Relationship Between Subjective Reports of Temporary Threshold Shift and the Prevalence of Hearing Problems in Military Personnel

Age Impacts Speech-in-Noise Recognition Differently for Nonnative and Native Listeners

PURPOSE

The purpose of this study was to explore potential differences in suprathreshold auditory function among native and nonnative speakers of English as a function of age.

METHOD

Retrospective analyses were performed on three large data sets containing suprathreshold auditory tests completed by 5,572 participants who were self-identified native and nonnative speakers of English between the ages of 18-65 years, including a binaural tone detection test, a digit identification test, and a sentence recognition test.

RESULTS

The analyses show a significant interaction between increasing age and participant group on tests involving speech-based stimuli (digit strings, sentences) but not on the binaural tone detection test. For both speech tests, differences in speech recognition emerged between groups during early adulthood, and increasing age had a more negative impact on word recognition for nonnative compared to native participants. Age-related declines in performance were 2.9 times faster for digit strings and 3.3 times faster for sentences for nonnative participants compared to native participants.

CONCLUSIONS

This set of analyses extends the existing literature by examining interactions between aging and self-identified native English speaker status in several auditory domains in a cohort of adults spanning young adulthood through middle age. The finding that older nonnative English speakers in this age cohort may have greater-than-expected deficits on speech-in-noise perception may have clinical implications on how these individuals should be diagnosed and treated for hearing difficulties.

Functional Hearing Difficulties in Blast-Exposed Service Members With Normal to Near-Normal Hearing Thresholds

OBJECTIVES

Estimated prevalence of functional hearing and communication deficits (FHCDs), characterized by abnormally low speech recognition and binaural tone detection in noise or an abnormally high degree of self-perceived hearing difficulties, dramatically increases in active-duty service members (SMs) who have hearing thresholds slightly above the normal range and self-report to have been close to an explosive blast. Knowing the exact nature of the underlying auditory-processing deficits that contribute to FHCD would not only provide a better characterization of the effects of blast exposure on the human auditory system, but also allow clinicians to prescribe appropriate therapies to treat or manage patient complaints.

DESIGN

Two groups of SMs were initially recruited: (1) a control group (N = 78) with auditory thresholds ≤20 dB HL between 250 and 8000 Hz, no history of blast exposure, and who passed a short FHCD screener, and (2) a group of blast-exposed SMs (N = 26) with normal to near-normal auditory thresholds between 250 and 4000 Hz, and who failed the FHCD screener (cutoffs based on the study by Grant et al.). The two groups were then compared on a variety of audiometric, behavioral, cognitive, and electrophysiological measures. These tests were selected to characterize various aspects of auditory system processing from the cochlear to the cortex. A third, smaller group of blast-exposed SMs who performed within normal limits on the FHCD screener were also recruited (N = 11). This third subject group was unplanned at the onset of the study and was added to evaluate the effects of blast exposure on hearing and communication regardless of performance on the FHCD screener.

RESULTS

SMs in the blast-exposed group with FHCD performed significantly worse than control participants on several metrics that measured peripheral and mostly subcortical auditory processing. Cognitive processing was mostly unaffected by blast exposure with the exception of cognitive tests of language-processing speed and working memory. Blast-exposed SMs without FHCD performed similarly to the control group on tests of peripheral and brainstem processing, but performed similarly to blast-exposed SMs with FHCD on measures of cognitive processing. Measures derived from EEG recordings of the frequency-following response revealed that blast-exposed SMs who exhibited FHCD demonstrated increased spontaneous neural activity, reduced amplitude of the envelope-following response, poor internal signal to noise ratio, reduced response stability, and an absent or delayed onset response, compared with the other two participant groups.

CONCLUSIONS

Degradation in the neural encoding of acoustic stimuli is likely a major contributing factor leading to FHCD in blast-exposed SMs with normal to near-normal audiometric thresholds. Blast-exposed SMs, regardless of their performance on the FHCD screener, exhibited a deficit in language-processing speed and working memory, which could lead to difficulties in decoding rapid speech and in understanding speech in challenging speech communication settings. Further tests are needed to align these findings with clinical treatment protocols being used for patients with suspected auditory-processing disorders.

Acute Hearing Deficits associated with Weapons Exposure in Section 734 Blast Overpressure Study (BOS)

INTRODUCTION

This prospective, multi-site, observational study describes ongoing efforts in support of the Fiscal Year 2018 National Defense Authorization Act (NDAA) Section 734 Blast Overpressure Study (BOS) to identify the acute effects impulse and blast exposure have on hearing abilities of the Warfighter in various military training environments.

MATERIALS AND METHODS

Hearing thresholds, a binaural tone detection task, and auditory symptoms were collected before and immediately following weapons exposure across nine military training environments from January 2020 to October 2022. An additional 25 non-exposed control participants also completed the behavioral test battery. A boothless audiometer was used to measure hearing ability in the field. Sound level meters were attached on-body to record the exposure environment throughout training.

RESULTS

Mean threshold change for the blast-exposed group was worse than the control group. Of the 188 blast-exposed participants, 23 experienced a temporary threshold shift (TTS) acutely after exposure. A decrease in binaural tone detection performance and increased symptom severity was found when comparing blast-exposed participants with a TTS versus those without a significant change in hearing. A complex but consistent relationship between measured exposure level (LAeq8hr) and the magnitude of the resulting TTS is suggested in the available data.

CONCLUSIONS

Recent discussions on Section 734 studies examining the effects of repetitive blast exposure have indicated that hearing-related issues were a critical problem that needed additional research. Study outcomes provide highly repeatable results across various weapons systems with hazardous blast exposure. This standardized set of hearing assessment tools for evaluating acute effects of noise under field conditions has been critically important in improving our understanding of TTS in prospective human subject research.

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.

Efficient Estimation of the Binaural Masking Level Difference Using a Technique Based on Manual Audiometry

PURPOSE

The Masking Level Difference (MLD) has been used for decades to evaluate the binaural listening advantage. Although originally measured using Bekesy audiometry, the most common clinical use of the MLD is the CD-based Wilson 500-Hz technique with interleaved N0S0 and N0Sπ components. Here, we propose an alternative technique based on manual audiometry as a faster way of measuring the MLD. The article describes the advantages to this administration technique and evaluates if it is a viable alternative for the Wilson technique.

METHOD

Data were retrospectively analyzed on 264 service members (SMs). All SMs completed both the Wilson and Manual MLDs. Descriptive and correlational statistics were applied to evaluate the comparisons between the two techniques and highlight the differences. Equivalence measures were also completed to compare the tests using a standardized cutoff score. Analyses were also made to compare both techniques to subjective and objective measures of hearing performance.

RESULTS

Moderate to high positive correlations were determined between Wilson and Manual measures of each threshold (N0Sπ and N0S0). Although the Manual and Wilson MLD techniques produced significantly different thresholds, simple linear transformations can be used to obtain approximately equivalent scores on the two tests, and agreement was high for using these transformed scores to identify individuals with substantial MLD deficits. Both techniques had moderate test-retest reliability. The Manual MLD and components had stronger correlations to the subjective and objective hearing measures than the Wilson.

CONCLUSIONS

The Manual technique is a faster method for obtaining MLD scores that is just as reliable as the CD-based Wilson test. With the significant reduction in assessment time and comparable results, the Manual MLD is a viable alternative for direct use in the clinic.

Field assessment of acute auditory responses to environmental exposures in close quarters tactics training

OBJECTIVE

The purpose of this study was to evaluate auditory performance of military instructors as part of a training course involving noise and blast exposure. Boothless audiometry was used to estimate the test-retest reliability of the auditory measures under realistic field conditions and to determine risk of acute auditory injury during standard training practices.

DESIGN AND STUDY SAMPLE

Thirteen U.S. Marine instructors participated in study activities. An audiologic testing suite embedded in a noise-attenuating headset was used to test various tone detection tasks on subjects after exposure. Acoustic exposures were captured with sound level meters.

RESULTS

Boothless audiometry provide highly repeatable results for various tests of auditory performance in the field environment. In this test population, changes in auditory performance pre- and post-noise exposure were minimal for most measures. The notable exception was binaural (NoSπ) tone detection, which showed significant degradations both as a function of pre- and post-noise exposure on the same day and as a result of cumulative noise exposure over the period of the study.

CONCLUSIONS

Study outcomes are consistent with prior laboratory and epidemiological work and suggest a link between the binaural processes required for NoSπ detection and the hearing-related issues reported by blast-exposed service members.

Noise-induced hearing disorders: Clinical and investigational tools

A series of articles discussing advanced diagnostics that can be used to assess noise injury and associated noise-induced hearing disorders (NIHD) was developed under the umbrella of the United States Department of Defense Hearing Center of Excellence Pharmaceutical Interventions for Hearing Loss working group. The overarching goals of the current series were to provide insight into (1) well-established and more recently developed metrics that are sensitive for detection of cochlear pathology or diagnosis of NIHD, and (2) the tools that are available for characterizing individual noise hazard as personal exposure will vary based on distance to the sound source and placement of hearing protection devices. In addition to discussing the utility of advanced diagnostics in patient care settings, the current articles discuss the selection of outcomes and end points that can be considered for use in clinical trials investigating hearing loss prevention and hearing rehabilitation.

Rapid Assessment of Subjective Hearing Complaints With a Modified Version of the Tinnitus and Hearing Survey

Hearing difficulties are frequently reported by patients in audiology clinics, including patients with normal audiometric thresholds. However, because all individuals experience some difficulty understanding speech in noisy environments, it can be difficult to assess hearing complaints objectively across patients. Normative values help address this issue by providing an objective cutoff score for determining what is or is not clinically significant. The goal of this study was to establish normative values for the four-item hearing subscale of the Tinnitus and Hearing Survey (THS-H). Respondents completing the THS-H rate the level of difficulty understanding speech in the situations most commonly reported as being difficult: in the presence of noise, on TV or in movies, soft voices and group conversations. In this study, 22,583 US Service Members (SMs) completed the THS-H using an 11-point scale ranging from 0 (not a problem) to 10 (a very big problem). Responses to the four items were summed to produce values between 0 and 40. The distribution of the final scores was analyzed based on severity of hearing loss, age, and sex. Only 5% of SMs with clinically normal hearing scored above 27, so this score was selected as a cutoff for "clinically significant hearing problems." Due to its ease of administration and interpretation, the THS-H could be a useful tool for identifying patients with subjective hearing difficulty warranting audiological evaluation and management.

Prospective measurements of hearing threshold during military rifle training with in-ear, protected, noise exposure monitoring

Although a causal relationship exists between military occupational noise exposure and hearing loss, researchers have struggled to identify and/or characterize specific operational noise exposures that produce measurable changes in hearing function shortly following an exposure. Growing evidence suggests that current standards for noise-exposure limits are not good predictors of true hearing damage. In this study, the aim was to capture the dose-response relationship during military rifle training exercises for noise exposure and hearing threshold. To capture exposure, a wearable system capable of measuring impulse noise simultaneously on-body and in-ear, behind hearing protection was used. To characterize hearing threshold changes, portable audiometry was employed within 2 h before and after exposure. The median 8-h time-weighted, protected, free-field equivalent in-ear exposure was 87.5 dBA at one site and 80.7 dBA at a second site. A significant dose-response correlation between in-ear noise exposure and postexposure hearing threshold changes across our population ( R = 0.40 , p = 0.0281) was observed. The results demonstrate an approach for establishing damage risk criteria (DRC) for in-ear, protected measurements based on hearing threshold changes. While an in-ear DRC does not currently exist, it may be critical for predicting the risk of injury for noise environments where protection is mandatory and fit status can vary.

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.

Does Exposure to Noise During Military Service Affect the Progression of Hearing Loss with Increasing Age?

It is traditionally believed that the effects of exposure to noise cease once the exposure itself has ceased. If this is the case, exposure to noise relatively early in life, for example during military service, should not affect the subsequent progression of hearing loss. However, recent data from studies using animals suggest that noise exposure can accelerate the subsequent progression of hearing loss. This paper presents new longitudinal data obtained from 29 former male military personnel. Audiograms obtained at the end of military service were compared with those obtained at least five years later. Rates of change of hearing threshold level (HTL) in dB/year were compared with those expected from ISO7029 (2017) for men at the 50^th percentile. The results are consistent with the hypothesis that noise exposure during military service accelerates the progression of hearing loss for frequencies where the hearing loss is absent or mild at the end of military service, by about 1.7 dB/year on average for frequencies from 3 to 8 kHz, but has no effect on or slows the progression of hearing loss for frequencies where the hearing loss exceeds about 50 dB. Acceleration appears to occur over a wide frequency range, including 1 kHz. There remains a need for further longitudinal studies using larger sample sizes. Longitudinal studies are also needed to establish whether exposure to other types of sounds, for example at rock concerts or from work in heavy industries, affects the subsequent progression of hearing loss.

Guidelines for Diagnosing and Quantifying Noise-Induced Hearing Loss

This paper makes recommendations for the diagnosis and quantification of noise-induced hearing loss (NIHL) in a medico-legal context. A distinction is made between NIHL produced by: steady broadband noise, as occurs in some factories; more impulsive factory sounds, such as hammering; noise exposure during military service, which can involve very high peak sound levels; and exposure to very intense tones. It is argued that existing diagnostic methods, which were primarily developed to deal with NIHL produced by steady broadband noise, are not adequate for the diagnosis of NIHL produced by different types of exposures. Furthermore, some existing diagnostic methods are based on now-obsolete standards, and make unrealistic assumptions. Diagnostic methods are proposed for each of the types of noise exposure considered. It is recommended that quantification of NIHL for all types of exposures is based on comparison of the measured hearing threshold levels with the age-associated hearing levels (AAHLs) for a non-noise exposed population, as specified in ISO 7029 (2017), usually using the 50^th percentile, but using another percentile if there are good reasons for doing so. When audiograms are available both soon after the end of military service and some time afterwards, the most recent audiogram should be used for diagnosis and quantification, since this reflects any effect of the noise exposure on the subsequent progression of hearing loss. It is recommended that the overall NIHL for each ear be quantified as the average NIHL across the frequencies 1, 2, and 4 kHz.

Modification of a Method for Diagnosing Noise-Induced Hearing Loss Sustained During Military Service

Moore (2020) proposed a method for diagnosing noise-induced hearing loss (NIHL) sustained during military service, based on an analysis of the shapes of the audiograms of military personnel. The method, denoted M-NIHL, was estimated to have high sensitivity but low-to-moderate specificity. Here, a revised version of the method, denoted rM-NIHL, was developed that gave a better balance between sensitivity and specificity. A database of 285 audiograms of military noise-exposed men was created by merging two previously used databases with a new database, randomly shuffling, and then splitting into two, one for development of the revised method and one for evaluation. Two comparable databases of audiograms of 185 non-exposed men were also created, again one for development and one for evaluation. Based on the evaluation databases, the rM-NIHL method has slightly lower sensitivity than the M-NIHL method, but the specificity is markedly higher. The two methods have similar overall diagnostic performance. If an individual is classified as having NIHL based on a positive diagnosis for either ear, the rM-NIHL method has a sensitivity of 0.98 and a specificity of 0.63. Based on a positive diagnosis for both ears, the rM-NIHL method has a sensitivity of 0.76 and a specificity of 0.95.

Temporary Threshold Shifts among Iron and Steel Factory Workers in Tanzania: A Pre-Interventional Study

Background

Workers in iron and steel factories in Tanzania are exposed to noise levels above recommended limit values, without using hearing protection devices. Exposure to noise levels above 85 dB(A) is associated with temporary threshold shifts (TTS) of human hearing. Nevertheless, there are few studies of noise and hearing from African countries.

Objective

To determine whether the normal hearing workers in Tanzania experiences TTS after full-shift occupational noise exposure of 85 dB(A) and above.

Methods

A total of 55 workers were included. Full-shift personal noise measurements were conducted. Pre- and post-shifts pure-tone audiometry were conducted for each worker. TTS was defined as a 10 dB or greater change at 1000, 2000, 3000 or 4000 Hz in either ear.

Results

We found that 85.5% of the workers developed TTS across the work shift. There was significant increase in mean hearing thresholds across shift at 1000, 2000, 3000 and 4000 Hz among the workers exposed to an average personal noise exposure (LAeq,8h) of 90.4 dB(A) (SD = 2.7). The difference in mean hearing thresholds was higher at 4000 Hz [Arithmetic Mean (AM) = 10 dB SD = 4 dB] compared to that of 1000 Hz (AM = 4 dB SD = 3 dB), 2000 Hz (AM = 4 dB SD = 4 dB), and 3000 Hz (AM = 9 dB SD = 6 dB), respectively.

Conclusions

Interventions to reduce occupational personal noise exposure are warranted to reduce the high risk of developing a permanent threshold shift with persistent high noise exposure. An intervention study is planned for this group of workers.