Hearing Conservation Research Articles

Noise-Induced Hearing Loss - A Preventable Disease? Results of a 10-Year Longitudinal Study of Workers Exposed to Occupational Noise.

Aims:To survey current, Danish industrial noise levels and the use of hearing protection devices (HPD) over a 10-year period and to characterise the association between occupational noise and hearing threshold shift in the same period. Furthermore, the risk of hearing loss among the baseline and the follow-up populations according to first year of occupational noise exposure is evaluated.Materials and Methods:In 2001–2003, we conducted a baseline survey of noise- and hearing-related disorders in 11 industries with suspected high noise levels. In 2009–2010, we were able to follow up on 271 out of the 554 baseline workers (49%). Mean noise levels per industry and self-reported HPD use are described at baseline and follow-up. The association between cumulative occupational noise exposure and hearing threshold shift over the 10-year period was assessed using linear regression, and the risk of hearing loss according to year of first occupational noise exposure was evaluated with logistic regression.Results:Over the 10-year period, mean noise levels declined from 83.9 dB(A) to 82.8 dB(A), and for workers exposed >85 dB(A), the use of HPD increased from 70.1 to 76.1%. We found a weak, statistically insignificant, inverse association between higher ambient cumulative noise exposure and poorer hearing (−0.10 dB hearing threshold shift per dB-year (95% confidence interval (CI): −0.36; 0.16)). The risk of hearing loss seemed to increase with earlier first year of noise exposure, but odds ratios were only statistically significant among baseline participants with first exposure before the 1980s (odds ratio: 1.90, 95% CI: 1.11; 3.22).Conclusions:We observed declining industrial noise levels, increased use of HPD and no significant impact on hearing thresholds from current ambient industrial noise levels, which indicated a successful implementation of Danish hearing conservation programs.

A faceoff with hazardous noise: Noise exposure and hearing threshold shifts of indoor hockey officials

ABSTRACTNoise exposure and hearing thresholds of indoor hockey officials of the Western States Hockey League were measured to assess the impact of hockey game noise on hearing sensitivity. Twenty-nine hockey officials who officiated the league in an arena in southeastern Wyoming in October, November, and December 2014 participated in the study. Personal noise dosimetry was conducted to determine if officials were exposed to an equivalent sound pressure level greater than 85 dBA. Hearing thresholds were measured before and after hockey games to determine if a 10 dB or greater temporary threshold shift in hearing occurred. Pure-tone audiometry was conducted in both ears at 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz. All noise exposures were greater than 85 dBA, with a mean personal noise exposure level of 93 dBA (SD = 2.2), providing 17.7% (SD = 6.3) of the officials' daily noise dose according to the OSHA criteria. Hearing threshold shifts of 10 dB or greater were observed in 86.2% (25/29) of officials, with 36% (9/25) of those threshold shifts equaling 15 dB or greater. The largest proportion of hearing threshold shifts occurred at 4000 Hz, comprising 35.7% of right ear shifts and 31.8% of left ear shifts. The threshold shifts between the pre- and post-game audiometry were statistically significant in the left ear at 500 (p=.019), 2000 (p=.0009), 3000 (p<.0001) and 4000 Hz (p=.0002), and in the right ear at 2000 (p=.0001), 3000 (p=.0001) and 4000 Hz (p<.0001), based on Wilcoxon-ranked sum analysis. Although not statistically significant at alpha = 0.05, logistic regression indicated that with each increase of one dB of equivalent sound pressure measured from personal noise dosimetry, the odds of a ≥ 10 dB TTS were increased in the left ear at 500 (OR=1.33, 95% CI 0.73-2.45), 3000 (OR=1.02, 95% CI 0.68-1.51), 4000 (OR=1.26, 95% CI 0.93-1.71) and 8000 Hz (OR=1.22, 95% CI 0.76-1.94) and in the right ear at 6000 (OR=1.03, 95% CI 0.14-7.84) and 8000 Hz (OR=1.29, 95% CI 0.12-13.83). These findings suggest that indoor hockey officials are exposed to hazardous levels of noise, experience temporary hearing loss after officiating games, and a hearing conservation program is warranted. Further temporary threshold shift research has the potential to identify officials of other sporting events that are at an increased risk of noise-induced hearing loss.

Noise dosimetry for tactical environments

Noise exposure and the subsequent hearing loss are well documented aspects of military life. Numerous studies have indicated high rates of noise-induced hearing injury (NIHI) in active-duty service men and women, and recent statistics from the U.S. Department of Veterans Affairs indicate a population of veterans with hearing loss that is growing at an increasing rate. In an effort to minimize hearing loss, the U.S. Department of Defense (DoD) updated its Hearing Conservation Program in 2010, and also has recently revised the DoD Design Criteria Standard Noise Limits (MIL-STD-1474E) which defines allowable noise levels in the design of all military acquisitions including weapons and vehicles. Even with such mandates, it remains a challenge to accurately quantify the noise exposure experienced by a Warfighter over the course of a mission or training exercise, or even in a standard work day. Noise dosimeters are intended for exactly this purpose, but variations in device placement (e.g., free-field, on-body, in/near-ear), hardware (e.g., microphone, analog-to-digital converter), measurement time (e.g., work day, 24-h), and dose metric calculations (e.g., time-weighted energy, peak levels, Auditory Risk Units), as well as noise types (e.g., continuous, intermittent, impulsive) can cause exposure measurements to be incomplete, inaccurate, or inappropriate for a given situation. This paper describes the design of a noise dosimeter capable of acquiring exposure data across tactical environments. Two generations of prototypes have been built at MIT Lincoln Laboratory with funding from the U.S. Army, Navy, and Marine Corps. Details related to hardware, signal processing, and testing efforts are provided, along with example tactical military noise data and lessons learned from early fieldings. Finally, we discuss the continued need to prioritize personalized dosimetry in order to improve models that predict or characterize the risk of auditory damage, to integrate dosimeters with hearing-protection devices, and to inform strategies and metrics for reducing NIHI.

A qualitative study of factors affecting the compliance of hearing protective device usage among factory workers in Kuantan

Introduction: Occupational noise-induced hearing loss (NIHL) is an acquired cumulative and irreversible hearing impairment which is totally preventable. Literature review concluded that noise hazard control via administrative and engineering methods are difficult to implement for many reasons. Thus, hearing protection device (HPD) is the best compromise to protect workers from the excessive noise. The purpose of this study is to qualitatively explore the factors affecting the HPD compliance among factory workers in Kuantan. Methods: A purposive sampling of twenty four male workers exposed to occupational noise of 85 dB and more for 8 hour-period was recruited from 15th July to 31st August 2013 to participate in four focus group discussions. The open-ended guided questions were used during the discussions to explore the workers’ perspective, knowledge, attitude and behaviour regarding the use of HPD. The data were analyzed using the conventional content analysis and the key themes were elicited in relation to the study, either toward the positive hearing protective behaviours or the factors that act as the barriers against it. Results: From the findings, five themes have emerged with their respective subthemes including perception of noise in the workplace, use of HPD, barriers against the use of HPD, workplace influence and value of hearing. Our studies found that the three main reasons for workers not to wear HPD are discomfort, cumbersome and impediment of speech / other wanted sounds. Conclusions: Effective hearing conservation programme, particularly on the use of HPD should therefore address these factors to ensure good compliance among the workers.

Awareness Investigation about Hearing Conservation Program of the Employee Who Work in Noisy Environments

Awareness Investigation about Hearing Conservation Program of the Employee Who Work in Noisy Environments

Performance in noise: Impact of reduced speech intelligibility on Sailor performance in a Navy command and control environment

Noise, hearing loss, and electronic signal distortion, which are common problems in military environments, can impair speech intelligibility and thereby jeopardize mission success. The current study investigated the impact that impaired communication has on operational performance in a command and control environment by parametrically degrading speech intelligibility in a simulated shipborne Combat Information Center. Experienced U.S. Navy personnel served as the study participants and were required to monitor information from multiple sources and respond appropriately to communications initiated by investigators playing the roles of other personnel involved in a realistic Naval scenario. In each block of the scenario, an adaptive intelligibility modification system employing automatic gain control was used to adjust the signal-to-noise ratio to achieve one of four speech intelligibility levels on a Modified Rhyme Test: No Loss, 80%, 60%, or 40%. Objective and subjective measures of operational performance suggested that performance systematically degraded with decreasing speech intelligibility, with the largest drop occurring between 80% and 60%. These results confirm the importance of noise reduction, good communication design, and effective hearing conservation programs to maximize the operational effectiveness of military personnel.

Hearing testing in the U.S. Department of Defense: Potential impact on Veterans Affairs hearing loss disability awards

Hearing loss is the second most common disability awarded by the U.S. Department of Veterans Affairs (VA) to former members of the U.S. uniformed services. Hearing readiness and conservation practices differ among the four largest uniformed military services (Air Force, Army, Marine Corps, and Navy). Utilizing a data set consisting of all hearing loss claims submitted to the VA from fiscal years 2003–2013, we examined characteristics of veterans submitting claims within one year of separation from military service. Our results indicate that having a hearing loss disability claim granted was significantly more likely for men, individuals over the age of 26 years at the time of the claim, individuals most recently serving in the U.S. Army, and those with at least one hearing loss diagnosis. Importantly, individuals with at least one test record in the Defense Occupational and Environmental Health Readiness System-Hearing Conservation (DOEHRS-HC) system were significantly less likely to have a hearing loss disability claim granted by the VA. Within the DOEHRS-HC cohort, those with at least one threshold shift or clinical hearing loss diagnosis while on active duty were more than two and three times more likely to have a hearing loss disability claim granted, respectively. These findings indicate that an established history of reduced hearing ability while on active duty was associated with a significantly increased likelihood of an approved hearing loss disability claim relative to VA claims without such a history. Further, our results show a persistent decreased rate of hearing loss disability awards overall. These findings support increased inclusion of personnel in DoD hearing readiness and conservation programs to reduce VA hearing loss disability awards.

Going global with hearing conservation: Regulations and trends

Noise is recognized universally as an occupational hazard; however, there is not a globally accepted regulatory approach toward protecting the noise-exposed workforce. The regulatory differences for hearing conservation around the world make it challenging for multinational companies to set policies for corporate hearing loss prevention programs. This presentation compares and contrasts selected aspects of various hearing conservation regulations to the United States Occupational Safety and Health Administration requirements. The following jurisdictions are included: Australia/New Zealand, Brazil, China, European Union, India, Japan, and Mexico. Details were collected from English translations of a country regulation as well as by consultation with an experienced, in-country resident whenever possible. Information includes noise exposure limits, noise control, hearing protection device use, standards, and attenuation derating schemes, audiometric testing and hearing shift criteria, and employee training requirements. Studying these criteria will also spark discussion as to best practices and emerging trends in hearing conservation.

Evaluation of extended-wear earplug technology as a transparent hearing-protection device

One of the greatest challenges in hearing conservation is providing adequate protection for those listeners who spend most of their time in quiet environments, but are occasionally exposed to high levels of noise that occur at unpredictable times. A classic example of this problem occurs for dismounted soldiers, who rely heavily on their natural hearing acuity to detect threats and opportunities on the battlefield but always face the risk of becoming engaged in a dangerously noisy firefight with little or no warning. One emerging technology that might have application in this domain is the extended-wear hearing aid, which is capable of remaining deep in the ear canal for weeks or months before being removed. Preliminary results suggest that the extended wear earplug can provide protection from blast or continuous noise that is comparable to a conventional earplug or muff, and that it can provide detection and localization performance comparable to that achieved with the open ear. Its form factor also makes it more likely to be compatible with headsets, radios, and personal protective equipment than traditional earplug or earmuff devices. The potential benefits and limitations of the extended-wear earplug as a hearing protector will be discussed. [Work supported by MRMC Grant W81XWH-14-1-0254; The opinions and assertions presented are the private views of the authors and are not to be construed as official or as necessarily reflecting the views of the Department of Defense.]

Introduction of a hearing conservation program in a Japanese enterprise

To prevent occupational hearing loss, the Ordinance of Industrial Safety and Health in Japan requires employers to measure sound levels in eight hazardous areas in the workplace. In addition, the Guidelines for the Prevention of Noise-Induced Impairments require employers to measure the sound levels in noisy workplaces or provide audiometric testing for employees exposed to occupational noise. However, measurement of personal noise exposure is not a legal requirement in Japan. The Japanese Working Environment Measurement Standards define how to measure occupational noise using a sound level meter (SLM). However, it is difficult to evaluate real noise exposure for employees who use a sound-emitting industrial tool. We measured this exposure using a dosimeter at a Japanese manufacturing enterprise producing transport machinery. The sound levels at some workshops that were evaluated as 85 dBA using a SLM were shown to be more than 90 dBA using a dosimeter. Following these results, we are introducing a Hearing Conservation Program at the enterprise. We would like to report how to develop this new noise management system in Japan and manage personal noise exposure.

Field fit testing with E-A-Rfit Dual-Ear validation system in China

This presentation introduces hearing protection fit testing on over 1000 workers in 6 different factories, each with different hearing conservation practices in China. The 3MTM E-A-RfitTM Dual-Ear validation system was used to measure the Personal Attenuation Rating (PAR), on three different types of Hearing Protection Devices (HPDs), including a foam earplug, a premolded earplug, and a headband earmuff at the work site. A follow up visit to repeat fit-testing was conducted approximately 6 months after the initial visit. Field attenuation of HPDs obtained by workers’ and the effects of training toward improving the attenuation were observed. In addition, PARs for the Peltor™X4A earmuff users were obtained at several points throughout the work shift to capture different fits. Result shows that there is wide variability in PARs and poor agreement between PAR and labelled noise attenuation ratings obtained from laboratory measurement. Hearing protection fit testing is essential to verify the sufficiency of a...

A comparison of an audiometric screening survey with an in-depth research questionnaire for hearing loss and hearing loss risk factors

Objective: We assessed the reliability of a hearing risk factor screening survey used by hearing conservation programmes for noise-exposed workers. Design: We compared workers’ answers from the screening survey to their answers to a confidential research questionnaire regarding hearing loss risk factors. We calculated kappa statistics to test the correlation between yes/no questions in the research questionnaire compared to answers from 1 and 5 years of screening surveys. Study sample: We compared the screening survey and research questionnaire answers of 274 aluminum plant workers. Results: Most of the questions in the in-company screening survey showed fair to moderate agreement with the research questionnaire (kappa range: −0.02, 0.57). Workers’ answers to the screening survey had better correlation with the research questionnaire when we compared 5 years of screening answers. For nearly all questions, workers were more likely to respond affirmatively on the research questionnaire than the screening survey. Conclusions: Hearing conservation programmes should be aware that workers may underreport hearing loss risk factors and functional hearing status on an audiometric screening survey. Validating company screening tools could help provide more accurate information on hearing loss and risk factors.

Serial Monitoring of Otoacoustic Emissions in Clinical Trials.

The purpose of this report is to provide guidance on the use of otoacoustic emissions (OAEs) as a clinical trial outcome measure for pharmaceutical interventions developed to prevent acquired hearing loss secondary to cochlear insult. OAEs are a rapid, noninvasive measure that can be used to monitor cochlear outer hair cell function. Serial monitoring of OAEs is most clearly established for use in hearing conservation and ototoxicity monitoring programs in which they exhibit more frequent and earlier changes compared with pure-tone audiometry. They also show promise in recent human trials of otoprotectants. Questions remain, however, concerning the most appropriate OAE protocols to use and what constitutes a "significant" OAE response change. Measurement system capabilities are expanding and test efficacy will vary across locations and patient populations. Yet, standardizing minimal measurement criteria and reporting of results is needed including documentation of test-retest variability so that useful comparisons can be made across trials. It is also clear that protocols must be theoretically sound based on known patterns of damage, generate valid results in most individuals tested, be accurate, repeatable, and involve minimal time. Based on the potential value added, OAEs should be included in clinical trials when measurement conditions and time permit.

Assessing the Effects of Pesticide Exposure on the Auditory System based on the Suppression of Transient-Evoked Otoacoustic Emissions

Introduction: Although noise-induced hearing loss is the most significant occupational hazard affecting the auditory system, studies on hearing conservation have shown that frequent exposure to chemicals in the workplace may also cause hearing disorders. Objective: The aim of this study was to evaluate the medial olivocochlear system in individuals exposed to pesticides. Method: This is a cross-sectional descriptive epidemiological study. After applying the inclusion criteria, we evaluated 205 students from an agricultural school located in the city of Nova Friburgo, state of Rio de Janeiro, Brazil, who were exposed to pesticides. Participants were evaluated based on a questionnaire to assess the degree of pesticide exposure, transient-evoked otoacoustic emissions (TEOAEs), and investigation of the suppressive effect of TEOAEs. Results: The assessment considering the suppression of TEOAEs demonstrated that 38% of participants had absence of suppression in the right ear, 45.9% had absence of suppression in the left ear, 38% had unilateral absence, and 39% had bilateral absence. Our findings suggest that there is an association between absence of suppression and quartiles of exposure. Conclusion: Chronic exposure to pesticides can affect the medial olivocochlear system, regardless of concomitant exposure to noise.

Earplug Usage in Preservice Music Teachers

In the past 10 years, educating university musicians about hearing protection for long-term career stability and success has become more common, as has the adoption of hearing conservation programs. The purpose of this study was to explore preservice music teachers’ self-reported use of earplugs. Undergraduate preservice teachers ( N = 129) were surveyed and results revealed that 21% ( n = 27) wore earplugs sometimes while practicing, rehearsing, performing, or teaching. While participants recognized that noise-induced hearing loss was preventable ( n = 124, 96%), 88% were seldom or sometimes concerned about their own hearing ( M = 2.39, SD = 1.05). Most participants believed that surgery and hearing aids were ways to correct noise-induced hearing loss ( n = 100, 78%). However, contrary to the preservice teachers’ beliefs, no viable correction is currently available for noise-induced hearing loss. Implications for further education are discussed.

Do hearing threshold levels in workers of the furniture industry reflect their exposure to noise?

The aim of the study was to analyze the hearing status of employees of a furniture factory with respect to their exposure to noise and the presence of additional risk factors of noise-induced hearing loss (NIHL). Noise measurements, questionnaire survey and assessment of hearing, using pure tone audiometry, were carried out in 50 male workers, aged 20-57 years, directly employed in the manufacture of furniture. The actual workers' hearing threshold levels (HTLs) were compared with the predictions calculated according to PN-ISO 1999:2000 based on age, gender and noise exposure. Workers under study were exposed to noise at daily noise exposure levels of 82.7-94.8 dB (mean: 90.9 dB) for a period of 3-14 years. In all subjects, mean HTL at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz did not exceed 25 dB. Nevertheless, high frequency notches were found in 11% of audiograms. The actual workers' HTLs at 3000-6000 Hz were similar to those predicted using PN-ISO 1999:2000. There were statistical significant differences between HTLs in subgroups of people with higher (> 78 mm Hg) and lower (≤ 78 mm Hg) diastolic blood pressure, smokers and non-smokers, and those working with organic solvents. Hearing loss was more evident in subjects affected by the additional risk factors specified above. The results confirm the need to consider, in addition to noise, also some other NIHL risk factors, such as tobacco smoking, elevated blood pressure, and co-exposure to organic solvents when estimating the risk of NIHL and developing the hearing conservation programs for workers. Med Pr 2016;67(3):337-351.

Noise-Induced Hearing Loss in the Campus

Noise-Induced Hearing Loss in the Campus

A cool approach to reducing electrode-induced trauma: Localized therapeutic hypothermia conserves residual hearing in cochlear implantation

ObjectiveThe trauma caused during cochlear implant insertion can lead to cell death and a loss of residual hair cells in the cochlea. Various therapeutic approaches have been studied to prevent cochlear implant-induced residual hearing loss with limited success. In the present study, we show the efficacy of mild to moderate therapeutic hypothermia of 4 to 6 °C applied to the cochlea in reducing residual hearing loss associated with the electrode insertion trauma. ApproachRats were randomly distributed in three groups: control contralateral cochleae, normothermic implanted cochleae and hypothermic implanted cochleae. Localized hypothermia was delivered to the middle turn of the cochlea for 20 min before and after implantation using a custom-designed probe perfused with cooled fluorocarbon. Auditory brainstem responses (ABRs) were recorded to assess the hearing function prior to and post-cochlear implantation at various time points up to 30 days. At the conclusion of the trials, inner ears were harvested for histology and cell count. The approach was extended to cadaver temporal bones to study the potential surgical approach and efficacy of our device. In this case, the hypothermia probe was placed next to the round window niche via the facial recess or a myringotomy. Main resultsA significant loss of residual hearing was observed in the normothermic implant group. Comparatively, the residual hearing in the cochleae receiving therapeutic hypothermia was significantly conserved. Histology confirmed a significant loss of outer hair cells in normothermic cochleae receiving the surgical trauma when compared to the hypothermia treated group. In human temporal bones, a controlled and effective cooling of the cochlea was achieved using our approach. SignificanceCollectively, these results suggest that therapeutic hypothermia during cochlear implantation may reduce traumatic effects of electrode insertion and improve conservation of residual hearing.

Effect of repetitive transcranial magnetic stimulation on auditory function following acoustic trauma.

Repetitive transcranial magnetic stimulation (rTMS) is one form of non-invasive brain stimulation and increasingly shows neuroprotection in multiple neurological disorders. However, the potential of rTMS for protective action on auditory function following acoustic trauma has not been investigated. Here, we examined effect of TMS on hearing conservation, neurons survival and brain-derived neurotrophin factor (BDNF) expression in the cochlea and auditory cortex following acoustic trauma in rats. Wistar rats were exposed to intense pure tone noise (10kHz, 120dB SPL for 2h) followed by rTMS treatment or sham treatment (handling control) daily for 14days. Auditory brainstem response revealed there was no significant difference in hearing threshold shifts between rTMS- and sham-treated rats, although rTMS-treated rats showed less neuron loss in the auditory cortex in comparison with sham rats. Additionally, acoustic trauma increased BDNF expression in the cochlea and auditory cortex, and this elevation could be attenuated by rTMS treatment. Our results suggest present regiment of rTMS does not protect hearing against acoustic trauma, but maybe have implications for tinnitus treatment.

Evaluating the Outcomes of a Hearing Screening Service for Grade One Learners in Urban Areas at Durban, South Africa.

Early intervention through hearing screening can reduce the negative impact of hearing loss for children. Optimal outcomes are achieved when an appropriate screening protocol is selected, a pathway for follow up care is established, and when a hearing conservation component is included. This study aimed to describe the outcomes of a hearing screening service provided to grade one learners in urban areas at Durban. A cross-sectional design was employed. Learners (n=241) were conveniently sampled from six randomly selected schools. They were screened using otoscopy, tympanometry and pure tone audiometry. Fifty eight participants (24%) obtained a refer result, with 33% referred for diagnostic assessments, 29% for middle ear pathology and 38% for cerumen management. Findings further revealed that only 33% of referrals were followed up indicating poor compliance. Association between test results and income levels (P=0.38) as well as distance to the nearest health care facility (P=0.22) did not influence test outcomes. School aged children do present with common ear problems. Appropriate protocol selection, ensuring compliance to recommendations and education on hearing conservation are essential components of any health initiative.