupational exposure histories. A strong effect of age and years of work in construction was observed at 4, 6, and 8 kHz for both HTLs and DPOAEs. Each year of construction work reported prior to baseline was associated with a 0.7 dB increase in HTL or 0.2 dB decrease DPOAE amplitude. Overall, there was a very similar pattern of effects between the HTLs and DPOAEs.

Conclusions: This analysis shows a relatively good correspondence between the associations of noise exposures and other risk factors with DPOAEs and the associations observed with pure-tone audiometric thresholds in a young adult working population. The results provide further evidence that DPOAEs can be used to assess damage to hearing from a variety of exposures including noise. Clarifying advantages of DPOAEs or HTLs in terms of sensitivity to early manifestations of noise insults, or their utility in predicting future loss in hearing will require longitudinal follow up.

     

10-Year prospective study of noise exposure and hearing damage among construction workers

Objectives To characterise the effects of noise exposure, including intermittent and peaky exposure, on hearing damage as assessed by standard pure-tone thresholds and otoacoustic emissions, a longitudinal study was conducted on newly hired construction apprentices and controls over a 10-year period. Methods Among the 456 subjects recruited at baseline, 316 had at least two (mean 4.6) examinations and were included in this analysis. Annual examinations included hearing threshold levels (HTLs) for air conducted pure tones and distortion product otoacoustic emission (DPOAE) amplitudes. Task-based occupational noise exposure levels and recreational exposures were estimated. Linear mixed models were fit for HTLs and DPOAEs at 3, 4 and 6 kHz in relation to time since baseline and average noise level since baseline, while controlling for hearing level at baseline and other risk factors. Results Estimated L(EQ) noise exposures were 87±3.6 dBA among the construction workers. Linear mixed modelling demonstrated significant exposure-related elevations in HTL of about 2-3 dB over a projected 10-year period at 3, 4 or 6 kHz for a 10 dB increase in exposure. The DPOAE models (using L1=40) predicted about 1 dB decrease in emission amplitude over 10 years for a 10 dB increase in exposure. Conclusions The study provides evidence of noise-induced damage at an average exposure level around the 85 dBA level. The predicted change in HTLs was somewhat higher than would be predicted by standard hearing loss models, after accounting for hearing loss at baseline. Limited evidence for an enhanced effect of high peak component noise was observed, and DPOAEs, although similarly affected, showed no advantage over standard hearing threshold evaluation in detecting effects of noise on the ear and hearing.     

Combined exposure to noise and vibration and its effects on workers' hearing

OBJECTIVE: To assess the exposure of bus drivers to noise and whole-body vibration (WBV) and to examine the possibility of an association between these risk factors for noise-induced hearing loss. METHODS: A cross-sectional study was carried out among 141 bus drivers who underwent an audiometry test. This group was classified and internally stratified in subgroups of "exposed" and "controls" according to cumulative working time as bus drivers. Their exposure to noise and vibration was assessed. The association between noise-induced hearing loss (NIHL) and the set of explanatory variables was analyzed through logistic regression. RESULTS: The average (+/- standard deviation) weekly noise exposure of front-engine bus drivers was 83.6 +/- 1.9 dB(A), while rear-engine bus drivers were exposed to 77.0 +/- 1.1 dB(A). The weighted average of vibration acceleration was 0.85/m(2). In the best adjusted model, the multivariable analysis showed that age (>44; OR=2.54; 95% CI=1.15-5.62), diabetes (OR=5.46; 95% CI=0.95-31.4), and the level of noise emission [>86.8 dB(A); OR=2.76; 95% CI=1.24-6.15] were risk factors for NIHL. In another model studied, WBV exposure was significant in determining NIHL. CONCLUSIONS: Bus drivers were exposed to significant WBV levels. The noise exposure was more pronounced in front engine than in rear-engine vehicles. No association between WBV exposure and NIHL was observed and no interaction was found between WBV and noise exposure. Further studies are required as other model indicated an association between WBV and NIHL.     

某汽车制造企业噪声作业工人不同频率听力损失影响因素分析

目的 分析广州市某汽车制造企业噪声作业工人不同频率听力损失状况及各频率听力损失影响因素。方法 以2018年1—12月广州市某汽车制造企业至广州市职业病防治院进行职业健康检查的噪声作业工人为研究对象,对其进行纯音听阈测试、噪声接触水平检测及问卷调查,计算累积噪声暴露量,采用单、多因素分析方法对各频率听力损失发生的影响因素进行分析。结果 2 605名噪声作业工人均为汉族男性,年龄为22（20,24）岁,工龄为3（1,4）年,噪声接触强度为83.50（82.10,86.10）dB（A）,累积噪声暴露量为87.97（85.11,90.81）dB（A）·年。听力损失检出率为34.40%（896/2 605）。左、右耳听力损失检出率,左、右耳语频、高频听力损失检出率的差异均无统计学意义（P>0.05）;左、右耳听力损失检出率均随着频率升高而逐渐增加（趋势χ²值分别为1111.38、1237.14,P<0.01）,且均以6.0 kHz最高。多因素Logistic回归分析显示,吸烟、饮酒与各频率听力损失无显著相关关系（P>0.05）;随着累积噪声暴露量（0.5~6.0 kHz的OR值分别为3.231、4.151、4.809、3.282、2.735、2.069）、年龄（0.5~6.0 kHz的OR值分别为2.167、2.323、2.508、1.776、1.414、1.276）的增加,各频率听力损失风险均逐渐增加（P<0.05）。结论 汽车制造企业噪声作业工人不同频率听力损失以6.0 kHz较为显著,累积噪声暴露量、年龄与各频率听力损失均存在剂量-反应关系。     

Absence of otoacoustic emissions in subjects with normal audiometric thresholds implies exposure to noise

Otoacoustic emissions and contra-lateral sound activated efferent suppression of emissions were examined to determine whether they provide any early indication of auditory damage from exposure to noise. Three groups were studied: noise exposed workers (n=50, mean age 42 years), patients with Meniere's disease (n=24, mean age 48 years) and normal subjects (n=24, mean age 41 years). All subjects underwent routine pure tone audiometry, tympanometry and otoacoustic emission testing. As a number of studies have shown that with hearing threshold better than 30 dB HL, emissions are almost always present and are generally absent with hearing loss greater than 30 dB HL, subjects in this study were sub grouped into these two categories in order to examine the incidence of emissions. Absence of emissions in subjects with mean hearing thresholds better than 30 dB HL varied from 0% in normal controls, 8% in patients with Meniere's disease and a significantly high 56% in noise exposed workers despite similar mean hearing thresholds for all groups. The mean transient emission levels for the noise exposed workers was significantly lower than the controls and Meniere's groups. This study clearly indicates that in the noise-exposed group there is sub clinical and sub audiometric damage to the outer hair cells responsible for generation of otoacoustic emissions. Of those with normal otoacoustic emissions, the efferent suppression was absent in 60% of noise exposed workers but in only 3.8% of control subjects implying that the efferent control may also be affected in a significant proportion despite normal hearing thresholds and emissions.     

2010—2012年某印刷厂噪声作业人员听力损失调查

目的 探讨生产性噪声对印刷厂车间噪声作业工人听力损失的连续性影响,为保护噪声职业接触者身体健康,控制职业病危害因素提供依据。 方法 回顾性分析某印刷厂车间噪声接触人员连续三年的纯音听阈测试结果,结合15个噪声监测点的现场噪声强度,分析连续3年听力损失的动态变化及其影响因素。 结果 随着噪声接触时间的延长,4.0 kHz及6.0 kHz频率听力损失的差异有统计学意义(F=1.333、1.045,P<0.01)。10年及以上工龄组工人听力损失率(46.51%)高于10年以下工龄组(14.48%)。性别、噪声强度、工龄、年龄是听力损失发生的独立危害因素,男性高于女性,85 dB (A)以上的噪声强度下及10年以上工龄者听力损失发生的风险较高,年龄≥ 50岁组发生听力损失的风险较<50岁组高(OR值分别为2.721、2.376、2.044、2.816)。 结论 噪声暴露剂量和听力损失存在一定的剂量-反应关系。     

Hearing loss of workers in mining--a 6-year longitudinal study

Hearing threshold level (HTL) in miners, was determined after six years interval characterized by the same noise exposure. An attempt was made to establish the prognosis regarding the hearing losses extent and the time interval involved in the occurrence of these modifications in the subjects applying the HTL values. 132 workers (miners and miner apprentices) underwent audiometrical examinations, after 6 years interval in the same testing conditions. To evaluate the vibrations possible effects on the HTL, the results registered in a group of workers exposed solely to noise (n = 33)-identical continuous equivalent level/week-were compared to those found in miners. According to age range and the duration of noise exposure, the yearly mean rate for both the low (500-2000 Hz) and high frequencies (2-8 kHz), were calculated based on the hearing threshold differences. The miners, simultaneously exposed to noise and vibration presented yearly decreased HTL values (up to 2000 Hz), as against the subjects exposed solely to noise. The prognosis indicates that in a miner with a duration of exposure above 21 years and/or a mean age of 38, one may expect a loss of the HTL exceeding 30 dB at 4 kHz.