An intracochlear DP-gram: Proof of principle in noise-damaged rabbits

Distortion-product otoacoustic emissions (DPOAEs) can be used to assess cochlear damage and are often evaluated by generating a DP-gram in which 2f₁-f₂ DPOAE levels are plotted as a function of the higher-frequency primary at f₂. DPOAEs are derived from the reverse propagation of distortion-product (DP) wavelets from their intracochlear sites of generation to emerge as measurable acoustic signals in the outer ear canal. However, at least, some of these same wavelets also propagate within the cochlea in the normal forward direction to the DP-frequency (f_dp) place, where they appear as intracochlear distortion products (iDPs). Depending on several factors, especially, the extent to which DP wavelets add or cancel with each other in phase, one might expect iDPs to differ from DPOAEs in their ability to map the frequency pattern of cochlear damage. In the present study, the behavior of 2f₁-f₂ iDPs was inferred by interacting a probe tone (f₃) with the iDP of interest to produce a 'secondary' DPOAE (i.e., DPOAE^2ry), which was then used to infer the level of 2f₁-f₂ iDPs as a function of the f₂-test frequency, thus, constituting a newly developed iDP-gram. To determine the feasibility of and potential applications for the iDP-gram procedure, noise-induced cochlear damage was assessed in two 'test' rabbits, one of which exhibited a well-defined punctate loss in their DP-gram, while the other exhibited a broader V-shaped loss. To validate the iDP-gram procedure, standard DP-grams were simultaneously collected and compared to their iDP-gram counterparts. Cochlear damage was independently assessed using auditory brainstem responses (ABRs) describing threshold-shift patterns to which both DP-gram types could be compared. Each DP-gram variety, to some extent, was able to detect a punctate loss in one rabbit and a broader V-shaped loss in the other. For the punctate-loss subject, the standard DP-gram showed a more generalized loss across test frequencies, while iDP-grams showed several localized notches superimposed on the generalized-loss pattern. In general, for the V-shaped loss pattern, both DP-gram types performed very well at detecting the large loss, with the lower primary-tone levels being most sensitive. At the narrow primary-tone ratios of f₂/f₁=1.05, standard DP-grams were unable to detect either loss pattern, while for the punctate loss, they paradoxically showed enhancement. Notably, the simultaneously collected iDP-grams performed favorably at the narrow-ratio setting, which is consistent with the notion that DPs travelling toward the 2f₁-f₂ f_dp place are not subject to the cancellation of wavelets typical for narrow primary-ratio conditions that can confound measures of DPs moving towards the ear canal to emerge as DPOAEs.

Method for protected noise exposure level assessment under an in-ear hearing protection device: a pilot study

OBJECTIVE

To properly measure the effective noise exposure level of workers with hearing protection devices (HPD), the use of in-ear noise dosimeters (IEND) is increasing. Commercial IENDs typically feature one in-ear microphone that captures all noises inside the ear and do not discriminate the residual noise in the earcanal from wearer-induced disturbances (WID) to calculate the in-ear sound pressure levels (SPL). A method to alleviate this particular issue with IENDs and calculate the hearing protection level on-site is therefore proposed.

DESIGN

The sound captured by an outer-ear microphone is filtered with the modelled HPD transfer function to estimate the in-ear SPL, this way part of the WIDs mostly captured by the in-ear microphone can be rejected from the SPL. The level of protection provided by the earplugs can then be estimated from the difference between in-ear and outer-ear SPLs. The proposed method is validated by comparing the outcome of the proposed WID rejection method to a reference method.

STUDY SAMPLE

The detailed methods are assessed on audio recordings from 16 industrial workers monitored for up to 4 days.

RESULTS

The merits of the proposed WID rejection approach are discussed in terms of residual SPL and hearing protection level estimation accuracy.

CONCLUSIONS

Based on the findings, a method to integrate the proposed WID rejection algorithm in future IENDs is suggested.

Evaluation of cochlear activity in normal-hearing musicians

OBJECTIVE

The present study compared wave I amplitude of auditory brainstem responses (ABRs), a potential indicator of cochlear synaptopathy, among musicians and non-musicians with normal audiograms.

DESIGN

Noise exposure background (NEB) was evaluated using an online questionnaire. Two-channel ABRs were recorded from the left ear using click stimuli. One channel utilized an ipsilateral tiptrode, and another channel utilized an ipsilateral mastoid electrode. ABRs were collected at 90, 75, and 60 dBnHL. A mixed model was used to analyze the effect of group, electrodes, and stimulus levels on ABR wave I amplitude.

STUDY SAMPLE

75 collegiate students with normal hearing participated in the study and were grouped into a non-music major group (n = 25), a brass major group (n = 25), and a voice major group (n = 25).

RESULTS

The NEB was negatively associated with the action potential (AP) and ABR wave I amplitude for click intensity levels at 75 dBnHL. The mean amplitude of the ABR wave I was not significantly different between the three groups.

CONCLUSION

The weak negative association of AP and ABR wave I amplitude with NEB cannot be solely attributed to evidence of cochlear synaptopathy in humans as the possibility of hair cell damage cannot be ruled out. Future research should investigate the effects of reduced cochlear output on the supra-threshold speech processing abilities of student musicians.

Investigating the effects of noise exposure on self-report, behavioral and electrophysiological indices of hearing damage in musicians with normal audiometric thresholds

Musicians are at risk of hearing loss due to prolonged noise exposure, but they may also be at risk of early sub-clinical hearing damage, such as cochlear synaptopathy. In the current study, we investigated the effects of noise exposure on electrophysiological, behavioral and self-report correlates of hearing damage in young adult (age range = 18-27 years) musicians and non-musicians with normal audiometric thresholds. Early-career musicians (n = 76) and non-musicians (n = 47) completed a test battery including the Noise Exposure Structured Interview, pure-tone audiometry (PTA; 0.25-8 kHz), extended high-frequency (EHF; 12 and 16 kHz) thresholds, otoacoustic emissions (OAEs), auditory brainstem responses (ABRs), speech perception in noise (SPiN), and self-reported tinnitus, hyperacusis and hearing in noise difficulties. Total lifetime noise exposure was similar between musicians and non-musicians, the majority of which could be accounted for by recreational activities. Musicians showed significantly greater ABR wave I/V ratios than non-musicians and were also more likely to report experience of - and/or more severe - tinnitus, hyperacusis and hearing in noise difficulties, irrespective of noise exposure. A secondary analysis revealed that individuals with the highest levels of noise exposure had reduced outer hair cell function compared to individuals with the lowest levels of noise exposure, as measured by OAEs. OAE level was also related to PTA and EHF thresholds. High levels of noise exposure were also associated with a significant increase in ABR wave V latency, but only for males, and a higher prevalence and severity of hyperacusis. These findings suggest that there may be sub-clinical effects of noise exposure on various hearing metrics even at a relatively young age, but do not support a link between lifetime noise exposure and proxy measures of cochlear synaptopathy such as ABR wave amplitudes and SPiN. Closely monitoring OAEs, PTA and EHF thresholds when conventional PTA is within the clinically 'normal' range could provide a useful early metric of noise-induced hearing damage. This may be particularly relevant to early-career musicians as they progress through a period of intensive musical training, and thus interventions to protect hearing longevity may be vital.

Too loud? Do powered hand dryers violate federal noise exposure standards?

OBJECTIVE

The aim of this study was to determine if high-powered air hand dryers produce sufficient noise to warrant concern over acoustic trauma as determined by federally established standards.

STUDY DESIGN

Prospective observational field data collection SETTING: Urban and suburban community SUBJECTS AND METHODS: Using a NIOSH developed and calibrated soundmeter app, powered hand dryers were measured throughout two metropolitan areas. Ear level measurements were performed while drying wet hands. Recorded variables included average LAeq, Time-Weighted Average, Max and Peak Levels, Noise Dose, and Projected Dose according to NIOSH and OSHA standards, and all three major weighting networks (A, C, and Z).

RESULTS

Fifty-four trials were performed at 27 locations. Average dryer run time was 28.9 s (range 14-45 s). Average LAeq (dBA), average maximum level (dBA), and average TWA (dBA) were 90.46 ± 5.32, 94.86 ± 5.73, 59.90 ± 6.80, respectively. The noise generated exceeded published manufacturer specifications. However, even with estimated cumulative daily exposure, the noise generated by these dryers did not exceed federal safety standards.

CONCLUSIONS

Air-powered hand dryers produce noise output at a level that many would find subjectively uncomfortable with some brands/models consistently producing noise in excess of 90 dBA. Nonetheless, these dryers do not produce sound exceeding NIOSH standards for noise exposure.

Community-based program to increase use of hearing conservation practices among farm and rural youth: a cluster randomized trial of effectiveness

BACKGROUND

Noise exposure and associated hearing loss affects an estimated 2 million farm youth who are exposed as farm residents, farm family workers, hired workers, children of migrant or seasonal workers, and farm visitors. Risk factors for farm youth include frequent exposure to high farm noise; farm work from an early age, and exposure to high recreational noise (e.g., firearms, ATVs, and personal listening devices).

METHODS

This study compared the effectiveness of two interventions and control. The programs included a community-based interactive youth educational program alone (Group A), a community-based interactive youth educational program followed by an Internet-based booster (Group B), and a no-interaction control (Group C). The study used a cluster randomized control design, with equal allocation ratio to each cluster, without blinding. Inclusion criteria included enrollment in grade 4, parental consent, English speaking, and attending a community-based educational event included in the cluster sampling. A total of 1979 youth were enrolled at 36 sites distributed across the 3 study arms in the following distribution: N = 662 in 13 sites (Group A), N = 680 in 12 sites (Group B), and N = 637 in 11 sites (Group C).

RESULTS

Comparison with pre-intervention data showed no difference in intent to use hearing conservation strategies in experimental groups. However, knowledge and attitudes toward hearing conservation were improved in the groups receiving the Internet-based booster. Participants reported frequent exposure to sources of hazardous noise (e.g., loud sporting events, firecrackers, personal listening devices).

CONCLUSIONS

It is feasible and acceptable to incorporate hearing health education into an already existing system designed to deliver health and safety educational programming to farm and rural youth. The program was adopted by the partner agency for dissemination to up to 100,000 youth annually. Results of this study inform future intervention studies, interventions aimed at farm youth, and interventions to increase use of hearing conservation strategies, as well as offer a base for developing programs for non-English speaking children.

TRIAL REGISTRATION

Clinicaltrials.gov registration CT02472821. Date of trial registration: 06/09/2015 (retrospectively registered).

The ongoing search for cochlear synaptopathy in humans: Masked thresholds for brief tones in Threshold Equalizing Noise

This study aimed to advance towards a clinical diagnostic method for detection of cochlear synaptopathy with the hypothesis that synaptopathy should be manifested in elevated masked thresholds for brief tones. This hypothesis was tested in tinnitus sufferers, as they are thought to have some degree of synaptopathy. Near-normal-hearing tinnitus sufferers and their matched controls were asked to detect pure tones with durations of 5, 10, 100, and 200 ms presented in low- and high-level Threshold Equalizing Noise. In addition, lifetime noise exposure was estimated for all participants. Contrary to the hypothesis, there was no significant difference in masked thresholds for brief tones between tinnitus sufferers and their matched controls. Masked thresholds were also not related to lifetime noise exposure. There are two possible explanations of the results: 1) the participants in our study did not have cochlear synaptopathy, or 2) synaptopathy does not lead to elevated masked thresholds for brief tones. This study adds a new approach to the growing list of behavioral methods that attempted to detect potential signs of cochlear synaptopathy in humans.

Occupational noise and age: A longitudinal study of hearing sensitivity as a function of noise exposure and age in South African gold mine workers

Background

A relationship exists between occupational noise exposure and age, which remains poorly understood.

Objectives

The aim of this study was to establish the relationship between hearing loss and age over time.

Method

Audiological data from 2583 mine workers in South Africa were utilised. Data were received from a non-noise exposed group (NNEG) (n = 951) and a noise exposed group (NEG) (≥85 dBA) (n = 1632). Data comprised a low-frequency average (LFA512) (average of audiological thresholds for 0.5 kHz, 1 kHz and 2 kHz) and high-frequency average (HFA346) (average of audiological thresholds for 3 kHz, 4 kHz and 6 kHz). Data were compared by using mixed-effects regression analysis.

Results

Base threshold values were higher for the NEG than for the NNEG across frequencies. All year-to-year increases in mean hearing thresholds were statistically significant (p < 0.01). When correcting for age, increases in mean hearing thresholds were higher for the NEG than for the NNEG for HFA346 (3.5 dB vs. 2.9 dB decline over a 4-year period) but similar for LFA512 (0.6 dB vs. 0.7 dB decline). Uncorrected for age, increases in mean hearing thresholds were higher than when age was corrected for.

Conclusion

Age and occupational noise exposure influence hearing thresholds over time. The continued increase in hearing thresholds of the NEG above that of the NNEG can be related to ineffective noise management programmes and/or the fact that early noise exposure leads to a higher burden of hearing loss over time – even after noise exposure had stopped.

[Nighttime transportation noise annoyance in Germany: personal and regional differences in the German National Cohort Study]

BACKGROUND

Noise annoyance is associated with adverse health-related conditions and reduced wellbeing. Thereby, subjective noise annoyance depends on the objective noise exposure and is modified by personal and regional factors.

OBJECTIVE

How many participants of the German National Cohort Study (GNC; NAKO Gesundheitsstudie) were annoyed by transportation noise during nighttime and what factors were associated with noise annoyance?

MATERIALS AND METHODS

This cross-sectional analysis included 86,080 participants from 18 study centers, examined from 2014 to 2017. We used multinomial logistic regression to investigate associations of personal and regional factors to noise annoyance (slightly/moderately or strongly/extremely annoyed vs. not annoyed) mutually adjusting for all factors in the model.

RESULTS

Two thirds of participants were not annoyed by transportation noise during nighttime and one in ten reported strong/extreme annoyance with highest percentages for the study centers Berlin-Mitte and Leipzig. The strongest associations were seen for factors related to the individual housing situation like the bedroom being positioned towards a major road (OR of being slightly/moderately annoyed: 4.26 [95% CI: 4.01;4.52]; OR of being strongly/extremely annoyed: 13.36 [95% CI: 12.47;14.32]) compared to a garden/inner courtyard. Participants aged 40-60 years and those in low- and medium-income groups reported greater noise annoyance compared to younger or older ones and those in the high-income group.

CONCLUSION

In this study from Germany, transportation noise annoyance during nighttime varied by personal and regional factors.

Separate auditory pathways for the induction and maintenance of tinnitus and hyperacusis?

Tinnitus and hyperacusis often occur together, however tinnitus may occur without hyperacusis or hyperacusis without tinnitus. Based on animal research one could argue that hyperacusis results from noise exposures that increase central gain in the lemniscal, tonotopically organized, pathways, whereas tinnitus requires increased burst firing and neural synchrony in the extra-lemniscal pathway. However, these substrates are not sufficient and require involvement of the central nervous system. The dominant factors in changing cortical networks in tinnitus patients are foremost the degree and type of hearing loss, and comorbidities such as distress and mood. So far, no definite changes have been established for tinnitus proper, albeit that changes in connectivity between the dorsal attention network and the parahippocampal area, as well as the default-mode network-precuneus decoupling, appear to be strong candidates. I conclude that there is still a strong need for further integrating animal and human research into tinnitus and hyperacusis.

High-resolution assessment of road traffic noise exposure in Denmark

Recent studies show associations between transportation noise and various diseases. However, selection bias remains an inherent limitation in many cohort studies. In this study, we aimed to model road traffic noise exposure across the entire Danish population and investigate its distribution in relation to area-level socioeconomic indicators and green space. Based on the Nordic prediction method, we estimated road traffic noise for all Danish residential addresses, in total 2,761,739 addresses, for the years 1995, 2000, 2005, 2010, and 2015 at the most and least exposed façades. Area-level sociodemographic variables encompassing education, income, and unemployment were collected and residential green within a 150 m radius buffer at the address level was estimated using high-resolution national land use classification data. Median levels of noise at both the most and least exposed facades across Denmark increased slightly from 1995 to 2015. Correlations between most and least exposed façades varied based on population density and building type, with the highest correlations between the most and least exposed façades found for semidetached homes and lowest for multistory buildings. Increasing median noise levels were observed across increasing levels of higher education, lower income, and higher unemployment. A decreasing trend in median noise levels with increasing levels of green space was observed. In conclusion, we showed that it is feasible to estimate nationwide, address-specific exposure over a long time-period. Furthermore, the low correlations found between most and least exposed façade for multistory buildings, which characterize metropolitan centers, suggests that the most exposed façade estimation used in most previous studies and predicts exposure at the silent façade relatively poorly.

Effects of road traffic noise on the prevalence of cardiovascular diseases: The case of Thessaloniki, Greece

Road traffic noise is a growing challenge for human health in the last decades. World Health Organization (WHO) summarized the scientific evidence on side effects of noise on public health and wellbeing since 1999 in its publication "Guidelines for community noise". The WHO's documentation was completed in 2009 with the Night Noise Guidelines for Europe and in 2011 with the Burden of disease from environmental noise highlighting the negative effects of environmental noise on health. In this paper, we studied and presented the overall noise levels and the exposure of the population in the city of Thessaloniki, Greece. The estimation of the exposure to road traffic noise was based on the census data for a 15-year time period (e.g. 2000-2015). The quantification of the environmental burden of cardiovascular diseases, due to urban traffic noise, is calculated in terms of DALYs. The calculation is based on the morbidity and mortality data from the hypertensive, ischemic heart, and cerebrovascular diseases of the total population. Our analysis proved that the road traffic noise in Thessaloniki causes almost 2000 DALYs lost in the total population each year. Also, the exposure to road traffic noise was estimated by three measuring points, two of them located in the urban Thessaloniki (a high traffic highway and a residential area) and the third one situated in one urban background area in the urban outskirts of Thessaloniki. The noise levels were measured for a 24-h period during a 3 year time period for every measuring point. The imposed WHO noise levels were exceeded in both high traffic highway and residential areas for almost the whole time of the measurement period.

Novel oral multifunctional antioxidant prevents noise-induced hearing loss and hair cell loss

Oxidative stress is a major contributor to noise-induced hearing loss, the most common cause of hearing loss among military personnel and young adults. HK-2 is a potent, orally-active, multifunctional, redox-modulating drug that has been shown to protect against a wide range of neurological disorders with no observed side effects. HK-2 protected cochlear HEI-OC1 cells against various forms of experimentally-induced oxidative stressors similar to those observed during and after intense noise exposure. The mechanisms by which HK-2 protects cells is twofold, first by its ability to reduce oxidative stress generated by free radicals, and second, by its ability to complex biologically active transition metals such as Fe⁺², thus reducing their availability to participate in the Fenton reaction where highly toxic hydroxyl radicals are generated. For the rat in vivo studies, HK-2 provided significant protection against noise-induced hearing loss and hair cell loss. Noise-induced hearing loss was induced by an 8-16 kHz octave band noises presented for 8 h/d for 21 days at an intensity of 95 dB SPL. In the Prevention study, HK-2 was administered orally beginning 5 days before the start of the noise and ending 10 days after the noise. Treatment with HK-2 dose-dependently reduced the amount of noise-induced hearing impairment, reflected in the cochlear compound action potential, and noise-induced hair cell loss. In a subsequent Rescue experiment in which HK-2 was administered for 10 days starting after the noise was turned off, HK-2 also significantly reduced the amount of hearing impairment, but the effect size was substantially less than in the Prevention studies. HK-2 alone did not adversely affect HEI-OC1 cell viability, nor did it cause any adverse changes in rat body weight, behavior, cochlear function or hair cell integrity. Thus, HK-2 is a novel, safe, orally-deliverable and highly effective otoprotective compound with considerable potential for preventing hearing loss from noise and other hearing disorders linked to excessive oxidative stress.

Noise-Induced loudness recruitment and hyperacusis: Insufficient central gain in auditory cortex and amygdala

Noise-induced hearing loss generally induces loudness recruitment, but sometimes gives rise to hyperacusis, a debilitating condition in which moderate intensity sounds are perceived abnormally loud. In an attempt to develop an animal model of loudness hyperacusis, we exposed rats to a 16-20 kHz noise at 104 dB SPL for 12 weeks. Behavioral reaction time-intensity functions were used to assess loudness growth functions before, during and 2-months post-exposure. During the exposure, loudness recruitment (R) was present in the region of hearing loss, but subtle evidence of hyperacusis (H) started to emerge at the border of the hearing loss. Unexpectedly, robust evidence of hyperacusis appeared below and near the edge of the hearing loss 2-months post-exposure. To identify the neural correlates of hyperacusis and test the central gain model of hyperacusis, we recorded population neural responses from the cochlea, auditory cortex and lateral amygdala 2-months post-exposure. Compared to controls, the neural output of the cochlea was greatly reduced in the noise group. Consistent with central gain models, the gross neural responses from the auditory cortex and amygdala were proportionately much larger than those from the cochlea. However, despite central amplification, the population responses in the auditory cortex and amygdala were still below the level needed to fully account for hyperacusis and/or recruitment. Having developed procedures that can consistently induce hyperacusis in rats, our results set the stage for future studies that seek to identify the neurobiological events that give rise to hyperacusis and to develop new therapies to treat this debilitating condition.

Effect of birdsongs and traffic noise on pedestrian walking speed during different seasons

Many studies have explored the effects of auditory and visual stimuli on the perception of an environment. However, there is a lack of investigations examining direct behavioral responses to noise in specific environments. In this study, a behavioral variable, walking speed, was analyzed, as a response to the sounds and visual features of a specific environment. The study examined the effects of birdsongs compared to traffic noise on walking speed in a real outdoor urban environment. It was supposed that the interaction of audition and vision in the perception of an environment may also be shaped by the perceived congruence of the visual and auditory features of the environment. The participants (N = 87 and N = 65), young university students, walked along a 1.8-km urban route. They listened to a soundtrack of crowded city noise or birdsongs, or they walked in the real outdoor environment without listening to any acoustic stimuli. To investigate the effect of the congruence between acoustic and visual stimuli, the experiment was conducted in two different seasons (fall and spring). The results did not show significant differences between the crowded city noise condition and the real outdoor condition. Listening to the soundtrack with birdsongs decreased walking speed, but this effect was significant only in the experiment conducted in spring. These findings can be explained in terms of the congruence between the sounds and the visual environment. The findings raise questions regarding the restorative function of urban greenery during different seasons.

Long-term exposure to moderate noise induces neural plasticity in the infant rat primary auditory cortex

Previous studies have reported that rearing infant rat pups in continuous moderate-level noise delayed the formation of topographic representational order and the refinement of response selectivity in the primary auditory (A1) cortex. The present study further verified that exposure to long-term moderate-intensity white noise (70 dB sound pressure level) from postnatal day (P) 12 to P30 elevated the hearing thresholds of infant rats. Compared with age-matched control rats, noise exposure (NE) rats had elevated hearing thresholds ranging from low to high frequencies, accompanied by decreased amplitudes and increased latencies of the two initial auditory brainstem response waves. The power of raw local field potential oscillations and high-frequency β oscillation in the A1 cortex of NE rats were larger, whereas the power of high-frequency γ oscillation was smaller than that of control rats. In addition, the expression levels of five glutamate receptor (GluR) subunits in the A1 cortex of NE rats were decreased with laminar specificity. These results suggest that the altered neural excitability and decreased GluR expression may underlie the delay of functional maturation in the A1 cortex, and may have implications for the treatment of hearing impairment induced by environmental noise.

3-year noise monitoring and strategic noise mapping in an extended motorway

It is well known that the quality of the acoustic environment is very often degraded by major environmental interventions such as extended motorways. Considering this, the European Union has imposed relevant legislation on its member states to monitor these environmental changes/interventions and to develop strategic noise maps and action plans, in order to protect the natural and human environment. Egnatia Odos is a major motorway that crosses northern Greece and connects the country with the main European Motorway network. In the present work, the results of an extended traffic noise measuring campaign at selected sections of the Egnatia motorway are presented, together with the strategic noise maps and calculations of the population exposure. It was concluded that, although the noise levels in the countryside were low, in the suburban areas near the city of Thessaloniki the traffic noise was reported high during both the day and night. However, the extent of the traffic noise issue was found considerably greater during night-time. The number of exceedances was rather limited, though a considerable amount of population (11.5% and 5.4% during the day and night, respectively) seems to be affected by relatively high noise levels, highlighting the importance of traffic noise monitoring.

A simple method to estimate noise levels in the workplace based on self-reported speech communication effort in noise

Objective: To validate a method using self-reported speech communication effort in noise to estimate occupational noise levels by comparing with measured noise levels. Design: A comparative observational study. Reported vocal effort to communicate with a person at a distance of 1.2 m during workplace-related tasks was used to provide an estimate of noise levels in the workplace. These estimated noise levels were compared against noise level measurements obtained using personal noise dosimetry badges for corresponding tasks undertaken by participants. Study sample: Participants (n = 168) aged 16-25 years were recruited from companies where workplace noise levels were at least 85 dB(A). Results: Estimated noise levels using speech communication ability were evenly distributed above and below the measured noise levels (n = 134), indicating a lack of systematic bias in the method. For 91% of participants, estimates of noise levels using speech communication were within ±6 dB of the measured levels, whilst 56% were within ±3 dB. Conclusions: Report of speech communication effort required in noise by employees is an effective method of estimating noise levels within the workplace. This can be used for retrospective noise level assessment where there are no recorded noise level measurements, such as for retrospective research studies or in medicolegal work.

Noise exposure as a risk factor for acoustic neuroma: a systematic review and meta-analysis

Objective: To investigate whether acoustic neuroma is associated with noise. Design: PubMed, Cochrane, Embase and CINAHL databases were searched. A meta-analysis was performed to calculate odds ratio (OR) and 95% confidence interval (CI) using quality-effect models. Study sample: A total of eight studies with moderate or high quality involving 75,571 participants met the inclusion criteria. Results: There was no significant relationship between overall noise exposure and acoustic neuroma (OR:1.02, 95% CI: 0.64-1.63). However, further subgroup analysis showed that leisure noise exposure (OR: 1.73, 95% CI: 1.10-2.73), above five years' exposure (OR: 1.81, 95% CI: 1.14-2.85) and continuous exposure (OR:2.77, 95% CI: 1.70-4.49) were associated with an increased risk of acoustic neuroma. Conclusions: These results suggest an elevated risk of acoustic neuroma among individuals who have been exposed to occupational noise when some subgroup analysis are conducted. Leisure noise in particular seems to play a significant role in the development of acoustic neuroma. However, due to the heterogeneity among the included studies, this conclusion should be interpreted with cautions, even though the continuous long-term consequences should not be ignored.

Expression and localization of diacylglycerol kinase ζ in guinea pig cochlea and its functional implication under noise-exposure stress conditions

Cochlear hair cells are essential for the mechanotransduction of hearing. Sensorineural hearing loss can be irreversible because hair cells have a minimal ability to repair or regenerate themselves once damaged. In order to develop therapeutic interventions to prevent hair cell loss, it is necessary to understand the signaling pathway operating in cochlear hair cells and its alteration upon damage. Diacylglycerol kinase (DGK) regulates intracellular signal transduction through phosphorylation of lipidic second messenger diacylglycerol. We have previously reported characteristic expression and localization patterns of DGKs in various organs under pathophysiological conditions. Nevertheless, little is known about morphological and functional aspects of this enzyme family in the cochlea. First RT-PCR analysis reveals predominant mRNA expression of DGKα, DGKε and DGKζ. Immunohistochemical analysis shows that DGKζ localizes to the nuclei of inner hair cells (IHCs), outer hair cells (OHCs), supporting cells and spiral ganglion neurons in guinea pig cochlea under normal conditions. It is well known that loud noise exposure induces cochlear damage, thereby resulting in hair cell loss. In particular, OHCs are highly vulnerable to noise exposure than IHCs. We found that after 1 week of noise exposure DGKζ translocates from the nucleus to the cytoplasm in damage-sensitive OHCs and gradually disappears thereafter. In sharp contrast, DGKζ remains to the nucleus in damage-resistant IHCs. These results suggest that DGKζ cytoplasmic translocation is well correlated with cellular damage under noise-exposure stress conditions and is involved in delayed cell death in cochlear outer hair cells.

Stress, health, noise exposures, and injuries among electronic waste recycling workers in Ghana

Background

Electronic waste (e-waste) recycling workers in low and middle-income countries have the potential for occupational injuries due to the nature of their work at informal e-waste sites. However, limited research exists on stress, noise, occupational injuries, and health risks associated with this work environment. This study evaluated injury experience, noise exposures, and stress risk factors among e-waste workers at the large recycling site in the Agbogbloshie market, Accra, Ghana.

Methods

Participants completed a survey addressing their work, health status, stress, exposures to several occupational hazards (including noise), use of personal protective equipment at work, and injury experience. A subset of participants also completed personal noise dosimetry measurements. Poisson regression was used to evaluate the association between the number of injuries experienced by participants and various factors evaluated in the survey.

Results

Forty-six male e-waste workers completed the survey, and 26 completed a noise dosimetry measurement. Participants experienced an average of 9.9 ± 9.6 injuries per person in the previous 6 months (range: 1–40). The majority of injuries were lacerations (65.2%), and the most common injury location was the hand (45.7%). Use of personal protective equipment was rare. The mean time-weighted average noise level was 78.8 ± 5.9 dBA. Higher perceived stress, greater age, poorer health status, not using gloves, and involvement in dismantling activities were associated with an increased number of injuries. After controlling for each of these risk factors, perceived stress level and perceived noise exposure were associated with a significantly greater number of injuries.

Conclusions

Our study identified a large number of injuries among informal e-waste recyclers, and we found that higher levels of perceived stress and perceived noise were associated with an increased number of occupational injuries, even after controlling for other injury risk factors.

Localized disorganization of the cochlear inner hair cell synaptic region after noise exposure

The prevalence and importance of hearing damage caused by noise levels not previously thought to cause permanent hearing impairment has become apparent in recent years. The damage to, and loss of, afferent terminals of auditory nerve fibres at the cochlear inner hair cell has been well established, but the effects of noise exposure and terminal loss on the inner hair cell are less known. Using three-dimensional structural studies in mice we have examined the consequences of afferent terminal damage on inner hair cell morphology and intracellular structure. We identified a structural phenotype in the pre-synaptic regions of these damaged hair cells that persists for four weeks after noise exposure, and demonstrates a specific dysregulation of the synaptic vesicle recycling pathway. We show evidence of a failure in regeneration of vesicles from small membrane cisterns in damaged terminals, resulting from a failure of separation of small vesicle buds from the larger cisternal membranes.

Capturing the spatial variability of noise levels based on a short-term monitoring campaign and comparing noise surfaces against personal exposures collected through a panel study

Environmental noise can cause important cardiovascular effects, stress and sleep disturbance. The development of appropriate methods to estimate noise exposure within a single urban area remains a challenging task, due to the presence of various transportation noise sources (road, rail, and aircraft). In this study, we developed a land-use regression (LUR) approach using a Generalized Additive Model (GAM) for LA_eq (equivalent noise level) to capture the spatial variability of noise levels in Toronto, Canada. Four different model formulations were proposed based on continuous 20-min noise measurements at 92 sites and a leave one out cross-validation (LOOCV). Models where coefficients for variables considered as noise sources were forced to be positive, led to the development of more realistic exposure surfaces. Three different measures were used to assess the models; adjusted R² (0.44-0.64), deviance (51-72%) and Akaike information criterion (AIC) (469.2-434.6). When comparing exposures derived from the four approaches to personal exposures from a panel study, we observed that all approaches performed very similarly, with values for the Fractional mean bias (FB), normalized mean square error (NMSE), and normalized absolute difference (NAD) very close to 0. Finally, we compared the noise surfaces with data collected from a previous campaign consisting of 1-week measurements at 200 fixed sites in Toronto and observed that the strongest correlations occurred between our predictions and measured noise levels along major roads and highway collectors. Our validation against long-term measurements and panel data demonstrates that manual modifications brought to the models were able to reduce bias in model predictions and achieve a wider range of exposures, comparable with measurement data.

Association between noise exposure and diabetes: A systematic review and meta-analysis

BACKGROUND

The prevalence of diabetes is on rise worldwide and environmental factors are being increasingly recognized to be involved in this rise. An emerging body of evidence has evaluated the impact of long-term exposure to noise on diabetes mellitus, highlighting the need to synthesize this evidence.

OBJECTIVES

To systematically review and conduct meta-analysis of the available evidence on the association between long-term exposure to transport and occupational noise exposure and diabetes mellitus.

METHODS

Selected databases were searched for available evidence published till September 13th, 2017 following MOOSE guidelines. The quality of articles was assessed using the Newcastle-Ottawa Scale. Random effects meta-analysis was applied to abstract combined estimates for diabetes mellitus per 5 dB increase in noise exposure. We evaluated the heterogeneity applying Cochran's Q test and quantified it using I² statistic. Meta-regressions were conducted to identify sources of heterogeneity. Publication bias was evaluated using funnel plot and Egger's test.

RESULTS

Fifteen studies met our inclusion criteria of which nine including five prospective cohorts, two cross-sectional and two case-control studies with a total number of 444460 adult participants and 17430 diabetes mellitus cases included in meta-analyses. We observed a 6% (95% confidence interval (CI): 3%, 9%) increase in the risk of diabetes mellitus per 5 dB increase in noise exposure regardless of its source. Source-specific analyses were suggestive for stronger associations for air traffic noise (combined odds ratio: 1.17; 95% CI: 1.06, 1.29 per 5 dB increase in exposure) flowed by road traffic noise (combined odds ratio: 1.07; 95% CI: 1.02, 1.12). We observed some indications of publication bias; however the findings were robust after trim and fill test. Meta-regression analyses showed that the adjustment in general, and not specifically related to air pollution, could predict the between-study heterogeneity in reported associations.

CONCLUSIONS

The results indicate an increased risk of diabetes mellitus associated with noise exposure, mainly related to air and road traffic.

Auditory central gain compensates for changes in cochlear output after prolonged low-level noise exposure

Remarkably, the central auditory system can modify the strength of its sound-evoked neural response based on prior acoustic experiences, a phenomenon referred to as central gain. Gain changes are well documented following traumatic noise exposure, but much less is known about central gain dynamics following prolonged exposure to low-level noise, a common acoustic experience in many urban and work environments. We recently reported that the neural output of the cochlea is reduced, while gain was enhanced in the inferior colliculus (IC) following a 5-week exposure to 75 dB noise. To determine if similar effects were present at even lower intensities, we exposed rats to a 65 dB noise expecting to see little to no change in the cochlea or IC. The exposure had little effect on distortion product otoacoustic emissions and did not cause any hair cell loss. However, the amplitude of the CAP, which reflects the neural output of cochlea, was depressed by 50-75%. Surprisingly, neural responses from the IC were enhanced up to 70%, mainly at frequencies within the noise exposure band. One-week post-exposure, CAP amplitudes returned to normal at frequencies within or above the exposure band, whereas responses evoked by frequencies below the exposure band were enhanced by more than 80%. In contrast, IC responses below the exposure frequency were depressed 10-20% whereas responses within the exposure frequency band were enhanced 10-20%. Thus, the central auditory system dynamically up- and down-regulates its gain to maintain supra-threshold neural responses within a narrow homeostatic range; a function that likely contributes to the prevention of sounds from being perceived as muffled or too loud.