Vestibular Injury After Low-Intensity Blast Exposure

Abstract

The increased use of close range explosives has led to a higher incidence of exposure to blast-related head trauma. Exposure to primary blast waves is a significant cause of morbidity and mortality. Active service members and civilians who have experienced blast waves report high rates of vestibular dysfunction, such as vertigo, oscillopsia, imbalance, and dizziness. Accumulating evidence suggests that exposure to blast-wave trauma produces damage to both the peripheral and central vestibular system; similar to previous findings that blast exposure results in damage to auditory receptors. In this study, mice were exposed to a 63 kPa peak blast-wave over pressure and were examined for vestibular receptor damage as well as behavioral assays to identify vestibular dysfunction. We observed perforations to the tympanic membrane in all blast animals. We also observed significant loss of stereocilia on hair cells in the cristae and macule up to 1 month after blast-wave exposure; damage that is likely permanent. Significant reductions in the ability to perform the righting reflex and balance on a rotating rod that lasted several weeks after blast exposure were prominent behavioral effects. We also observed a significant reduction in horizontal vestibuloocular reflex gain and phase lags in the eye movement responses that lasted many weeks following a single blast exposure event. OKN responses were absent immediately following blast exposure, but began to return after several weeks’ recovery. These results show that blast-wave exposure can lead to peripheral vestibular damage (possibly central deficits as well) and provides some insight into causes of vestibular dysfunction in blast-trauma victims.

Exposure to blast shock waves via the ear canal induces deficits in vestibular afferent function in rats

“…Effects of blast shock waves on the middle and inner ear structures were examined. First, consistent with earlier reports ( Lien and Dickman, 2018 in mice; Hickman et al., 2018 in chinchillas), blast exposure ruptured the tympanic membranes of all the 14 blast treated ears, but not the untreated ears. Blast shocks also disrupted the ossicular chain and damaged both the anterior and posterior crus and the front of the footplate of the stapes ( Fig.…”

“…While the focus of the study was on effects of blast exposure on vestibular afferent function and the VORs, we performed morphological analyses of the inner ears in three SD rats one week after blast exposure to determine the blast-induced inner ear structural damage and allow comparison to that reported in the literature ( Lien and Dickman, 2018 ). Under deep pentobarbital anesthesia, rats were perfused transcardially first with phosphate buffered saline with pH of 7.4, then with 10% phosphate buffered 4% paraformaldehyde.…”

“…However, in contrast to numerous animal studies on blast-induced hearing loss, few animal studies have examined blast-induced damage to vestibular peripheral end organs in the inner ear. A recent study reported that blast waves delivered to the whole body not only ruptured the tympanic membrane and disrupted the conductive structures of the middle ear (i.e., the ossicles), but also caused damage to the vestibular hair cells located in the bony labyrinth and to the VORs in mice ( Lien and Dickman, 2018 ). However, whether the blast exposure causes deficits in vestibular afferent function needs to be demonstrated for two reasons.…”

Glial Activation in the Thalamus Contributes to Vestibulomotor Deficits Following Blast-Induced Neurotrauma

“…Few preclinical studies have reported on vestibular disorders following bTBI. Lien and Dickman investigated vestibular injury following low intensity blast exposure using the rotor rod behavioral task ( 10 ). They found a significant reduction in the ability of the animals to perform the balance task on the rotating rod for several weeks following blast exposure.…”

“…Acute vestibulomotor deficits have been noted in 98% of patients diagnosed with bTBI and 72% of these patients report long-term vestibular impairment ( 8 , 9 ). Clinical manifestations of vestibular damage includes motor impairments leading to imbalance, motion intolerance, postural instability and dizziness ( 1 , 10 ). In most cases, there are also significant behavioral concerns that overlap with blast-related impairments such as anxiety, attention, fear, memory, and problem-solving deficits ( 11 – 13 ).…”