Vestibular function testing confirms a greater incidence of peripheral vestibular hypofunction in dizzy service members with blast-related TBI relative to those who are asymptomatic. Additionally, oculomotor abnormalities and/or nystagmus consistent with central involvement were present in 10 of the 24 study participants tested. The precise cause of these findings remains unknown.

The incidence of vestibular and audiologic injury related to blast injury remains underreported. The primary objective of this study was to document self-reported otovestibular impairment in blast-injured amputees. Secondary objectives include a description of the Walter Reed Army Medical Center Blast Injury Questionnaire and other aspects of the audiology service and amputee physical therapy section standards of care for blast injury management. A case study illustrates the application of these standards of care. Thirty-three patients were evaluated by audiologists and physical therapists using the Walter Reed Army Medical Center Blast Injury Questionnaire, followed by audiologic and vestibular screening; 24% of patients reported symptoms of vertigo or oscillopsia following blast trauma, and 51% reported subjective hearing loss. The case study subject reported an increase in function after vestibular rehabilitation therapy. Thorough screening by audiologists and physical therapists can facilitate appropriate diagnosis and management for blast-injured patients.

Background:The study evaluates a group of Military Service Members specialized in blast explosive training called “Breachers” who are routinely exposed to multiple low-level blasts while teaching breaching at the U.S. Marine Corps in Quantico Virginia. The objective of this study was to determine if there are any acute or long-term auditory changes due to repeated low-level blast exposures used in training. The performance of the instructor group “Breachers” was compared to a control group, “Engineers”.Methods:A total of 11 Breachers and four engineers were evaluated in the study. The participants received comprehensive auditory tests, including pure-tone testing, speech-in-noise (SIN) measures, and central auditory behavioral and objective tests using early and late (P300) auditory evoked potentials over a period of 17 months. They also received shorter assessments immediately following the blast-exposure onsite at Quantico.Results:No acute or longitudinal effects were identified. However, there were some interesting baseline effects found in both groups. Contrary to the expected, the onsite hearing thresholds and distortion product otoacoustic emissions were slightly better at a few frequencies immediately after blast-exposure than measurements obtained with the same equipment weeks to months after each blast-exposure.Conclusions:To date, the current study is the most comprehensive study that evaluates the long-term effects of blast-exposure on hearing. Despite extensive testing to assess changes, the findings of this study suggest that the levels of current exposures used in this military training environment do not seem to have an obvious deleterious effect on hearing.

The objective of this study was to use a prospective cohort of United States Marine Corps (USMC) instructors to identify any acute or long-term vestibular dysfunction following repeated blast exposures during explosive breaching training. They were assessed in clinic and on location during training at the USMC Methods of Entry School, Quantico, VA. Subjects received comprehensive baseline vestibular assessments and these were repeated in order to identify longitudinal changes. They also received shorter assessments immediately following blast exposure in order to identify acute findings. The main outcome measures were the Neurobehavioral Symptom Inventory, vestibular Visual Analog Scale (VAS) of subjective vestibular function, videonystagmography (VNG), vestibular evoked myogenic potentials (VEMP), rotary chair (including the unilateral centrifugation test), computerized dynamic posturography, and computerized dynamic visual acuity. A total of 11 breachers and 4 engineers were followed for up to 17 months. No acute effects or longitudinal deteriorations were identified, but there were some interesting baseline group differences. Upbeat positional nystagmus was common, and correlated (p<0.005) with a history of mild traumatic brain injury (mTBI). Several instructors had abnormally short low-frequency phase leads on rotary chair testing. This study evaluated breaching instructors over a longer test period than any other study, and the results suggest that this population appears to be safe from a vestibular standpoint at the current exposure levels. Upbeat positional nystagmus correlated with a history of mTBI in this population, and this has not been described elsewhere. The data trends also suggest that this nystagmus could be an acute blast effect. However, the reasons for the abnormally short phase leads seen in rotary chair testing are unclear at this time. Further investigation seems warranted.

Objectives: The Subjective Visual Vertical (SVV) test and the closely related Rod and Disk Test (RDT) are measures of perceived verticality measured in static and dynamic visual backgrounds. However, the equipment used for these tests is variable across clinics and is often too expensive or too primitive to be appropriate for widespread use. Commercial virtual reality technology, which is now widely available, may provide a more suitable alternative for collecting these measures in clinical populations. This study was designed to investigate verticality perception in symptomatic patients using a modified RDT paradigm administered through a head-mounted display (HMD). Design: A group of adult patients referred by a physician for vestibular testing based on the presence of dizziness symptoms and a group of healthy adults without dizziness symptoms were included. We investigated degree of visual dependence in both groups by measuring SVV as a function of kinematic changes to the visual background. Results: When a dynamic background was introduced into the HMD to simulate the RDT, significantly greater shifts in SVV were found for the patient population than for the control population. In patients referred for vestibular testing, the SVV measured with the HMD was significantly correlated with traditional measures of SVV collected in a rotary chair when accounting for head tilt. Conclusions: This study provides initial proof of concept evidence that reliable SVV measures in static and dynamic visual backgrounds can be obtained using a low-cost commercial HMD system. This initial evidence also suggests that this tool can distinguish individuals with dizziness symptomatology based on SVV performance in dynamic visual backgrounds.