Otologic assessment of blast and nonblast injury in returning Middle East-deployed service members

Blast Exposure Associations With Hearing Loss and Self-Reported Hearing Difficulty

OBJECTIVE

Examine associations between military blast exposures on hearing loss and self-reported hearing difficulties among Active-Duty Service Members (ADSM) and Veterans from the Noise Outcomes in Servicemembers Epidemiology (NOISE) study.

STUDY DESIGN

Cross-sectional.

SETTING

Multi-institutional tertiary referral centers.

METHODS

Blast exposure was assessed with a comprehensive blast questionnaire. Outcome measures included pure-tone hearing thresholds; Speech Recognition in Noise Test; Hearing Handicap Inventory for Adults (HHIA); and Speech, Spatial and Qualities of Hearing Scale (SSQ)-12.

RESULTS

Twenty-one percent (102/494) of ADSM and 36.8% (196/533) of Veterans self-reported blast exposure. Compared to ADSM without blast exposure, blast-exposed ADSM had increased odds of high frequency (3-8 kHz) and extended-high frequency (9-16 kHz) hearing loss (odds ratio [OR] = 2.5, CI: 1.3, 4.7; OR = 3.7, CI: 1.9, 7.0, respectively). ADSM and Veterans with blast exposure were more likely than their nonblast exposed counterparts to report hearing difficulty on the HHIA (OR = 1.9, CI: 1.1, 3.3; OR = 2.1, CI: 1.4, 3.2, respectively). Those with self-reported blast exposure also had lower SSQ-12 scores (ADSM mean difference = -0.6, CI: -1.0, -0.1; Veteran mean difference: -0.9, CI: -1.3, -0.5).

CONCLUSION

Results suggest that blast exposure is a prevalent source of hearing injury in the military. We found that among ADSM, blast exposure was associated with hearing loss, predominately in the higher frequencies. Blast exposure was associated with poorer self-perceived hearing ability in ADSM and Veterans. IRB: #FWH20180143H Joint Base San Antonio (JBSA) Military Healthcare System; #3159/9495 Joint VA Portland Health Care System (VAPORHCS) Oregon Health and Science University (OHSU).

Mild Traumatic Brain Injury and the Auditory System: An Overview of the Mechanisms, Clinical Presentations, and Current Diagnostic Modalities

The acute and long-term consequences of mild traumatic brain injury (mTBI) are far reaching. Though it may often be overlooked due to the now expansive field of research dedicated to understanding the consequences of mTBI on the brain, recent work has revealed that substantial changes in the vestibulo-auditory system can also occur due to mTBI. These changes, termed "labyrinthine" or "cochlear concussion," include hearing loss, vertigo, and tinnitus that develop after mTBI in the setting of an intact bony labyrinthine capsule (as detected on imaging). In the review that follows, we focus our discussion on the effects of mTBI on the peripheral structures and pathways of the auditory and vestibular systems. Although the effects of indirect trauma (e.g., noise and blast trauma) have been well-investigated, there exists a profound need to improve our understanding of the effects of direct head injury (such as mTBI) on the auditory and vestibular systems. Our aim is to summarize the current evidentiary foundation upon which labyrinthine and/or cochlear concussion are based to shed light on the ways in which clinicians can refine the existing modalities used to diagnose and treat patients experiencing mTBI as it relates to hearing and balance.

Time-dependent effects of acoustic trauma and tinnitus on extracellular levels of amino acids in the inferior colliculus of rats

Chronic tinnitus is a debilitating condition with very few management options. Acoustic trauma that causes tinnitus has been shown to induce neuronal hyperactivity in multiple brain areas in the auditory pathway, including the inferior colliculus. This neuronal hyperactivity could be attributed to an imbalance between excitatory and inhibitory neurotransmission. However, it is not clear how the levels of neurotransmitters, especially neurotransmitters in the extracellular space, change over time following acoustic trauma and the development of tinnitus. In the present study, a range of amino acids were measured in the inferior colliculus of rats during acoustic trauma as well as at 1 week and 5 months post-trauma using in vivo microdialysis and high-performance liquid chromatography. Amino acid levels in response to sound stimulation were also measured at 1 week and 5 months post-trauma. It was found that unilateral exposure to a 16 kHz pure tone at 115 dB SPL for 1 h caused immediate hearing loss in all the animals and chronic tinnitus in 58 % of the animals. Comparing to the sham condition, extracellular levels of GABA were significantly increased at both the acute and 1 week time points after acoustic trauma. However, there was no significant difference in any of the amino acid levels measured between sham, tinnitus positive and tinnitus negative animals at 5 months post-trauma. There was also no clear pattern in the relationship between neurochemical changes and sound frequency/acoustic trauma/tinnitus status, which might be due to the relatively poorer temporal resolution of the microdialysis compared to electrophysiological responses.

[Blast and explosion traumas-effects on the middle and inner ear based on the example of Bundeswehr foreign missions]

Despite all protective measures, blast and explosion traumas are a frequent pattern of injury in Bundeswehr missions abroad. Due to body protection measures, head injuries, particularly of the ears, are higher in number compared to injuries in other regions of the body. Perforations of the tympanic membrane are the most frequent lesions of the middle ear, acute sensorineural hearing loss is the most frequent lesion of the inner ear, often accompanied by tinnitus and dizziness. With a high spontaneous recovery rate, prompt specialist care for these injuries is provided according to medical standards comparable to those in the home country.

Otologic Injuries Secondary to Explosive Attack

The frequency of injuries secondary to terrorist attack explosion is globally increasing. Like any other country, our country experienced multiple suicide bombings in recent years. Otologic injuries may be observed after these kinds of attacks. Considering otologic complaints are well known medical results of explosion attacks, routine otologic evaluation in the first examining hospital-even in case of no relevant complaint- is crucial for establishing causal relation in following forensic medicine evaluation. In this study, 33 cases from 6 suicide bomber attacks in 4 different incidents that happened in Turkey were evaluated for otologic injuries. Two out of three patients were not evaluated for otologic injuries in their first hospital visit. It was considered that 8 cases had a loss of hearing and 9 cases had tympanic membrane rupture secondary to the explosion. Complaints such as hearing loss and tinnitus very often after a bomb attack, we saw that 22 of 33 included patients did not have an ear nose, and throat examination at the time of the incident. In this kind of attack, there can be various life-threatening injuries and therefore relatively less important evaluations such as ENT examination can often be overlooked.

Correlation of blast-induced tympanic membrane perforation with peripheral cochlear synaptopathy

The auditory organs, including the tympanic membrane, cochlea, and central auditory pathway, are the most fragile components of the human body when exposed to blast overpressure. Tympanic membrane perforation (TMP) is the most frequent symptom in blast-exposed patients. However, the impact of TMP on the inner ear and central auditory system is not fully understood. We aimed to analyze the effect of blast-induced TMP on the auditory pathophysiological changes in mice after blast exposure. Mice aged 7 weeks were exposed to blast overpressure to induce TMP and allowed to survive for 2 months. All TMP cases had spontaneously healed by week 3 following the blast exposure. Compared to controls, blast-exposed mice exhibited a significant elevation in hearing thresholds and an apparent disruption of stereocilia in the outer hair cells, regardless of the occurrence or absence of TMP. The reduction in synapses in the inner hair cells, which is known as the most frequent pathology in blast-exposed cochleae, was significantly more severe in mice without TMP. However, a decrease in the number of excitatory central synapses labeled by VGLUT-1 in the cochlear nucleus was observed regardless of the absence or presence of TMP. Our findings suggest that blast-induced TMP mitigates peripheral cochlear synaptic disruption but leaves the central auditory synapses unaffected, indicating that central synaptic disruption is independent of TMP and peripheral cochlear synaptic disruption. Synaptic deterioration in the peripheral and central auditory systems can contribute to the promotion of blast-induced hearing impairment, including abnormal auditory perception.

Long-Term Sensorineural Hearing Loss in Patients With Blast-Induced Tympanic Membrane Perforations

OBJECTIVE

To describe characteristics of sensorineural hearing loss (SNHL) in patients with blast-induced tympanic membrane (TM) perforations that required surgery.

DESIGN

A retrospective review of hearing outcomes in those who had tympanoplasty for combat blast-induced TM perforations. These were sequential cases from one military otolaryngologist from 2007 to 2012. A total of 87 patients were reviewed, and of those, 49 who had appropriate preinjury, preoperative, and long-term audiograms were included. Those with pre-existing hearing loss were excluded. Preinjury audiograms were used to assess how sensorineural thresholds changed in the ruptured ears, and in the contralateral ear in those with unilateral perforations.

RESULTS

The mean time from injury to the final postoperative audiogram was 522 days. In the ears with TM perforations, 70% had SNHLs of 10 dB or less (by bone conduction pure tone averages). Meanwhile, approximately 8% had threshold shifts >30 dB, averaging 50 dB. The strongest predictor of severe or profound hearing loss was ossicular discontinuity. Thresholds also correlated with bilateral injury and perforation size. In those with unilateral perforations, the SNHL was almost always larger on the side with the perforation. Those with SNHL often had a low-to-mid frequency threshold shift and, in general, audiograms that were flatter across frequencies than those of a typical population of military personnel with similar levels of overall hearing loss.

CONCLUSIONS

There is a bimodal distribution of hearing loss in those who experience a blast exposure severe enough to perforate at least one TM. Most ears recover close to their preinjury thresholds, but a minority experience much larger sensorineural threshold shifts. Blast exposed ears also tend to have a flatter audiogram than most service members with similar levels of hearing loss.

Effect of shock wave power spectrum on the inner ear pathophysiology in blast-induced hearing loss

Blast exposure can induce various types of hearing impairment, including permanent hearing loss, tinnitus, and hyperacusis. Herein, we conducted a detailed investigation of the cochlear pathophysiology in blast-induced hearing loss in mice using two blasts with different characteristics: a low-frequency dominant blast generated by a shock tube and a high-frequency dominant shock wave generated by laser irradiation (laser-induced shock wave). The pattern of sensorineural hearing loss (SNHL) was low-frequency- and high-frequency-dominant in response to the low- and high-frequency blasts, respectively. Pathological examination revealed that cochlear synaptopathy was the most frequent cochlear pathology after blast exposure, which involved synapse loss in the inner hair cells without hair cell loss, depending on the power spectrum of the blast. This pathological change completely reflected the physiological analysis of wave I amplitude using auditory brainstem responses. Stereociliary bundle disruption in the outer hair cells was also dependent on the blast’s power spectrum. Therefore, we demonstrated that the dominant frequency of the blast power spectrum was the principal factor determining the region of cochlear damage. We believe that the presenting models would be valuable both in blast research and the investigation of various types of hearing loss whose pathogenesis involves cochlear synaptopathy.

Acute High Level Noise Exposure Can Cause Physiological Dysfunction in Macaque Monkeys: Insight on the Medical Protection for Special Working Environmental Personnel

The high level noise caused by intense acoustic weapons and blasting is a common source of acute acoustic trauma faced by some special environmental personnel. Studies have shown that high level noise can cause auditory and non-auditory effects. However, there are few reports on the biological effects, especially the non-auditory effects of acute high level noise exposure in simulated special working environments, and the great differences between experimental animals and human beings make it difficult to extrapolate from research conclusions. In this study, macaque monkeys were used to detect the effects of acute high level noise exposure on hearing, cognition, and cardiovascular function. Auditory brainstem response, auditory P300, and electrocardiogram (ECG) of macaque monkeys were measured. Results showed that acute high level noise exposure caused permanent hearing threshold shifts; partial hearing loss which couldn’t recover to normal levels in the detection period; pathological changes in T wave and QRS complexes; and large fluctuations in cognitive ability after exposure, which finally recovered to normal. These alterations may be a combination of effects caused by stress-induced neuroendocrine dysfunction and mechanical damage of auditory organs. To elaborate the exact mechanism, further studies are still needed. Meanwhile, positive measures should be taken to reduce the incidence of acute high level noise injury.

Impact of TBI, PTSD, and Hearing Loss on Tinnitus Progression in a US Marine Cohort

INTRODUCTION

Mild TBI (TBI) is associated with up to a 75.7% incidence of tinnitus, and 33.0% of tinnitus patients at the US Veterans Administration carry a diagnosis of post-traumatic stress syndrome (PTSD). Yet factors contributing to new onset or exacerbation of tinnitus remain unclear.

MATERIALS AND METHODS

Here we measure intermittent and constant tinnitus at two time points to ascertain whether pre-existing or co-occurring traumatic brain injury (TBI), hearing loss, or post-traumatic stress disorder (PTSD) predicts new onset, lack of recovery and/or worsening of tinnitus in 2,600 United States Marines who were assessed before and after a combat deployment.

RESULTS

Ordinal regression revealed that constant tinnitus before deployment was likely to continue after deployment (odds ratio [OR] = 28.62, 95% confidence interval [CI]: 9.84,83.26). Prior intermittent tinnitus increased risk of post-deployment constant tinnitus (OR = 4.95, CI: 2.97,8.27). Likelihood of tinnitus progression increased with partial PTSD (OR = 2.39, CI: 1.50,3.80) and TBI (OR = 1.59, CI: 1.13,2.23), particularly for blast TBI (OR = 2.01, CI: 1.27,3.12) and moderate to severe TBI (OR = 2.57, CI: 1.46,4.51). Tinnitus progression also increased with low frequency hearing loss (OR = 1.94, CI: 1.05,3.59), high frequency loss (OR = 3.01, CI: 1.91,4.76) and loss across both low and high frequency ranges (OR = 5.73, CI: 2.67,12.30).

CONCLUSIONS

Screening for pre-existing or individual symptoms of PTSD, TBI, and hearing loss may allow for more focused treatment programs of comorbid disorders. Identification of those personnel vulnerable to tinnitus or its progression may direct increased acoustic protection for those at risk.

Update on treatment options for blast-induced hearing loss

PURPOSE OF REVIEW

The incidence of blast injuries has increased, and the ear is the highest risk organ. Ear injury induced by blast exposure is important in both military and civilian conditions. The permanent hearing loss caused by blast exposure is associated with a decline in the quality of life. In this review, I describe recent therapeutic strategies for each of the ear pathologies caused by blast exposure.

RECENT FINDINGS

For tympanic membrane perforation after blast exposure, basic fibroblast growth factor (bFGF) has been used as a less invasive treatment to repair the tympanic membrane. The closure rates of tympanic membrane perforations treated with bFGF were reported to be comparable to those following conventional tympanoplasty.For sensorineural hearing loss after blast exposure, treatment with neurotrophic factors, such as nerve growth factor (NGF) or neurotrophin-3, antioxidants, and Atoh1 induction have recently been applied, and some of them were considered for clinical application.

SUMMARY

Recent advances of therapeutics for blast-induced hearing loss, based on their pathologies, have been outlined. There are several promising therapeutic approaches for both middle and inner ear disorders after blast exposure; however, further research is needed to establish new treatments for blast-induced hearing dysfunction.

The Development of a Tympanic Membrane Model and Probabilistic Dose-Response Risk Assessment of Rupture Because of Blast

INTRODUCTION

There is no dose-response model available for the assessment of the risk of tympanic membrane rupture (TMR), commonly known as eardrum rupture, from exposures to blast from nonlethal flashbangs, which can occur concurrently with temporary threshold shift. Therefore, the objective of this work was to develop a fast-running, lumped parameter model of the tympanic membrane (TM) with probabilistic dose-dependent prediction of injury risk.

MATERIALS AND METHODS

The lumped parameter model was first benchmarked with a finite element model of the middle ear. To develop the dose-response curves, TMR data from a historic cadaver study were utilized. From these data, the binary probability response was constructed and logistic regression was applied to generate the respective dose-response curves at moderate and severe eardrum rupture severity.

RESULTS

Hosmer-Lemeshow statistical and receiver operation characteristic analyses showed that maximum stored TM energy was the overall best dose metric or injury correlate when compared with total work and peak TM pressure.

CONCLUSIONS

Dose-response curves are needed for probabilistic risk assessments of unintended effects like TMR. For increased functionality, the lumped parameter model was packaged as a software library that predicts eardrum rupture for a given blast loading condition.

Assessment of hearing loss induced by tympanic membrane perforations under blast environment

PURPOSES

This study provides an approach to estimating tympanic membrane perforation-induced hearing loss (HL) using a human middle ear model.

METHODS

Sixty-one cases of tympanic membrane perforation originating from fireworks were reported from the Ear-Nose-Throat Department. The otoscope, audiometry data and diagnosis records were organized, and gender, age, etiology, perforation size and diseased ear side were classified as independent variables. A multinomial regression model was used to analyze the potential effects of the variables on HL. Meanwhile, a human middle ear model was implemented to calculate the ensued HL resulting from different perforation areas and sites. In addition, linear regression models were used to establish functions between perforation size and HL.

RESULTS

The audiometry data indicate that HL at high frequencies (f > 2 kHz) is much more profound than that at the speech frequency band (f < 1 kHz). Compared with mild HL (<15 dB), mediate HL (15-30 dB) was correlated with the perforation area (p < 0.05, 95% CI), while severe HL (>30 dB) was affected by both perforation size and age (p < 0.05, 95% CI). However, other factors, including gender and diseased ear side, do not show a statistically significant effect on HL. Furthermore, the Kruskal-Wallis test result reveals that HL at frequencies of 0.25 kHz ≤ f ≤ 8 kHz is strongly associated with the perforation size (p < 0.05, 95% CI).

CONCLUSIONS

It is conclusive that HL is positively proportional to the perforation size. However, HL is not correlated with the perforation site for small perforation areas of < 10% (p > 0.05, 95% CI).

Traumatic Injuries of the Ear, Nose and Throat

This article reviews the presentation, diagnosis, and management of common traumatic injuries of the ear, nose, and throat, including laryngeal trauma, auricular and septal hematomas, and tympanic membrane rupture.

Blast-induced cochlear synaptopathy in chinchillas

When exposed to continuous high-level noise, cochlear neurons are more susceptible to damage than hair cells (HCs): exposures causing temporary threshold shifts (TTS) without permanent HC damage can destroy ribbon synapses, permanently silencing the cochlear neurons they formerly activated. While this "hidden hearing loss" has little effect on thresholds in quiet, the neural degeneration degrades hearing in noise and may be an important elicitor of tinnitus. Similar sensory pathologies are seen after blast injury, even if permanent threshold shift (PTS) is minimal. We hypothesized that, as for continuous-noise, blasts causing only TTS can also produce cochlear synaptopathy with minimal HC loss. To test this, we customized a shock tube design to generate explosive-like impulses, exposed anesthetized chinchillas to blasts with peak pressures from 160-175 dB SPL, and examined the resultant cochlear dysfunction and histopathology. We found exposures that cause large >40 dB TTS with minimal PTS or HC loss often cause synapse loss of 20-45%. While synaptopathic continuous-noise exposures can affect large areas of the cochlea, blast-induced synaptopathy was more focal, with localized damage foci in midcochlear and basal regions. These results clarify the pathology underlying blast-induced sensory dysfunction, and suggest possible links between blast injury, hidden hearing loss, and tinnitus.

Neurological disease in the aftermath of terrorism: a review

The purpose of our review is to discuss current knowledge on long-term sequelae and neurological disorders in the aftermath of a terrorist attack. The specific aspects of both psychological and physical effects are mentioned in more detail in this review. Also, the outcomes such as stress-related disorders, cardiovascular disease, and neurodegenerative disease are explained. Moreover, PTSD and posttraumatic structural brain changes are a topic for further investigations of the patients suffering from these attacks. Not only the direct victims are prone to the after effects of the terroristic attacks, but the rescue workers, physicians, witnesses and worldwide citizens may also be affected by PTSD and other neurological diseases as well. The determination of a whole series of risk factors for developing neurological disorders can be a means to set up early detection, preventative measures, to refine treatment and thus to gain better outcome in the future.

Analysis of Otologic Injuries Due to Blast Trauma by Handmade Explosives

Objective

The aim of this study is to identify the otologic injuries due to handmade explosive-welded blast travma in the law enforcement officers during the combat operations in the curfew security region and to specify the disorders that Otolaryngology and Head Neck Surgery (OHNS) physicians can face during such operations.

Methods

Medical records of patients in law enforcement who were initially treated by OHNS physicians of Silopi State Hospital during combat operations, between December 14, 2015 and January 15, 2016 were reviewed. Twenty-five patients with otologic injuries due to blast trauma were included in the study. Trauma characteristics, physical examination findings, and beginning treatments were identified.

Results

Primary blast injury (PBI) was identified as the major disorder in all 24 cases. Tinnitus and hearing loss were the most frequent complaints. In physical examination, tympanic membrane perforations were found in four ears of three patients. Oral methylprednisolone in decreasing doses for 10 days was commenced as an initial treatment in patients with PBI. Secondary blast injury presented in the form of soft tissue damage in the auricular helix due to shrapnel pieces in one patient and a minor surgery was performed.

Conclusion

Otologic injuries due to blast trauma may often develop during this type of combat operations. Otologic symptoms should be checked, otoscopic examination should be performed, and patients should consult OHNS physicians as soon as possible after trauma.

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.

Blast-induced hearing loss

The incidence of blast injury has increased recently. As the ear is the organ most sensitive to blast overpressure, the most frequent injuries seen after blast exposure are those affecting the ear. Blast overpressure affecting the ear results in sensorineural hearing loss, which is untreatable and often associated with a decline in the quality of life. Here, we review recent cases of blast-induced hearing dysfunction. The tympanic membrane is particularly sensitive to blast pressure waves, since such waves exert forces mainly at air-tissue interfaces within the body. However, treatment of tympanic membrane perforation caused by blast exposure is more difficult than that caused by other etiologies. Sensorineural hearing dysfunction after blast exposure is caused mainly by stereociliary bundle disruption on the outer hair cells. Also, a reduction in the numbers of synaptic ribbons in the inner hair cells and spiral ganglion cells is associated with hidden hearing loss, which is strongly associated with tinnitus or hyperacusis.

Brain Metabolic Changes in Rats following Acoustic Trauma

Acoustic trauma is the most common cause of hearing loss and tinnitus in humans. However, the impact of acoustic trauma on system biology is not fully understood. It has been increasingly recognized that tinnitus caused by acoustic trauma is unlikely to be generated by a single pathological source, but rather a complex network of changes involving not only the auditory system but also systems related to memory, emotion and stress. One obvious and significant gap in tinnitus research is a lack of biomarkers that reflect the consequences of this interactive "tinnitus-causing" network. In this study, we made the first attempt to analyse brain metabolic changes in rats following acoustic trauma using metabolomics, as a pilot study prior to directly linking metabolic changes to tinnitus. Metabolites in 12 different brain regions collected from either sham or acoustic trauma animals were profiled using a gas chromatography mass spectrometry (GC/MS)-based metabolomics platform. After deconvolution of mass spectra and identification of the molecules, the metabolomic data were processed using multivariate statistical analysis. Principal component analysis showed that metabolic patterns varied among different brain regions; however, brain regions with similar functions had a similar metabolite composition. Acoustic trauma did not change the metabolite clusters in these regions. When analyzed within each brain region using the orthogonal projection to latent structures discriminant analysis sub-model, 17 molecules showed distinct separation between control and acoustic trauma groups in the auditory cortex, inferior colliculus, superior colliculus, vestibular nucleus complex (VNC), and cerebellum. Further metabolic pathway impact analysis and the enrichment overview with network analysis suggested the primary involvement of amino acid metabolism, including the alanine, aspartate and glutamate metabolic pathways, the arginine and proline metabolic pathways and the purine metabolic pathway. Our results provide the first metabolomics evidence that acoustic trauma can induce changes in multiple metabolic pathways. This pilot study also suggests that the metabolomic approach has the potential to identify acoustic trauma-specific metabolic shifts in future studies where metabolic changes are correlated with the animal's tinnitus status.

Pathophysiology of the inner ear after blast injury caused by laser-induced shock wave

The ear is the organ that is most sensitive to blast overpressure, and ear damage is most frequently seen after blast exposure. Blast overpressure to the ear results in sensorineural hearing loss, which is untreatable and is often associated with a decline in the quality of life. In this study, we used a rat model to demonstrate the pathophysiological and structural changes in the inner ear that replicate pure sensorineural hearing loss associated with blast injury using laser-induced shock wave (LISW) without any conductive hearing loss. Our results indicate that threshold elevation of the auditory brainstem response (ABR) after blast exposure was primarily caused by outer hair cell dysfunction induced by stereociliary bundle disruption. The bundle disruption pattern was unique; disturbed stereocilia were mostly observed in the outermost row, whereas those in the inner and middle rows stereocilia remained intact. In addition, the ABR examination showed a reduction in wave I amplitude without elevation of the threshold in the lower energy exposure group. This phenomenon was caused by loss of the synaptic ribbon. This type of hearing dysfunction has recently been described as hidden hearing loss caused by cochlear neuropathy, which is associated with tinnitus or hyperacusis.

Posttraumatic dizziness and vertigo

Traumatic brain injury is an increasingly common public health issue, with the mild variant most clinically relevant for this chapter. Common causes of mild traumatic brain injury (mTBI) include motor vehicle accidents, athletics, and military training/deployment. Despite a range of clinically available testing platforms, diagnosis of mTBI remains challenging. Symptoms are primarily neurosensory, and include dizziness, hearing problems, headaches, cognitive, and sleep disturbances. Dizziness is nearly universally present in all mTBI patients, and is the easiest symptom to objectify for diagnosis. Aside from a thorough history and physical exam, in the near future specialized vestibular function tests will be key to mTBI diagnosis. A battery of oculomotor (antisaccade, predictive saccade) and vestibular tasks (head impulse test) has been demonstrated to sensitively and specifically identify individuals with acute mTBI. Vestibular therapy and rehabilitation have shown improvements for mTBI patients in cognitive function, ability to return to activities of daily living, and ability to return to work. Dizziness, as a contributor to short- and long-term disability following mTBI, is ultimately crucial not only for diagnosis but also for treatment.

Noise-induced hearing loss: a military perspective

PURPOSE OF REVIEW

To summarize relevant literature occurring over the past 12-18 months forwarding understanding of noise-induced hearing loss in relation to military service.

RECENT FINDINGS

Hearing loss prior to entry into military service is highly predictive of subsequent hearing loss and hearing loss disability. Tightly controlled organic solvent exposure may not be a significant risk factor for noise-induced hearing loss. Increasingly detailed analysis of high intensity noise, impulse and blast noise exposures, and the methods used to mitigate these exposures are leading to breakthroughs in understanding and predicting hearing loss in military service.

SUMMARY

Prevention, mitigation, treatment, and prediction of the effects of hazardous noise exposure in military service continue to require a multidisciplinary team of individuals from around the world fully aware of the detrimental effect to service members and their societies of hearing loss disability.