Distortion-Product Otoacoustic Emissions as a Screening Tool for Noise-Induced Hearing Loss

Noise-induced hearing loss includes both temporary (TTS) and permanent (PTS) threshold shifts. Although TTS and PTS have many similarities, their underlying mechanisms are different. Both TTS and PTS are seen in hearing-conservation programs, making it important to consider both when making physiological measurements of inner-ear damage in applied settings. There are many ways that physiological mechanisms could be useful in screening for NIHL. Can normal-hearing and NIHL ears be differentiated from one another? Can the physiological measure be used in place of behavioural hearing-threshold measures of TTS and PTS? Can it be used to indicate sub-clinical damage (i.e., noise-induced permanent alterations to the inner ear without a corresponding hearing decrement)? Can it be used to indicate pre-clinical hearing loss (i.e., the sub-clinical damage eventually turns into hearing loss)? Finally, can the physiological measure be used to predict susceptibility to NIHL? Evoked otoacoustic emissions (EOAEs) depend on normal outer hair cells for their generation. Because this is the site in the inner ear in humans that is most susceptible to noise, there has been considerable interest in the application of EOAEs to NIHL screening. In this review, the application of distortion-product EOAEs (DPOAEs) is considered for this purpose, emphasizing work from our laboratory, but including that of others as well. Wherever possible, we compare the performance of DPOAEs as a screening tool to transient-evoked otoacoustic emissions (TEOAEs). We emphasize the importance of how well DPOAEs perform in screening for NIHL in individuals rather than for groups of people; the importance of using large numbers of subjects; and the importance of longitudinal studies.     

噪声性听力损失易感基因的研究进展

噪声性听力损失是现阶段全球最主要的职业性损伤之一.以往的研究显示,噪声的易感性存在个体差异,本文综述报道目前国内外关于基因多态性与噪声性听力损失之间关系的现有研究状况.     

Individual Risk Factors in the Development of Noise-Induced Hearing Loss

We have analysed the association of noise-induced hearing loss with various risk factors among 685 workers in forest, shipyard, and paper mills. Occupational histories, health, environmental factors, and noise exposures of each worker were retrieved from the database of NoiseScan, our expert program on hearing. The mean hearing level at 4 kHz was 21.5 dB +/- 20.3 dB HL. It correlated significantly with age, noise emission level and noise exposure level. However, these factors could only explain about 2 dB HL of the variation in hearing level. Impulse noise in the shipyard work caused increase in hearing level of 12 dB HL at 4 kHz when compared to steady state noise exposure of forest work. Hearing level correlated with serum cholesterol levels, use of analgesics, blood pressure and smoking. An elevated cholesterol level increased hearing loss in both the high- and low-exposure groups. The use of analgesics did not increase a permanent threshold shift in the low-exposure group, but did in the high-exposure group. Systolic blood pressure, smoking, cholesterol level and the use of painkillers explained 36 % of the variation in hearing level at 4 kHz, whereas noise exposure alone explained 25 % of the corresponding variation.     

Evidence of a Common Pathway in Noise-Induced Hearing Loss and Carboplatin Ototoxicity

In spite of the differences in the nature of the insult, the hearing loss from ototoxic drugs and noise exposure share a number of similarities in cochlear pathology. This paper explores the common factors between noise-induced hearing loss and ototoxicity by experimentally manipulating cochlear glutathione (GSH). In the first experiment, chinchillas were treated with a drop of saline (50 &mgr;l) on the round window of one ear and a drop of buthionine sulfoximine (BSO, 50 &mgr;l of 200 mM) on the other ear. BSO is a drug that blocks GSH synthesis and it was hypothesised that GSH-depressed ears would be more vulnerable to noise. Six hours after treatment, the animals were exposed to a 105 dB 4 kHz octave band noise for 4 hours, then a second dose of BSO was applied 2 hours later. The BSO treated ears showed more temporary threshold shifts and reduced GSH staining at day 4 post exposure, but there was no BSO effect in terms of greater permanent threshold shift (PTS) or hair cell loss. In the second experiment, chinchillas were pretreated with BSO and 3 days later were given either a single dose of carboplatin (25 mg/kg i.p.), a double dose (day 3 and 7) or only BSO. Chinchillas that received BSO and the double dose of carboplatin had significantly greater loss of inner and outer hair cells than the carboplatin chinchillas. In addition, the BSO and carboplatin chinchillas also had larger decreases in evoked response amplitudes suggesting that GSH depletion potentiated the ototoxicity of carboplatin. These results are discussed in terms of the role of reactive oxygen species in creating hearing loss and the potential protective role of glutathione.     

某冶金企业噪声作业人员听力损伤的特点

目的为进一步了解太钢噪声作业人员听力损伤的特点,为控制和消除职业性噪声聋的发生提供依据。方法对15个生产厂256个噪声作业点进行现场监测。并对1 628名噪声作业人员进行健康体检,分析其噪声特性和双耳纯音听力损伤的特点。结果1 628名噪声作业人员按其接触噪声性质不同分为6个工种,听力损伤以轧钢系统岗位最严重,其次为流动性岗位,辅助性岗位最低。同时非稳态噪声听力损伤比稳态噪声严重。结论非稳态噪声、高频噪声引起的听力损伤比稳态/中、低频噪声引起的听力损伤严重。     

Otoacoustic Emissions: A Valid, Efficient First-Line Hearing Screen for Preschool Children

Background:  Normal hearing during the preschool years is essential for speech, language, social, emotional, and preacademic development. Children of low socioeconomic status may be particularly vulnerable to the negative effects of late identification and intervention. While a mass-screening effort focused on preschool children does not have broad support, focused screening remains important to identify children at risk. This project was conducted to address 3 primary aims: develop and implement an initial hearing screen using transient evoked otoacoustic emissions (TEOAEs) for at-risk preschoolers, verify speed and tolerability of the screen, and assess the test performance of TEOAEs screening compared to pure tone audiometry in a group of 142 preschool children.
Methods:  A total of 744 preschool children attending preschools in an underserved, urban community completed TEOAEs screening by a school nurse. A secondary cohort of 142 children was screened first by TEOAEs and then followed by pure tone audiometry and results compared.
Results:  A total of 680 children passed screening. Forty-one children (5.5%) had a "refer" result. Two-year-olds had the highest refusal rate (10.5%). Mean testing time was 43 seconds per ear. Secondary cohort analysis revealed 1 subject did not pass either TEOAEs or pure tone screening; no subject passed TEOAEs and then did not pass pure tone audiometry. TEOAEs screening test sensitivity was 1.00 (95% confidence interval 0.054-1.00) and specificity 0.94 (0.88-0.97).
Conclusions:  TEOAEs screening performed by school nurses is a fast, efficient, and feasible model. Children who pass TEOAEs screening have a very high likelihood of being free from hearing impairment. Application may be particularly relevant in underserved communities.     

The Consequences of Noise-Induced Hearing Loss on Dairy Farm Communities in New Zealand

ABSTRACT

The objective of this study was to investigate how noise-induced hearing loss (NIHL) or noise injury (NI) affects individuals and others of dairy farm communities in New Zealand. Using “grab” or opportunistic sampling at DairyNZ discussion groups and a recreational function, a survey questionnaire was completed by 74 participants from two dairy farming communities in New Zealand. Self-reported hearing difficulties were highlighted by 48% (42) of the 74 participants. The effects of NI on individuals and others included communication difficulties leading to the development of coping strategies, social isolation; decreased employment opportunities, loss of productivity, and increased effort and adjustments by family and work colleagues. Frustration, anxiety, stress, resentment, depression, and fatigue are also negative consequences that may contribute to a loss of quality of life and contribute to further health costs. Increased lateness, absenteeism, sickness and other behavioral aspects were not expressed as normal issues in the workplace, as the majority of the individuals are/were self-employed or working in a family business. This study shows that each year in New Zealand NI results in significant negative social, psychological, and economic consequences for those individuals affected, along with their families, friends, and work colleagues.     

The Influence of Superoxide Dismutase and Glutathione Peroxidase Deficiencies on Noise-Induced Hearing Loss in Mice

One consequence of noise exposure is increased production of reactive oxygen species (ROS), such as superoxide, hydrogen peroxide, and hydroxyl radicals, in the cochlea. ROS can cause oxidative damage to diverse cellular components, including membranes, proteins, and DNA, if they are not "neutralised" by antioxidant defences. Two important enzymes of the cochlear antioxidant defense system are cytosolic copper/zinc superoxide dismutase (SOD1) and selenium-dependent glutathione peroxidase (GPx1). These metalloenzymes work together to regulate ROS production in virtually every cell in the body, and they may be important for limiting cochlear damage associated with aging and acoustic overexposure. In this chapter, we describe a series of experiments using mice with targeted deletions of Sod1 or Gpx1, the mouse genes that code for SOD1 and GPx1, respectively, to study the cellular mechanisms underlying noise-induced hearing loss (NIHL). The results from Sod1 and Gpx1 knockout mice provide insights into the link between endogenous levels of antioxidant enzymes and susceptibility to NIHL.     

全新耳聋诊断方法让儿童远离无声世界——晶芯(R)遗传性耳聋基因检测芯片试剂盒

1 为什么要进行耳聋检查 耳聋是临床上最常见的遗传性疾病,由遗传性因素导致的约占60%左右;2006年第二次残疾人抽样调查显示,我国残疾人总数8千万,听力残疾者2670万;1～7岁听障儿童约有80万;我国每年2000万新生儿中,严重听力障碍发生率为1‰～3‰. 基于以上情况,国家和省市级政府对新生儿听力筛查越来越重视.     

噪声作业工人的畸变产物耳声发射观察

目的观察畸变产物耳声发射（DPOAE）在早期发现噪声性听力损失方面的应用价值。方法对54例非噪声作业工人（对照组）和96例纯音听阈正常的噪声作业工人（噪声组）进行纯音测听和DPOAE测试，比较两组的纯音听阈、DPOAE幅值和引出率。结果①噪声组和对照组各频率纯音听闻比较，差异无显著性（P〉0．05）；②噪声组的DPOAE幅值在3kHz、4kHz、6kHz处明显下降，与对照组比较有统计学意义（P〈0．01）；③噪声组在3kHz、4kHz和6kHz三个频率处的DPOAE引出率明显降低，与对照组比较，差异有显著性（P〈0．05，P〈0．01）：结论DPOAE能早期发现噪声性听力损失。     

镁对噪声性听力损伤的影响

目的 研究镁对噪声性听力损伤（NIHL）的影响,以及在NIHL进展中的作用.方法 随机抽取219名噪声作业工人为研究对象,另外随机抽取非噪声作业工人200名,测定其血清镁的含量为对照,用双向t检验比较不同年龄段2组工人不同浓度血清镁的人数有无统计学上的差异.结果 不同年龄段2组工人中不同浓度血清镁的人数差异均无统计学意义（P＞0.05）.结论 镁元素在噪声性听力损伤（NIHL）进展过程中如何起作用的,以及如何决定着NIHL的程度,有待进一步研究证实.     

Genetic Variation in GSTM1 Is Associated With Susceptibility to Noise-Induced Hearing Loss in a Chinese Population

OBJECTIVES:: To investigate whether glutathione S-transferases (GST) genetic polymorphisms (GSTT1 rs1049055, GSTM1 rs10712361, and GSTP1 rs1695) are associated with susceptibility to noise-induced hearing loss (NIHL). METHODS:: These polymorphisms were analyzed in 444 NIHL and 445 normal hearing workers. In addition, total plasma GST activity was measured in all subjects. RESULTS:: Individuals with the GSTM1 null genotype had a statistically significantly increased risk of NIHL (odds ratio [OR] = 1.64, 95% confidence interval [CI] = 1.26 to 2.13) compared with those carrying a wild-type GSTM1 genotype. This effect was more pronounced among the workers exposed to 86 to 91 dB(A) (OR = 3.35, 95% CI = 1.54 to 7.31). Glutathione S-transferase activity of the NIHL workers was also lower than that of normal hearing workers (14.5 ± 5.1 U/ml vs 15.9 ± 6.3 U/ml, P = 0.010). CONCLUSION:: Our results suggest that GSTM1 polymorphism is associated with susceptibility to NIHL.     

Temporary and Permanent Hearing Loss

Long-term exposure to the dust of fiber glass used for insulation causes no demonstrable gross or microscopic pulmonary damage. This conclusion is based on the results of a postmortem study of the lungs of 20 fiber glass workers, who had had exposures to the dust of fibrous glass which ranged from slight to severe and for periods which ranged from 16 to 32 years, and a comparison of this study’s results with those obtained in a similar study of the lungs of 26 urban dwellers of both sexes, who presumably had not been exposed occupationally to fibrous glass dust, which showed that the average total amount of dust, the average total number of fibers per gram of dry lung, and the average dimensions of the fibers found in the lungs were not significantly different.     

Click-Evoked Otoacoustic Emissions in Children and Adolescents with Gender Identity Disorder

Click-evoked otoacoustic emissions (CEOAEs) are echo-like sounds that are produced by the inner ear in response to click-stimuli. CEOAEs generally have a higher amplitude in women compared to men and neonates already show a similar sex difference in CEOAEs. Weaker responses in males are proposed to originate from elevated levels of testosterone during perinatal sexual differentiation. Therefore, CEOAEs may be used as a retrospective indicator of someone’s perinatal androgen environment. Individuals diagnosed with Gender Identity Disorder (GID), according to DSM-IV-TR, are characterized by a strong identification with the other gender and discomfort about their natal sex. Although the etiology of GID is far from established, it is hypothesized that atypical levels of sex steroids during a critical period of sexual differentiation of the brain might play a role. In the present study, we compared CEOAEs in treatment-naïve children and adolescents with early-onset GID (24 natal boys, 23 natal girls) and control subjects (65 boys, 62 girls). We replicated the sex difference in CEOAE response amplitude in the control group. This sex difference, however, was not present in the GID groups. Boys with GID showed stronger, more female-typical CEOAEs whereas girls with GID did not differ in emission strength compared to control girls. Based on the assumption that CEOAE amplitude can be seen as an index of relative androgen exposure, our results provide some evidence for the idea that boys with GID may have been exposed to lower amounts of androgen during early development in comparison to control boys.     

畸变产物诱发耳声发射在新生儿听力筛查中的应用

随着我国新生儿听力筛查工作的推广,很多医院都开展了新生儿听力筛查,因此,如何提高筛查质量,减少假阳性,避免假阴性,就显得特别重要。我院应用畸变产物耳声发射（distortion product otoacoustic emissions,DPOAE）为684例新生儿听力进行了筛查,现总结分析如下。     

Correlations among Distortion Product Otoacoustic Emissions,Thresholds and Sensory Cell Impairments

Distortion product otoacoustic emissions (DPOAE) are increasingly used as an objective test for noninvasive hearing screening. When two pure tones with frequencies f1 and f2 are sent to the cochlea, the most prominent DPOAE is the cubic one produced at 2f1-f2, and this presentation will mainly emphasize its properties. DPOAEs are undoubtedly generated by cochlear nonlinearities. It is widely held that they arise from certain stages of sound processing by the outer hair cells (OHC) and that OHCs ensure normal cochlear sensitivity and tuning. Thus, DPOAEs should provide a privileged tool for monitoring the harmful effects of loud sound because OHCs are known to be one of the main targets of NIHL. Although DPOAEs provide the clinicians with a reliable screening limit of about 30 dB HL around f2, no reliable relationship has been found thus far between possible residual DPOAEs and either hearing loss or amount of impaired sensory cells. Furthermore, puzzling contradictory findings have been reported as to the presence of DPOAEs despite a large hearing loss (i.e. >30-40 dB) notably with high-level stimuli. These observations raise the following issues. What is the generation site of DPOAEs in a normal or pathological cochlea (OHCs, basilar membrane, place tuned to f2, 2f1-f2, places basal to f2.)? Is it necessary to account for interferences between several discrete sources, arising from different locations or different mechanisms and possibly exhibiting differential susceptibility to sensory cell damage? Do DPOAE changes depend on the nature of OHC pathology (NIHL, anoxia, ototoxic drugs, genetics.)? Once a source of DPOAE is characterized, is there any means of modelling the physiological process of its generation and deriving what might quantitatively relate DPOAE amount to sensory cell activity and thresholds? The goal of this presentation is to examine these issues, review the available data and propose a comparatively simple model.