Acute Acoustic Trauma Research Articles

Recovery rate after acute acoustic trauma: a case series and meta-analysis.

Steroids given systemically, locally, or both are the mainstay of treatment for acute acoustic trauma (AAT). The overall recovery rate (full, partial, and none) is undetermined. Original case series and systematic literature review. Case series of a tertiary referral center and a systematic literature review. Cases of AAT between 2012 and 2022 were retrospectively analyzed for demographics, acoustic trauma characteristics, treatment modality and delay and prognosis. This case series was added to the series identified by a systematic literature review. This review included "Medline" via "PubMed", "EMBASE", and "Google scholar". All series were pooled for meta-analysis defining prognosis following steroidal treatment for AAT patients. The pooled analyses included 662 ears, out of which 250 underwent complete recovery of hearing (overall proportion = 0.2809, 95%confidence interval [CI] = 0.1611-0.4178). Any recovery was recorded for 477 ears (overall proportion = 0.7185, 95% CI = 0.5671-0.8493) and no recovery was documented for 185 ears (overall proportion = 0.2815, 95% CI = 0.1507-0.4329). The rate of overall recovery for AAT is around 70%, and around 30% for full recovery when steroids are initiated within the first 2 weeks following the insult.

Состояние слухового анализатора на фоне акустической травмы. Экспериментальное исследование

Sensorineural hearing loss is a pressing medical and social problem of modern society. A large proportion of the population is at risk of acoustic injury every day. The high incidence of acoustic trauma, coupled with insufficient diagnosis and treatment, necessitates experimental studies to identify the mechanisms of injury and to develop effective prevention and treatment. The similarities in the anatomy and physiology of the auditory analyzer of mice and humans, the relatively inexpensive keeping, and the available set of genetic tools make the mouse model extremely useful in hearing organ research. The purpose of the study was to assess changes in the auditory function of mice caused by acute acoustic trauma. The simulation of the acoustic trauma was carried out using narrow-band noise with a basic frequency of 4,000–6,000 Hz of high intensity for 4 hours. As a result, a significant increase (deterioration) in hearing thresholds was recorded in all voiced mice. On the 5th, 14th, and 28th days, there was a change in hearing in most mice. Hearing changes were uneven over time. The greatest improvement occurred from the 1st to the 5th day. With further observation, the rate of hearing recovery decreased. On the 28th day, no hearing restoration occurred in any mouse. Experimental model of acute acoustic trauma with damage parameters in this work combined with the recording of short-latency auditory induced potentials (SAEPs) can be used in further study of different types of hearing loss and development of methods of their treatment.

Long-Term Hearing Loss after Acute Acoustic Trauma inthe French Military: A Retrospective Study.

Acute acoustic trauma (AAT) is characterized by cochlea-vestibular signs following intense noise exposure, often caused by impulse noise. French military faces a high risk of AAT because of the use of weapons with peak sound levels exceeding 150 dB. Hearing loss (HL) resulting from AAT can have a significant impact on quality of life and operational capacity. The aim of this study was to assess the prevalence of long-term hearing impairment after AAT. The study involved a retrospective review of computer-based patient records from four military medical centers in Northeast France between January 2016 and December 2021. The inclusion criteria required the presence of cochlea-vestibular signs following impulse acoustic exposure and the absence of other causes. Sociodemographic and clinical data were collected, including audiometric data before and after exposure. The primary end point was the presence of a threshold elevation greater than 10 dB between reference and late audiograms. A total of 419 patients were included in the analysis, with a majority of males (n = 419; 84.7%) and a mean age of 23.6 yrs. The most common causative agent was the 5.56-mm assault rifle (n = 327; 78.0%). Tinnitus was the most frequent symptom (n = 366; 87.4%), followed by hypoacusis (n = 147; 35.1%) and earache (n = 89; 21.2%). The initial audiograms showed no HL in 31.0% of cases, while the mean deficit across all frequencies was 15.4 dB. All patients received corticosteroid therapy, with a mean duration of 6.0 d. Late audiograms conducted at an average interval of 448.0 d after AAT revealed a prevalence of long-term HL exceeding 20%. Higher doses of corticosteroid therapy (>1 mg/kg) were associated with a reduced frequency of long-term HL. This study highlights the prevalence of long-term hearing impairment after AAT in the French military. The findings emphasize the importance of preventive measures, including proper use of hearing protection devices, and the need for timely diagnosis and treatment. Further research is warranted to explore gender susceptibility to AAT and evaluate the impact of different weapons on AAT characteristics. The study also underscores the potential benefits of higher doses of corticosteroid therapy in reducing the risk of long-term hearing impairment. Overall, the findings contribute to a better understanding of AAT and can inform strategies for its prevention and management in military settings.

Acute Acoustic Trauma after Exposure to Assault Rifle Noise among Conscripts in the Finnish Defence Forces—A Population-Based Survey

Conscripts are exposed to various sources of impulse noise despite hearing protection recommendations. The aim of this study was to investigate the frequency of acute acoustic trauma (AAT) among conscripts after exposure to assault rifle noise in the Finnish Defence Forces (FDF). This nationwide population-based cohort comprised all conscripts (>220,000) in the FDF during the years 1997-2003 and 2008-2010. We included those who claimed to have AAT symptoms from assault rifle noise during the study periods. During the investigated 10 years, 1617 conscripts (annual variation, 75-276) experienced a new hearing loss due to AAT. Altogether, 1456 (90%) of all AAT-induced hearing losses were caused by rifle-caliber weapons and 1304 (90%) of them when firing a blank cartridge. There was no clear diminishing trend in the annual numbers of AATs. In 1277 (88%) incidents, no hearing protector was used. Tinnitus was the most prominent symptom. Hearing losses after AAT were typically mild, but serious deficits also occurred. In conclusion, we found that 0.7-1.5% of the conscripts experienced an AAT during their service in the FDF. Most incidents occurred when firing a blank cartridge with a rifle-caliber weapon and with no hearing protector in use.

Peculiarities of the acoustic reflex registration thresholds in relation to the parameters of the thresholds tone audiometry in patients with acute combat trauma

Aim: study of threshold ratios between indicators of acoustic impedance and threshold tonal audiometry in military personnel – participants in hostilities. Materials and methods: the results of audiometric and impedancemetric examinations of 43 servicemen aged 18 to 42 years who received combat acute trauma in the period March-August 2022 and 20 patients with severe sensorineural deafness (2, 3, 4 stages according international classification) of non-acutraumatic genesis as a comparison group. Results and their discussion: During the examination of 43 soldiers, it was found that with significant sensorineural hearing loss on both sides (3 and 4 stages according international classification), the patients registered a full-fledged acoustic reflex during ipsilateral and contralateral stimulation. When conducting an impedanceometric examination of patients in the comparison group, it was found that in most patients the acoustic reflex was not registered at all. Conclusions: 1. In combat acute acoustic trauma, it is possible to register acoustic middle-ear-muscle reflex with severe hearing loss, which may be caused by damage to the receptor part of the auditory analyzer and the accompanying symptom of the phenomenon of accelerated loudness, by a central mechanism, or by a combination of central and peripheral mechanisms. 2. Dissociation of acoustic middle-ear-muscle reflex threshold values and threshold tonal audiometry is a characteristic feature of acutraumatic damage to the auditory analyzer. 3. Identified features, such as registration of acoustic middle-ear-muscle reflex in severe hearing loss, dissociation of acoustic reflex thresholds and tonal audiometry may be useful for further study of the pathogenesis of combat acute trauma, which, in turn, will contribute to improving the quality of diagnosis and finding ways to correct disorders of the auditory system in individuals, who suffered as a result of hostilities.

Noise-Induced Hearing Loss in Police Officers: Systematic Review.

Introduction:Noise-induced hearing loss (NIHL) is defined as the sensorineural hearing loss caused by acute acoustic trauma or chronic exposure to high-intensity noises. Exposure to noises can lead to irreversible damage to the inner ear and, consequently, to a permanent shift of the hearing threshold. Police officers are particularly at risk of acute or chronic hearing damages. The aim of this study is to evaluate the hearing loss of police officers in relation to the occupational risk factors and clinical-anamnestic characteristics by collecting and analyzing existing data and evidence available in public databases.Materials and Methods:A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses group (PRISMA). Studies were included if they met inclusion and exclusion criteria. Study selection, data extraction, and quality assessment were conducted independently by two researchers. Results:Our initial literature search yielded 29 peer-reviewed articles. Out of 29 papers, only 10 were included in the review, after inclusion and exclusion criteria were applied the.Conclusions:Hypertension, smoking and alcohol intake significantly affect hearing performance. In addition, a history of acoustic trauma, use of ototoxic drugs, exposure to noise in leisure-time activities and failure to use ear protectors are often found in a fair number of subjects. NIHL is also related to the age of the subjects as well as the extent and duration of noise exposure. Furthermore, NIHL is also influenced by shooting practice sessions police officers are required to undertake as well as by the chronic exposure to traffic noise, especially in motorcycle police officers.

Hydrogen Gas Inhalation Attenuates Acute Impulse Noise Trauma: A Preclinical In Vivo Study.

Molecular hydrogen (H2) has shown therapeutic potential in several oxidative stress-related conditions in humans, is well-tolerated, and is easily administered via inhalation.The aim of this preclinical in vivo study was to investigate whether impulse noise trauma can be prevented by H2 when inhaled immediately after impulse noise exposure. Guinea pigs (n = 26) were subjected to impulse noise (n = 400; 156 dB SPL; 0.33/s; n = 11; the Noise group), to impulse noise immediately followed by H2 inhalation (2 mol%; 500 ml/min; 1 hour; n = 10; the Noise + H2 group), or to H2 inhalation (n = 5; the H2 group). The acoustically evoked ABR threshold at 3.15, 6.30, 12.5, 20.0, and 30.0 kHz was assessed before and 4 days after impulse noise and/or H2 exposure. The cochleae were harvested after the final ABR assessment for quantification of hair cells. Noise exposure caused ABR threshold elevations at all frequencies (median 35, 35, 30, 35, and 35 dB SPL, the Noise group; 20, 25, 10, 13, and 20 dB SPL, the Noise + H2 group; P < .05) but significantly less so in the Noise + H2 group (P < .05). Outer hair cell (OHC) loss was in the apical, mid, and basal regions 8.8%, 53%, and 14% in the Noise group and 3.5%, 22%, and 1.2% in the Noise + H2 group. The corresponding inner hair cell (IHC) loss was 0.1%, 14%, and 3.5% in the Noise group and 0%, 2.8%, and 0% in the Noise + H2 group. The difference between the groups was significant in the basal region for OHCs (P = .003) and apical (P = .033) and basal (P = .048) regions for IHCs. Acute acoustic trauma can be reduced by H2 when inhaled immediately after impulse noise exposure.

Efficacy of Oral Steroids for Acute Acoustic Trauma

Objective: This study aimed to study the effect of steroid treatment on new-onset sensorineural hearing loss (SNHL) in subjects presenting shortly after an audiometry-confirmed acute acoustic trauma (AAT) injury. Study Design: This is a case-control study. Methods: We identified healthy military personnel who presented with AAT injury to the Israeli Defense Forces Medical Corps Otolaryngology/Audiology Services during 2016–2020. Patients were nonrandomly allocated to a treatment arm, where they received steroids (prednisone, 1 mg/kg, 60 mg maximal daily dose), administered for either ≥7 days or <7 days, or to a control arm, in which no treatment was offered besides loud noise avoidance. Audiometries were conducted within 7 days following the AAT and within 1 month later. We compared changes in bone conduction (BC) and air conduction (AC) thresholds at 2–8 kHz. Results: Of the 263 enrolled subjects, 137 (52%) received steroids and 126 (48%) received no treatment. Subjects who were treated early (<24 h) with high-dose steroids and for ≥7 days demonstrated significantly better hearing outcomes, compared with the nontreatment group. Subjects in the steroids group demonstrated 13–14 dB average improvement in BC thresholds at 3 and 4 kHz (p = 0.001) and additional 7–8 dB average improvement in AC thresholds at 6 and 8 kHz, compared with the nontreatment group (p < 0.0001). These observations were more compelling in patients who initially presented with worse hearing losses (>35 dB). No statistically significant differences were observed in AC/BC pure tone average between the two groups. Conclusions: Early oral steroids are recommended in AAT injuries and were shown to improve hearing outcomes within 1 month.

An Overview of Noise-Induced Hearing Loss: Systematic Review

The term &quot;noise-induced hearing loss&quot; (NIHL) refers to sensorineural hearing loss brought on by either acute acoustic trauma or prolonged exposure to loud noises. Noise exposure has the potential to permanently change the hearing threshold due to irreparable damage to the inner ear. Many risk factors affect the incidence of NIHL including personal factors; such as genetic factors, age, sex, and lifestyle; and elements relating to the noise; such as the length of exposure, its volume, a

Метаболические изменения в эндолимфе при профилактическом и лечебном применении производного триазино-индола на модели акустической травмы

Objective of the study. To investigate the effect of triazino-indole derivative on the parameters of glycolysis in the endolymph during preventive and therapeutic use on the model of acoustic trauma. Experimental animals and methods. The experiments were carried out on 82 mice, female F1 hybrids of the CBA and C57BL/6 lines weighing at least 17 g at the age of 4–12 weeks. When simulating an acute acoustic trauma, an animal was exposed to white noise with a level of 107 dB SPL and frequency band 3–100,000 kHz. For therapeutic purposes, a single intravenous injection of a triazino-indole derivative was carried out immediately after noise exposure. The drug was administered at doses of 5, 7, and 10 mg/kg of animal weight. For prophylactic purposes, the intramuscular drug injection was administered before the acoustic trauma application. The drug was administered at doses of 5, 7, and 10 mg/kg of animal weight once a day for 3 days before noise exposure. The Cytoflavin was a reference drug. A normal saline was administered to the control group. When using the acoustic trauma models, the metabolic processes level in the cochlea was assessed by the glucose and lactic acid (lactate) content in the labyrinth fluid before and 2 hours after pathological exposure. Results and discussion. The triazino-indole derivative, both during preventive and therapeutic administration, significantly corrects changes in the glycolysis (glucose, lactate) indicators in the endolymph, thereby improving the bioenergetics of the inner ear cells. The best effect is observed when the drug is administered at a dose of 10 mg/kg. When compared with Cytoflavin, the antihypoxic effect of the triazino-indole derivative is more pronounced.

Effects of Oxygen Therapies in Experimental Acute Acoustic Trauma.

Background: Acute acoustic trauma is defined as a sudden sensorineural hearing loss that occurs after an exposure to acoustic overstimulation. Increasing the oxygen in perilymph can be a treatment modality. Our study aims to investigate the influence of normobaric oxygen therapy on the recovery of acute acoustic trauma and to compare it with the hyperbaric oxygen therapy.Methods:Three groups of rats (5 rats each) were exposed to white noise for 1 hour. Sensorineural hearing loss was identified using distortion product otoacoustic emission. Subsequently, the first group was treated with hyperbaric oxygen therapy, the second group was treated with normobaric oxygen therapy, and the third group did not receive any treatment and was used as a control group.Results:There was a statistically significant difference within time for frequencies of 1, 1.5, and 2 kHz, but there was no statistically significant difference between groups. For frequencies of 3, 4, 5, and 6 kHz, there was a statistically significant difference within time and between groups. Between groups, recovery of distortion product otoacoustic emission values in all frequencies was better in the control group by the third, fifth, and seventh days. Comparing the values of hyperbaric oxygen therapy and normobaric oxygen therapy groups, it was observed that by the third day, the hyperbaric oxygen therapy values were better than those of the normobaric oxygen therapy values. However, by the fifth and seventh days, the normobaric oxygen therapy values were better (except at a frequency of 1 kHz).Conclusion:Because there is a high rate of spontaneous recovery, physicians should be more selective to treat patients with oxygen therapies.

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.

Effect and Biocompatibility of a Cross-Linked Hyaluronic Acid and Polylactide-co-glycolide Microcapsule Vehicle in Intratympanic Drug Delivery for Treating Acute Acoustic Trauma.

The treatment of acute hearing loss is clinically challenging due to the low efficacy of drug delivery into the inner ear. Local intratympanic administration of dexamethasone (D) and insulin-like growth factor 1 (IGF1) has been proposed for treatment, but they do not persist in the middle ear because they are typically delivered in fluid form. We developed a dual-vehicle drug delivery system consisting of cross-linked hyaluronic acid and polylactide-co-glycolide microcapsules. The effect and biocompatibility of the dual vehicle in delivering D and IGF1 were evaluated using an animal model of acute acoustic trauma. The dual vehicle persisted 10.9 times longer (8.7 days) in the middle ear compared with the control (standard-of-care vehicle, 0.8 days). The dual vehicle was able to sustain drug release over up to 1 to 2 months when indocyanine green was loaded as the drug. One-third of the animals experienced an inflammatory adverse reaction. However, it was transient with no sequelae, which was validated by micro CT findings, endoscopic examination, and histological assessment. Hearing restoration after acoustic trauma was satisfactory in both groups, which was further supported by comparable numbers of viable hair cells. Overall, the use of a dual vehicle for intratympanic D and IGF1 delivery may maximize the effect of drug delivery to the target organ because the residence time of the vehicle is prolonged.

It's all about timing, early treatment with hyperbaric oxygen therapy and corticosteroids is essential in acute acoustic trauma

BackgroundAcute acoustic trauma (AAT) is an acute hearing impairment caused by intense noise-impact. The current management strategy for AAT with substantial hearing loss in the Dutch military is the combination therapy with corticosteroids and hyperbaric oxygen therapy (HBOT). In a previous study, early initiation of the combination therapy was associated with better outcomes. Therefore, we performed a new analysis to assess the difference in hearing outcome between patients in whom combination therapy was started within two days, versus after more than two days. MethodsA retrospective analysis was performed on military patients diagnosed with AAT with substantial hearing loss who presented between February 2018 and March 2020. Absolute and relative hearing improvement between first and last audiograms were calculated for all affected frequencies (defined as loss of ≥20 dB on initial audiogram). We also determined the amount of patients who recovered to the level of Dutch military requirement, and performed speech discrimination tests. ResultsIn this analysis, 30 male patients (49 ears) with AAT were included. The median age was 24.5 years (IQR 23–29). The median time to initiation of therapy with corticosteroids and HBOT were one and two days, respectively. HBOT was started within two days in 31 ears, and after more than two days in 18 ears. The mean absolute and relative hearing gains were 18.8 dB (SD 14.6) and 46.8% (SD 31.3) on all affected frequencies. The 100% discrimination/speech perception level improved from 64.0 dB to 51.7 dB (gain 12.3 dB ± 14.1). There was significantly more improvement in absolute and relative hearing improvement when HBOT was started in ≤2 days, compared to >2 days. ConclusionOur analysis shows results in favor of early initiation (≤2 days) of the combination treatment of HBOT and corticosteroids in patients with AAT.

The Use of Hyperbaric Oxygen Therapy and Corticosteroid Therapy in Acute Acoustic Trauma: 15 Years' Experience at the Czech Military Health Service.

Background: Acute acoustic trauma (AAT) ranks, among others, as one common cause of inner ear function impairment, especially in terms of military personnel, who are at an increased exposure to impulse noises from firearms. Aim of this study: 1. We wanted to demonstrate whether early treatment of AAT means a higher chance for the patient to improve hearing after trauma. 2. We find the answer to the question of whether hyperbaric oxygen therapy (HBO2) has a positive effect in the treatment of AAT. Methods: We retrospectively analyzed data for the period 2004–2019 in patients with AAT. We evaluated the therapeutic success of corticosteroids and HBO2 in a cohort of patients with AAT n = 108 patients/n = 141 affected ears. Results: Hearing improvement after treatment was recorded in a total of 111 ears (79%). In terms of the data analysis we were able to ascertain, utilizing success of treatment versus timing: within 24 h following the onset of therapy in 56 (40%) ears—54 (96%) ears had improved; within seven days following the onset the therapy was used in 55 (39%) ears—41 (74%) ears had improved; after seven days the therapy started in 30 (21%) ears—16 (53%) ears had improved. Parameter latency of the beginning of the treatment of AAT was statistically significant (p = 0.001 and 0.017, respectively). The success of the medical protocols was apparent in both groups—group I (treated without HBO2): n = 61 ears, of which 50 (82%) improved, group II (treated with HBO2): n = 73 ears, of which 56 (77%) improved. Group II shows improvement at most frequencies (500–2000 Hz). The most serious sensorineural hearing loss after AAT was at a frequency of 6000 Hz. Conclusion: Analysis of our data shows that there is a statistically significant higher rate of improvement if AAT treatment was initiated within the first seven days after acoustic trauma. Early treatment of AAT leads to better treatment success. HBO2 is considered a rescue therapy for the treatment of AAT. According to our recommendation, it is desirable to start corticosteroid therapy immediately after acoustic trauma. If hearing does not improve during the first seven days of corticosteroid therapy, then HBO2 treatment should be initiated.

A Prospective Study to Elucidate the Efficacy of 4 Oral Prednisolone Regimens in Acute Acoustic Trauma.

Noise induced hearing loss affects around 5% of the population and acoustic trauma to military personnel accounts for 30% of all injuries inflicted during active service. Initial treatment for acoustic trauma involves administration of steroids, however there are no studies regarding oral steroid regimens for best outcomes. Comparing and elucidating the benefits of four oral steroid regimens on hearing gain in patients with acute acoustic trauma. A prospective study of 4 different steroid regimens was done in 200 soldiers from July 2014 - July 2020. In the first group, oral Prednisolone 60mg was administered for 6days, in the second group for 8days, in the third group for 10days and in the fourth group for 12days. Medication was tapered over the next 5days in all the groups. Data analysed included demographics, Pure Tone Audiograms at admission and at 4weeks, time of reporting to hospital, onset of treatment and type of treatment given. Multivariate linear regression model was done to consider the risk factors responsible for average hearing gain at all pure tones. Box-and-whisker plot, Mann-Whitney-Wilcoxon test, Kruskal Wallis test, Reciever Operating Characteristic curve were used to analyse the independent samples. p value of < 0.05 was considered statistically significant. Age, time of onset of prednisolone therapy and acoustic trauma due to blast or gunshot injury did not show correlation (R2 = 0.01, 0.01 and 0.35 respectively and p = 0.09, 0.71, 0.80 respectively). Prednisolone therapy, average initial hearing at pure tones were considered as factors responsible for hearing gain as they showed correlation (R2 = 0.22, and 0.34 respectively and p < 0.001 and < 0.01 respectively). Significant hearing gain was found in all groups. The hearing gain was statistically better in group 3 and 4 as compared to group 1 and 2. There was no statistically significant difference in hearing gain between groups 3 and 4. So there was no additional advantage of giving 60mg oral prednisolone for more than 10days. The best oral prednisolone regimen recommended is 60mg/day for 10days which is tapered over the next 5days.

Noise-Induced Hearing Loss Treatment: Systematic Review and Meta-analysis.

To determine the efficacy of steroid and hyperbaric oxygen therapy (HBOT) in the setting of acute noise-induced hearing loss. Systematic review and meta-analysis of noise-induced hearing loss treatment studies that reported on patients who (1) reported individual frequencies up to 8,000 Hz with mean and SDs; (2) were treated only with steroids ± HBOT; and (3) sustained acute acoustic trauma. The Newcastle-Ottawa Scale was used to assess risk of bias across cohorts. Data sources were Embase, Web of Science, Cochrane Databases (via Ovid EBM Reviews), and PubMed. Four studies were of retrospective cohorts and one of a prospective cohort. Only one study examined blast acoustic trauma, and the remaining four examined gunfire acoustic trauma. This meta-analysis used a random-effects model for pure tone average (PTA) (0.5, 1, and 2 kHz) and "high-frequency" PTA (HPTA) (4, 6, and 8 kHz) for the five studies included. Steroid therapy demonstrated a 6.55-dB (95% CI, 0.08-13.17 dB) PTA (n = 55) improvement and a 9.02-dB (95% CI, 1.45-16.59 dB) HPTA (n = 71) improvement. Steroid with HBOT demonstrated a 7.00-dB (95% CI, 0.84-13.17 dB) PTA (n = 133) improvement and a 12.41-dB (95% CI, 3.97-20.86 dB) HPTA (n = 150) improvement. According to our statistical analysis of the pooled studies' heterogeneity, there was moderate inconsistency in the cross-study results of both treatment groups. Steroids with or without HBOT appear to improve both low and high hearing thresholds following acoustic trauma. Future studies will require inclusion of control groups, precise definition of acoustic trauma intensity and duration, and genetic polymorphisms.

Hsp70/Bmi1-FoxO1-SOD Signaling Pathway Contributes to the Protective Effect of Sound Conditioning against Acute Acoustic Trauma in a Rat Model.

Sound conditioning (SC) is defined as “toughening” to lower levels of sound over time, which reduces a subsequent noise-induced threshold shift. Although the protective effect of SC in mammals is generally understood, the exact mechanisms involved have not yet been elucidated. To confirm the protective effect of SC against noise exposure (NE) and the stress-related signaling pathway of its rescue, we observed target molecule changes caused by SC of low frequency prior to NE as well as histology analysis in vivo and verified the suggested mechanisms in SGNs in vitro. Further, we investigated the potential role of Hsp70 and Bmi1 in SC by targeting SOD1 and SOD2 which are regulated by the FoxO1 signaling pathway based on mitochondrial function and reactive oxygen species (ROS) levels. Finally, we sought to identify the possible molecular mechanisms associated with the beneficial effects of SC against noise-induced trauma. Data from the rat model were evaluated by western blot, immunofluorescence, and RT-PCR. The results revealed that SC upregulated Hsp70, Bmi1, FoxO1, SOD1, and SOD2 expression in spiral ganglion neurons (SGNs). Moreover, the auditory brainstem responses (ABRs) and electron microscopy revealed that SC could protect against acute acoustic trauma (AAT) based on a significant reduction of hearing impairment and visible reduction in outer hair cell loss as well as ultrastructural changes in OHCs and SGNs. Collectively, these results suggested that the contribution of Bmi1 toward decreased sensitivity to noise-induced trauma following SC was triggered by Hsp70 induction and associated with enhancement of the antioxidant system and decreased mitochondrial superoxide accumulation. This contribution of Bmi1 was achieved by direct targeting of SOD1 and SOD2, which was regulated by FoxO1. Therefore, the Hsp70/Bmi1-FoxO1-SOD signaling pathway might contribute to the protective effect of SC against AAT in a rat model.

Hearing Outcomes of Treatment for Acute Noise-induced Hearing Loss: A Systematic Review and Meta-analysis.

To determine the efficacy of various treatment modalities used for acute noise-induced hearing loss (aNIHL) from acute acoustic trauma (AAT) via a systematic review and meta-analysis. PubMed, Cochrane, and Scopus databases. The scientific literature was searched up to October 2018 for articles evaluating hearing outcomes after treatment of aNIHL. The following were extracted: Oxford level of evidence, number of patients, mean age, time to presentation, source of noise exposure, method of treatment/intervention, baseline hearing threshold, posttreatment hearing threshold, hearing gain, proportion of patients with no recovery, partial recovery, or complete recovery, and treatment complications. Sixteen studies with 932 patients met inclusion criteria for systematic review and four studies with 187 patients were included in the meta-analysis. Treatment modalities identified were steroids, vascular agents, nootropics, antioxidants, vitamins, cell apoptosis inhibitors, and hyperbaric oxygen therapy. Meta-analysis demonstrated significant improvement in mean hearing threshold for patients with high-frequency hearing loss, those treated within 48 hours, and those receiving treatment with a nootropic agent. Significant heterogeneity was present in experimental design among included studies and many were of lower levels of evidence. More prospective, large scale, randomized, double-blinded, placebo-controlled clinical trials are required to determine optimal treatment regimens for patients suffering from aNIHL caused by AAT.

Biocompatibility and Therapeutic Effect of 3 Intra-Tympanic Drug Delivery Vehicles in Acute Acoustic Trauma

Introduction: The aim of this study was to assess the biocompatibility of several intra-tympanic (IT) drug delivery vehicles and to compare hearing outcomes. Materials and Methods: After acute acoustic trauma, rats were treated with IT 10 mg/mL dexamethasone phosphate (D) and divided into the following groups for drug delivery: saline + D (n = 15), hyaluronic acid (HA) + D (n = 17), and methoxy polyethylene glycol-b-polycaprolactone block copolymer (MP) + D (n = 24). Results: No inflammation was found in the saline + D or HA + D groups. The duration of vehicle/drug persistence in the bulla was significantly longer for the MP + D (47.5 days) and HA + D groups (1.8 days) than for the saline + D group (<1 day). The tympanic membrane was significantly thicker in the MP + D group than in the saline + D and HA + D groups. The proportion of ears with good hearing outcome was significantly higher (63.6%) in the HA + D group than in the MP + D group. The number of hair cells in the hearing loss (HL) control group was significantly lower than in the MP + D group. Discussion/Conclusion: HA shows great potential as a biocompatible vehicle for D delivery via the IT route, without an inflammatory reaction and with better hearing outcomes. Considering inflammation and hearing, MP may not be a good candidate for IT drug delivery.