A single dose of AC102 restores hearing in a guinea pig model of noise-induced hearing loss to almost prenoise levels.

Although sudden sensorineural hearing loss (SSNHL) is a serious condition, there are currently no approved drugs for its treatment. Nevertheless, there is a growing understanding that the cochlear pathologies that underlie SSNHL include apoptotic death of sensory outer hair cells (OHCs) as well as loss of ribbon synapses connecting sensory inner hair cells (IHCs) and neurites of the auditory nerve, designated synaptopathy. Noise-induced hearing loss (NIHL) is a common subtype of SSNHL and is widely used to model hearing loss preclinically. Here, we demonstrate that a single interventive application of a small pyridoindole molecule (AC102) into the middle ear restored auditory function almost to prenoise levels in a guinea pig model of NIHL. AC102 prevented noise-triggered loss of OHCs and reduced IHC synaptopathy suggesting a role of AC102 in reconnecting auditory neurons to their sensory target cells. Notably, AC102 exerted its therapeutic properties over a wide frequency range. Such strong improvements in hearing have not previously been demonstrated for other therapeutic agents. In vitro experiments of a neuronal damage model revealed that AC102 protected cells from apoptosis and promoted neurite growth. These effects may be explained by increased production of adenosine triphosphate, indicating improved mitochondrial function, and reduced levels of reactive-oxygen species which prevents the apoptotic processes responsible for OHC death. This action profile of AC102 might be causal for the observed hearing recovery in in vivo models.

The influencing factors of hearing protection device usage among noise-exposed workers in Guangdong Province: a structural equation modeling-based survey.

BACKGROUND: There are numerous complex barriers and facilitators to continuously wearing hearing protection devices (HPDs) for noise-exposed workers. Therefore, the present study aimed to investigate the relationship between HPD wearing behavior and hearing protection knowledge and attitude, HPD wearing comfort, and work-related factors. METHOD: A cross-sectional study was conducted with 524 noise-exposed workers in manufacturing enterprises in Guangdong Province, China. Data were collected on hearing protection knowledge and attitudes, HPD wearing comfort and behavior, and work-related factors through a questionnaire. Using structural equation modeling (SEM), we tested the association among the study variables. RESULTS: Among the total workers, 69.47% wore HPD continuously, and the attitudes of hearing protection (26.17 ± 2.958) and total HPD wearing comfort (60.13 ± 8.924) were satisfactory, while hearing protection knowledge (3.54 ± 1.552) was not enough. SEM revealed that hearing protection knowledge had direct effects on attitudes (ß = 0.333, p < 0.01) and HPD wearing behavior (ß = 0.239, p < 0.01), and the direct effect of total HPD wearing comfort on behavior was ß = 0.157 (p < 0.01). The direct effect also existed between work shifts and behavior (ß=-0.107, p < 0.05). Indirect relationships mainly existed between other work-related factors, hearing protection attitudes, and HPD wearing behavior through knowledge. Meanwhile, work operation had a direct and negative effect on attitudes (ß=-0.146, p < 0.05), and it can also indirectly and positively affect attitudes through knowledge (ß = 0.08, p < 0.05). CONCLUSION: The behavior of wearing HPD was influenced by hearing protection knowledge, comfort in wearing HPD, and work-related factors. The results showed that to improve the compliance of noise-exposed workers wearing HPD continuously when exposed to noise, the HPD wearing comfort and work-related factors must be taken into consideration. In addition, we evaluated HPD wearing comfort in physical and functional dimensions, and this study initially verified the availability of the questionnaire scale of HPD wearing comfort.

Synaptic ribbon dynamics after noise exposure in the hearing cochlea.

Moderate noise exposure induces cochlear synaptopathy, the loss of afferent ribbon synapses between cochlear hair cells and spiral ganglion neurons, which is associated with functional hearing decline. Prior studies have demonstrated noise-induced changes in the distribution and number of synaptic components, but the dynamic changes that occur after noise exposure have not been directly visualized. Here, we describe a live imaging model using RIBEYE-tagRFP to enable direct observation of pre-synaptic ribbons in mature hearing mouse cochleae after synaptopathic noise exposure. Ribbon number does not change, but noise induces an increase in ribbon volume as well as movement suggesting unanchoring from synaptic tethers. A subgroup of basal ribbons displays concerted motion towards the cochlear nucleus with subsequent migration back to the cell membrane after noise cessation. Understanding the immediate dynamics of synaptic damage after noise exposure may facilitate identification of specific target pathways to treat cochlear synaptopathy.

[Research progress in genetics of noise-induced hearing loss].

Noise-induced hearing loss（NIHL） is an acquired sensorineural hearing loss induced by long-term noise exposure. The susceptibility of exposed people may vary even in the same noise environment. With the development of sequencing techniques, genes related to oxidative stress, immunoinflammatory, ion homeostasis, energy metabolism, DNA damage repair and other mechanisms in NIHL have been reported continuously. And some genes may interact with noise exposure indexes. In this article, population studies on NIHL-related gene polymorphisms and gene-environment interactions in the past 20 years are reviewed, aimed to providing evidence for the construction of NIHL-related risk prediction models and the formulation of individualized interventions.

Sensitivity of Methods for Diagnosing Noise-Induced Hearing Loss in Cases of Exposures Including Intense Low-Frequency Noise.

Exposure to intense low-frequency sounds, for example inside tanks and armoured vehicles, can lead to noise-induced hearing loss (NIHL) with a variable audiometric pattern, including low- and mid-frequency hearing loss. It is not known how well existing methods for diagnosing NIHL apply in such cases. Here, the audiograms of 68 military personnel (mostly veterans) who had been exposed to intense low-frequency noise (together with other types of noise) and who had low-frequency hearing loss (defined as a pure-tone average loss at 0.25, 0.5 and 1 kHz ≥20 dB) were used to assess the sensitivity of three diagnostic methods: the method of Coles, Lutman and Buffin, denoted CLB, which depends on the identification of a notch or bulge in the audiogram near 4 kHz, and two methods specifically intended for diagnosing NIHL sustained during military service, the rM-NIHL method, which depends on the identification of a notch or bulge in the audiogram near 4 kHz and/or a hearing loss at high frequencies greater than expected from age alone, and the MLP(18) method based on a multi-layer perceptron. The proportion of individuals receiving a positive diagnosis for either or both ears, which provides an approximate measure of sensitivity, was 0.40 for the CLB method, 0.79 for the rM-NIHL method and 1.0 for the MLP(18) method. It is concluded that the MLP(18) method is suitable for diagnosing NIHL sustained during military service whether or not the exposure includes intense low-frequency sounds.

Noise-Induced Hearing Loss and Use of Hearing Protection Awareness among Medical Students in Saudi Arabia: Mixed Qualitative and Quantitative Study.

BACKGROUND: Noise-Induced Hearing Loss (NIHL) is a prevalent occupational hazard among healthcare professionals, including medical students. Despite its detrimental effects, the awareness and utilization of hearing protection measures among medical students in Saudi Arabia remain understudied. OBJECTIVE: Is to determine the level of awareness and understanding of NIHL among medical students in Saudi Arabia, as well as their knowledge and usage of hearing protection measures and to identify potential barriers and facilitators for hearing protection utilization. METHODS: A mixed-methods approach was employed, involving a questionnaire survey and semi-structured interviews. The survey collected data on demographics, knowledge of NIHL, and hearing protection practices among medical students. Subsequently, a semi-structured interview was conducted to obtain in-depth insights into the students' experiences, attitudes, and beliefs regarding NIHL and the use of hearing protection. RESULTS: The level about NIHL was 59.32%. Better access to information is associated with increased odds of awareness (odds ratio=3.07, p=0.012). Having relatives with hearing loss increases the odds of awareness (odds ratio =2.49, p=0.034). Individuals with hearing loss or impairment have higher odds of awareness (odds ratio =2.27, p=0.046). Ear Pain, temporary hearing loss, tinnitus, or ringing in the ear: These factors are not significantly associated with awareness of noise-induced hearing loss (p>0.05). Using hearing aids is strongly associated with increased odds of awareness (odds ratio =3.94, p=0.006).The quantitative analysis provided statistical information on the prevalence rates and factors influencing hearing protection usage, while the qualitative analysis uncover nuanced perspectives and experiences. CONCLUSION: This research will contribute to the understanding of NIHL and hearing protection practices among medical students in Saudi Arabia. Improving hearing protection awareness and practices among medical students can ultimately reduce the incidence of NIHL and promote a healthier work environment within the healthcare sector.

Statistical estimation of noise induced hearing loss among the drivers in one of the most polluted cities of India.

In the present study, an attempt has been made to assess the impact of vehicular noise upon the 3-wheeler tempo drivers and to know whether there is any relationship between hearing loss and cumulative noise exposure. For this purpose, 3-wheeler tempo drivers (Exposed group) and non-commercial light motor vehicle car drivers (Unexposed group) were chosen as study subjects. Three traffic routes were selected to assess the noise level during waiting and running time in the exposed and unexposed groups. Among all three routes, the highest mean noise level (Leq) was observed on the Chowk to Dubagga route for waiting and en-route noise measurement. It was measured as 84.13 dB(A) and 86.36 dB(A) for waiting and en-route periods of 7.68 ± 3.46 and 31.05 ± 6.6 min, respectively. Cumulative noise exposure was found to be significantly different (p < 0.001) in all age groups of exposed and unexposed drivers. Audiometric tests have been performed over both exposed and unexposed groups. The regression analysis has been done keeping hearing loss among tempo drivers as the dependent variable and age (years) and Energy (Pa2 Hrs) as the independent variable using three different criteria of hearing loss definitions, i.e., World Health Organization, National Institute for Occupational Safety and Health (NIOSH), Occupational Safety and Health Administration criteria. Among these three criteria, the NIOSH criterion of hearing loss best explained the independent variables. It could explain the total variation in dependent variable by independent variable quite well, i.e., 68.1%. The finding showed a linear relationship between cumulative noise exposures (Pa2 Hrs) and the exposed group's hearing loss (dB), i.e., hearing loss increases with increasing noise dose. Based on the findings, two model equations were developed to identify the safe and unsafe noise levels with exposure time.

Noise-induced synaptic loss and its post-exposure recovery in CBA/CaJ vs. C57BL/6J mice.

Acute noise-induced loss of synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs) has been documented in several strains of mice, but the extent of post-exposure recovery reportedly varies dramatically. If such inter-strain heterogeneity is real, it could be exploited to probe molecular pathways mediating neural remodeling in the adult cochlea. Here, we compared synaptopathy repair in CBA/CaJ vs. C57BL/6J, which are at opposite ends of the reported recovery spectrum. We evaluated C57BL/6J mice 0 h, 24 h, 2 wks or 8 wks after exposure for 2 h to octave-band noise (8-16 kHz) at either 90, 94 or 98 dB SPL, to compare with analogous post-exposure results in CBA/CaJ at 98 or 101 dB. We counted pre- and post-synaptic puncta in immunostained cochleas, using machine learning to classify paired (GluA2 and CtBP2) vs. orphan (CtBP2 only) puncta, and batch-processing to quantify immunostaining intensity. At 98 dB, both strains show ongoing loss of ribbons and synapses between 0 and 24 h, followed by partial recovery, however the extent and degree of these changes were greater in C57BL/6J. Much of the synaptic recovery is due to transient reduction in GluA2 intensity in synaptopathic regions. In contrast, CtBP2 intensity showed only transient increases (at 2 wks). Neurofilament staining revealed transient extension of ANF terminals in C57BL/6J, but not in CBA/CaJ, peaking at 24 h and reverting by 2 wks. Thus, although interstrain differences in synapse recovery are dominated by reversible changes in GluA2 receptor levels, the neurite extension seen in C57BL/6J suggests a qualitative difference in regenerative capacity.

Impact of occupational noise exposure on the hearing level in hospital staffs: a longitudinal study.

The study aimed to evaluate the impact of occupational noise on hearing loss among healthcare workers using audiometry. A longitudinal study was conducted with a six-month follow-up period in a hospital with 21 participants, divided into high-noise-exposure (HNE) and low-noise-exposure (LNE) groups. Mean noise levels were higher in the HNE group (70.4 ± 4.5 dBA), and hearing loss was measured using pure-tone audiometry at baseline and follow-up. The HNE group had significantly higher mean threshold levels at frequencies of 0.25 kHz, 0.5 kHz, 4.0 kHz, and an average of 0.5, 1, 2, and 4 kHz (all p-values < 0.05) after the follow-up period. After adjusting for confounding factors, the HNE group had significantly higher hearing loss levels at 0.25 kHz, 0.5 kHz, and average frequencies of 0.5, 1, 2, and 4 kHz compared to the LNE group at the second measurement. Occupational noise levels above 65 dBA over six months were found to cause significant threshold changes at frequencies of 0.25 kHz, 0.5 kHz, and an average of 0.5-4.0 kHz. This study highlights the risk of noise-induced hearing loss among healthcare workers and emphasizes the importance of implementing effective hearing conservation programs in the workplace. Regular monitoring and assessment of noise levels and hearing ability, along with proper use of personal protective equipment, are crucial steps in mitigating the impact of occupational noise exposure on the hearing health of healthcare workers.

Hidden hearing loss: Fifteen years at a glance.

Hearing loss affects approximately 18% of the population worldwide. Hearing difficulties in noisy environments without accompanying audiometric threshold shifts likely affect an even larger percentage of the global population. One of the potential causes of hidden hearing loss is cochlear synaptopathy, the loss of synapses between inner hair cells (IHC) and auditory nerve fibers (ANF). These synapses are the most vulnerable structures in the cochlea to noise exposure or aging. The loss of synapses causes auditory deafferentation, i.e., the loss of auditory afferent information, whose downstream effect is the loss of information that is sent to higher-order auditory processing stages. Understanding the physiological and perceptual effects of this early auditory deafferentation might inform interventions to prevent later, more severe hearing loss. In the past decade, a large body of work has been devoted to better understand hidden hearing loss, including the causes of hidden hearing loss, their corresponding impact on the auditory pathway, and the use of auditory physiological measures for clinical diagnosis of auditory deafferentation. This review synthesizes the findings from studies in humans and animals to answer some of the key questions in the field, and it points to gaps in knowledge that warrant more investigation. Specifically, recent studies suggest that some electrophysiological measures have the potential to function as indicators of hidden hearing loss in humans, but more research is needed for these measures to be included as part of a clinical test battery.

Associations Between Recreational Noise Exposure and Hearing Function in Adolescents and Young Adults: A Systematic Review.

PURPOSE: There is an increasing concern regarding hazardous recreational noise exposure among adolescents and young adults. Daily exposure to loud sound levels over a long period of time can increase the risk of noise-induced hearing loss. The full extent of the impact of recreational noise on hearing is not yet fully understood. The purpose of this review was to synthesize research that investigated hearing function in relation to recreational noise exposure in adolescents and young adults. METHOD: A systematic literature search of five databases covering the years 2000-2023 was performed. The articles included investigated audiological measurements of hearing function in relation to recreational noise exposure. RESULTS: Four hundred sixty records were identified, of which 20 met the inclusion criteria and were included in the results. This review showed that although some recreational noise activities can be potentially harmful, there is an unclear relationship between exposure and outcome. Some findings indicated hearing threshold shifts or reduced otoacoustic emission amplitudes after recreational noise exposure, but most changes were short term and in the extended high-frequency range. CONCLUSIONS: There seemed to be inconsistencies regarding the utilization of methods of measuring exposure and outcome between studies. This might be one reason for the differing results in studies on the reported impact on hearing function from recreational noise exposure. To draw more certain conclusions about long-term effects, there is a need for longitudinal research that utilizes sound level measurements to assess low and high degrees of recreational noise exposure in relation to hearing function. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.25114193.

Association of noise exposure, plasma microRNAs with metabolic syndrome and its components among Chinese adults.

AIMS: We aimed to evaluate the association of occupational noise with metabolic syndrome (MetS) and its components, and to assess the potential role of miRNAs in occupational noise-associated MetS. METHODS: A total of 854 participants were enrolled in our study. Cumulative noise exposure (CNE) was estimated in conjunction with workplace noise test records and research participants' employment histories. Logistic regression models adjusted for potential confounders were used to assess the association of CNE and miRNAs with MetS and its components. RESULTS: We observed linear positive dose-response associations between occupational noise exposure and the prevalence of MetS (OR: 1.031; 95 % CI: 1.008, 1.055). And linear and nonlinear relationship were also found for the association of occupational noise exposure with high blood pressure (OR: 1.024; 95 % CI: 1.007, 1.041) and reduced high-density lipoprotein (OR: 1.051; 95 % CI: 1.031, 1.072), respectively. MiR-200a-3p, miR-92a-3p and miR-21-5p were inversely associated with CNE, or the prevalence of MetS and its components (all P < 0.05). However, we did not find any statistically significant mediation effect of miRNAs in the associations of CNE with MetS. Furthermore, the prevalence of bilateral hearing loss in high-frequency increased (OR: 1.036; 95 % CI: 1.008, 1.067) with CNE level rising, and participants with bilateral hearing loss in high-frequency had a significantly higher risk of MetS (OR: 1.727; 95 % CI: 1.048, 2.819). CONCLUSION: Our study suggests that occupational noise exposure is associated with MetS and its components, and the role of miRNAs in noise-induced increasing MetS risk needs to be confirmed in future studies.

A novel model of sensorineural hearing loss induced by repeated exposure to moderate noise in mice: the preventive effect of resveratrol.

Sensorineural hearing loss (SNHL) induced by noise has increased in recent years due to personal headphone use and noisy urban environments. The study shows a novel model of gradually progressive SNHL induced by repeated exposure to moderate noise (8-kHz octave band noise, 90-dB sound pressure level) for 1 hr exposure per day in BALB/cCr mice. The results showed that the repeated exposure led to gradually progressive SNHL, which was dependent on the number of exposures, and resulted in permanent hearing loss after 5 exposures. Repeated exposure to noise causes a loss of synapses between the inner hair cells and the peripheral terminals of the auditory nerve fibers. Additionally, there is a reduction in the expression levels of c-fos and Arc, both of which are indicators of cochlear nerve responses to noise exposure. Oral administration of resveratrol (RSV, 50 mg/kg/day) during the noise exposure period significantly prevented the noise exposure-induced synapse loss and SNHL. Furthermore, the study found that RSV treatment prevented the noise-induced increase in the gene expression levels of the proinflammatory cytokine interleukin-1ß in the cochlea. These results demonstrated the potential usefulness of RSV in preventing noise-induced SNHL in the animal model established as gradually progressive SNHL.

The perception of ultrasonic vocalizations by laboratory mice following intense noise exposures.

Noise-induced hearing loss interacts with age, sex, and listening conditions to affect individuals' perception of ecologically relevant stimuli like speech. The present experiments assessed the impact of age and sex on vocalization detection by noise-exposed mice trained to detect a downsweep or complex ultrasonic vocalization in quiet or in the presence of a noise background. Daily thresholds before and following intense noise exposure were collected longitudinally and compared across several factors. All mice, regardless of age, sex, listening condition, or stimulus type showed their poorest behavioral sensitivity immediately after the noise exposure. There were varying degrees of recovery over time and across factors. Old-aged mice had greater threshold shifts and less recovery compared to middle-aged mice. Mice had larger threshold shifts and less recovery for downsweeps than for complex vocalizations. Female mice were more sensitive, had smaller post-noise shifts, and had better recovery than males. Thresholds in noise were higher and less variable than thresholds in quiet, but there were comparable shifts and recovery. In mice, as in humans, the perception of ecologically relevant stimuli suffers after an intense noise exposure, and results differ from simple tone detection findings.

An acoustical environment survey of student music practice.

Chronic exposure to loud sound leads to noise-induced hearing loss. This is especially common in collegiate-level musicians. Existing methods for estimating exposure typically do not consider genre- or instrument-specific variability in soundscape/spectral characteristics. We measured sound exposure levels (SELs) across instruments, bands, and genres at a university music school. We found (1) considerable variability in SELs across instruments and bands, (2) that Jazz musicians are consistently exposed to the highest sound levels, and (3) that spectral features of music differ between instrument type and genre, and based on room size. These findings highlight the need for tailored guidelines that moderate the implementation of hearing conservation initiatives for collegiate musicians.

[Study on the fit testing for the workers wearing hearing protection device in machinery manufacturing enterprises].

Objective: To investigate the occupational noise hazards in five machinery manufacturing enterprises, and to evaluate the individual noise reduction values and influencing factors of workers wearing hearing protection device (HPD) by individual fit testing. Methods: From November 2021 to January 2022, 5 machinery manufacturing enterprises in Bao'an District of Shenzhen were selected to conduct an occupational health survey to understand the noise exposure level of workers. The 3MTM E-A-RfitTM fitness test system was used to test the baseline individual sound attenuation value level (PAR) of the daily wear of the ear protecters for 485 workers in typical noise working positions. Workers whose PAR values could not meet the requirements of noise reduction at work were instructed to wear and repeated tests were conducted. PAR results of the workers before and after the intervention were collected and analyzed. Results: The noise workers who received the suitability test were mainly distributed in 24 types of work, the job noise exposure level was 80.2 dB (A) ~ 95.0 dB (A), and the job noise excess rate was 52.5% (138/263). The median baseline PAR [M (Q(1), Q(3)) ] for 485 workers was 6.0 (0.0, 14.0) dB. The baseline PAR of male workers, those with more than 15 years of working experience, those with more than 15 years of using ear guards, those who considered ear guards comfortable to wear, those with college degree or above, and those exposed to noise level 90 dB (A) were higher, and the difference was statistically significant (P<0.05). A total of 275 workers (56.7%) did not pass the baseline PAR test, and there was no statistically significant difference in the intervention rate of workers in different noise groups (P>0.05). PAR in subjects who did not pass baseline after intervention increased from 0.0 (0.0, 3.0) dB to 15.0 (12.0, 18.2) dB. Conclusion: The workplace noise hazard of machinery manufacturing enterprises is serious, and there is a great difference between the baseline PAR and the nominal value of the hearing guard worn by the noise exposed workers. The intervention measures can effectively improve the protective effect of wearing ear protectors.

Noise-induced hearing loss and hearing protection: Attitudes at a South African coal mine.

BACKGROUND:  Negative attitudes and beliefs are major contributing factors to the rising numbers of noise-induced hearing loss (NIHL) cases in coal mines both locally and internationally. International literature confirms limited knowledge surrounding employees' attitudes and beliefs regarding NIHL and hearing protection devices (HPDs), hence the need for the study. OBJECTIVES:  To ascertain the attitudes and beliefs about NIHL and HPD use among employees at a large scale underground coal mine in Mpumalanga. METHOD:  A descriptive and exploratory cross-sectional study was conducted using a self-administered questionnaire, developed by the National Institute for Occupational Safety and Health (NIOSH) on Beliefs about Hearing Protection and Hearing Loss (BHPHL). Participants (n = 241) included employees from a coal mine in Mpumalanga, South Africa. RESULTS:  Out of 241 completed surveys, this study found that 84% were aware of when to replace earmuffs; 95% believed wearing HPDs could prevent hearing loss in noisy environments; 83% felt their hearing was impacted by loud noise. Additionally, 86% mentioned discomfort from earmuff pressure; 95% emphasised HPD importance; and 95% used HPDs around loud sounds. Moreover, 98% knew how to properly wear earplugs, while lower education levels were linked to higher susceptibility to NIHL. CONCLUSION:  The study identified positive attitudes towards NIHL and HPD use, but existing NIHL cases must be acknowledged. Organisations can use the findings to develop tailored hearing conservation programmes (HCP), including education, involving employees in protection decisions and promoting diligent HPD usage.Contribution: This study contributes to the limited literature on noise perceptions, NIHL, and HPD use in mining, emphasising the impact attitude has on HPD use and assessing the effect of miners NIHL knowledge on compliance. The findings, unique to coal mining, hold significance for enhancing hearing conservation and reducing NIHL.

Occupational noise and hypertension in Southern Chinese workers: a large occupational population-based study.

INTRODUCTION: An increasing number of original studies suggested that occupational noise exposure might be associated with the risk of hypertension, but the results remain inconsistent and inconclusive. In addition, the attributable fraction (AF) of occupational noise exposure has not been well quantified. We aimed to conduct a large-scale occupational population-based study to comprehensively investigate the relationship between occupational noise exposure and blood pressure and different hypertension subtypes and to estimate the AF for hypertension burden attributable to occupational noise exposure. METHODS: A total of 715,135 workers aged 18-60 years were included in this study based on the Key Occupational Diseases Surveillance Project of Guangdong in 2020. Multiple linear regression was performed to explore the relationships of occupational noise exposure status, the combination of occupational noise exposure and binaural high frequency threshold on average (BHFTA) with systolic and diastolic blood pressure (SBP, DBP). Multivariable logistic regression was used to examine the relationshipassociation between occupational noise exposure status, occupational noise exposure combined with BHFTA and hypertension. Furthermore, the attributable risk (AR) was calculated to estimate the hypertension burden attributed to occupational exposure to noise. RESULTS: The prevalence of hypertension among occupational noise-exposed participants was 13·7%. SBP and DBP were both significantly associated with the occupational noise exposure status and classification of occupational noise exposure combined with BHFTA in the crude and adjusted models (all P < 0·0001). Compared with workers without occupational noise exposure, the risk of hypertension was 50% greater among those exposed to occupational noise in the adjusted model (95% CI 1·42-1·58). For participants of occupational noise exposed with BHFTA normal, and occupational noise exposed with BHFTA elevated, the corresponding risks of hypertension were 48% (1·41-1·56) and 56% (1·46-1·63) greater than those of occupational noise non-exposed with BHFTA normal, respectively. A similar association was found in isolated systolic hypertension (ISH) and prehypertension. Subgroup analysis by sex and age showed that the positive associations between occupational noise exposure and hypertension remained statistically significant across all subgroups (all P < 0.001). Significant interactions between occupational noise status, classification of occupational noise exposure combined with BHFTA, and age in relation to hypertension risk were identified (all P for interaction < 0.001). The associations of occupational noise status, classification of occupational noise exposure combined with BHFTA and hypertension were most pronounced in the 18-29 age groups. The AR% of occupational noise exposure for hypertension was 28·05% in the final adjusted model. CONCLUSIONS: Occupational noise exposure was positively associated with blood pressure levels and the prevalence of hypertension, ISH, and prehypertension in a large occupational population-based study. A significantly increased risk of hypertension was found even in individuals with normal BHFTA exposed to occupational noise, with a further elevated risk observed in those with elevated BHFTA. Our findings provide epidemiological evidence for key groups associated with occupational noise exposure and hypertension, and more than one-fourth of hypertension cases would have been prevented by avoiding occupational noise exposure.

How 'hidden hearing loss' noise exposure affects neural coding in the inferior colliculus of rats.

Exposure to brief, intense sound can produce profound changes in the auditory system, from the internal structure of inner hair cells to reduced synaptic connections between the auditory nerves and the inner hair cells. Moreover, noisy environments can also lead to alterations in the auditory nerve or to processing changes in the auditory midbrain, all without affecting hearing thresholds. This so-called hidden hearing loss (HHL) has been shown in tinnitus patients and has been posited to account for hearing difficulties in noisy environments. However, much of the neuronal research thus far has investigated how HHL affects the response characteristics of individual fibres in the auditory nerve, as opposed to higher stations in the auditory pathway. Human models show that the auditory nerve encodes sound stochastically. Therefore, a sufficient reduction in nerve fibres could result in lowering the sampling of the acoustic scene below the minimum rate necessary to fully encode the scene, thus reducing the efficacy of sound encoding. Here, we examine how HHL affects the responses to frequency and intensity of neurons in the inferior colliculus of rats, and the duration and firing rate of those responses. Finally, we examined how shorter stimuli are encoded less effectively by the auditory midbrain than longer stimuli, and how this could lead to a clinical test for HHL.

Complete Restoration of Hearing Loss and Cochlear Synaptopathy via Minimally Invasive, Single-Dose, and Controllable Middle Ear Delivery of Brain-Derived Neurotrophic Factor-Poly(dl-lactic acid-co-glycolic acid)-Loaded Hydrogel.

Noise-induced hearing loss (NIHL) often accompanies cochlear synaptopathy, which can be potentially reversed to restore hearing. However, there has been little success in achieving complete recovery of sensorineural deafness using nearly noninvasive middle ear drug delivery before. Here, we present a study demonstrating the efficacy of a middle ear delivery system employing brain-derived neurotrophic factor (BDNF)-poly-(dl-lactic acid-co-glycolic acid) (PLGA)-loaded hydrogel in reversing synaptopathy and restoring hearing function in a mouse model with NIHL. The mouse model achieved using the single noise exposure (NE, 115 dBL, 4 h) exhibited an average 20 dBL elevation of hearing thresholds with intact cochlear hair cells but a loss of ribbon synapses as the primary cause of hearing impairment. We developed a BDNF-PLGA-loaded thermosensitive hydrogel, which was administered via a single controllable injection into the tympanic cavity of noise-exposed mice, allowing its presence in the middle ear for a duration of 2 weeks. This intervention resulted in complete restoration of NIHL at frequencies of click, 4, 8, 16, and 32 kHz. Moreover, the cochlear ribbon synapses exhibited significant recovery, whereas other cochlear components (hair cells and auditory nerves) remained unchanged. Additionally, the cochlea of NE treated mice revealed activation of tropomyosin receptor kinase B (TRKB) signaling upon exposure to BDNF. These findings demonstrate a controllable and minimally invasive therapeutic approach that utilizes a BDNF-PLGA-loaded hydrogel to restore NIHL by specifically repairing cochlear synaptopathy. This tailored middle ear delivery system holds great promise for achieving ideal clinical outcomes in the treatment of NIHL and cochlear synaptopathy.