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.

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 60 mg was administered for 6 days, in the second group for 8 days, in the third group for 10 days and in the fourth group for 12 days. Medication was tapered over the next 5 days in all the groups. Data analysed included demographics, Pure Tone Audiograms at admission and at 4 weeks, 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 60 mg oral prednisolone for more than 10 days. The best oral prednisolone regimen recommended is 60 mg/day for 10 days which is tapered over the next 5 days.

Review of blast noise and the auditory system

The auditory system is particularly vulnerable to blast injury due to the ear's role as a highly sensitive pressure transducer. Over the past several decades, studies have used a variety of animal models and experimental procedures to recreate blast-induced acoustic trauma. Given the developing nature of this field and our incomplete understanding of molecular mechanisms underlying blast-related auditory disturbances, an updated discussion about these studies is warranted. Here, we comprehensively review well-established blast-related auditory pathology including tympanic membrane perforation and hair cell loss. In addition, we discuss important mechanistic studies that aim to bridge gaps in our current understanding of the molecular and microstructural events underlying blast-induced cochlear, auditory nerve, brainstem, and central auditory system damage. Key findings from the recent literature include the association between endolymphatic hydrops and cochlear synaptic loss, blast-induced neuroinflammatory markers in the peripheral and central auditory system, and therapeutic approaches targeting biochemical markers of blast injury. We conclude that blast is an extreme form of noise exposure. Blast waves produce cochlear damage that appears similar to, but more extreme than, the standard noise exposure protocols used in auditory research. However, experimental variations in studies of blast-induced acoustic trauma make it challenging to compare and interpret data across studies.

Blast injury on harbour porpoises (Phocoena phocoena) from the Baltic Sea after explosions of deposits of World War II ammunition

Harbour porpoises are under pressure from increasing human activities. This includes the detonation of ammunition that was dumped in large amounts into the sea during and after World War II. In this context, forty-two British ground mines from World War II were cleared by means of blasting in the period from 28 to 31 August 2019 by a NATO unit in the German Exclusive Economic Zone within the marine protected area of Fehmarn Belt in the Baltic Sea, Germany. Between September and November 2019, 24 harbour porpoises were found dead in the period after those clearing events along the coastline of the federal state of Schleswig-Holstein and were investigated for direct and indirect effects of blast injury. Health evaluations were conducted including examinations of the brain, the air-filled (lungs and gastrointestinal tract) and acoustic organs (melon, acoustic fat in the lower jaw, ears and their surrounding tissues). The bone structure of the tympano-periotic complexes was examined using high-resolution peripheral quantitative computed tomography (HR-pQCT). In 8/24 harbour porpoises, microfractures of the malleus, dislocation of middle ear bones, bleeding, and haemorrhages in the melon, lower jaw and peribullar acoustic fat were detected, suggesting blast injury. In addition, one bycaught animal and another porpoise with signs of blunt force trauma also showed evidence of blast injury. The cause of death of the other 14 animals varied and remained unclear in two individuals. Due to the vulnerability and the conservation status of harbour porpoise populations in the Baltic Sea, noise mitigation measures must be improved to prevent any risk of injury. The data presented here highlight the importance of systematic investigations into the acute and chronic effects of blast and acoustic trauma in harbour porpoises, improving the understanding of underwater noise effects and herewith develop effective measures to protect the population level.

Change in gene expression levels of GABA, glutamate and neurosteroid pathways due to acoustic trauma in the cochlea

The characteristic feature of noise-induced hearing loss (NIHL) is the loss or malfunction of the outer hair cells (OHC) and the inner hair cells (IHC) of the cochlea. 90-95% of the spiral ganglion neurons, forming the cell bodies of cochlear nerve, synapse with the IHCs. Glutamate is the most potent excitatory neurotransmitter for IHC-auditory nerve synapses. Excessive release of glutamate in response to acoustic trauma (AT), may cause excitotoxicity by causing damage to the spiral ganglion neurons (SGN) or loss of the spiral ganglion dendrites, post-synaptic to the IHCs. Another neurotransmitter, GABA, plays an important role in the processing of acoustic stimuli and central regulation after peripheral injury, so it is potentially related to the regulation of hearing function and sensitivity after noise. The aim of this study is to evaluate the effect of AT on the expressions of glutamate excitotoxicity, GABA inhibition and neurosteroid synthesis genes.We exposed 24 BALB/c mice to AT. Controls were sacrificed without exposure to noise, Post-AT(1) and Post-AT(15) were sacrificed on the 1st and 15th day, respectively, after noise exposure. The expressions of various genes playing roles in glutamate, GABA and neurosteroid pathways were compared between groups by real-time PCR.Expressions of Cyp11a1, Gls, Gabra1, Grin2b, Sult1a1, Gad1, and Slc1a2 genes in Post-AT(15) mice were significantly decreased in comparison to control and Post-AT(1) mice. No significant differences in the expression of Slc6a1 and Slc17a8 genes was detected.These findings support the possible role of balance between glutamate excitotoxicity and GABA inhibition is disturbed during the post AT days and also the synthesis of some neurosteroids such as pregnenolone sulfate may be important in this balance.

High Blood Glucose Levels Affect Auditory Brainstem Responses after Acoustic Overexposure in Rats

INTRODUCTION

Diabetes mellitus (DM) is a systemic disease characterized by hyperglycemia and several pathological changes. DM-related hearing dysfunctions are associated with histological changes. Here, we explore hearing function and synaptic changes in the inner hair cells (IHCs) of rats with streptozotocin (STZ)-induced diabetes.

METHODS

STZ was injected to trigger diabetes. Rats with DM were exposed to narrow-band noise (105 dB SPL) for 2 h, and hearing function was analyzed 1, 3, 7, and 14 days later. Both the hearing threshold and the peak 1 amplitude of the tone auditory brainstem response were assessed. After the last functional test, animals were sacrificed for histological evaluation.

RESULTS

We found no changes in the baseline hearing threshold; however, the peak 1 amplitude at the low frequency (4 kHz) was significantly higher in both DM groups than in the control groups. The hearing threshold had not fully recovered at 14 days after diabetic rats were exposed to noise. The peak 1 amplitude at the higher frequencies (16 and 32 kHz) was significantly larger in both DM groups than in the control groups. The histological analysis revealed that the long-term DM group had significantly more synapses in the 16 kHz region than the other groups.

CONCLUSIONS

We found that high blood glucose levels increased peak 1 amplitudes without changing the hearing threshold. Diabetic rats were less resilient in threshold changes and were less vulnerable to peak 1 amplitude and synaptic damage than control animals.

Metabolic changes in the brain and blood of rats following acoustic trauma, tinnitus and hyperacusis

It has been increasingly recognized that tinnitus is likely to be generated by complex network changes. Acoustic trauma that causes tinnitus induces significant changes in multiple metabolic pathways in the brain. However, it is not clear whether those metabolic changes in the brain could also be reflected in blood samples and whether metabolic changes could discriminate acoustic trauma, hyperacusis and tinnitus. We analyzed brain and serum metabolic changes in rats following acoustic trauma or a sham procedure using metabolomics. Hearing levels were recorded before and after acoustic trauma and behavioral measures to quantify tinnitus and hyperacusis were conducted at 4 weeks following acoustic trauma. Tissues from 11 different brain regions and serum samples were collected at about 3 months following acoustic trauma. Among the acoustic trauma animals, eight exhibited hyperacusis-like behavior and three exhibited tinnitus-like behavior. Using Gas chromatography-mass spectrometry and multivariate statistical analysis, significant metabolic changes were found in acoustic trauma animals in both the brain and serum samples with a number of metabolic pathways significantly perturbated. Furthermore, metabolic changes in the serum were able to differentiate sham from acoustic trauma animals, as well as sham from hyperacusis animals, with high accuracy. Our results suggest that serum metabolic profiling in combination with machine learning analysis may be a promising approach for identifying biomarkers for acoustic trauma, hyperacusis and potentially, tinnitus.

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.

Pharmacological Evaluation of Drugs in Animal Models of Tinnitus

Despite the pressing need for effective drug treatments for tinnitus, currently, there is no single drug that is approved by the FDA for this purpose. Instead, a wide range of unproven over-the-counter tinnitus remedies are available on the market with little or no benefit for tinnitus but with potential harm and adverse effects. Animal models of tinnitus have played a critical role in exploring the pathophysiology of tinnitus, identifying therapeutic targets and evaluating novel and existing drugs for tinnitus treatment. This review summarises and compares the studies on pharmacological evaluation of tinnitus treatment in different animal models based on the pharmacological properties of the drug and provides insights into future directions for tinnitus drug discovery.

Effects of parenteral papaverine and piracetam administration on cochlea following acoustic trauma

Introduction

Noise exposure, the main cause of hearing loss in countries with lot of industries, may result both in temporary or permanent hearing loss. The goal of this study was to investigate the effects of parenteral papaverine and piracetam administration following an acoustic trauma on hearing function with histopathologic correlation.

Materials and Methods

Eighteen Wistar albino rats exposed to noise for 8 h in a free environment were included. We divided the study population into three groups, and performed daily intraperitoneal injections of papaverine, piracetam, and saline, respectively, throughout the study. We investigated the histopathologic effects of cellular apoptosis on inner hair cells (IHCs) and outer hair cells (OHCs) and compared the distortion product otoacoustic emissions (DPOAEs) thresholds among the groups.

Results and Discussion

On the 3^rd and 7^th days, DPOAE thresholds at 8 kHz were significantly higher both in papaverine and piracetam groups compared with the control group (P = 0.004 for 3^rd day, P = 0.016 and P = 0.028 for 7^th day, respectively). On the 14^th day, piracetam group had significantly higher mean thresholds at 8 kHz (P = 0.029); however, papaverine group had similar mean thresholds compared to the control group (P = 0.200). On the 3^rd and 7^th days following acoustic trauma, both IHC and OHC loss were significantly lower in both papaverine and piracetam groups. On the 7^th day, the mean amount of apoptotic IHCs and OHCs identified using Caspase-3 method were significantly lower in both groups, but the mean amount identified using terminal deoxynucleotidyl transferase dUTP nick end labeling method were similar in both groups compared to the control group.

Conclusion

We demonstrated the effects of papaverine and piracetam on the recovery of cochlear damage due to acoustic trauma on experimental animals using histopathologic and electrophysiologic examinations.

Targeting dysregulation of redox homeostasis in noise-induced hearing loss: Oxidative stress and ROS signaling

Hearing loss caused by exposure to recreational and occupational noise remains a worldwide disabling condition and dysregulation of redox homeostasis is the hallmark of cochlear damage induced by noise exposure. In this review we discuss the dual function of ROS to both promote cell damage (oxidative stress) and cell adaptive responses (ROS signaling) in the cochlea undergoing a stressful condition such as noise exposure. We focus on animal models of noise-induced hearing loss (NIHL) and on the function of exogenous antioxidants to maintaining a physiological role of ROS signaling by distinguishing the effect of exogenous "direct" antioxidants (i.e. CoQ₁₀, NAC), that react with ROS to decrease oxidative stress, from the exogenous "indirect" antioxidants (i.e. nutraceutics and phenolic compounds) that can activate cellular redox enzymes through the Keap1-Nrf2-ARE pathway. The anti-inflammatory properties of Nrf2 signaling are discussed in relation to the ROS/inflammation interplay in noise exposure. Unveiling the mechanisms of ROS regulating redox-associated signaling pathways is essential in providing relevant targets for innovative and effective therapeutic strategies against NIHL.

Validación y confiabilidad del Cuestionario de Tamizaje Auditivo Escolar en adolescentes usuarios de reproductores de música comprimida

Introducción

El uso frecuente de reproductores de archivos de música y la intensidad del volumen son factores de riesgo para el desarrollo de hipoacusia.

Objetivo

Validar el Cuestionario de Tamizaje Auditivo Escolar (CUTAE) para identificar alteraciones auditivas en adolescentes usuarios de reproductores de archivos música comprimida (RPAMC).

Método

Se estudiaron adolescentes usuarios de RPAMC, sin hipoacusia ni patología de oído medio. Se aplicó el CUTAE y se realizó audiometría. Se determinó reproducibilidad (coeficiente correlación intraclase-CCI), consistencia interna (alfa de Cronbach), validez de apariencia (técnica Delphi), validez concurrente CUTAE-audiometría (correlación de Pearson) y validez predictiva (regresión múltiple) del cuestionario.

Resultados

Se evaluaron 59 adolescentes (118 oídos), 66 % del sexo femenino, con edad promedio fue de 13 años; 90 oídos con parámetros normales, 18 con umbral menor de 20 dB con morfología de trauma acústico (TA) en la frecuencia de 6 KHz y 10 con TA. El cuestionario tuvo CCI de 0.788, alfa de Cronbach de 0.807, correlación de Pearson de 0.290 a 0.368 (p < 0.05); las variables predictivas fueron horas de uso del dispositivo, dificultad para escuchar a las personas (p < 0.05) y tipo de zumbido (p = 0.07).

Conclusión

El CUTAE tiene propiedades clinimétricas para considerarlo una prueba de tamizaje en la detección de alteraciones auditivas en adolescentes usuarios de RPAMC.

Introduction

Frequent use of audio file players and volume intensity are risk factors for the development of hypoacusis.

Objective

To validate the school-age hearing screening questionnaire (CUTAE, by its Spanish acronym) for hearing disorders detection in teenage users of compressed audio file players (CAFP).

Methods

Adolescent CAFP users without hypoacusis or middle ear pathology were studied. The CUTAE was applied and audiometry was carried out. Reproducibility (intraclass correlation coefficient-ICC), internal consistency (Cronbach’s alpha), face validity (Delphi technique), CUTAE-audiometry concurrent validity (Pearson’s correlation) and predictive validity (multiple regression) of the questionnaire was assessed.

Results

Fifty nine adolescents (118 ears), 66% females, average age of 13 years, were assessed. Ninety ears had normal parameters, 18 showed a threshold decrease < 20 dB, with morphology associated with acoustic trauma (AT) at 6 kHz and 10 with AT. The questionnaire had an ICC of 0.788, a Cronbach alpha-value of 0.807, Pearson’s correlation values of 0.290 to 0.368 (p < 0.05); the predictive variables were usage hours, difficulty hearing others (p < 0.05) and type of buzzing (p = 0.07).

Conclusion

The CUTAE has adequate clinimetric properties to be considered as a screening test in the detection of hearing disorders in adolescent users of CAFP.

Methionine Sulfoxide Reductase A Knockout Mice Show Progressive Hearing Loss and Sensitivity to Acoustic Trauma

Methionine sulfoxide reductases (MsrA and MsrB) protect the biological activity of proteins from oxidative modifications to methionine residues and are important for protecting against the pathological effects of neurodegenerative diseases. In the current study, we characterized the auditory phenotype of the MsrA knockout mouse. Young MsrA knockout mice showed small high-frequency threshold elevations for auditory brainstem response and distortion product otoacoustic emission compared to those of wild-type mice, which progressively worsened in older MsrA knockout mice. MsrA knockout mice showed an increased sensitivity to noise at young and older ages, suggesting that MsrA is part of a mechanism that protects the cochlea from acoustic damage. MsrA mRNA in the cochlea was increased following acoustic stimulation. Finally, expression of mRNA MsrB1 was compromised at 6 months old, but not in younger MsrA knockout mice (compared to controls). The identification of MsrA in the cochlea as a protective mediator from both early onset hearing loss and acoustic trauma expands our understanding of the pathways that may induce protection from acoustic trauma and foster further studies on how to prevent the damaging effect of noise exposure through Msr-based therapy.

Persistent hair cell malfunction contributes to hidden hearing loss

Noise exposures that result in fully reversible changes in cochlear neural threshold can cause a reduced neural output at supra-threshold sound intensity. This so-called "hidden hearing loss" has been shown to be associated with selective degeneration of high threshold afferent nerve fiber-inner hair cell (IHC) synapses. However, the electrophysiological function of the IHCs themselves in hidden hearing loss has not been directly investigated. We have made round window (RW) measurements of cochlear action potentials (CAP) and summating potentials (SP) after two levels of a 10 kHz acoustic trauma. The more intense acoustic trauma lead to notch-like permanent threshold changes and both CAP and SP showed reductions in supra-threshold amplitudes at frequencies with altered thresholds as well as from fully recovered regions. However, the interpretation of the results in normal threshold regions was complicated by the likelihood of reduced contributions from adjacent regions with elevated thresholds. The milder trauma showed full recovery of all neural thresholds, but there was a persistent depression of the amplitudes of both CAP and SP in response to supra-threshold sounds. The effect on SP amplitude in particular shows that occult damage to hair cell transduction mechanisms can contribute to hidden hearing loss. Such damage could potentially affect the supra-threshold output properties of surviving primary afferent neurons.

Effects of intratympanic dexamethasone on noise-induced hearing loss: An experimental study

AIM

Aim of the study was to evaluate the effect of intratympanic steroid treatment on hearing based on oto-acoustic emission.

METHODS

A total of 16 healthy female Wistar albino rats weighing were used in this study. They were divided in to 2 groups and each group was exposed to noise at 110dB for 25min to induce acoustic trauma. Intratympanic dexamethasone was administered to the middle ears of animals in the experimental group on the same day as exposure to noise. The control group was given 0.09% saline solution. Distortion product otoacoustic emission measurements were performed on days 7 and 10.

RESULTS

There were no differences between the emission results of two groups before treatment at 4004, 4761, 5652, 6726, and 7996Hz. There were significant group differences on measurement days 7 and 10 at all frequencies.

CONCLUSION

Our study revealed a significant difference in DPOAE measurements on days 7 and 10 between the experimental and control groups. We detected a positive effect of dexamethasone on noise-induced hearing loss.

Reduction of permanent hearing loss by local glucocorticoid application : Guinea pigs with acute acoustic trauma

BACKGROUND

High-intensity noise exposure from impulse and blast noise events often leads to acute hearing loss and may cause irreversible permanent hearing loss as a long-term consequence. Here, a treatment regime was developed to limit permanent damage based on a preclinical animal model of acute noise trauma.

AIM

To develop clinical trials for the treatment of acute noise traumas using approved drugs. The otoprotective potential of glucocorticoids applied locally to the inner ear was examined.

MATERIALS AND METHODS

A series of experiments with different impulse noise exposures were performed. Permanent hearing loss and hair cell density were assessed 14 days after exposure. Hearing and hair cell preservation were investigated as a function of the glucocorticoid dose.

RESULTS

After impulse noise exposure, local application to the round window of the cochlea of high-dose prednisolone (25 mg/ml) or methylprednisolone (12.5 mg/ml) resulted in a statistically significant reduction in hearing loss compared with the control group.

CONCLUSION

The local application of high doses of the drugs to the round window of the cochlea appears to be an effective treatment for acute noise trauma.

Curcumin protects against acoustic trauma in the rat cochlea

OBJECTIVES

In this study we evaluated the therapeutic utility of curcumin in a rodent model of acoustic trauma using histopathology, immunohistochemical, and distortion product otoacoustic emission (DPOAEs) measurements.

METHODS

28 Wistar albino rats were included in the study and randomly assigned to 4 treatment groups. The first group (group 1) served as the control and was exposed to acoustic trauma alone. Group 2 was the curcumin group. Group 3 was the curcumin plus acoustic trauma group. Group 4 was the saline plus acoustic trauma group. Otoacoustic emission measurements were collected at the end of the experiment and all animals were sacrificed. Cochlea were collected and prepared for TUNEL (TdT-mediated deoxyuridinetriphosphate nick end-labelling) staining assay.

RESULTS

Group 3 maintained baseline DPOAEs values at 3000 Hz, 4000 Hz and 8000 Hz on the 3rd and 5th day of the experiment. DPOAEs results were correlated with the immunohistochemical and histopathological findings in all groups. In comparison to the histopathologic control group, Group 1 exhibited a statistically significant increase in apoptotic indices in the organ of Corti, inner hair cell, and outer hair cell areas (p < 0.05). Relative to the control group, rats in Group 3 showed little increase in inner hair cell and outer hair cell apoptotic indices.

CONCLUSIONS

Our results support the conclusion that curcumin may protect the cochlear tissues from acoustic trauma in rats. Curcumin injection prior to or after an acoustic trauma reduces cochlear hair cell damage and may protect against hearing loss.

Protective Effect of Nigella Sativa Oil on Acoustic Trauma Induced Hearing Loss in Rats

Acoustic trauma is a common reason for hearing loss. Different agents are used to prevent the harmful effect of acoustic trauma on hearing. The aim of this study was to evaluate the potential preventive effect of Nigella sativa (black cumin) oil in acoustic trauma. Our experimental study was conducted with 20 Sprague Downey female rats (mean age, 12 months; mean weight 250 g). All of the procedures were held under general anesthesia. Following otoscopic examinations, baseline-hearing thresholds were obtained using auditory brainstem responses (ABR). To create acoustic trauma, the rats were then exposed to white band noise of 4 kHz with an intensity level of 107 dB in a soundproof testing room. On Day 1 following acoustic trauma, hearing threshold measurements were repeated. The rats were divided into two groups as the study group (n: 10) and the controls (n: 10). 2 mL/kg/day of Nigella sativa oil was given to the rats in the study group orally. On Day 4 following acoustic trauma, ABR measurements were repeated again. There was no difference between the baseline hearing thresholds of the rats before acoustic trauma (P>0.005). After the acoustic trauma, hearing thresholds were increased and there was no significant statistically difference between the hearing thresholds of the study and control groups (P=0.979). At the 4^th day following acoustic trauma, hearing thresholds of the rats in control group were found to be higher than those in the study group (P=0.03). Our results suggest that Nigella sativa oil has a protective effect against acoustic trauma in early period. This finding should be supported with additional experimental and clinical studies, especially to determine the optimal dose, duration and frequency of potential Nigella sativa oil therapy.

Short-Term Effect of Gabapentin on Subjective Tinnitus in Acoustic Trauma Patients

INTRODUCTION

Although several treatment approaches have been proposed for tinnitus, there are currently no Food and Drug Administration (FDA)-approved agents available to treat this condition. In this study, we evaluated the effect of gabapentin on the sensation of subjective tinnitus in patients with acoustic trauma referring to the ear, nose and throat (ENT) clinic of Taleghani Hospital during 2014.

MATERIALS AND METHODS

In this double-blind, randomized clinical trial, 103 patients with tinnitus due to acoustic trauma who were referred to the ENT clinic of Taleghani Hospital during 2014 were randomized to the gabapentin (300 mg bid, n=55) or control (n=48) groups. The two groups were then compared before and after 6 weeks of treatment using a visual analog scale (VAS). At least a 30% reduction in VAS was considered a response to treatment.

RESULTS

Differences between the two groups regarding sex, age, duration of disease, and audiometry results was not significant (P>0.05). After 6 weeks' treatment, the VAS significantly decreased in both groups (P<0.001), but the reduction was significantly greater in the gabapentin group compared with control (P<0.001). Forty-nine patients (89%) in the gabapentin group and 28 control patients (58.3%) responded to treatment (≥30% reduction in VAS), with the difference between the two groups being statistically significant (P<0.001).

CONCLUSION

We conclude that gabapentin 300 mg bid for 6 weeks is an effective treatment for acoustic tinnitus. In addition, the placebo effect in relieving tinnitus is remarkable.

The therapeutic effect of thymoquinone on acoustic trauma-induced hearing loss in rats

Thymoquinone has antioxidant properties. We hypothesized that thymoquinone may prevent or alleviate hearing loss induced by acoustic trauma. We aimed to study thymoquinone's effect on hearing function with distortion-product otoacoustic emissions and auditory brainstem response. Thirty adult Spraque Dawley rats were randomized into four groups following exposure to acoustic trauma for 4 h. Control group (n = 7) did not receive further treatment. Thymoquinone-20 (n = 8) and Thymoquinone-40 (n = 8) received 20 and 40 mg/kg of intraperitoneal thymoquinone, respectively. Corn-oil group (n = 7) received 1 ml of corn oil intraperitoneally. Hearing function of both ears was tested with distortion-product otoacoustic emission and auditory brainstem response before, and shortly after acoustic trauma, and 96 h following acoustic trauma. Post-trauma signal/noise ratios and wave V amplitude/latencies of all groups were significantly low compared with pre-trauma values, which indicate no preventive effect of thymoquinone. Rats in Thymoquinone-20 showed a significantly improved distortion-product otoacoustic emission and auditory brainstem response results at 4000 frequency and above in post-treatment tests (p < 0.05). Improvement in Thymoquinone-40 at the same frequencies was insignificantly inferior to Thymoquinone-20, yet superior to control and corn-oil groups (p < 0.05). We conclude that thymoquinone may not prevent acoustic trauma-induced hearing loss, however, at 20 mg/kg for 96 h, may repair the damage.

Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes

Sensory hair cells are the mechanotransductive receptors that detect gravity, sound, and vibration in all vertebrates. Damage to these sensitive receptors often results in deficits in vestibular function and hearing. There are currently two main reasons for studying the process of hair cell loss in fishes. First, fishes, like other non-mammalian vertebrates, have the ability to regenerate hair cells that have been damaged or lost via exposure to ototoxic chemicals or acoustic overstimulation. Thus, they are used as a biomedical model to understand the process of hair cell death and regeneration and find therapeutics that treat or prevent human hearing loss. Secondly, scientists and governmental natural resource managers are concerned about the potential effects of intense anthropogenic sounds on aquatic organisms, including fishes. Dr. Arthur N. Popper and his students, postdocs and research associates have performed pioneering experiments in both of these lines of fish hearing research. This review will discuss the current knowledge regarding the causes and consequences of both lateral line and inner ear hair cell damage in teleost fishes.

Suppression Measured from Chinchilla Auditory-Nerve-Fiber Responses Following Noise-Induced Hearing Loss: Adaptive-Tracking and Systems-Identification Approaches

The compressive nonlinearity of cochlear signal transduction, reflecting outer-hair-cell function, manifests as suppressive spectral interactions; e.g., two-tone suppression. Moreover, for broadband sounds, there are multiple interactions between frequency components. These frequency-dependent nonlinearities are important for neural coding of complex sounds, such as speech. Acoustic-trauma-induced outer-hair-cell damage is associated with loss of nonlinearity, which auditory prostheses attempt to restore with, e.g., "multi-channel dynamic compression" algorithms.Neurophysiological data on suppression in hearing-impaired (HI) mammals are limited. We present data on firing-rate suppression measured in auditory-nerve-fiber responses in a chinchilla model of noise-induced hearing loss, and in normal-hearing (NH) controls at equal sensation level. Hearing-impaired (HI) animals had elevated single-fiber excitatory thresholds (by ~ 20-40 dB), broadened frequency tuning, and reduced-magnitude distortion-product otoacoustic emissions; consistent with mixed inner- and outer-hair-cell pathology. We characterized suppression using two approaches: adaptive tracking of two-tone-suppression threshold (62 NH, and 35 HI fibers), and Wiener-kernel analyses of responses to broadband noise (91 NH, and 148 HI fibers). Suppression-threshold tuning curves showed sensitive low-side suppression for NH and HI animals. High-side suppression thresholds were elevated in HI animals, to the same extent as excitatory thresholds. We factored second-order Wiener-kernels into excitatory and suppressive sub-kernels to quantify the relative strength of suppression. We found a small decrease in suppression in HI fibers, which correlated with broadened tuning. These data will help guide novel amplification strategies, particularly for complex listening situations (e.g., speech in noise), in which current hearing aids struggle to restore intelligibility.

The immediate effects of acoustic trauma on excitation and inhibition in the inferior colliculus: A Wiener-kernel analysis

Noise-induced tinnitus and hyperacusis are thought to correspond to a disrupted balance between excitation and inhibition in the central auditory system. Excitation and inhibition are often studied using pure tones; however, these responses do not reveal inhibition within the excitatory pass band. Therefore, we used a Wiener-kernel analysis, complemented with singular value decomposition (SVD), to investigate the immediate effects of acoustic trauma on excitation and inhibition in the inferior colliculus (IC). Neural responses were recorded from the IC of three anesthetized albino guinea pigs before and immediately after a one-hour bilateral exposure to an 11-kHz tone of 124 dB SPL. Neural activity was recorded during the presentation of a 1-h continuous 70 dB SPL Gaussian-noise stimulus. Spike trains were subjected to Wiener-kernel analysis in which the second-order kernel was decomposed into excitatory and inhibitory components using SVD. Hearing thresholds between 3 and 22 kHz were elevated (13-47 dB) immediately after acoustic trauma. The presence and frequency tuning of excitation and inhibition in units with a low characteristic frequency (CF; < 3 kHz) was not affected, inhibition disappeared whereas excitation was not affected in mid-CF units (3 < CF < 11 kHz), and both excitation and inhibition disappeared in high-CF units (CF > 11 kHz). This specific differentiation could not be identified by tone-evoked receptive-field analysis, in which inhibitory responses disappeared in all units, along with excitatory responses in high-CF units. This study is the first to apply Wiener-kernel analysis, complemented with SVD, to study the effects of acoustic trauma on spike trains derived from the IC. With this analysis, a reduction of inhibition and preservation of good response thresholds was shown in mid-CF units immediately after acoustic trauma. These neurons may mediate noise-induced tinnitus and/or hyperacusis. Moreover, an immediate profound high-frequency hearing loss was reflected by reduced evoked firing rates and loss of both excitation and inhibition in high-CF units.

Evaluation of Inner Ear Damage by Using Otoacoustic Emissions in Patients Who Underwent Mastoidectomy and Tympanoplasty Operations in the Early Period

Objective

We aim to demonstrate inner ear damage caused by drilling in the early period. Healthy contralateral ears of patients who underwent mastoidectomy using drill or tympanoplasty without using drill were compared.

Methods

A total of 38 patients (mastoidectomy: 22, tympanoplasty: 16) who were diagnosed as chronic otitis media and were scheduled for surgery were included. Distortion product (dp) otoacoustic emissions measurements were performed on healthy contralateral ears of patients on pre- and post-operative 1. hour, 1. day, 2. day, 3. day, and 4. day.

Results

In mastoidectomy group, dp otoacoustic emission values on post-operative 1. hour, 1. day, 2. day, 3. day, and 4. day at a frequency of 4000 Hz were significantly lower than in tympanoplasty group (p<0.05). In mastoidectomy group, dp values on post-operative 1. hour, 1. day, 2. day, 3. day, and 4. day at 4000 Hz significantly decreased in comparison with pre-operative period (p<0.05). In comparison with pre-operative period, decrease in dp values on post-operative 1. hour, 1. day, and 2. day at 4000 Hz in mastoidectomy group is significantly higher than those in tympanoplasty group (p<0.05). In tympanoplasty group, dp values on post-operative 1. hour at 4000 Hz significantly decreased in comparison with pre-operative period (p<0.05).

Conclusion

Drilling used in mastoidectomy operation damage healthy contralateral ears by causing acoustic trauma. This damage can be determined by otoacoustic emissions in the early period. According to our study, hearing loss is temporary and more distinct at higher frequencies.

Rosmarinic acid up-regulates the noise-activated Nrf2/HO-1 pathway and protects against noise-induced injury in rat cochlea

Noise-induced hearing loss depends on progressive increase of reactive oxygen species and lipoperoxidative damage in conjunction with the imbalance of antioxidant defenses. The redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) plays a critical role in the regulation of cellular defenses against oxidative stress, including heme oxygenase-1 (HO-1) activation. In this work we describe a link between cochlear oxidative stress damage, induced by noise exposure, and the activation of the Nrf2/HO-1 pathway. In our model, noise induces superoxide production and overexpression of the lipid peroxidation marker 4-hydroxy-nonenals (4-HNE). To face the oxidative stress, the endogenous defense system is activated as well, as shown by the slight activation of superoxide dismutases (SODs). In addition, we observed the activation of the Nrf2/HO-1 pathway after noise exposure. Nrf2 appears to promote the maintenance of cellular homeostasis under stress conditions. However, in this model the endogenous antioxidant system fails to counteract noise-induced cell damage and its activation is not effective enough in preventing cochlear damage. The herb-derived phenol rosmarinic acid (RA) attenuates noise-induced hearing loss, reducing threshold shift, and promotes hair cell survival. In fact, RA enhances the endogenous antioxidant defenses, as shown by decreased superoxide production, reduced expression of 4-HNE, and up-regulation of SODs. Interestingly, RA potentiates the Nrf2/HO-1 signaling pathway, as shown by immunohistochemical and Western blot analyses. Thus, protective effects of RA are associated with the induction/activation of the Nrf2-ARE signaling pathway in addition to RA direct scavenging capability.

Age effects on tinnitus and hearing loss in CBA/CaJ mice following sound exposure

Tinnitus is a maladaptive neuropathic condition that develops in humans and laboratory animals following auditory insult. In our previous study we demonstrated that sound exposure leads to development of behavioral evidence of tinnitus in a sample of exposed mice. However, this tinnitus mouse model did not account for long-term maladaptive plasticity or aging, factors that are commonly linked to the human tinnitus population. Therefore the same group of mice was monitored for tinnitus for 360 days post exposure. Tinnitus was assessed behaviorally by measuring gap-induced pre-pulse suppression of the acoustic startle (GPIAS). Cochlear histology was performed on both control (unexposed) and experimental mice to determine whether sound exposure caused any evident cochlear damage. We found that 360 days after exposure the vast majority of exposed mice exhibited similar gap detection deficits as detected at 84 days post exposure. These mice did not demonstrate significant loss of inner/outer hair cells or spiral ganglion neurons compared to the control sample. Lastly, we demonstrated that GPIAS deficits observed in exposed animals were unlikely exclusively caused by cochlear damage, but could be a result of central auditory maladaptive plasticity. We conclude that CBA/CaJ mice can be considered a good animal model to study the possible contribution of age effects on tinnitus development following auditory insult.

Drill-induced noise level during cochleostomy

CONCLUSIONS

Noise induced by drilling during cochleostomy is of high level and can cause acoustic trauma to the inner ear, particularly after the membranous labyrinth has been exposed. Our method utilizes non-invasive noise measurement and the equipment that is connected to the operative area can be sterilized, thus it can be applied to intraoperative recordings.

OBJECTIVES

To investigate the noise level generated by otological electrical drills during the cochleostomy procedure and to further explore the feasibility of noise monitoring in vivo.

METHODS

Acoustic measurements during drilling on the promontory of cochleae were carried out on 16 human cadavers (19 ears) using an ER7C probe microphone system.

RESULTS

The peak noise level generated during cochleostomy differed obviously from specimen to specimen and ranged from 85.9 to 131.5 dB SPL. We found three cases in which the peak noise level exceeded 130 dB SPL when the running burr touched the endosteal membrane.

[Acoustic trauma generated by exposure to gun powder]

BACKGROUND

Noise-induced hearing loss has increased due to factors such as industrialization. It is estimated that one third of the world's population suffers from some degree of hearing loss caused by exposure to high-intensity noise. Exposure to noise can cause disease of various ear structures, especially destruction of outer hair cells, causing varying degrees of hearing lossObjective: To describe the audiological findings in a group of subjects who were exposed to a source of fireworks explosion in the state of Tlaxcala Mexico.

METHODOLOGY

We carried out an audiometric study in eight patients admitted to CENIAQ-INR who were exposed to a firecracker explosion. In each subject, airway with conventional pure tone audiometry from 125 to 8000 Hz was assessed using a clinical audiometer (model 622, Minimate, Madsen) Clinical case: Hearing loss at all frequencies was found in all eight patients, from mild to severe in both ears. Audiogram showed decreases from 4000 Hz, diagnosing third-degree acoustic trauma in all patients.

CONCLUSIONS

The main symptom was reported by patients with tinnitus. Other scenarios in which patients report the presence of tinnitus are acoustic trauma due to use of audio players in symphony orchestra musicians and detonating military firearms. Audiometric assessment is recommended after an explosive accident as an accurate method to determine if there is any hearing impairment.

[Auditory fatigue]

INTRODUCTION AND OBJECTIVES

Given the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor. Our objectives were to determine peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies.

MATERIAL AND METHOD

We used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it.

RESULTS

Using a 60dB pure tone acoustic stimulation, we obtained a microphonic response at 20dB. We then caused fatigue with 100dB of the same frequency, reaching a loss of approximately 11dB after 15minutes; after that, the deterioration slowed and did not exceed 15dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100dB and over an hour of overstimulation.

CONCLUSIONS

No fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials.

The effect of alprazolam on acoustic stapedius reflex thresholds in healthy volunteers

Alprazolam, a widely used drug, has widespread, nonspecific depressant effects on the central nervous system, similar to other benzodiazepines. This inhibitor effect may cause changes in reflex thresholds by affecting the acoustic stapedial reflex (ASR) arc. This study was performed on 31 healthy volunteers. Initially, the basal ASR thresholds were measured and measured again 2 h after oral intake of 1 mg of alprazolam; by measuring the reflex thresholds once again the mean values of thresholds before and after the drug were compared. Only the left ipsilateral and contralateral 2,000 Hz increases were significantly different. The left ipsilateral and contralateral 500, 1000, and 4000 Hz, and the right ipsilateral and contralateral 500, 1000, 2000, and 4000 Hz measurements showed no differences. Although an increase in ART thresholds was generally observed after the intake of alprazolam, it was not significant. Its use in healthy adults does not statistically produce an additional risk of acoustic trauma at most of the frequencies, but its use with the agents potentiating the effect of alprazolam may increase this risk.

Time evolution of noise induced oxidation in outer hair cells: role of NAD(P)H and plasma membrane fluidity

BACKGROUND

Noise exposure impairs outer hair cells (OHCs). The common basis for OHC dysfunction and loss by acoustic over-stimulation is represented by reactive oxygen species (ROS) overload that may affect the membrane structural organization through generation of lipid peroxidation.

METHODS

Here we investigated in OHC different functional zones the mechanisms linking metabolic functional state (NAD(P)H intracellular distribution) to the generation of lipid peroxides and to the physical state of membranes by two photon fluorescence microscopy.

RESULTS

In OHCs of control animals, a more oxidized NAD(P)H redox state is associated to a less fluid plasma membrane structure. Acoustic trauma induces a topologically differentiated NAD(P)H oxidation in OHC rows, which is damped between 1 and 6h. Peroxidation occurs after ~4h from noise insult, while ROS are produced in the first 0.2h and damage cells for a period of time after noise exposure has ended (~7.5h) when a decrease of fluidity of OHC plasma membrane occurs. OHCs belonging to inner rows, characterized by a lower metabolic activity with respect to other rows, show less severe metabolic impairment.

CONCLUSIONS

Our data indicate that plasma membrane fluidity is related to NAD(P)H redox state and lipid peroxidation in hair cells.

GENERAL SIGNIFICANCE

Our results could pave the way for therapeutic intervention targeting the onset of redox umbalance.

Medical ozone therapy for the inner ear acoustic trauma

OBJECTIVES

The goal of the study was to look at the potential protective effect of ozone therapy by studying its antioxidant and vasodilatation effects against hearing loss caused by acoustic trauma.

METHODS

Thirty-two male Wistar Albino rats were divided into four groups of eight. The 1st group was exposed to acoustic trauma, the 2nd group was treated with ozone initially, and was exposed to acoustic trauma 24 h later, the 3rd group received ozone without trauma, while the 4th group was the control group. The 1st and 2nd groups were exposed to acoustic trauma with 105 dB SPL white band noise for 4h. DPOAE and ABR tests were conducted in all groups on the 1st, 5th, and 10th days after trauma.

RESULTS

In the 1st group, the effects of acoustic trauma continued on days 1, 5 and 10. The 2nd group's DPOAE and ABR results on days 5 and 10 showed significant improvement at all frequencies compared to deterioration on day 1, and the readings were comparable to baseline measurements.

CONCLUSION

Acoustic trauma is a pathology that is experienced frequently and leads to many problems in terms of health and cost. Ozone was demonstrated to be a reparative substance against acoustic trauma and, in addition, it can be supplied and applied easily.

The function of BDNF in the adult auditory system

The inner ear of vertebrates is specialized to perceive sound, gravity and movements. Each of the specialized sensory organs within the cochlea (sound) and vestibular system (gravity, head movements) transmits information to specific areas of the brain. During development, brain-derived neurotrophic factor (BDNF) orchestrates the survival and outgrowth of afferent fibers connecting the vestibular organ and those regions in the cochlea that map information for low frequency sound to central auditory nuclei and higher-auditory centers. The role of BDNF in the mature inner ear is less understood. This is mainly due to the fact that constitutive BDNF mutant mice are postnatally lethal. Only in the last few years has the improved technology of performing conditional cell specific deletion of BDNF in vivo allowed the study of the function of BDNF in the mature developed organ. This review provides an overview of the current knowledge of the expression pattern and function of BDNF in the peripheral and central auditory system from just prior to the first auditory experience onwards. A special focus will be put on the differential mechanisms in which BDNF drives refinement of auditory circuitries during the onset of sensory experience and in the adult brain. This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'.

Abnormal cortical sensorimotor activity during "Target" sound detection in subjects with acute acoustic trauma sequelae: an fMRI study

The most common consequences of acute acoustic trauma (AAT) are hearing loss at frequencies above 3 kHz and tinnitus. In this study, we have used functional Magnetic Resonance Imaging (fMRI) to visualize neuronal activation patterns in military adults with AAT and various tinnitus sequelae during an auditory "oddball" attention task. AAT subjects displayed overactivities principally during reflex of target sound detection, in sensorimotor areas and in emotion-related areas such as the insula, anterior cingulate and prefrontal cortex, in premotor area, in cross-modal sensory associative areas, and, interestingly, in a region of the Rolandic operculum that has recently been shown to be involved in tympanic movements due to air pressure. We propose further investigations of this brain area and fine middle ear investigations, because our results might suggest a model in which AAT tinnitus may arise as a proprioceptive illusion caused by abnormal excitability of middle-ear muscle spindles possibly link with the acoustic reflex and associated with emotional and sensorimotor disturbances.

Noise-induced hearing loss in children: A 'less than silent' environmental danger

A review of the problems of noise-induced hearing loss in children, especially related to recreational music and the use of personal entertainment devices. The pathophysiology of noise-induced hearing loss and its associated problems (eg, tinnitus) are discussed. The evidence for an increase in noise-induced hearing loss in children and young people is reviewed. Some practical advice (for clinicians, caregivers and children) on hearing loss prevention is provided.

Protective effects of N-acetylcysteine on noise-induced hearing loss in guinea pigs

Increasing evidence suggests the involvement of oxidative stress in noise-induced hearing loss. The present study analysed, in an animal experimental model, the time course of the pathogenic mechanisms of noise-induced cochlear damage and the efficacy of the antioxidant drug N-acetylcysteine in reducing noise ototoxicity. Animals were divided into two groups, exposed to noise one treated with N-acetylcysteine for 3 days and one (the control group) with saline. Acoustic trauma was induced by a continuous pure tone of 6 kHz, at 120 dB SPL for 30 minutes. Electrocochleographic recordings were made from an implanted round window electrode and the compound action potentials were measured daily at 2-16 kHz for 7 days. Morphological changes were analysed by scanning electron microscopy. The acoustic threshold measured 1 hour after acoustic trauma was elevated in the control group to 70-90 dB in the higher frequencies of the compound action potential audiogram, with a maximum threshold elevation ranging between 12 and 16 kHz. During the first 24 h, following acoustic trauma, there was a partial recovery of compound action potential thresholds of about 20 dB to reach a final threshold elevation of about 50-70 dB; there was no further improvement over the remaining experimental week. Animals treated with N-acetylcysteine showed a similar temporary threshold shift but a clear improvement in the recovery of compound action potential thresholds, with significantly reduced permanent threshold shift and hair cell loss. These data suggest that N-acetylcysteine is able to attenuate the toxic effect of acoustic trauma and could represent an interesting molecule for preventing inner ear injuries.

Bomb blast injury: effect on middle and inner ear

OBJECTIVE

To study the symptomatology, clinical findings and the effects of blast injury on middle and inner ear in survivors of bomb blast. Settings City of Mumbai, India.

METHODS

The study group consisted of 52 patients exposed to the bomb blast that occurred on 25th August 2003.

RESULT AND ANALYSIS

The distance of the victim from the blast site has no major infiuence in producing effects on middle and inner ear in our study of the surviving individuals. Rupture of the tympanic membrane occurs due to the positive wave but both everted and inverted edges can be found in multiple perforations of the tympanic membrane.