Localization of Vehicle Back-Up Alarms by Users of Level-Dependent Hearing Protectors under Industrial Noise Conditions Generated at a Forge

The use of hearing protectors in various noisy workplaces is often necessary. For safety reasons, auditory information may be required to correctly localize the direction of an auditory danger signal. The purpose of this study was to verify if the selection of a specific level-dependent hearing protector may be important for the ability to localize a vehicle back-up alarm signal. The laboratory conditions reflected industrial conditions, under which an impulse noise was emitted against a background of continuous noise. A passive mode and a level-dependent mode (maximum and incomplete amplification) were considered. Four different models of level-dependent earmuffs and one model of level-dependent earplugs were included in the tests. The tests enabled differentiation between the individual hearing protectors. The use of earplugs in level-dependent mode did not significantly affect the ability to correctly localize the back-up alarm signal. For the earmuffs, the global assessment of the impact of a mode change revealed that, depending on the model of the earmuffs, the impact may be insignificant, but may also result in considerable impairment of the ability to localize the back-up alarm signal.

Occupational noise-induced hearing loss among dental professionals

OBJECTIVE

The purpose of this study was to determine whether the persistent high-frequency noise produced by dental equipment could cause hearing impairment among the dental professionals in the United Arab Emirates (UAE).

METHOD AND MATERIALS

This cross-sectional study was conducted to evaluate the hearing capacity of 90 randomly selected dental practitioners from different specialties working in the UAE. The participants were approached in their workplace and their hearing capacity was evaluated using the pure tone audiometer.

RESULTS

Twenty dental practitioners suffered from hearing impairment, which constitutes 22.2% of the studied sample. At high frequencies, left ears were more affected than right ears, but this was not statistically significant. There was a direct relationship between working hours per week and the hearing capacity, but this did not reach a statistically significant level. The lowest hearing capacity was detected in males at a significantly lower value compared to females.

CONCLUSIONS

Positive correlation was found between years of experience and reduced hearing capacity among dental practitioners. In addition, males had a significantly higher median count of severely affected hearing frequencies compared to females. Online pure tone audiometric testing is an easy, cost-effective tool that can be used to self-assess the hearing capacity of dental professionals, and it is recommended to perform this test annually.

Noise-Induced Hearing Loss in Mice: Effects of High and Low Levels of Noise Trauma in CBA Mice

Acoustic trauma can induce temporary or permanent noise-induced hearing loss (NIHL). Noise exposed animal models allow us to study the effects of various noise trauma insults on the cochlea and auditory pathways. Here we studied the short-term and long-term functional changes occurring in the auditory system following exposure to two different noise traumas. Several measures of hearing function known to change following noise exposure were examined: Temporary (TTS) and permanent (PTS) threshold shifts were measured using auditory brainstem responses (ABR), outer hair cell function was examined using distortion product otoacoustic emissions (DPOAEs), and auditory temporal processing was assessed using a gap-in-noise (GIN) ABR paradigm. Physiological measures were made before and after the exposure (24 hours, 2 weeks, 4 weeks, and 1 year). The animals were perfused and their brain, and cochlea were collected for future biomarker studies. Young adult mice were exposed to 110 dB and 116 dB octave-band noise levels for 45 minutes, and both groups demonstrated significant threshold shifts 1 day post-noise exposure across all frequencies. However 2 weeks postexposure, PTS within the 110 dB group was significantly reduced compared to 1 day post trauma, this improvement in thresholds was not as great in the 116 dB exposure group. At 2 weeks post-trauma, differences between the measured PTS in the two groups was significant for 4 of the 7 measured frequencies. At this 1 year time point after exposure, mice in the 110 dB group showed very minor PTS, but the 116 dB group showed a large PTS comparable to their 2 and 4 week PTS. At this time point, PTS variation between the two groups was significant across all frequencies. DPOAE amplitudes measured 2 weeks post exposure showed recovery for all frequencies within 10 dB (average) of the baseline in the 110 dB group, however for the 116 dB exposure DP amplitudes were elevated by about 30 dB. The differences in DPOAE amplitudes between the 110 dB and 116 dB groups were significant at 2 weeks, 4 weeks, and 1 year post-trauma in the mid frequency range. At 2 weeks, 4 weeks, and 1 year, DPOAE thresholds returned to within 10 dB of the baseline for the 110 dB group in the low and mid frequency range, whereas the 116 dB group still showed shifts of 30 dB for all frequency ranges. For Gap ABRs, there was a significant decrease in both noise burst 1 (NB1) and noise burst 2 (NB2) amplitudes for peaks 1 and 4 in the 116 dB group relative to the 110 dB group when measured at 1 year post trauma. These results indicate that a 6 dB increase in noise exposure intensity results in a significant increased ototrauma in both the peripheral and central auditory systems.

Hearing Loss, Tinnitus, Hyperacusis, and Diplacusis in Professional Musicians: A Systematic Review

Professional musicians (PMs) are at high risk of developing hearing loss (HL) and other audiological symptoms such as tinnitus, hyperacusis, and diplacusis. The aim of this systematic review is to (A) assess the risk of developing HL and audiological symptoms in PMs and (B) evaluate if different music genres (Pop/Rock Music—PR; Classical Music—CL) expose PMs to different levels of risk of developing such conditions. Forty-one articles including 4618 PMs were included in the study. HL was found in 38.6% PMs; prevalence was significantly higher among PR (63.5%) than CL (32.8%) PMs; HL mainly affected the high frequencies in the 3000-6000 Hz range and was symmetric in 68% PR PMs and in 44.5% CL PMs. Tinnitus was the most common audiological symptom, followed by hyperacusis and diplacusis. Tinnitus was almost equally distributed between PR and CL PMs; diplacusis was more common in CL than in PR PMs, while prevalence of hyperacusis was higher among PR PMs. Our review showed that PR musicians have a higher risk of developing HL compared to CL PMs; exposure to sounds of high frequency and intensity and absence of ear protection may justify these results. Difference in HL symmetry could be explained by the type of instruments used and consequent single-sided exposure.

Status of Hearing Impairment among Handloom Workers in Tangail District of Bangladesh

Industrial noise is one of the major sources of noise pollution. Handloom industry is the biggest handicraft industry in our country; it is the second largest source of rural employment after agriculture. The workers of the handloom industry worked within excessive level of sound. This cross-sectional study was an attempt to see the status of hearing impairment among handloom worker at Tangail District, Bangladesh from August 2016 to December 2016. A total 180 handloom workers were included in this current study. All the respondents were male as handloom work is a strenuous work. The mean age of respondents was 38.18±11.529 years where most of the respondents were of middle age group (21-50) year's age group. Among the participants less than one-fourth was illiterate and rest had primary to secondary level of education. The average income of handloom workers was 13805.56±2764.696 BDT per month. Handloom workers spend average 10 hour for working per day. They were exposed to sound beyond NIOSH recommendation (70-83 dB around handloom machines and 80-90 dB around power loom machines). By self-assessment hearing impairment perception 76.7% participants reported that they had hearing problem. Based on the interpretation of Rinne, Webers and ABC test data indicate that among the respondents around 32.2% were identified with bilateral sensorineural hearing impairment and of them through Pure tone audiometry (PTA) around half were diagnosed as suffering from moderate to severe Noise induced hearing loss (NIHL). Using personal protective measure like ear muffle/ear musk has been recommended.

Noise levels, noise annoyance, and hearing-related problems in a dental college

Through a cross-sectional survey and integrated sound level meter, this research examined noise exposure and auditory- and nonauditory-related problems experienced by students of a dentistry college located in the United Arab Emirates (UAE). A structured interview questionnaire was used to examine hearing-related problems, noise annoyance, and awareness of 114 students toward noise. The results showed that maximum noise levels were between 65 and 79 dB(A) with peak levels (high and low frequencies) ranging between 89 and 93 dB(A). Around 80% of the students experienced a certain degree of noise annoyance; 54% reported one of the hearing-related problems; and about 10% claimed to have hearing loss to a certain extent. It is recommended that sound-absorbent materials be used during the construction of dental clinics and laboratories to reduce the noise levels.

Time course of cell death due to acoustic overstimulation in the mouse medial geniculate body and primary auditory cortex

It has previously been shown that acoustic overstimulation induces cell death and extensive cell loss in key structures of the central auditory pathway. A correlation between noise-induced apoptosis and cell loss was hypothesized for the cochlear nucleus and colliculus inferior. To determine the role of cell death in noise-induced cell loss in thalamic and cortical structures, the present mouse study (NMRI strain) describes the time course following noise exposure of cell death mechanisms for the ventral medial geniculate body (vMGB), medial MGB (mMGB), and dorsal MGB (dMGB) and the six histological layers of the primary auditory cortex (AI 1-6). Therefore, a terminal deoxynucleotidyl transferase dioxyuridine triphosphate nick-end labeling assay (TUNEL) was performed in these structures 24 h, 7 days, and 14 days after noise exposure (3 h, 115 dB sound pressure level, 5-20 kHz), as well as in unexposed controls. In the dMGB, TUNEL was statistically significant elevated 24 h postexposure. AI-1 showed a decrease in TUNEL after 14 days. There was no statistically significant difference between groups for the other brain areas investigated. dMGB's widespread connection within the central auditory pathway and its nontonotopical organization might explain its prominent increase in TUNEL compared to the other MGB subdivisions and the AI. It is assumed that the onset and peak of noise-induced cell death is delayed in higher areas of the central auditory pathway and takes place between 24 h and 7 days postexposure in thalamic and cortical structures.

The efficacy of sound regulations on the listening levels of pop concerts

This analysis of new and previously collected data was done to validate the efficacy of recommendations for limits regarding sound exposure levels at live pop concerts. After the World Health Organization (WHO) recommended limiting the sound levels at such concerts to avoid noise induced hearing damage among the audience, the actual levels at concerts where these recommendations are observed, have stabilized around 100 dBA. This is a level that is considered acceptable by WHO. At concerts where there are no limitations, however, the sound levels in the audience area are still increasing far beyond safe limits and thus the exposure may represent a serious threat to people's hearing.

Pre-conditioning with near infrared photobiomodulation reduces inflammatory cytokines and markers of oxidative stress in cochlear hair cells

Hearing loss is a serious occupational health problem worldwide. Noise, aminoglycoside antibiotics and chemotherapeutic drugs induce hearing loss through changes in metabolic functions resulting in sensory cell death in the cochlea. Metabolic sequelae from noise exposure increase production of nitric oxide (NO) and Reactive Oxygen Species (ROS) contributing to higher levels of oxidative stress beyond the physiologic threshold levels of intracellular repair. Photobiomodulation (PBM) therapy is a light treatment involving endogenous chromophores commonly used to reduce inflammation and promote tissue repair. Near infrared light (NIR) from Light Emitting Diodes (LED) at 810 nm wavelength were used as a biochemical modulator of cytokine response in cultured HEI-OC1 auditory cells placed under oxidative stress. Results reported here show that NIR PBM at 810 nm, 30 mW/cm² , 100 seconds, 1.0 J, 3 J/cm² altered mitochondrial metabolism and oxidative stress response for up to 24 hours post treatment. We report a decrease of inflammatory cytokines and stress levels resulting from NIR applied to HEI-OC1 auditory cells before treatment with gentamicin or lipopolysaccharide. These results show that cells pretreated with NIR exhibit reduction of proinflammatory markers that correlate with inhibition of mitochondrial superoxide, ROS and NO in response to continuous oxidative stress challenges. Non-invasive biomolecular down regulation of proinflammatory intracellular metabolic pathways and suppression of oxidative stress via NIR may have the potential to develop novel therapeutic approaches to address noise exposure and ototoxic compounds associated with hearing loss.

[Cooperation between Otolaryngologists and Occupational Health Support Centers]

Although prevention of noise-induced hearing loss is important, the risk of exposure to high-level sounds is not well recognized at workplaces. Occupational health support centers are expected to provide care resources for workers, wherein the workers can see an otolaryngologist to prevent noise-induced hearing loss. The Committee of Occupational and Environmental Health in the Oto-Rhino-Laryngological Society of Japan was planned to promote cooperation with occupational health support centers by means of registration of otolaryngologists as occupational health advisors. The committee conducted a survey using a questionnaire about the occupational health advisor registration process. Subsequently, there was an increase in the number of otolaryngologists who participated as occupational health advisors, with registrations occurring in 20 of the 47 occupational health support centers in Japan. Cooperation between otolaryngologists and occupational health support centers appears to be proceeding reasonably well and is the first step toward a more widespread effort for the prevention of noise-induced hearing loss at workplaces.

An exploratory study of noise exposures in educational and private dental clinics

Exposures to noise and resulting noise-induced hearing loss (NIHL) are not well understood in the dental profession. Previous studies have focused primarily on practicing dental professionals, and have often evaluated hearing loss in the absence of adequate noise exposure assessment. This study was conducted to evaluate exposures among students and staff working in four clinics within a major U.S. university dental school, and to compare these exposures to those among dental professionals in a private general-practice clinic. We measured equivalent continuous average (LEQ) noise exposure levels at 3.75-min intervals across a variety of procedures in the evaluated clinics, and also had participants complete a brief survey with questions on their experience and perceptions of noise exposure. We collected 79 partial- or full-shift Time-Weighted Average (TWA) dosimetry measurements on 46 individuals. The mean 3.75-min interval LEQ level was 63.6 ± 13.3 dBA, while the highest 3.75-min interval LEQ was 103.5 dBA. Students from the dental school clinics had the highest variability in average exposure levels, while the pediatric clinic evaluated had the highest average and maximum exposures. Nearly 4% of standardized 8-hr TWA measurements exceeded the 85 dBA Recommended Exposure Limit established by the National Institute for Occupational Safety and Health. Concerns about the potential effects of dental noise on participants' hearing were significantly correlated with metrics of TWA noise exposure, as well as variability of exposure (as assessed by the SD of the 3.75-min LEQ levels). Our results suggest that dental students and staff may have some risk of developing noise-induced hearing loss, particularly in pediatric clinical settings.

Potential protective effect of resveratrol on acoustic trauma: electron microscopy study

OBJECTIVE

To investigate the potential preventive effect of resveratrol in rats exposed to acoustic trauma (AT).

MATERIALS AND METHODS

In this experimental study, Wistar albino rats were divided into three groups: Group 1 (Control, n = 6), Group 2 (AT, n = 6), and Group 3 (resveratrol + AT). The rats in Group 2 were exposed to AT. The rats in Group 3 received resveratrol (300 mg/kg/day) via gavage for 7 days. On day 7, the rats were exposed to AT 10 min following resveratrol treatment. Histological sections of the cochleae were examined using light microscopy, transmission (TEM), and scanning electron microscopy (SEM).

RESULTS

The cochlear hair cells, stereocilia, and Deiters' cells of the control group appeared normal in all microscopic evaluations. In Group 2, light microscopy revealed predominantly inner hair cell loss, although the outer hair cells were affected. TEM and SEM examination showed severe loss of stereocilia and SEM revealed stereocilia arranged in an asymmetric array. The cochlear structure in Group 3 appeared well preserved under the light microscope, and although TEM and SEM revealed stereocilia loss, the hair cells and stereocilia appeared near normal compared with those of Group 2.

CONCLUSIONS

Resveratrol may have a protective effect against AT damage in the cochlea, most likely through its antioxidant activity. Our results may be useful for studies in humans exposed to AT and noise-induced hearing loss related to chronic exposure to occupational noise.

[Influencing factors for the use of earplugs in workers exposed to noise in a city]

OBJECTIVE

To investigate the current status of hearing loss and the use of earplugs in workers exposed to noise who have been provided earplugs in a city, as well as major influencing factors for the use of earplugs.

METHODS

Cluster random sampling was used to conduct a questionnaire survey in workers exposed to noise who had been provided earplugs in 15 enterprises with noise exposure in a city from June to December, 2014.

RESULTS

In the workers exposed to noise who had been provided earplugs, the rate of high-frequency anomaly in both ears was 57.8%, and the workers who kept wearing earplugs only accounted for 55.4%. The results of binary logistic regression analysis showed that the protective factors for the use of earplugs included workers' own feeling of hearing condition (OR=1.704), comfort of earplugs (OR= 1.892), enterprise's inspection of the use of earplugs (OR=1.461), workers' knowledge of the function and usage of earplugs (OR=1.581), workers' understanding of the necessity of earplugs (OR=4.482), workers' initiative to search for related data (OR=4.029), the use of earplugs by colleagues (OR=5.071), and reminders from family members or friends (OR=2.678) (all P<0.05).

CONCLUSION

The workers exposed to noise in this city have a high rate of abnormal hearing, and only half of the workers keep wearing earplugs during work. The use of earplugs is related to the factors including workers' own feeling of hearing condition, comfort of earplugs, workers' knowledge of protection, the enterprise' s management of hearing protection, and environmental support.