Hearing loss associated with US military combat deployment

Strategies of Hearing Preservation With Military Personnel: A Scoping Review

PURPOSE

The purpose of this study was to map the strategies used in hearing health education with military personnel during the Hearing Preservation Program (HPP).

METHOD

This study is a scoping review, with electronic searches conducted in online databases and gray literature: Latin American and Caribbean Literature in Health Sciences, PubMed/Medline, Scopus, Web of Science, ASHAWire, Google Scholar, and ProQuest Dissertation & Theses. Only studies describing, analyzing, or evaluating the application of the HPP to active duty or training military personnel were included.

RESULTS

A total of 3,478 references were retrieved, and 12 studies met the inclusion criteria. The strategies were classified into five categories: focus group aimed at exploring knowledge and perceptions regarding hearing health (five studies), training on the proper fitting of hearing protection devices (four studies), the utilization of audiovisual materials (seven studies), questionnaires administrated before and after educational intervention (five studies), and feedback survey concerning the implemented hearing health education (three studies).

CONCLUSION

There are five strategies that aimed at assessing knowledge and attitudes, improving hearing health education, facilitating information access, and evaluating the applied actions.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.25219589.

Modern In Vitro Techniques for Modeling Hearing Loss

Sensorineural hearing loss (SNHL) is a prevalent and growing global health concern, especially within operational medicine, with limited therapeutic options available. This review article explores the emerging field of in vitro otic organoids as a promising platform for modeling hearing loss and developing novel therapeutic strategies. SNHL primarily results from the irreversible loss or dysfunction of cochlear mechanosensory hair cells (HCs) and spiral ganglion neurons (SGNs), emphasizing the need for innovative solutions. Current interventions offer symptomatic relief but do not address the root causes. Otic organoids, three-dimensional multicellular constructs that mimic the inner ear's architecture, have shown immense potential in several critical areas. They enable the testing of gene therapies, drug discovery for sensory cell regeneration, and the study of inner ear development and pathology. Unlike traditional animal models, otic organoids closely replicate human inner ear pathophysiology, making them invaluable for translational research. This review discusses methodological advances in otic organoid generation, emphasizing the use of human pluripotent stem cells (hPSCs) to replicate inner ear development. Cellular and molecular characterization efforts have identified key markers and pathways essential for otic organoid development, shedding light on their potential in modeling inner ear disorders. Technological innovations, such as 3D bioprinting and microfluidics, have further enhanced the fidelity of these models. Despite challenges and limitations, including the need for standardized protocols and ethical considerations, otic organoids offer a transformative approach to understanding and treating auditory dysfunctions. As this field matures, it holds the potential to revolutionize the treatment landscape for hearing and balance disorders, moving us closer to personalized medicine for inner ear conditions.

Prevalence and Characteristics of Veterans with Severe Hearing Loss: A Descriptive Study

Hearing loss is common among Veterans, and extensive hearing care resources are prioritized within the Veterans Administration (VA). Severe hearing loss poses unique communication challenges with speech understanding that may not be overcome with amplification. We analyzed data from the VA Audiometric Repository between 2005 and 2017 and the relationship between hearing loss severity with speech recognition scores. We hypothesized that a significant subset of Veterans with severe or worse hearing loss would have poor unaided speech perception outcomes even with adequate audibility. Sociodemographic characteristics and comorbidities were compiled using electronic medical records as was self-report measures of hearing disability. We identified a cohort of 137,500 unique Veterans with 232,789 audiograms demonstrating bilateral severe or worse hearing loss (four-frequency PTA > 70 dB HL). The median (IQR; range) age of Veterans at their first audiogram with severe or worse hearing loss was 81 years (74 to 87; 21-90+), and a majority were male (136,087 [99%]) and non-Hispanic white (107,798 [78.4%]). Among those with bilateral severe or worse hearing loss, 41,901 (30.5%) also had poor speech recognition scores (<50% words), with greater hearing loss severity correlating with worse speech perception. We observed variability in speech perception abilities in those with moderate-severe and greater levels of hearing loss who may derive limited benefit from amplification. Veterans with communication challenges may warrant alternative approaches and treatment strategies such as cochlear implants to support communication needs.

Prevalence of Self-Reported Voice Concerns and Associated Risk Markers in a Nonclinical Sample of Military Service Members

INTRODUCTION

Difficult communication environments are common in military settings, and effective voice use can be critical to mission success. This study aimed to estimate the prevalence of self-reported voice disorders among U.S. military service members and to identify factors that contribute to their voice concerns.

METHOD

A nonclinical sample of 4,123 active-duty service members was recruited across Department of Defense hearing conservation clinics. During their required annual hearing evaluation, volunteers provided responses to voice-related questions including a slightly adapted version of the Voice Handicap Index-10 (VHI-10) as part of a larger survey about communication issues. Changepoint detection was applied to age and years of service to explore cohort effects in the reporting of voice concerns. Logistic regression analyses examined multiple available factors related to communication to identify factors associated with abnormal results on the VHI-10.

RESULTS

Among the respondents, 41% reported experiencing vocal hoarseness or fatigue at least several times per year, and 8.2% (n = 336) scored above the recommended abnormal cut-point value of 11 on the VHI-10. Factors independently associated with the greatest risk for self-reported voice concerns were sex (female), cadmium exposure, vocal demands (the need for a strong, clear voice), and auditory health measures (frequency of experiencing temporary threshold shifts; self-reported hearing difficulties).

CONCLUSIONS

Based on self-reported voice concerns and false negative rates reported in the literature, the prevalence of dysphonia in a large sample of active-duty service members is estimated to be 11.7%, which is higher than that in the general population. Certain predictors for voice concerns were expected based on previous literature, like female sex and voice use, but frequency of temporary threshold shifts and exposure to cadmium were surprising. The strong link between voice and auditory problems has particular implications regarding the need for effective communication in high-noise military and other occupational environments.

A Clinician's Guide to Occupational Exposures in the Military

PURPOSE OF REVIEW

Adverse occupational and environmental exposures are common causes of respiratory disease and health consequences requiring medical care. Understanding how these various exposures affect patients and how to elicit an adequate history is critical for any clinician. Military personnel are often overlooked when discussing groups at risk for environmental exposure-associated airway disease. There are close to 20 million active duty and veterans in the USA, and nearly all clinicians will at some point care for a patient that has served in the military.

RECENT FINDINGS

Exposures related to military work include burn pits, chemicals/toxins, sandstorms, and living conditions. Burn pits and military waste are increasingly recognized as potential hazards attributed to the ongoing conflicts in the Middle East. The link between these various military exposures and acute or chronic airway diseases remains difficult. Epidemiological studies are emerging to demonstrate correlations with chronic lung disease and prolonged burn pit exposure. This review provides an overview of potential occupational and environmental exposures that may affect current and/or former military service men and women.

Cochlear Implants in Veterans: 10-Year Experience at a Single Referral Center

PURPOSE

Severe hearing loss is particularly prevalent among Veterans. In response, the Veterans Affairs (VA) provides hearing aids and cochlear implants as part of their comprehensive hearing loss treatment. The VA's national health care system and integrated electronic health records offer a unique opportunity to examine patterns and outcomes in the management of severe hearing loss.

METHOD

We retrospectively reviewed an urban VA center's database for all Veterans who underwent cochlear implantation between 2010 and 2019. We collected preoperative demographic and audiological data including cochlear implant outcomes.

RESULTS

During the study period, 61 Veterans received a cochlear implant, totaling 70 ears implanted. Median age at implantation was 70.2 years. Over 90% of Veterans reported preoperative hearing aid use, and median preoperative four-frequency pure-tone average and aided word recognition score in the ear to be implanted were 100 dB HL and 7%, respectively. The median onset of severe hearing loss bilaterally was over 4 years prior to cochlear implant evaluation based on available audiometric data. Postoperative word recognition score was negatively correlated with self-reported duration of hearing loss.

CONCLUSIONS

This study provides unique insights into how Veterans with severe hearing loss are managed at one VA center. Compared to data published on cochlear implant recipients in the civilian population, Veterans in this cohort were older and had higher rates of preoperative hearing aid use. Available VA data suggest most Veterans were appropriate candidates for cochlear implant referral years prior to undergoing an evaluation. Reasons for treatment delays in this population remain to be studied.

An Observational Study to Compare Prevalence and Demography of Sensorineural Hearing Loss Among Military Personnel and Civilian Population

To evaluate the pattern of sensorineural hearing loss (SNHL) in patients attending ENT OPD in a military setup as well as to compare the incidence of hearing loss in Military Personnel with civilian population. This observational cross sectional comparative study was conducted over a period of April 2018 to July 2019. A total of 300 patients with hearing loss (HL) were included. Demographic characteristics along with laterality of sensorineural hearing impairment were compared between military personnel and civilians. Data was statistically compared between civilians and military personnel. A P-value of < 0.05 was considered statistically significant. We report an overall prevalence of 3.78% SNHL in the ENT OPD. Specifically the prevalence of SNHL among military personnel was 2.17% and in civilian population was 4.83% (P < 0.0001). The mean age of the military personnel was significantly less than civilians (62.53 ± 10.03 vs 65.98 ± 12.46, P = 0.003). There were 68% Males and 32% females. Significantly higher number of males were present in military group as all participants were males (100% vs 58.62%, P < 0.0001). There was no significant difference in the laterality of SNHL between Military personnel and the civilian population with bilateral involvement being common in both populations. It can be concluded that bilateral SNHL type is the most common type of hearing impairment among military personnel as well as civilians complaining of HL. Males of 51-70 years are most affected with SNHL.

The α9α10 nicotinic acetylcholine receptor: a compelling drug target for hearing loss?

INTRODUCTION

Hearing loss is a major health problem, impacting education, communication, interpersonal relationships, and mental health. Drugs that prevent or restore hearing are lacking and hence novel drug targets are sought. There is the possibility of targeting the α9α10 nicotinic acetylcholine receptor (nAChR) in the prevention of noise-induced, hidden hearing loss and presbycusis. This receptor mediates synaptic transmission between medial olivocochlear efferent fibers and cochlear outer hair cells. This target is key since enhanced olivocochlear activity prevents noise-induced hearing loss and delays presbycusis.

AREAS COVERED

The work examines the α9α10 nicotinic acetylcholine receptor (nAChR), its role in noise-induced, hidden hearing loss and presbycusis and the possibility of targeting. Data has been searched in Pubmed, the World Report on Hearing from the World Health Organization and the Global Burden of Disease Study 2019.

EXPERT OPINION

The design of positive allosteric modulators of α9α10 nAChRs is proposed because of the advantage of reinforcing the medial olivocochlear (MOC)-hair cell endogenous neurotransmission without directly stimulating the target receptors, therefore avoiding receptor desensitization and reduced efficacy. The time is right for the discovery and development of α9α10 nAChRs targeting agents and high throughput screening assays will support this.

Self-reported auditory problems are associated with adverse mental health outcomes and alcohol misuse in the UK Armed Forces

PURPOSE

Auditory problems, such as hearing loss and tinnitus, have been associated with mental health problems and alcohol misuse in the UK general population and in the US Armed Forces; however, few studies have examined these associations within the UK Armed Forces. The present study examined the association between auditory problems and probable common mental disorders, post-traumatic stress disorder and alcohol misuse.

METHODS

5474 serving and ex-service personnel from the UK Armed Forces were examined, selected from those who responded to phase two (data collection 2007-09) and phase three (2014-16) of a military cohort study. Multivariable logistic regression was used to examine the association between auditory problems at phase two and mental health problems at phase three.

RESULTS

9.7% of participants reported ever experiencing hearing problems alone, 7.9% reported tinnitus within the last month alone, and 7.8% reported hearing problems with tinnitus. After adjustment, hearing problems with tinnitus at phase two was associated with increased odds of probable common mental disorders (AOR = 1.50, 95% CI 1.09-2.08), post-traumatic stress disorder (AOR = 2.30, 95% CI 1.41-3.76), and alcohol misuse (AOR = 1.94, 95% CI 1.28-2.96) at phase three. Tinnitus alone was associated with probable post-traumatic stress disorder (AOR = 1.80, 95% CI 1.03-3.15); however, hearing problems alone were not associated with any outcomes of interest.

CONCLUSIONS

The association between auditory problems and mental health problems emphasises the importance of the prevention of auditory problems in the Armed Forces: through enhanced audiometric screening, improved hearing protection equipment, and greater levels of utilisation of such equipment.

[Treatment of victims with mine-explosive injuries]

OBJECTIVE

To study the incidence and structure of combat gunshot surgical trauma received during the 2^nd Karabakh War and to analyze the results of treatment of these victims.

MATERIAL AND METHODS

We analyzed surgical treatment of 60 victims with combat gunshot surgical trauma received during the 2^nd Karabakh war. In 25 (41.7%) victims, injury occurred as a result of mine-explosive trauma. These victims were divided into 3 groups depending on mechanism of mine-explosive injury. The 1^st group included 7 (28%) patients who received mine-explosive injury due to indirect (propelling) effect of blast wave. The 2^nd group included 14 (56%) victims in whom mine-explosive injury was caused by non-contact (distant) impact of mine fragments. The 3^rd group consisted of 4 (16%) patients whose mine-explosive injuries were caused by direct impact of explosion factors on various anatomical areas. Patients were also ranked into 3 groups depending on the nature and severity of mine-explosive injury: wounded with isolated injuries (n=16, 64%), wounded with concomitant injuries (n=2.8%), wounded with combined and multiple injuries (n=7, 28%).

RESULTS

Most patients underwent organ-sparing procedures. Resections were performed only in 4 cases (splenectomy - 3, nephrectomy - 1). Postoperative complications developed in 23 (38.3%) wounded (suppuration of postoperative wounds - 13, post-traumatic pleuritis - 5, clotted hemothorax - 2, subphrenic abscess - 1, phlegmon of perineum and perianal region - 2). Mortality rate was 1.7%.

CONCLUSION

Timely sorting and evacuation of victims, early qualified surgical care and correct postoperative management with monitoring of vital functions can improve the results of treatment of victims with mine-explosive trauma. Autologous skin grafting for extensive defects and closure of colostomy with restoration of colon continuity were essential in rehabilitation of these patients.

The Millennium Cohort Study: The First 20 Years of Research Dedicated to Understanding the Long-Term Health of US Service Members and Veterans

The Millennium Cohort Study, the US Department of Defense's largest and longest running study, was conceived in 1999 to investigate the effects of military service on service member health and well-being by prospectively following active duty, Reserve, and National Guard personnel from all branches during and following military service. In commemoration of the Study's 20th anniversary, this paper provides a summary of its methods, key findings, and future directions. Recruitment and enrollment of the first 5 panels occurred between 2001 and 2021. After completing a baseline survey, participants are requested to complete follow-up surveys every 3 to 5 years. Study research projects are categorized into 3 core portfolio areas (psychological health, physical health, and health-related behaviors) and several cross-cutting areas and have culminated in more than 120 publications to date. For example, some key Study findings include that specific military service-related factors (e.g., experiencing combat, serving in certain occupational subgroups) were associated with adverse health-related outcomes and that unhealthy behaviors and mental health issues may increase following the transition from military service to veteran status. The Study will continue to foster stakeholder relationships such that research findings inform and guide policy initiatives and health promotion efforts.

The Effect of Using an Active Earmuff on High Frequency Hearing in United States Marine Corps Weapons Instructors

OBJECTIVES

To investigate the change in hearing and perceived comfort over 1 year related to using an active hearing protection device (HPD) among United States Marine Corps (USMC) personnel routinely exposed to hazardous noise.

METHODS

USMC Weapons Instructors (n = 127) were issued an active earmuff that met military standards and was compatible with other protective equipment. These participants completed pre- and post-hearing tests and comfort surveys. A control cohort (n = 94) was also included to compare individual changes in high-frequency pure tone average (HF-PTA) over 1 year.

RESULTS

The control group's HF-PTA was 3 dB worse than the intervention group after only 1 year. Survey responses revealed perceived improvements in the ability to hear and understand, situational awareness, and safety.

CONCLUSIONS

Active HPDs can reduce hearing loss and improve hearing-related occupational tasks.

The Impact of Deployment and Combat Exposure on Physical Health Among Military Personnel: A Systematic Review of Incidence, Prevalence, and Risks

OBJECTIVES

The impact of deployment and combat on mental health of military personnel is well described. Less evidence is available to demonstrate and summarize the incidence, prevalence, and risks of these exposures on physical health. This study aims to (1) systematically review the available literature to determine the incidence and prevalence of physical health conditions among military personnel during and after deployment and (2) investigate the risks of deployment and combat exposure on physical health.

METHODS

A systematic review using the PubMed and EMBASE databases was performed. The literature search was limited to articles written in English, published from 2000 through 2019. The quality of studies was assessed with the Joanna Briggs Institute Appraisal Checklist. The results were grouped per system or condition of physical health and presented by forest plots without a combined effect size estimate.

RESULTS

Thirty-two studies were found eligible for this review. We identified a wide variety of incidence and prevalence rates of numerous physical health conditions and a high heterogeneity across the included studies. Acute respiratory symptoms, diarrhea, musculoskeletal injuries, pain, and tinnitus were found to be the most incident or prevalent conditions. Except for hearing loss, no associations with deployment and physical health problems were observed. An increased risk for asthma, headache, hearing loss, and pain was reported in relation to the combat exposure.

CONCLUSION

Given the characteristics of included studies and extracted data, the magnitude of the found differences in incidence and prevalence rates is most likely to be due to methodological heterogeneity. The specific exposures (e.g., infrastructure, environmental conditions, and activities during deployment) are suggested to be the determinants of (post) deployment physical health problems and need to be addressed to decrease the impact of deployment. Findings from this systematic review highlight which conditions should be addressed in response to service members' health and wellness needs in the (post)deployment phase and may be used by clinicians, researchers, and policy-makers. However, knowledge gaps regarding the potential risk factors during deployment and combat still exist. Studies using consistent methods to define and measure the physical health conditions and specific exposures are needed.

Hearing impairment in military personnel in Eastern Saudi Arabia

BACKGROUND:

Noise exposure is one of the most common occupational hazards worldwide. Studies have shown that the prevalence of hearing loss and tinnitus is higher in military personnel than in other occupations. This study aimed to estimate the prevalence of hearing impairment in military personnel in Eastern Saudi Arabia.

MATERIALS AND METHODS:

A cross-sectional study was conducted among 409 military personnel. A self-administered questionnaire collected data on level of awareness, hearing impairment, and protection of hearing. Pure-tone audiometry (PTA) was conducted on 141 participants to determine the prevalence and pattern of hearing impairment. Multivariate analysis was used to determine the predictors of hearing loss in military personnel.

RESULTS:

More than half of the participants (54.3%) were unaware of the consequences of noise exposure and none used proper hearing protection. A small percentage (5.9%) complied with the annual hearing examination, and only 23% had had a previous hearing evaluation. More than half of the participants (58.4%) had one or more abnormal hearing-related symptoms, with tinnitus as the most common symptom (43.8%). PTA showed hearing impairment in 71.6% of the participants. Multivariate analysis showed older age as only significant factor associated with hearing impairment in military personnel.

CONCLUSION:

Noise-induced hearing loss and tinnitus are common occupational disabilities in military personnel. Hearing conservation programs have to be initiated to ensure the application of hearing protection measures and control the effects of exposure to noise.

Hearing Problems Among the Members of the Defence Forces in Relation to Personal and Occupational Risk Factors

INTRODUCTION

The Defence Forces' members are exposed to high-level noise that increases their risk of hearing loss (HL). Besides military noise, the other risk factors include age and gender, ototoxic chemicals, vibration, and chronic stress. The current study was designed to study the effects of personal, work conditions-related risk factors, and other health-related traits on the presence of hearing problems.

MATERIALS AND METHODS

A cross-sectional study among active military service members was carried out. Altogether, 807 respondents completed a questionnaire about their health and personal and work-related risk factors in indoor and outdoor environments. The statistical analysis was performed using statistical package of social sciences (descriptive statistics) and R (correlation and regression analysis) software.

RESULTS

Almost half of the active service members reported HL during their service period. The most important risk factors predicting HL in the military appeared to be age, gender, and service duration. Also, working in a noisy environment with exposure to technological, vehicle, and impulse noise shows a statistically significant effect on hearing health. Moreover, we could identify the effect of stress on tinnitus and HL during the service period. Most importantly, active service members not using hearing protectors, tend to have more tinnitus than those who use it.

CONCLUSIONS

The members of the Defence Forces experience noise from various sources, most of it resulting from outdoor activities. Personal and work conditions-related risk factors as well as stress increase the risk of hearing problems.

Hearing loss among military personnel in relation to occupational and leisure noise exposure and usage of personal protective equipment

Context:

Hearing loss (HL) is a major health concern among military personnel due to noise from shooting, blasts, military vehicles, and noisy training environments. Nevertheless, one’s exposure can be partially reduced by using personal protective equipment (PPE). The aim of this study is to estimate the prevalence of HL among military personnel, to analyse associations between HL and self-reported occupational and leisure noise exposure, and use of PPEs.

Materials and Methods:

A cross-sectional study was conducted among 150 military personnel during their routine medical examinations. First, all participants filled in a questionnaire about their exposure to noise and later the respondents went through an audiometric test. The diagnostic criteria for slight, moderate, and severe HL was HL of 25–40, 41–60, and >60 dB at 4 and 6 kHz, respectively. The associations between noise exposure and HL were studied with multinomial logistic regression analysis.

Results:

The prevalence of slight to severe HL in high frequencies (4 and 6 kHz) among study participants was 62.7%. Nevertheless, the majority of it was slight, as the prevalence of severe HL was 9.3%. The prevalence of any kind of HL was highest in the Navy and the prevalence of severe HL was highest in the Central Command Units. The relative risk ratios (RRRs) for HL were higher among those who had been working for a long time in a noisy environment, working with noise-producing equipment, driving in a PASI or a Bandvagn or had been shooting with blanks at least once per week. It also appeared that military personnel who had HL, reported tinnitus more often. Respondents’ previous health problems, music-listening habits, and amount of exposure to loud noise in non-military environments were not independently associated with HL, but in several cases it increased the RRRs together with military exposure. We also found significantly more frequent HL among those never using PPEs.

Conclusion:

HL loss was more prevalent among personnel who are more often exposed to military noise, especially among those who never use PPEs. The effect was enhanced by leisure time noise, but it was not independently associated to HL.

Opioid-Induced Hearing Loss and Neonatal Abstinence Syndrome: Clinical Considerations for Audiologists and Recommendations for Future Research

Purpose Over the last two decades, the number of Americans misusing opioids has reached epidemic levels. With such drastic increases in opioid misuse, audiologists are more likely to have patients with opioid-induced hearing loss or neonatal abstinence syndrome (NAS) than in previous years. More attention is needed on how these increases might influence clinical practice and such a discussion could be useful for audiologists. The goal of this article, therefore, is to summarize what is currently known regarding the relationship between opioid misuse and audiology to help guide hearing health care providers (with a particular focus on opioid-induced hearing loss and NAS). This article (a) summarizes the overlap in opioid misuse and hearing loss populations, (b) describes the evidence linking opioid misuse to hearing loss, (c) discusses clinical implications that opioid-induced hearing loss and NAS have for practicing audiologists, and (d) recommends directions for future audiological research on opioid-induced hearing loss and NAS. Conclusions There is considerable overlap between populations at-risk for hearing loss and opioid misuse. Additionally, compelling evidence exists linking opioid misuse to hearing loss, but the specific causal mechanisms remain unclear, indicating a need for additional research. This article attempts to fill a gap in the audiological literature and has the potential to serve as a guide for hearing health care providers to make more informed clinical decisions regarding patients with opioid-induced hearing loss and NAS. Clinicians may wish to consider the concerns raised in this article before intervening with such concerns, especially in the absence of best practice protocols.

Characteristics and Impact of U.S. Military Blast-Related Mild Traumatic Brain Injury: A Systematic Review

As a result of armed conflict, head trauma from exposure to blasts is an increasing critical health issue, particularly among military service members. Whilst numerous studies examined the burden of blast-related brain injuries on service members', few systematic reviews have been published. This work provides a comprehensive summary of the evidence on blast-related mild traumatic brain injury (mTBI) burden in active U.S. military service members and inactive Veterans, describing characteristics and outcomes. Records published up to April 2017 were identified through a search of PubMed, Web of Science, Scopus, Ovid MEDLINE, and Cochrane Library. Records-based and original research reporting on U.S. military service members and Veterans with mild blast TBI were included. Data on subject characteristics, exposure, diagnostic criterion, and outcomes were extracted from included studies using a standardized extraction form and were presented narratively. Of the 2,290 references identified by the search, 106 studies with a total of 37,515 participants met inclusion criteria for blast-related mTBI. All but nine studies were based out of military or Veteran medical facilities. Unsurprisingly, men were over-represented (75–100%). The criteria used to define blast-related mTBI were consistent; however, the methodology used to ascertain whether individuals met those criteria for diagnosis were inconsistent. The diagnosis, most prevalent among the Army, heavily relied on self-reported histories. Commonly reported adverse outcomes included hearing disturbances and headaches. The most frequently associated comorbidities were post-traumatic stress disorder, depression, anxiety, sleep disorders, attention disorders, and cognitive disorders. The primary objective of this review was to provide a summary of descriptive data on blast-related mTBI in a U.S. military population. Low standardization of the methods for reaching diagnosis and problems in the study reporting emphasize the importance to collect high-quality data to fill knowledge gaps pertaining to blast-related mTBI.

How hearing conservation training format impacts personal attenuation ratings in U.S. Marine Corps Training Recruits

OBJECTIVE

The purpose of this fit-testing study in the field was to systematically compare three Hearing Protection Device (HPD) fit-training methods and determine whether they differ in the acquisition of HPD fitting skill and resulting amount of earplug attenuation.

DESIGN

Subjects were randomly assigned to receive HPD fit-training using one of three training methods: current, experiential HPD (eHPD), and integrated. Personal Attenuation Ratings (PARs) were acquired via HPD fit-testing and used to verify attenuations pre- and post-training.

STUDY SAMPLE

US Marine training recruits (n = 341) identified via HPD fit-testing for remedial HPD fit-training and assigned to three cohorts.

RESULTS

The post-training HPD fit-test passing rate differed by training method, with pass rates ranging from 50% (current) to nearly 92% (eHPD). The difference between group delta PAR values were significantly higher (>9 dB) in both the eHPD and integrated methods compared to the current method.

CONCLUSION

The HPD fit-training methods that teach "what right feels like" (eHPD and integrated) provided a greater number of trainees with the skill to achieve noise attenuation values required for impulse noise exposures encountered during basic training. The attenuation achieved by those methods was significantly greater than the current training method.

Acquired Central Auditory Processing Disorder in Service Members and Veterans

Purpose A growing body of evidence suggests that military service members and military veterans are at risk for deficits in central auditory processing. Risk factors include exposure to blast, neurotrauma, hazardous noise, and ototoxicants. We overview these risk factors and comorbidities, address implications for clinical assessment and care of central auditory processing deficits in service members and veterans, and specify knowledge gaps that warrant research. Method We reviewed the literature to identify studies of risk factors, assessment, and care of central auditory processing deficits in service members and veterans. We also assessed the current state of the science for knowledge gaps that warrant additional study. This literature review describes key findings relating to military risk factors and clinical considerations for the assessment and care of those exposed. Conclusions Central auditory processing deficits are associated with exposure to known military risk factors. Research is needed to characterize mechanisms, sources of variance, and differential diagnosis in this population. Existing best practices do not explicitly consider confounds faced by military personnel. Assessment and rehabilitation strategies that account for these challenges are needed. Finally, investment is critical to ensure that Veterans Affairs and Department of Defense clinical staff are informed, trained, and equipped to implement effective patient care.

Veterans with dizziness recruit compensatory saccades in each semicircular canal plane although VOR gain is normal

BACKGROUND

Exposure to brain injury via blast or blunt mechanisms disrupts multiple sensorimotor systems simultaneously. Large numbers of US Gulf War era and Operation Iraqi/Enduring Freedom veterans with traumatic brain injury (TBI) are suffering the symptom of dizziness - presumed due to "Multi-Sensory Impairment", a clinical pattern of damage to the auditory, visual and vestibular sensorimotor systems.

OBJECTIVE

To describe the oculomotor response to rapid head rotation in a population of veterans with dizziness. We also describe the reliability of using the video head impulse test (vHIT) in a veteran population.

METHODS

We used the vHIT to evaluate the vestibular-ocular reflex (VOR) gain and presence of compensatory saccades (CS) in each semicircular canal of 81 veterans (31% TBI) with dizziness. Data was collected using the ICS Otometric™ vHIT. Data was processed using both the Otometric™ software and custom software written in MATLAB™. This data was evaluated through Kruskal-Wallis rank-sum test and analysis of regression.

RESULTS

Veterans with dizziness recruit CS in all semicircular canal planes even though their VOR gain is normal. The vHIT is a reliable clinical test to quantify the metrics of the VOR and CS in veterans.

CONCLUSION

Veterans with dizziness symptoms use compensatory saccades in all planes of semicircular canal rotation, despite having normal peripheral VOR gain during rapid head rotation. The video head impulse test is a stable measure of vestibular slow phase and metrics of compensatory saccades in veterans with dizziness.

Hearing Damage Induced by Blast Overpressure at Mild TBI Level in a Chinchilla Model

Introduction

The peripheral auditory system and various structures within the central auditory system are vulnerable to blast injuries, and even blast overpressure is at relatively mild traumatic brain injury (TBI) level. However, the extent of hearing loss in relation to blast number and time course of post-blast is not well understood. This study reports the progressive hearing damage measured in chinchillas after multiple blast exposures at mild TBI levels (103–138 kPa or 15–20 psi).

Materials and Methods

Sixteen animals (two controls) were exposed to two blasts and three blasts, respectively, in two groups with both ears plugged with foam earplugs to prevent the eardrum from rupturing. Auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) were measured in pre- and post-blasts. Immunohistochemical study of chinchilla brains were performed at the end of experiment.

Results

Results show that the ABR threshold and DPOAE level shifts in 2-blast animals were recovered after 7 days. In 3-blast animals, the ABR and DPOAE shifts remained at 26 and 23 dB, respectively after 14 days. Variation of auditory cortex damage between 2-blast and 3-blast was also observed in immunofluorescence images.

Conclusions

This study demonstrates that the number of blasts causing mild TBI critically affects hearing damage.

Characterization of acute hearing changes in United States military populations

Until recently, most hearing conservation programs, including those in the military, have used permanent shifts in the pure-tone audiometric threshold as the gold standard for measuring hearing impairment in noise-exposed populations. However, recent results from animal studies suggest that high-level noise exposures can cause the permanent destruction of synapses between the inner hair cells and auditory nerve fibers, even in cases where pure-tone audiometric thresholds eventually return to their normal pre-exposure baselines. This has created a dilemma for researchers, who are now increasingly interested in studying the long-term effects that temporary hearing shifts might have on hearing function, but are also concerned about the ethical considerations of exposing human listeners to high levels of noise for research purposes. One method that remains viable to study the effects of high noise exposures on human listeners, or to evaluate the efficacy of interventions designed to prevent noise-related inner ear damage, is to identify individuals in occupations with unavoidable noise exposures and measure hearing before and as soon as possible after exposure. This paper discusses some of the important factors to be considered in studies that attempt to measure acute hearing changes in noise-exposed military populations.

Hearing Loss in Agricultural Workers Exposed to Pesticides and Noise

Agricultural workers who have concurrent exposure to pesticides and noise are at increased risk of hearing loss. We recruited 163 Thai conventional and 172 organic farmers to answer our questionnaires about personal demographics, agricultural activities, and pesticide and agricultural machinery use. This information was used to calculate the years of conventional (pesticide use) farming and the years of agricultural noise exposure, and to estimate semiquantitative metrics for pesticide exposure (cumulative intensity score-years) and cumulative noise exposure (dB(A)-years) for each conventional farmer. All participants underwent pure tone audiometric testing. The mean hearing threshold in the low-frequency band (0.5-2 kHz) and high-frequency band (3-6 kHz) were used for analysis. Years involved in conventional farming and years using agricultural machinery were associated with an increase in the average hearing threshold for the high-frequency band after controlling for age, ever exposed to industrial noise and cigarette smoking. The highest category of cumulative insecticide exposure (score-years), cumulative organophosphates exposure (score-years) and cumulative noise exposure (dB(A)-years) were also associated with an increased high-frequency band hearing threshold among conventional farmers. Results from the full cohort and the subcohort of conventional farmers support each other and the hypothesis that pesticide and noise have an additive effect on hearing, since no model interactions were significant.

Comparison of oral steroid regimens for acute acoustic trauma caused by gunshot noise exposure

Background

There are no definite guidelines regarding the most adequate steroid regimens for acute acoustic trauma.

Objective

To elucidate the dose-dependent differing benefits of oral steroids on hearing improvement following acute acoustic trauma.

Methods

Twenty-nine patients treated with oral steroids following a diagnosis of unilateral acute acoustic trauma were retrospectively reviewed. Patients were sorted into two groups with an oral steroid regimen. Group 1 received a 14-day course of treatment: 60 mg prednisolone daily for 10 days, tapering off over days 11–14. Group 2 received prednisolone for a total of 10 days: 60 mg for 5 days, tapering down each day for the remainder. Multivariable linear regression analysis was performed to evaluate the factors associated with the hearing gain.

Results

In the multivariable regression (R2 = 0.51, p < 0.001), patients in group 1 showed more significant improvement in the degree of hearing gain compared to group 2 (p = 0.03).

Conclusion

After comparing the differing benefits of oral steroids on hearing improvement by dosage, we recommend a high dose of prednisolone (60 mg per day) for 10 days, tapering over the remaining 4 days, for better hearing recovery following acute acoustic trauma.

In-vehicle noise exposure among military personnel depending on type of vehicle, riding compartment and road surface

Introduction

Noise-induced hearing loss is one of the most common health problems among military service personnel. Exposure to noise in military vehicles constitutes a large proportion of total noise exposure. This pilot study aimed to evaluate in-vehicle noise levels depending on the type of vehicle, riding compartment and road surface.

Method

Noise levels were measured in armoured personnel carriers and heavy all-terrain trucks, in the cab and rear passenger compartment, while driving on paved or off-road surfaces. The results were compared with national LLV and allowed noise exposure times were calculated per vehicle and surface.

Results

The equivalent noise levels in the cab of SISU XA-188 (p=0.001) and peak noise levels in MAN 4620 (p=0.0001) and DAF 4440 (p=0.0047) were higher on paved road, compared with off-road. The equivalent noise levels in the canvas covered rear compartment of MAN 4620 were significantly higher than in the cab on both paved (p=0.004) and off-road (p=0.0003). Peak noise levels in the cab of DAF 4440 exceeded the parameters measured in the canvas covered rear compartment on both paved (p=0.002) and off-road (p=0.0002). In most cases, peak noise levels were below the LLV (p=0.02–0.0001). The maximum noise exposure to passengers in the canvas covered rear compartment of MAN 4620 despite road surface was calculated 0.6 hours per working day.

Conclusion

A high risk of noise-induced hearing loss among military personnel occurs during long distance transportation with vehicles showing noise levels higher than allowed LLV.

Asymmetric Hearing Loss Prompting MRI Referral in a Military Population: Redefining Audiometric Criteria

Objective

To reevaluate asymmetric sensorineural hearing loss (ASNHL) criteria used to justify magnetic resonance imaging (MRI) in the evaluation of retrocochlear tumors in a military population.

Study Design

Retrospective case-control study.

Setting

Tertiary care military medical center.

Subjects and Methods

Patients with military service and a history of ASNHL prompting referral for MRI, with or without retrocochlear tumors, were compared between 2005 and 2016. Predictor variables included pure tone ASNHL, speech audiometry, and a history of noise exposure. Logistic regression models for hearing asymmetries were performed, and receiver operator curves were used to calculate sensitivity and specificity.

Results

Thirty-eight retrocochlear tumors were identified. The MRI diagnosis rate for patients with ASHNL was 0.85%. Patients with tumors were slightly older (42 vs 37 years, P = .021) and had less noise exposure (47% vs 85%, P < .001). A sensitivity of 0.83 and a specificity of 0.58 were calculated for asymmetries ≥10 dB at 2000 Hz without adjusting for noise exposure. Instituting this imaging threshold would have reduced the number of MRI scans by half while missing 16% of tumors.

Conclusion

The tumor diagnosis rate among those undergoing MRI for ASNHL is low in the military population, likely because service-related noise exposure commonly causes ASNHL. Optimal MRI referral criteria should conserve resources while balancing the risks of over- and underdiagnosis. For those with a history of military service, an asymmetry ≥10 dB at 2000 Hz among patients meeting current ANSHL referral criteria is most predictive of a retrocochlear tumor.

Impact of Blast Injury on Hearing in a Screened Male Military Population

Exposure to hazardous intensity levels of combat noise, such as blast, may compromise a person's ability to detect and recognize sounds and communicate effectively. There is little previous examination of the onset of hearing health outcomes following exposure to blast in representative samples of deployed US military personnel. Data from the prospective Blast-Related Auditory Injury Database were analyzed. We included only those participants with qualified hearing tests within a period of 12 months prior to, and following, injury (n = 1,574). After adjustment for relevant covariates and potential confounders, those who sustained a blast injury had significantly higher odds of postinjury hearing loss (odds ratio = 2.21; 95% confidence interval: 1.42, 3.44), low-frequency hearing loss (odds ratio = 1.95; 95% confidence interval: 1.01, 3.78), high-frequency hearing loss (odds ratio = 2.45; 95% confidence interval: 1.43, 4.20), and significant threshold shift compared with a group with non-blast-related injury. An estimated 49% of risk for hearing loss in these blast-injured, deployed military members could be attributed to the blast-related injury event. This study reinforced that it is imperative to identify at-risk populations for early intervention and prevention, as well as to consistently monitor the effects of blast injury on hearing outcomes.

Work-Related Noise Exposure in a Cohort of Patients with Chronic Tinnitus: Analysis of Demographic and Audiological Characteristics

Work-related noise exposure is one of the major factors contributing to the development of adult-onset hearing loss and tinnitus. The aim of this study was to analyze, in patients with chronic tinnitus and long-term occupational noise exposure, (A) characteristics of hearing loss, tinnitus, comorbidities, demographic characteristics and a history of work-related noise exposure and (B) differences among individuals employed in occupations with high and low risk of developing work-related noise-induced hearing loss (NIHL). One hundred thirty six patients with chronic tinnitus and at least a 10 year-long working history were divided into two groups based on the risk of their profession to induce NIHL. Individuals employed in jobs at high risk for NIHL were mostly males and exhibited a poorer hearing threshold, more evident in the left ear. Tinnitus was mostly bilateral; the next largest presentation was left-sided; patients described their tinnitus as buzzing or high-pitched. Correlation between age, length of tinnitus and worse hearing was found. Patients with a higher degree of hearing impairment were mostly males and were more likely to have a family history of hearing loss and at least one cardiovascular comorbidity. Our study shows some differences in individuals with tinnitus and a history of a profession associated with increased exposure to NIHL compared to those without such a history.

Emerging Therapies for Sensorineural Hearing Loss

OBJECTIVE

To critically review and evaluate the proposed mechanisms and documented results of the therapeutics currently in active clinical drug trials for the treatment of sensorineural hearing loss.

DATA SOURCES

US National Institutes of Health (NIH) Clinical Trials registry, MEDLINE/PubMed.

STUDY SELECTION & DATA EXTRACTION

A review of the NIH Clinical Trials registry identified candidate hearing loss therapies, and supporting publications were acquired from MEDLINE/PubMed. Proof-of-concept, therapeutic mechanisms, and clinical outcomes were critically appraised.

DATA SYNTHESIS

Twenty-two active clinical drug trials registered in the United States were identified, and six potentially therapeutic molecules were reviewed. Of the six molecules reviewed, four comprised mechanisms pertaining to mitigating oxidative stress pathways that presumably lead to inner ear cell death. One remaining therapy sought to manipulate the cell death cascade, and the last remaining therapy was a novel cell replacement therapy approach to introduce a transcription factor that promotes hair cell regeneration.

CONCLUSION

A common theme in recent clinical trials registered in the United States appears to be the targeting of cell death pathways and influence of oxidant stressors on cochlear sensory neuroepithelium. In addition, a virus-delivered cell replacement therapy would be the first of its kind should it prove safe and efficacious. Significant challenges for bringing these bench-to-bedside therapies to market remain. It is never assured that results in non-human animal models translate to effective therapies in the setting of human biology. Moreover, as additional processes are described in association with hearing loss, such as an immune response and loss of synaptic contacts, additional pathways for targeting become available.

The viability of hearing protection device fit-testing at navy and marine corps accession points

Introduction:

The viability of hearing protection device (HPD) verification (i.e., fit-testing) on a large scale was investigated to address this gap in a military accession environment.

Materials and Methods:

Personal Attenuation Ratings (PARs) following self-fitted (SELF-Fit) HPDs were acquired from 320 US Marine Corps training recruits (87.5% male, 12.5% female) across four test protocols (1-, 3-, 5-, and 7- frequency). SELF-Fit failures received follow-up to assess potential causes. Follow-up PARs were acquired (Experimenter fit [EXP-Fit], followed by Subject re-fit [SUB Re-Fit]). EXP-Fit was intended to provide a perception (dubbed “ear canal muscle memory”) of what a correctly fitted HPD should feel like. SUB Re-Fit was completed following EXP-Fit to determine whether a training recruit could duplicate EXP-Fit on her/his own without assistance.

Results:

A one-way analysis of variance (ANOVA) (N=320) showed that SELF-Fit means differed significantly between protocols (P < 0.001). Post-hoc analyses showed that the 1-freq SELF-Fit mean was significantly lower than all other protocols (P < 0.03) by 5.6 dB or more. No difference was found between the multi-frequency protocols. For recruits who were followed up with EXP-Fit (n=79), across all protocols, a significant (P < 0.001) mean improvement of 25.68 dB (10.99) was found, but PARs did not differ (P = 0.99) between EXP-Fit protocols. For recruits in the 3-freq and 5-freq protocol groups who experienced all three PAR test methods (n=33), PAR methods differed (P < 0.001) but no method by protocol interaction was found (P = 0.46). Post hoc tests showed that both EXP-Fit and SUB Re-Fit had significantly better attenuation than SELF-Fit (P < 0.001), but no difference was found between EXPFit and SUB Re-Fit (P = 0.59). For SELF-Fit, the 1-freq protocol resulted in a 35% pass rate, whereas the 3-, 5-, and 7-freq protocols resulted in >60% pass rates. Results showed that once recruits experienced how HPDs should feel when inserted correctly, they were able to properly replicate the procedure with similar results to the expert fit suggesting “ear canal muscle memory” may be a viable training strategy concomitant with HPD verification. Fit-test duration was also measured to examine the tradeoff between results accuracy and time required to complete each protocol.

Discussion:

Results from this study showed the critical importance of initial selection and fitting of HPDs followed by verification (i.e., fit-testing) at Navy and Marine Corps accession points. Achieving adequate protection from an HPD is fundamentally dependent on obtaining proper fit of the issued HPD as well as the quality of training recruits receive regarding HPD use.

Acute acoustic trauma in the French armed forces during 2007-2014

CONTEXT

Despite existing preventive measures, the number of acute acoustic trauma (AAT) cases reported to the French Military Epidemiological Surveillance System (MESS) remains high.

AIMS

The objective of this study was to describe AAT and the preventive measures already implemented.

SUBJECTS AND METHODS

We conducted a descriptive cross-sectional analysis of AAT using data from the MESS for the period 2007-2014. In addition, we reviewed the current prevention measures that exist in the French armed forces.

STATISTICAL ANALYSIS USED

Comparisons between different incidence rates were made by Poisson and quasi-Poisson regression.

RESULTS

Between 2007 and 2014, 10,487 AAT cases were reported to the MESS, with a significant decrease in 2013 (P < 0.001). AAT incidence rates were the highest among those aged <25 years - 14.3 per 1000 person-years (PYs) (P < 0.001), and those in the army; with 8.1 per 1000 PYs (P < 0.001), and men had almost twice the risk of women (P < 0.001). AAT mainly occurred in training schools or at camps during exercises. The main prevention actions identified were the following: official regulations, education, making hearing protection devices (HPDs) available for all service members, and regular hearing monitoring. A working group has been set up and has proposed an informative chapter in the weapon handling instruction book, an AAT simulator, and a new HPD, the 3M® earplug, with an information brochure.

CONCLUSIONS

AAT rates decreased from 2007 to 2014 in the French armed forces. Further analysis is needed to identify the underlying factors involved to improve the prevention actions proposed. The MESS and targeted surveys will assess the impact of the different prevention measures implemented.

Cellular mechanisms of noise-induced hearing loss

Exposure to intense sound or noise can result in purely temporary threshold shift (TTS), or leave a residual permanent threshold shift (PTS) along with alterations in growth functions of auditory nerve output. Recent research has revealed a number of mechanisms that contribute to noise-induced hearing loss (NIHL). The principle cause of NIHL is damage to cochlear hair cells and associated synaptopathy. Contributions to TTS include reversible damage to hair cell (HC) stereocilia or synapses, while moderate TTS reflects protective purinergic hearing adaptation. PTS represents permanent damage to or loss of HCs and synapses. While the substrates of HC damage are complex, they include the accumulation of reactive oxygen species and the active stimulation of intracellular stress pathways, leading to programmed and/or necrotic cell death. Permanent damage to cochlear neurons can also contribute to the effects of NIHL, in addition to HC damage. These mechanisms have translational potential for pharmacological intervention and provide multiple opportunities to prevent HC damage or to rescue HCs and spiral ganglion neurons that have suffered injury. This paper reviews advances in our understanding of cellular mechanisms that contribute to NIHL and their potential for therapeutic manipulation.