Hearing threshold shift measured by otoacoustic emissions after shooting noise exposure in soldiers using hearing protectors

Auditory changes following firearm noise exposure, a review

Firearms produce peak sound pressure levels (peak SPL) between ∼130 and 175 dB peak SPL, creating significant risk of noise-induced hearing loss (NIHL) in those exposed to firearm noise during occupational, recreational, and/or military operations. Noise-induced tinnitus and hearing loss are common in military service members, public safety officers, and hunters/shooters. Given the significant risk of NIHL due to firearm and other noise sources, there is an interest in, and demand for, interventions to prevent and/or treat NIHL in high-risk populations. However, research and clinical trial designs assessing NIHL prevention have varied due to inconsistent data from the literature, specifically with end point definitions, study protocols, and assessment methodologies. This article presents a scoping review of the literature pertaining to auditory changes following firearm noise exposure. Meta-analysis was not possible due to heterogeneity of the study designs. Recommendations regarding audiologic test approach and monitoring of populations at risk for NIHL are presented based on critical review of the existing literature.

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.

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

OBJECTIVE

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.

DATA SOURCES

PubMed, Cochrane, and Scopus databases.

STUDY SELECTION

The scientific literature was searched up to October 2018 for articles evaluating hearing outcomes after treatment of aNIHL.

DATA EXTRACTION

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.

DATA SYNTHESIS

Sixteen studies with 932 patients met inclusion criteria for systematic review and four studies with 187 patients were included in the meta-analysis.

CONCLUSIONS

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.

Utility of Hyperbaric Oxygen Therapy for Acute Acoustic Trauma: 20 years' Experience at the Japan Maritime Self-Defense Force Undersea Medical Center

Introduction  Acute acoustic trauma, which is a kind of sensorineural hearing loss, is caused by acoustic overstimulation. Hyperbaric oxygen therapy (HBOT) is reported to be effective against acute acoustic trauma.

Objective  We aimed to evaluate the efficacy of HBOT against acoustic hearing loss based on our 20 years of experience with such cases.

Methods  Patients who were treated with HBOT for acute acoustic trauma between April 1997 and August 2017 were evaluated in this study. Thirty-five patients with a mean age of 25.7 ± 9.2 (range: 16–48) years were included. Thirty-nine out of 70 ears (35 patients) were damaged. We investigated the initial level of hearing loss; the extent to which hearing recovered; subjective symptoms, such as tinnitus and aural fullness; and the treatment administered.

Results  The planned HBOT was completed in 37 of 39 ears. Twenty-six of the 37 ears (70.2%) displayed improved hearing, and 31 of the 37 ears (83.9%) exhibited symptom improvement. Twenty-three (76.7%) and 26 (86.7%) of the 30 ears treated with steroids demonstrated improvements in hearing and subjective symptoms, respectively.

Conclusion  A combination of HBOT and steroids should be considered as a treatment for acute acoustic trauma in cases involving symptoms such as tinnitus and aural fullness.

Temporary threshold shift after impulse-noise during video game play: laboratory data

OBJECTIVE

Prevention of temporary threshold shift (TTS) after laboratory-based exposure to pure-tones, broadband noise, and narrowband noise signals has been achieved, but prevention of TTS under these experimental conditions may not accurately reflect protection against hearing loss following impulse noise. This study used a controlled laboratory-based TTS paradigm that incorporated impulsive stimuli into the exposure protocol; development of this model could provide a novel platform for assessing proposed therapeutics.

DESIGN

Participants played a video game that delivered gunfire-like sound through headphones as part of a target practice game. Effects were measured using audiometric threshold evaluations and distortion product otoacoustic emissions (DPOAEs). The sound level and number of impulses presented were sequentially increased throughout the study.

STUDY SAMPLE

Participants were normal-hearing students at the University of Florida who provided written informed consent prior to participation.

RESULTS

TTS was not reliably induced by any of the exposure conditions assessed here. However, there was significant individual variability, and a subset of subjects showed TTS under some exposure conditions.

CONCLUSIONS

A subset of participants demonstrated reliable threshold shifts under some conditions. Additional experiments are needed to better understand and optimize stimulus parameters that influence TTS after simulated impulse noise.