Prevalence of hearing loss in college students: a meta-analysis

Introduction

Hearing loss among college students, specifically noise-induced hearing loss (NIHL), appears to be increasing. This may be particularly challenging for this population as college students are required to listen to lectures in classrooms that may have suboptimal listening environments. College-aged musicians are at a particularly high risk due to repeated and extended exposure to loud noise. Therefore, the purpose of the current study was (1) to examine the prevalence of hearing loss in college students and (2) to emphasize the importance of detecting hearing loss at 6,000 Hz.

Methods

A meta-analysis was conducted using the PRISMA model. The literature search yielded 8 studies (1,950 subjects) that tested hearing loss using an audiogram and Distortion Product Otoacoustic Emissions (DPOAEs). All studies used audiologic tests to detect hearing loss among college students between the ages of 17-35 years.

Results

Results indicate that the prevalence of hearing loss in college students is 19%. In addition, the prevalence of hearing loss at 6,000 Hz is 85% among student musicians. For this meta-analysis, slight sensorineural hearing loss, or thresholds greater than 20 dB bilaterally or unilaterally, qualified as hearing loss.

Discussion

Decreased hearing at 6,000 Hz may lead to an individual's inability to hear important environmental factors and high frequency speech sounds. College students without full auditory function at this frequency may have difficulties performing in class based on decreased attention, comprehension, and memory. Although students may not realize the influence of their 6,000 Hz hearing loss or be unaware of its presence, it could significantly change their likelihood to succeed in college. Therefore, implementing a hearing conservation program may be advised for colleges and universities to help prevent hearing loss in students, particularly for collegiate musicians. In addition, it may be beneficial to screen hearing in college students at 6,000 Hz for better detection of hearing loss overall.

What can insects teach us about hearing loss?

Over the last three decades, insects have been utilized to provide a deep and fundamental understanding of many human diseases and disorders. Here, we present arguments for insects as models to understand general principles underlying hearing loss. Despite ∼600 million years since the last common ancestor of vertebrates and invertebrates, we share an overwhelming degree of genetic homology particularly with respect to auditory organ development and maintenance. Despite the anatomical differences between human and insect auditory organs, both share physiological principles of operation. We explain why these observations are expected and highlight areas in hearing loss research in which insects can provide insight. We start by briefly introducing the evolutionary journey of auditory organs, the reasons for using insect auditory organs for hearing loss research, and the tools and approaches available in insects. Then, the first half of the review focuses on auditory development and auditory disorders with a genetic cause. The second half analyses the physiological and genetic consequences of ageing and short- and long-term changes as a result of noise exposure. We finish with complex age and noise interactions in auditory systems. In this review, we present some of the evidence and arguments to support the use of insects to study mechanisms and potential treatments for hearing loss in humans. Obviously, insects cannot fully substitute for all aspects of human auditory function and loss of function, although there are many important questions that can be addressed in an animal model for which there are important ethical, practical and experimental advantages.

Estrogen as a guardian of auditory health: Tsp1-CD47 axis regulation and noise-induced hearing loss

OBJECTIVES

This study aimed to analyze the role of estrogen in noise-induced hearing loss (NIHL) and uncover underlying mechanisms.

METHODS

An ovariectomized Sprague-Dawley rat model (OVX) was constructed to investigate the hearing threshold and auditory latency before and after noise exposure using the auditory brainstem response (ABR) test. The morphological changes were assessed using immunofluorescence, scanning electron microscopy and transmission electron microscopy. Proteomics and bioinformatics were used to analyze the mechanism. The findings were further verified through western blot and Luminex liquid suspension chip technology.

RESULTS

After noise exposure, OVX rats exhibited substantially elevated hearing thresholds. A conspicuous delay in ABR wave I latency was observed, alongside increased loss of outer hair cells, severe collapse of stereocilia and pronounced deformation of the epidermal plate. Accordingly, OVX rats with estrogen supplementation exhibited tolerance to NIHL. Additionally, a remarkable upregulation of the thrombospondin 1 (Tsp1)-CD47 axis in OVX rats was discovered and verified.

CONCLUSIONS

OVX rats were more susceptible to NIHL, and the protective effect of estrogen was achieved through regulation of the Tsp1-CD47 axis. This study presents a novel mechanism through which estrogen regulates NIHL and offers a potential intervention strategy for the clinical treatment of NIHL.

Noise risk assessments within the adequately controlled and reasonably practicable philosophies

Background

The entire risk assessment process is fraught with methodological and technical uncertainties, exacerbated by the introduction in legislation of ambiguous technical terms such as adequately controlled and reasonably practicable. The combination of these factors renders the risk assessment process opaque regarding required employer actions for securing legal compliance within the noise risk assessment context.

Aim

This study aims to evaluate how companies are applying and interpreting the adequately controlled and reasonably practicable philosophies within the context of hearing conservation programmes (HCPs) and noise risk assessment processes.

Setting

Four manufacturing and utilities companies.

Methods

The four companies, selected through convenience sampling, submitted noise risk assessment records for evaluation through document analysis to determine the companies' interpretation of the adequately controlled and reasonably practicable philosophies.

Results

In the reviewed noise risk assessment records, the adequately controlled and reasonably practicable philosophies were poorly discerned. Specifically, the hierarchical approach for noise control outlined in the noise induced hearing loss regulations, for which the basis for adequately controlled philosophy ensues, remains misinterpreted by employers. Furthermore, cost-benefit analysis, which enables decision-making on the tolerability of risk within the reasonably practicable philosophy, was also omitted in the assessments.

Conclusion

The adequately controlled and reasonably practicable philosophies were poorly applied and interpreted by the participating companies, to the detriment of tangible noise control.

Contribution

This study provides insights on company application and interpretation of the adequately controlled and reasonably practicable philosophies, and HCPs, which contributes to inaction on noise control.

Risk-taking propensity as a risk factor for noise-induced hearing loss in the general population

OBJECTIVES

To examine general risk propensity in relation to perceptions of noise, risk behaviour, and hearing loss in the general population.

DESIGN

Participants completed an online survey using the Amazon Mechanical Turk crowdsourcing platform.

STUDY SAMPLE

The sample comprised 1274 adults from the United States.

RESULTS

Higher general risk propensity was associated with an increased likelihood to engage in noise-risk behaviours. Lower general risk propensity was associated with increased knowledge of noise risks and an increased perception of noise as risky. The frequency of self-reported exposures to hazardous noise resulted in estimated annual noise doses exceeding standard hazard limits in 40% of the surveyed population.

CONCLUSIONS

Results revealed limited knowledge of the risks and associated health consequences of noise exposure in the general population Results of this study suggest a high rate of self-exposure to hazardous noise by the general population. Those with higher general risk propensity are more likely to engage in risky noise behaviour. Risky noise behaviour is associated with age, gender, race, ethnicity, and general risk propensity. Intervention programs to modify risky noise behaviour in the general population should focus on both increasing knowledge and establishing accurate perceptions of risk.

Risk factors associated with occupational noise-induced hearing loss in the Hispanic community health study/study of Latinos: A cross-sectional epidemiologic investigation

The purpose of this study was to estimate the prevalence of occupational noise exposure and risk factors of occupational noise-induced hearing loss (NIHL) in Hispanic/Latino adults included in the baseline wave of the Hispanic Community Health Study/Study of Latinos collected from 2008 to 2011. Sequential multiple linear regression modeled the relationship between occupational NIHL (defined as a 3-, 4-, 6-kHz pure-tone average [PTA]) and occupation type, self-reported noise exposure, cardiovascular disease (CVD) risk score, and hearing protective device (HPD) use. The final model controlled for sex, age, and recreational noise exposure. Among 12,851 included participants, approximately 40% (n = 5036) reported occupational noise exposure "Sometimes" (up to 50% of the time) or "Frequently" (75-100% of the time). In the final fitted model, longest-held occupation and CVD risk were associated with poorer hearing. Specifically, those in non-skilled, service, skilled, and military/police/other job categories had between 2.07- and 3.29-dB worse PTA than professional/office workers. Additionally, a shift in the CVD risk score category from low to medium was associated with a 2.25- and 8.20-dB worse PTA for medium and high CVD risk, respectively. Age and sex were also significantly associated with poorer hearing, such that men presented with 6.08 dB worse PTA than women, and for every one-year increase in age, PTA increased by 0.62 dB (ps < .001). No interactions were seen between noise*sometimes or frequent exposure to other ototoxic agents and PTA (ps = .33 & .92, respectively). The prevalence of occupational noise exposure was high in this cross-sectional investigation of adults from Hispanic/Latino backgrounds. Findings contribute to the extant literature by demonstrating that risk factors for occupational NIHL in adults from varying Hispanic/Latino backgrounds are consistent with those of other previously studied groups.

Noise Exposure and Hearing Loss among Workers at a Hammer Forge Company

The National Institute for Occupational Safety and Health (NIOSH) evaluated continuous and impact noise exposures and hearing loss among workers at a hammer forge company. Full-shift personal noise exposure measurements were collected on forge workers across 15 different job titles; impact noise characteristics and one-third octave band noise levels were assessed at the forge hammers; and 4,750 historic audiometric test records for 483 workers were evaluated for hearing loss trends. Nearly all workers' noise exposures exceeded regulatory and/or recommended exposure limits. Workers working in jobs at or near the hammers had full-shift time-weighted average noise exposures above 100 decibels, A-weighted. Impact noise at the hammers reached up to 148 decibels. Analysis of audiometric test records showed that 82% of workers had experienced a significant threshold shift, as defined by NIOSH, and 63% had experienced a standard threshold shift, as defined by the Occupational Safety and Health Administration (OSHA). All workers with an OSHA standard threshold shift had a preceding NIOSH significant threshold shift which occurred, on average, about 7 years prior. This evaluation highlights forge workers' exposures to high levels of noise, including impact noise, and how their hearing worsened with age and length of employment.

Electrophysiological Changes Associated with the Progression of Noise-Induced Hearing Loss

BACKGROUND

The aim of this study is to evaluate the clinical characteristics and electrophysiological changes in patients with different degrees of noise-induced hearing loss compared with those of normal controls to elucidate the progression of auditory neural damage attributed to noise exposure.

METHODS

A retrospective cohort study was conducted through a review of the medical records for the patients who presented to a tertiary referral center. Sixty-nine participants were included in the study: 29 had noise-induced hearing loss, and 40 were healthy controls. All the participants underwent electrophysiological tests and pure-tone audiometry.

RESULTS

Nine patients showed mild hearing loss (mild hearing loss group), while the others showed worse than moderate hearing loss on puretone audiometry (severe hearing loss group). Significantly reduced wave I and V amplitudes of auditory brainstem response were present in both mild and severe hearing loss groups compared to the control group (P -lt; .001 and P=.002, respectively), without significant differences between the mild and severe hearing loss groups. In the multivariate analysis, auditory brainstem response wave V amplitude was negatively associated with auditory brainstem response wave I-V inter-peak latency delay (B=-0.48, P=.02).

CONCLUSION

The results of the present study confirm the similarity in the electrophysiological characteristics between the mild and severe hearing loss groups. Thus, widespread disruption in the auditory neural conduction could have been established in the early period when the patient developed mild hearing loss following noise exposure.

Peripheral vestibular loss in noise-exposed firefighters

Introduction

Occupational workers are increasingly aware of the risk of noise overexposure to the auditory system but lack awareness about potential risks to the vestibular system. The purpose of this study was to investigate changes in vestibular end organ function in a known at-risk noise-exposed population, firefighters compared to age- and sex-matched controls using electrophysiologic measures of cervical vestibular evoked myogenic potentials (cVEMP).

Methods

A cross-sectional observational study compared cVEMP response characteristics in 38 noise-exposed firefighters. Firefighters were grouped by years of exposure in the fire service. The cVEMP responses were compared within firefighter groups and between firefighters and age- and sex-matched controls. Dependent variables included the response characteristics of amplitude, latency and threshold.

Results

cVEMP response amplitudes were significantly decreased in firefighters compared to their age- and sex-matched controls. Threshold of the cVEMP responses were significantly higher in firefighters compared to controls and firefighters had a higher incidence of absent cVEMP responses compared to controls. Response amplitudes decreased with increasing years in the fire-service at an increased rate compared to their age- and sex-matched controls. Latency of the cVEMP response was not significantly different in firefighters compared to controls. These findings are consistent with both animal and human studies suggesting noise-induced changes in the sacculocollic pathway.

Discussion

In the absence of any reported vestibular symptoms or auditory indicators of noise-induced hearing loss, these early effects on the vestibular system point to a potential hidden vestibular loss.

Prevalence and Pattern of Hearing Loss among Young Adults in Tertiary Institutions with Habitual Headphone/Earphone Usage in Kaduna Metropolis

Background

World Health Organisation estimates that 1.1 billion young people worldwide could be at risk of hearing loss due to unsafe listening practises and nearly half of the teenagers and young adults are exposed to unsafe levels of sound from the use of personal audio devices.

Aim

This study aimed to determine the prevalence and pattern of hearing loss among students with habitual use of headphone/earphone in tertiary institutions in Kaduna.

Participants and Methods

This was a prospective cross-sectional study of young adults with prolonged headphone/earphone usage in Kaduna and a group of nonheadphone/earphone users matched for age and sex as controls. Ethical approvals were obtained from relevant bodies and informed consent was also obtained from all participants. Data were obtained by clinical interview and audiometric evaluation of the participants and the data obtained were descriptively analysed using SPSS version 20.0. Frequency tables were generated and chi-square test and Student's t test were used to test for a possible association of variables. The level of significance was set at P < 0.05.

Results

Two hundred and seventy-two prolonged headphone/earphone users with same number of controls participated in this study. The mean age for subjects and controls was 22.6 ± 3.4 and 23.2 ± 4.2, respectively. Using the better hearing ear, 48 and 20 of the subjects and controls, respectively, had hearing loss, giving a prevalence of 17.6% and 7.4% among the subjects and controls, respectively. Of the 48 subjects with hearing loss, 89.6% had a mild hearing loss. Majority, 91.7% had sensorineural hearing loss and the hearing loss was bilateral in all the participants (both subjects and controls). High frequencies were the most affected (64.6%).

Conclusion

This study revealed that hearing impairment was more common among prolonged headphone/earphone users. In the majority of the prolonged headphone/earphone users, the hearing impairment was bilateral, mild, sensorineural, and mostly affects higher frequencies.

Noise-Related Hearing Disorder Among Vector Control Workers in Kuala Lumpur

Introduction Noise-related hearing disorder (NRHD) is the second most common sensorineural hearing loss, right after age-related hearing loss (presbycusis). It is the highest reported occupational disease and a major compensable occupational hazard in Malaysia. With the increase in dengue cases, the need for vector control workers to control the spread of dengue at the expense of being exposed to noisy fogging machines is critical. Methods This was a cross-sectional study of vector control workers conducted by a local authority in Kuala Lumpur. Participants were categorised as either vector control workers who were directly involved in fogging activities or those who were not. A self-administered questionnaire was used to collect sociodemographic, medical and occupational information. NRHD was confirmed by an audiogram test. Results This study found a high prevalence of NRHD among vector control workers exposed to fogging activity (occupational noise hazards), with 51.4% of them experiencing this condition. The predictors of NRHD include fogging status adjusted odds ratio (aOR) 1.94 (95% CI: 1.19 - 3.17), sex 18.28 (95% CI: 2.33 - 143.16) and age 2.03 (95% CI: 1.27 - 3.25). Conclusion The findings of this study imply that vector control workers are at risk of NRHD. The predictors of NRHD are fogging status, sex and age. These findings emphasise the major impact of occupational noise hazards on NRHD and emphasise the importance of addressing this issue to preserve employees' health; especially among male and older employees with chronic noise exposure.

Metformin Protects Against Noise-Induced Hearing Loss in Male Mice

HYPOTHESIS

Metformin treatment will protect mice from noise-induced hearing loss (NIHL).

BACKGROUND

We recently identified metformin as the top-ranking, Food and Drug Administration-approved drug to counter inner ear molecular changes induced by permanent threshold shift-inducing noise. This study is designed to functionally test metformin as a potential otoprotective drug against NIHL.

METHODS

Male and female B6CBAF1/J mice were obtained at 7 to 8 weeks of age. A cohort of the females underwent ovariectomy to simulate menopause and eliminate the effect of ovarian-derived estrogens. At 10 weeks of age, mice underwent a permanent threshold shift-inducing noise exposure (102.5 or 105 dB SPL, 8-16 kHz, 2 h). Auditory brainstem response (ABR) thresholds were obtained at baseline, 24 h after noise exposure, and 1 week after noise exposure. Mice were administered metformin (200 mg/kg/d) or a saline control in their drinking water after the baseline ABR and for the remainder of the study. After the 1-week ABR, mice were euthanized and cochlear tissue was analyzed.

RESULTS

Metformin treatment reduced the 1-week ABR threshold shift at 16 kHz ( p < 0.01; d = 1.20) and 24 kHz ( p < 0.01; d = 1.15) as well as outer hair cell loss in the 32-45.5 kHz range ( p < 0.0001; d = 2.37) in male mice. In contrast, metformin treatment did not prevent hearing loss or outer hair cell loss in the intact or ovariectomized female mice.

CONCLUSIONS

Metformin exhibits sex-dependent efficacy as a therapeutic for NIHL. These data compel continued investigation into metformin's protective effects and demonstrate the importance of evaluating the therapeutic efficacy of drugs in subjects of both sexes.

The effect of cumulative noise exposure on distortion product otoacoustic emissions

OBJECTIVE

This study aimed to identify the characteristics of distortion product otoacoustic emissions (DPOAEs) that can be used to differentiate noise-induced hearing loss (NIHL) from age-related hearing loss. A potential index to detect NIHL was defined in terms of its susceptibility to cumulative noise exposure but not to age.

DESIGN

In this cross-sectional cohort study, a job-exposure matrix was used to calculate the cumulative noise exposure. Multivariate linear regression models were used to examine how age and cumulative noise exposure associated with DPOAEs at individual frequencies after adjusting for hypertension, dyslipidaemia, tobacco use and alcohol consumption.

STUDY SAMPLE

The pure-tone audiometry and DPOAEs data collected from 239 male workers in a steel factory.

RESULTS

DPOAEs and DPOAE signal-to-noise ratios (SNRs) at all frequencies were found to be correlated with age, and those at 2, 3, 4 and 6 kHz were correlated with both age and noise exposure. The difference between DPOAE SNR at 1 and 3 kHz showed significant correlation with noise exposure but not with age.

CONCLUSIONS

The results showed that this DPOAE index, the DPOAE SNR at 1 kHz minus the DPOAE SNR at 3 kHz, could add values to audiometric evaluation of NIHL.

Healthcare Professionals and Noise-Generating Tools: Challenging Assumptions about Hearing Loss Risk

Hearing loss is a significant global health concern, affecting billions of people and leading to various physical, mental, and social consequences. This paper focuses on the risk of noise-induced hearing loss (NIHL) among specific healthcare professionals, especially ear surgeons, orthopaedic surgeons, dentists, and dental hygienists, who frequently use noisy instruments in their professions. While studies on these professionals' noise exposure levels are limited, certain conditions and factors could pose a risk to their hearing. Measures such as engineering and administrative controls, regular audiometric testing, and the use of hearing protection devices are crucial in preventing NIHL. Early detection and intervention are also vital to mitigate further damage. This paper proposes the results of a modified screening protocol, including questionnaires, audiometry, and additional diagnostic tests to identify and address potential hearing disorders. Specific healthcare professionals should remain aware of the risks, prioritize hearing protection, and undergo regular monitoring to safeguard their long-term auditory well-being.

Preclinical prospects of investigational agents for hearing loss treatment

INTRODUCTION

: Hearing loss has a high prevalence, with aging, noise exposure, ototoxic drug therapies, and genetic mutations being some of the leading causes of hearing loss. Health conditions such as cardiovascular disease and diabetes are associated with hearing loss, perhaps due to shared vascular pathology in the ear and in other tissues.

AREAS COVERED

: Issues in the design of preclinical research preclude the ability to make comparisons regarding the relative efficacy of different drugs of interest for possible hearing loss prevention or hearing restoration. This has not slowed the advancement of candidate therapeutics into human clinical testing. There is a robust pipeline with drugs that have different mechanisms of action providing diverse candidate therapies and opportunities for combination therapies to be considered.

EXPERT OPINION

: Much of the preclinical research literature lacks standard study design elements such as dose response testing, and lack of standardization of test protocols significantly limits conclusions regarding relative efficacy. Nonetheless, the many positive results to date have supported translation of preclinical efforts into clinical trials assessing potential human benefits. Approval of the first hearing loss prevention therapeutic is a major success, providing a pathway for other drugs to follow.

Developmental Exposure to Polychlorinated Biphenyls Prevents Recovery from Noise-Induced Hearing Loss and Disrupts the Functional Organization of the Inferior Colliculus

Exposure to combinations of environmental toxins is growing in prevalence; and therefore, understanding their interactions is of increasing societal importance. Here, we examined the mechanisms by which two environmental toxins, polychlorinated biphenyls (PCBs) and high-amplitude acoustic noise, interact to produce dysfunction in central auditory processing. PCBs are well established to impose negative developmental impacts on hearing. However, it is not known whether developmental exposure to this ototoxin alters the sensitivity to other ototoxic exposures later in life. Here, male mice were exposed to PCBs in utero, and later as adults were exposed to 45 min of high-intensity noise. We then examined the impacts of the two exposures on hearing and the organization of the auditory midbrain using two-photon imaging and analysis of the expression of mediators of oxidative stress. We observed that developmental exposure to PCBs blocked hearing recovery from acoustic trauma. In vivo two-photon imaging of the inferior colliculus (IC) revealed that this lack of recovery was associated with disruption of the tonotopic organization and reduction of inhibition in the auditory midbrain. In addition, expression analysis in the inferior colliculus revealed that reduced GABAergic inhibition was more prominent in animals with a lower capacity to mitigate oxidative stress. These data suggest that combined PCBs and noise exposure act nonlinearly to damage hearing and that this damage is associated with synaptic reorganization, and reduced capacity to limit oxidative stress. In addition, this work provides a new paradigm by which to understand nonlinear interactions between combinations of environmental toxins.SIGNIFICANCE STATEMENT Exposure to common environmental toxins is a large and growing problem in the population. This work provides a new mechanistic understanding of how the prenatal and postnatal developmental changes induced by polychlorinated biphenyls (PCBs) could negatively impact the resilience of the brain to noise-induced hearing loss (NIHL) later in adulthood. The use of state-of-the-art tools, including in vivo multiphoton microscopy of the midbrain helped in identifying the long-term central changes in the auditory system after the peripheral hearing damage induced by such environmental toxins. In addition, the novel combination of methods employed in this study will lead to additional advances in our understanding of mechanisms of central hearing loss in other contexts.

Intrinsic mechanism and pharmacologic treatments of noise-induced hearing loss

Noise accounts for one-third of hearing loss worldwide. Regretfully, noise-induced hearing loss (NIHL) is deemed to be irreversible due to the elusive pathogenic mechanisms that have not been fully elucidated. The complex interaction between genetic and environmental factors, which influences numerous downstream molecular and cellular events, contributes to the NIHL. In clinical settings, there are no effective therapeutic drugs other than steroids, which are the only treatment option for patients with NIHL. Therefore, the need for treatment of NIHL that is currently unmet, along with recent progress in our understanding of the underlying regulatory mechanisms, has led to a lot of new literatures focusing on this therapeutic field. The emergence of novel technologies that modify local drug delivery to the inner ear has led to the development of promising therapeutic approaches, which are currently under clinical investigation. In this comprehensive review, we focus on outlining and analyzing the basics and potential therapeutics of NIHL, as well as the application of biomaterials and nanomedicines in inner ear drug delivery. The objective of this review is to provide an incentive for NIHL's fundamental research and future clinical translation.

Hearing Conservation Programme Costs at Selected South African Companies

The Occupational Health and Safety Act 1993 and its attending Regulations in South Africa, require employers to conduct cost analysis studies to inform decision-making related to exposure control for occupational health hazard such as noise. Cost analysis, as per South African National Standard/ISO 31000 risk assessment guideline, is an important input for the decision-making process of the risk management process. The costs of administrating a hearing conservation programme intended to minimise noise-induced hearing loss is an example of a cost analysis. This study enrolled four companies from the South African manufacturing and utilities sectors with the aim of establishing whether cost analysis is included during the noise risk assessment process; and determining administration costs of HCP administration. A HCP cost questionnaire was completed by each company's occupational hygiene professionals and risk officers. None of the companies in the study included cost analysis in their respective risk assessment processes. The overall costs, derived from the HCP cost item questionnaire, was much greater for Company A (4 290 014 Rands) than all of the other companies combined (970 685 Rands). Hearing protection device expenditures across the four companies were the greatest expense, while audiometry was the smallest expense owing to service internalisation. The HCP expenditures are incurred on periodic basis, yearly or biennial, and are internalised in companies as direct costs. Cost analysis can enhance the noise risk assessment process by providing additional input to support the decision-making process related to noise control. This challenges the occupational hygiene profession to pursue new frontiers and decision-making models in the scope of noise risk management, beyond noise measurements and hearing protection device use recommendation.

Antioxidant Therapy as an Effective Strategy against Noise-Induced Hearing Loss: From Experimental Models to Clinic

Cochlear redox unbalance is the main mechanism of damage involved in the pathogenesis of noise-induced-hearing loss. Indeed, the increased free radical production, in conjunction with a reduced efficacy of the endogenous antioxidant system, plays a key role in cochlear damage induced by noise exposure. For this reason, several studies focused on the possibility to use exogenous antioxidant to prevent or attenuate noise-induce injury. Thus, several antioxidant molecules, alone or in combination with other compounds, have been tested in both experimental and clinical settings. In our findings, we tested the protective effects of several antioxidant enzymes, spanning from organic compounds to natural compounds, such as nutraceuticals of polyphenols. In this review, we summarize and discuss the strengths and weaknesses of antioxidant supplementation focusing on polyphenols, Q-Ter, the soluble form of CoQ10, Vitamin E and N-acetil-cysteine, which showed great otoprotective effects in different animal models of noise induced hearing loss and which has been proposed in clinical trials.

The Effect of Noise Exposure on Hearing Function and Vestibular Evoked Myogenic Potentials

Purpose

Exposure to noise can cause damage to both auditory and vestibular systems. The objective of this study is to evaluate how noise exposure affects the hearing and vestibular systems in individuals with noise-induced hearing loss (NIHL).

Methods

This study included 80 subjects (40 subjects with NIHL, and 40 controls), between 26 and 59 years old. For hearing assessment, pure-tone audiometry, extended high-frequency audiometry, tympanometry, acoustic reflex threshold, and distortion product otoacoustic emission tests were used; for vestibular assessment, the cervical and ocular vestibular evoked myogenic potentials tests were used.

Results

Statistically significant differences were found between the two groups in 3 to 6 kHz frequency thresholds; in extended high-frequency audiometry tests, there were also significant differences between groups at all frequencies from 9.5 to 16 kHz. The cervical and ocular vestibular evoked myogenic potentials thresholds were significantly higher and N1-P1 amplitudes were significantly lower in the NIHL group.

Conclusion

Noise can lead to damage to both auditory and vestibular functions. Therefore, audiological assessments and vestibular evoked myogenic potentials could be clinically useful for examining patients with NIHL.

Macrophages Promote Repair of Inner Hair Cell Ribbon Synapses following Noise-Induced Cochlear Synaptopathy

Resident cochlear macrophages rapidly migrate into the inner hair cell synaptic region and directly contact the damaged synaptic connections after noise-induced synaptopathy. Eventually, such damaged synapses are spontaneously repaired, but the precise role of macrophages in synaptic degeneration and repair remains unknown. To address this, cochlear macrophages were eliminated using colony stimulating factor 1 receptor (CSF1R) inhibitor, PLX5622. Sustained treatment with PLX5622 in CX3CR1 GFP/+ mice of both sexes led to robust elimination of resident macrophages (∼94%) without significant adverse effects on peripheral leukocytes, cochlear function, and structure. At 1 day (d) post noise exposure of 93 or 90 dB SPL for 2 hours, the degree of hearing loss and synapse loss were comparable in the presence and absence of macrophages. At 30 d after exposure, damaged synapses appeared repaired in the presence of macrophages. However, in the absence of macrophages, such synaptic repair was significantly reduced. Remarkably, on cessation of PLX5622 treatment, macrophages repopulated the cochlea, leading to enhanced synaptic repair. Elevated auditory brainstem response thresholds and reduced auditory brainstem response Peak 1 amplitudes showed limited recovery in the absence of macrophages but recovered similarly with resident and repopulated macrophages. Cochlear neuron loss was augmented in the absence of macrophages but showed preservation with resident and repopulated macrophages after noise exposure. While the central auditory effects of PLX5622 treatment and microglia depletion remain to be investigated, these data demonstrate that macrophages do not affect synaptic degeneration but are necessary and sufficient to restore cochlear synapses and function after noise-induced synaptopathy.SIGNIFICANCE STATEMENT The synaptic connections between cochlear inner hair cells and spiral ganglion neurons can be lost because of noise over exposure or biological aging. This loss may represent the most common causes of sensorineural hearing loss also known as hidden hearing loss. Synaptic loss results in degradation of auditory information, leading to difficulty in listening in noisy environments and other auditory perceptual disorders. We demonstrate that resident macrophages of the cochlea are necessary and sufficient to restore synapses and function following synaptopathic noise exposure. Our work reveals a novel role for innate-immune cells, such as macrophages in synaptic repair, that could be harnessed to regenerate lost ribbon synapses in noise- or age-linked cochlear synaptopathy, hidden hearing loss, and associated perceptual anomalies.

Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) is the second most common cause of sensorineural hearing loss, after age-related hearing loss, and affects approximately 5% of the world's population. NIHL is associated with substantial physical, mental, social, and economic impacts at the patient and societal levels. Stress and social isolation in patients' workplace and personal lives contribute to quality-of-life decrements which may often go undetected. The pathophysiology of NIHL is multifactorial and complex, encompassing genetic and environmental factors with substantial occupational contributions. The diagnosis and screening of NIHL are conducted by reviewing a patient's history of noise exposure, audiograms, speech-in-noise test results, and measurements of distortion product otoacoustic emissions and auditory brainstem response. Essential aspects of decreasing the burden of NIHL are prevention and early detection, such as implementation of educational and screening programs in routine primary care and specialty clinics. Additionally, current research on the pharmacological treatment of NIHL includes anti-inflammatory, antioxidant, anti-excitatory, and anti-apoptotic agents. Although there have been substantial advances in understanding the pathophysiology of NIHL, there remain low levels of evidence for effective pharmacotherapeutic interventions. Future directions should include personalized prevention and targeted treatment strategies based on a holistic view of an individual's occupation, genetics, and pathology.

The adaptation of noise-induced temporary hearing threshold shift predictive models for modelling the public health policy

OBJECTIVES

It has been shown that monitoring temporary threshold shift (TTS) after exposure to noise may have a predictive value for susceptibility of developing permanent noise-induced hearing loss. The aim of this study is to present the assumptions of the TTS predictive model after its verification in normal hearing subjects along with demonstrating the usage of this model for the purposes of public health policy.

MATERIAL AND METHODS

The existing computational predictive TTS models were adapted and validated in a group of 18 bartenders exposed to noise at the workplace. The performance of adapted TTS predictive model was assessed by receiver operating characteristic (ROC) analysis. The demonstration example of the usage of this model for estimating the risk of TTS in general unscreened population after exposure to loud music in discotheque bars or music clubs is provided.

RESULTS

The adapted TTS predictive model shows a satisfactory agreement in distributions of actual and predicted TTS values and good correlations between these values in examined bartenders measured at 4 kHz, and as a mean at speech frequencies (0.5-4 kHz). An optimal cut-off level for recognizing the TTS events, ca. 75% of young people (aged ca. 35 years) may experience TTS >5 dB, while <10% may exhibit TTS of 15-18 dB.

CONCLUSIONS

The final TTS predictive model proposed in this study needs to be validated in larger groups of subjects exposed to noise. Actual prediction of TTS episodes in general populations may become a helpful tool in creating the hearing protection public health policy. Int J Occup Med Environ Health. 2023;36(1):125-38.

Effects of Varying Laser Parameters During Laser Stapedotomy on Intracochlear Pressures

OBJECTIVE

Sensorineural hearing loss is a known complication of stapes surgery. We previously showed that laser stapedotomy can result in intracochlear pressures that are comparable to high sound pressure levels. Optimizing laser settings to those that correspond with the lowest pressure changes may mitigate risk for postoperative hearing loss. Here we quantify the effects of various laser parameters on intracochlear pressures and test the hypothesis that intracochlear pressure changes are proportional to the laser energy delivered.

STUDY DESIGN

Basic and translational science.

SETTING

Cadaveric dissection and basic science laboratory.

METHODS

Cadaveric human heads underwent mastoidectomies. Intracochlear pressures were measured via fiber-optic pressure probes placed in scala vestibuli and tympani. Pulses of varied stimulus power and duration from a 980-nm diode laser were applied to the stapes footplate.

RESULTS

Sustained high-intensity pressures were observed in the cochlea during all laser applications. Observed pressure magnitudes increased monotonically with laser energy and rose linearly for lower stimulus durations and powers, but there was increased variability for laser applications of longer duration (200-300 ms) and/or higher power (8 W).

CONCLUSIONS

Results confirm that significant pressure changes occur during laser stapedotomy, which we hypothesize may cause injury. Overall energy delivered depends predictably on duration and power, but surgeons should use caution at the highest stimulus levels and longest pulse durations due to the increasing variability in intracochlear pressure under these stimulus conditions. While the risk to hearing from increased intracochlear pressures from laser stapedotomy remains unclear, these results affirm the need to optimize laser settings to avoid unintended injury.

Prevalence of Hearing Loss and Perceptions of Hearing Health and Protection among Florida Firefighters

Firefighters are exposed to extensive hazardous noise while on the job, both during routine tasks at the station and when responding to calls. However, little is known about firefighters' occupational noise hazards. This study employed mixed methods, including focus groups, a survey, and audiometric testing, to identify sources of noise in the firefighters' work environment, determine hearing protective strategies, discern firefighters' perceptions of occupational noise exposure and impacts to their health, and quantify the prevalence of hearing loss among South Florida firefighters. A total of 6 senior officers served in an expert panel, 12 participated in focus groups, 300 completed the survey, and 214 received audiometric tests. Most firefighters were unaware of the risk and their departments' policies, and did not participate in hearing protection practices and avoided using hearing protection devices, which they believed impede team communication and situational awareness. Nearly 30% of participating firefighters showed mild to profound hearing loss, a prevalence that is considerably worse than expected by normal aging alone. Educating firefighters about noise-induced hearing loss early in their careers may have significant health implications for their future. These findings provide insights for developing technologies and programs to mitigate the effects of noise exposure in the firefighting population.