Mechanisms of Hearing Loss after Blast Injury to the Ear

Sung-Il Cho,Simon S Gao,Felipe T Salles,Patrick D Raphael,Jongmin Baek,Rosalie Wang,Anping Xia,David Jacobs,Homer Abaya,Jacqueline Wachtel,Matthew N Rasband,John S Oghalai,Jonathan I Matsui

doi:10.1371/journal.pone.0067618

Abstract

Given the frequent use of improvised explosive devices (IEDs) around the world, the study of traumatic blast injuries is of increasing interest. The ear is the most common organ affected by blast injury because it is the body’s most sensitive pressure transducer. We fabricated a blast chamber to re-create blast profiles similar to that of IEDs and used it to develop a reproducible mouse model to study blast-induced hearing loss. The tympanic membrane was perforated in all mice after blast exposure and found to heal spontaneously. Micro-computed tomography demonstrated no evidence for middle ear or otic capsule injuries; however, the healed tympanic membrane was thickened. Auditory brainstem response and distortion product otoacoustic emission threshold shifts were found to be correlated with blast intensity. As well, these threshold shifts were larger than those found in control mice that underwent surgical perforation of their tympanic membranes, indicating cochlear trauma. Histological studies one week and three months after the blast demonstrated no disruption or damage to the intra-cochlear membranes. However, there was loss of outer hair cells (OHCs) within the basal turn of the cochlea and decreased spiral ganglion neurons (SGNs) and afferent nerve synapses. Using our mouse model that recapitulates human IED exposure, our results identify that the mechanisms underlying blast-induced hearing loss does not include gross membranous rupture as is commonly believed. Instead, there is both OHC and SGN loss that produce auditory dysfunction.

Highlights

Improvised explosive devices (IEDs; commonly used as roadside bombs) are a common cause of combat injury in the wars in Afghanistan and Iraq
Our findings in a mouse model exposed to a blast wave and wind equal to or greater than that of a typical IED injury sustained by a soldier suggest that this pathology is not typical
While the surgically-perforated mice had full recovery of their Auditory Brainstem Responses (ABRs) thresholds, their Distortion Product Otoacoustic Emissions (DPOAEs) thresholds remained elevated. This result is consistent with a persistent conductive hearing loss, which has a greater impact on DPOAE than ABR thresholds [24]

Summary

Introduction

Improvised explosive devices (IEDs; commonly used as roadside bombs) are a common cause of combat injury in the wars in Afghanistan and Iraq. They are often used as weapons of terror, inflicting severe injuries on non-combatants around the world, including within the United States. High pressure gasses are released that expand away from the point of detonation. This compresses the surrounding air and produces both a blast wave and a blast wind that propagate away from the explosion in a spherical pattern [1]. Besides the obvious disabilities resulting from damage to the ear, there are significant long-term health care costs for society

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