Hearing loss in the Royal Norwegian Navy: A longitudinal study

Establishing multifactorial risk factors for adult-onset hearing loss: A systematic review with topic modelling and synthesis of epidemiological evidence

BACKGROUND

This systematic review explores the multifaceted nature of risk factors contributing to adult-onset HL. The objective was to synthesise the most recent epidemiological evidence to generate pooled proportional incidences for the identified risk factors.

METHODS

We conducted an extensive search of electronic databases (MEDLINE, EMBASE, and psychINFO) for studies providing epidemiological evidence of risk factors associated with hearing loss. Topic modelling using Latent Dirichlet Allocation (LDA) was first conducted to determine how many risk factor themes were available from the papers. Data were analysed by calculating the pooled proportional incidence using a meta-analysis of proportions.

RESULTS

From the 72 studies reviewed, six key risk factor themes emerged through LDA topic modelling. The review identified ototoxicity, primarily caused by cancer treatments and antibiotics, infectious diseases like COVID-19, occupational noise exposure, lifestyle factors, health conditions, biological responses, and age progression as significant risk factors for HL. The highest proportional incidence was found with cancer-related ototoxicity at 55.4% (95%CI: 39.0-70.7), followed closely by ototoxicity from infectious diseases at 50.0% (95%CI: 28.5-71.5). This high proportional incidence suggests the need to explore less destructive therapies and proactively monitor hearing function during treatments.

CONCLUSIONS

The findings of this review, combined with the synthesis of epidemiological evidence, enhance our understanding of hearing loss (HL) pathogenesis and highlight potential areas for intervention, thereby paving the way for more effective prevention and management of adult-onset hearing loss in our ageing global population.

Effects of Noise and Chemical Exposure on Peripheral and Central Auditory Pathways in Normal-hearing Workers

Objectives

To assess the effects of noise and chemical exposure on peripheral and central auditory pathways in normal-hearing workers exposed to chemicals or high noise levels and compare the groups with each other and with workers not exposed to either of these agents.

Methods

A total of 54 normal-hearing workers were divided into three groups (chemical, noise, control) and submitted to the following assessments: conventional and extended high-frequency pure-tone audiometry; transient and distortion-product otoacoustic emissions, the inhibitory effect of the efferent auditory pathway; and Staggered Spondaic Word (SSW) and Pitch Pattern Sequence (PPS) test.

Results

There were no significant differences between the groups in extended high-frequency hearing thresholds. Significantly lower amplitudes were observed in the noise group for otoacoustic emissions. There were significantly more absences of the inhibitory effect of the efferent system in the noise group. There was no difference between the groups in the SSW test, while in PPS, the noise group performed worse than the control group.

Conclusion

These findings suggest that noise exposure produced deleterious effects on the workers' peripheral and central auditory systems, despite their normal hearing thresholds. The chemical group did not have significantly different results from those of the control group. It is important that individuals exposed to noise or chemicals have their auditory pathways monitored with complementary assessments.

[Triggers and predictors of development and formation of sensorineural hearing loss]

The purpose of the study is to review the results of scientific researches in recent years in an expanded interdisciplinary view of the problem of etiopathogenesis of sensorineural hearing loss, as well as the role of comorbidities and triggers in the formation of persistent changes in the audio-receiving part of the auditory analyzer.

Distortion product otoacoustic mapping measured pre- and post-loud sound exposures

OBJECTIVE

Sampling distortion product otoacoustic emissions (DPOAEs) at multiple f₂/f₁ ratios and f₂ frequency values produces a DPOAE "map." This study examined the efficacy of DPOAE mapping compared with pure tone audiometry and standard DPOAEs for detecting noise effects in subjects exposed to loud sound.

DESIGN

A map significance score was developed as a single measure of map change. Significance scores were evaluated before and after exposure to: loud music (LM), controlled noise (CN), and firing range noise (FR) in three separate sets of subjects. Scores were compared to audiometry and standard DPOAE results in the LM study.

STUDY SAMPLE

The LM and CN exposure studies involved 22, and 20 healthy young subjects respectively with normal hearing. Eight Marines were studied before and after FR exposure.

RESULTS

After LM exposure, audiometry showed significant changes at 1, 2, 4, and 6 kHz. Standard DPOAE measures were also significantly different at several frequencies. Map significance scores detected changes more effectively and showed the distribution of DPOAE alterations.

CONCLUSIONS

Map significance scores detected changes after noise exposure more reliably than audiometry and standard DPOAEs. Additionally, maps showed a diffuse response to sound exposure perhaps explaining why individual DP-grams appear less sensitive.

Comparative Study of Evoked Otoacoustic Emissions in Offshore and Onshore Seafaring Workers

PURPOSE

To evaluate the cochlear function of offshore and onshore seafaring workers of a naval company in the city of Rio de Janeiro and to estimate the degree of association between occupational exposure to noise and/or chemical substances and alteration in cochlear function.

METHODS

This study evaluated seafaring workers aged 20 to 49, of both genders, without auditory symptoms, divided into two groups: the Offshore Group, operating in the high seas with occupational exposure; and the Onshore Group, operating in offices without occupational exposure. Exams were performed to evaluate cochlear function, including transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE).

RESULTS

The TEOAE and DPOAE responses were on average lower in the Offshore Group, for all frequencies analyzed. The proportion of failures observed was also higher in the exposure group (Offshore), for general response and specific frequency, mainly for the frequencies of 4 kHz for TEOAE and 6 kHz for DPOAE.

CONCLUSION

The results suggest that exposure to noise and/or chemical substances can contribute to alterations in cochlear function in seafarers even without manifesting auditory symptoms.

Fatores de risco para perda auditiva em militares da Marinha: uma revisão

Resumo Introdução: militares estão expostos ao ruído em grande parte de suas atividades profissionais. Objetivo: identificar os fatores de risco e descrever os danos à audição relacionados à exposição ao ruído em atividades militares navais. Métodos: revisão de literatura nas bases bibliográficas Scopus, Web of Science e SciELO. Buscou-se artigos originais publicados de 2007 a 2017. A qualidade metodológica dos estudos foi classificada segundo critérios da Cochrane Collaboration. Resultados: de 47 estudos encontrados, sete atenderam aos critérios de inclusão. Os artigos selecionados evidenciaram que as atividades militares apresentam riscos para a saúde auditiva do pessoal militar naval. Os estudos confirmaram que os casos de perda auditiva aumentam com o tempo de serviço em atividade militar e pós-atividades operativas, tanto de combate quanto a bordo de navios. A prevalência de perda auditiva aumenta junto à idade e ao tempo de exposição dos indivíduos e se apresenta de acordo com o tipo de ruído. É mais frequente entre homens brancos e atinge predominantemente as altas frequências da audição, sendo de tipo sensório-neural. Conclusão: a vulnerabilidade desse grupo reforça a necessidade de inserção de programa de conservação auditiva nas organizações militares a fim de monitorar e desenvolver ações preventivas voltadas a essa categoria profissional.

Sound Level Measurements in Berthing Areas of an Aircraft Carrier

BACKGROUND

Personnel assigned to aircraft carriers work and live in environments where hazardous noise areas and hearing recovery spaces such as sleeping areas are in close proximity to one another. Hazardous noise exposure occurring during on-duty time periods and elevated noise levels during off-duty periods in sleeping areas may be prohibiting adequate hearing recovery, thus potentially leading to hearing loss and may lead to adverse effects on sleep, leading to crew-member fatigue. This investigation characterizes Equivalent sound level (Leq) and standardized octave band center frequency noise levels according to berthing (sleeping) area location during flight operation and nonflight operation time periods on a US Navy aircraft carrier. In addition, the investigation compares noise measurements in sleeping areas to noise levels associated with auditory rest and poor sleep quality and quantity.

METHODS

Noise levels were measured in berthing areas aboard a US Navy Nimitz-class aircraft carrier during a routine at-sea period. Sixty noise measurements were taken in eight sleeping locations. Leq in decibels 'A' weighted (dBA) and noise levels from 16 to 16 000 Hz in (dB) were measured during flight operations [Leq (flt ops)] and nonflight operations [Leq (nonflt ops)]. Leq was also measured according to sleep area shipboard locations of forward (FWD) Leq (FWD), middle (MID) Leq (MID), and rear (AFT) Leq (AFT). These data were compared to the 70 dBA American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for effective quiet areas. In addition, these data were compared to noise levels associated with hearing loss and sleep parameters. Statistical analysis was conducted with R version 3.5.2 using an alpha level of 0.05.

RESULTS

Leq (flt ops) in sleeping areas was a statistically significant (P < 0.05) 6.4 dBA higher than the Leq (nonflt ops). Leq (FWD) and Leq (MID) in sleeping areas was a statistically significant (P < 0.05) 15.2 and 15.0 dBA higher, respectively, than the Leq (AFT) noise levels. Mean noise levels at standardized center (1/1) octave bands were highest between 500 and 4000 Hz, ranging from 65.2 to 69.8 dB. A total of 72% of all area Leq measurements exceeded the 70 dBA ACGIH TLV classified as effective quiet to allow for temporary threshold shift recovery. All noise measurements exceeded the World Health Organization's noise threshold where adverse effects on sleep begin.

DISCUSSION/CONCLUSIONS

Results suggest that sleeping area location in close proximity to relatively high noise sources and activities occurring on an aircraft carrier (i.e. flight operations) increase noise levels in sleeping areas. These findings raise serious concerns since high noise exposures both on duty and during off-duty/sleeping periods may inhibit auditory recovery from hazardous noise exposures. In addition, results suggest noise levels in sleeping areas are high enough to evoke negative sleep effects.

Association of Flying Time with Hearing Loss in Military Pilots

Background:

Military pilots are exposed to harmful noise levels, and the two possible effects of this are hearing loss and tinnitus.

Objective:

This study was conducted to determine the prevalence of noise-induced hearing loss among Saudi military pilots and to determine its association with total flight hours and aircraft type (i.e., fixed and rotary wing).

Materials and Methods:

This cross-sectional study was conducted at the Armed Forces Aeromedical Centre, Dhahran, Saudi Arabia, between November 2015 and October 2016. A total of 150 Saudi military pilots were interviewed using a structured questionnaire. Pure-tone audiometry was used to measure hearing thresholds. Hearing threshold levels were compared between age groups and aircraft category. The association between total flying hours and the development of noise-induced hearing loss was analyzed.

Results:

The overall prevalence of noise-induced hearing loss in the military pilots was 18.4%, with a higher prevalence among fixed-wing pilots (42%) as compared with rotary-wing pilots (23%). Pilots with ≥2000 flying hours had a significantly higher hearing threshold compared with those in other categories. Age was a statistically significant risk factor.

Conclusions:

This study found that active pilots of both fixed- and rotary-wing aircrafts are at a high risk of noise-induced hearing loss; however, fixed-wing pilots with ≥2000 flying hours are at a higher risk. These findings support recommendations requiring instructions on the proper use of hearing protection devices to avoid noise-induced hearing loss.