Tracking Recovery of Vestibular Function in Individuals With Blast-Induced Head Trauma Using Vestibular-Visual-Cognitive Interaction Tests

Gottshall, Kim R. PT, PhD, ATC; Hoffer, Michael E. MD, CAPT MC USN

Journal of Neurologic Physical Therapy:
doi: 10.1097/NPT.0b013e3181dead12

Background and Purpose: Traumatic brain injury secondary to blast exposure is a significant international concern and a growing rehabilitation issue. Our objective was to determine whether a novel battery of vestibular-visual-cognitive interaction tests provides objective data to document functioning, and the changes in functioning associated with vestibular physical therapy (VPT) treatment, in individuals with blast-induced balance disorder.

Methods: Eighty-two individuals with blast-induced mild traumatic brain injury were evaluated at baseline using a set of vestibular-visual-cognitive tests. Testing was repeated at 4-week intervals after beginning VPT. The tests included static visual acuity, perception time, target acquisition, target following (TF), dynamic visual acuity (DVA), and gaze stabilization tests. The VPT program consisted of exercise procedures that targeted the vestibulo-ocular reflex, cervico-ocular reflex, and depth perception. Somatosensory balance exercises, dynamic gait, and aerobic function exercises were also included. Participants attended VPT twice weekly for 1-hour appointments and were instructed to perform the exercises at home on other days. Mean test values were determined and compared with normative values previously collected in our laboratory from individuals without vestibular dysfunction.

Results: Mean participant pre-VPT measures for perception time and target acquisition were similar to normative values, and there was no significant change in these measures. Initially, TF and DVA scores were below normative levels but returned to normative levels after 8 weeks of VPT. Gaze stabilization scores were below normative levels pre-VPT but improved by the time of the week 8 evaluation.

Conclusions: This battery of vestibular-visual-cognitive tests seems to be reasonable to establish initial status and to evaluate participant progress associated with participation in VPT. Our data suggest meaningful improvement in TF and DVA after 8 weeks of treatment. A treatment period of 12 weeks or longer may be required for gaze stabilization scores to return to normative values.

Author Information

Naval Medical Center, San Diego, California.

Correspondence: Kim R. Gottshall, E-mail:

The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government.

Article Outline
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Mild traumatic brain injury (mTBI) secondary to blast exposure and blunt head trauma is the most common battlefield injury seen in Iraq and Afghanistan, and is an increasingly important injury pattern in the civilian world. Blunt and blast mTBI are common causes of vestibular disorders.1–3 Our group at Naval Medical Center San Diego has described the patterns of dizziness from both blunt and blast injury in the past.1–3 Awareness of these patterns is useful in several ways, including guiding diagnosis and management, and predicting prognosis. Vestibular physical therapy (VPT) is an important tool for restoring function in this group of individuals. The objective outcome measures are vital to the evaluation of programs designed to promote functional improvement in balance and gait stability. The purpose of this study was to determine whether a novel battery of vestibular-visual-cognitive interaction tests provides objective data to assess functioning and document change in functioning after a VPT program in soldiers with blast-induced mTBI.

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We studied 82 participants (79 men and 3 women; mean age = 24 years, range = 19–34 years) with mTBI who were treated with VPT. All participants were soldiers who had mTBI secondary to blast injuries sustained in Iraq or Afghanistan, with no other associated physical injuries. The participants were diagnosed as having 1 of 4 vestibular disorders: (1) benign paroxysmal positional vertigo, (2) exertion-induced dizziness, (3) blast-induced disequilibrium, and (4) blast-induced disequilibrium with vertigo. Diagnostic characteristics for each classification are shown in Table 1. All participants underwent a comprehensive physical therapy and neurologic history and physical described elsewhere.1–3 We used a rotary chair as the objective test of vestibular function. This study was approved by the institutional review board at Naval Medical Center San Diego (IRB S2003.0143). All subjects consented to participation in the study.

The testing and VPT were the same for all participants regardless of diagnosis. We applied a standardized battery of tests at baseline and follow-up for all participants referred for VPT after blast injury. These tests included computerized dynamic posturography (CDP) in which the sensory organization test (SOT) and motor control test (MCT) were administered.4 The dynamic gait index (DGI) test was performed to assess overall dynamic gait function and fall risk.5 Tests of vestibular-visual-cognitive function were administered using the Neurocom inVision Tunnel. The vestibular-visual-cognitive battery of tests was performed in a darkened room with an effective viewing distance of 10 feet. The test battery included static visual acuity, perception time (PT), target acquisition (TA), target following (TF), dynamic visual acuity (DVA), and gaze stabilization tests (GSTs). PT was measured by calculating the time, in milliseconds, that a randomly presented target must be on the screen before accurate recognition by the subject. TA was the time required for the eyes to make a saccade from the center of the screen to the new optotype position up, down, right, or left; TA did not involve measuring eye velocity. TF was a functional measure of smooth pursuit speed in degrees per second. The subject was asked to track a symbol when the velocity of the target was fixed (horizontally or vertically); TF did not involve measuring eye velocity. DVA was measured in logMAR DVA loss (ie, change in function from stable acuity to head motion acuity as measured in logarithm of the minimal angle of resolution) with active horizontal or vertical head motion. A GST was the speed in degrees per second at which the subject could accurately hold a visual target and maintain recognition while performing active horizontal or vertical head motion. For each of the vestibular-visual-cognitive tests, participants gave a verbal response and the answer was entered by the operator.

The aim of the study was to assess performance on SOT, MCT, DGI, PT, TA, TF, DVA, and GST at the initial physical therapy visit, week 4, and week 8 visit. Group mean values were compared with normative data previously collected in the laboratory (but not previously published) as part of another study of individuals without vestibular dysfunction.6 The sample for the normative data set was 80 participants (55 men and 35 women), mean age 30.6 years (range, 20–39 years); therefore, the normative data group contained a higher proportion of men and was slightly older than the current study sample. Normative values are summarized in Table 2. In participants whose scores were outside the range of normative scores at week 8, additional testing was performed at subsequent 4-week intervals after completing more therapy. In all cases, the final measurements represent that point in time when the participant's scores were within the range of normative values and rehabilitation was terminated.

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Vestibular Rehabilitation

The VPT program consisted of exercise procedures that targeted the vestibulo-ocular reflex, cervico-ocular reflex, depth perception, somatosensory retraining, dynamic gait, and aerobic function. The vestibulo-ocular reflex, cervico-ocular reflex, and depth perception exercises were graded in difficulty, based on velocity of head and object motion, and progression of body positioning from sitting to standing to walking. The SS exercises were graded in difficulty by narrowing the base of support, making the surface uneven, or changing the surface from firm to soft. Walking exercises were graded in difficulty by changing direction, performing with the eyes closed, increasing speed, walking on soft surfaces, or navigating stairs. The aerobic exercise home program was progressively increased by adjusting the time, speed, or distance. All subjects were encouraged to work at their maximum tolerance while performing the VPT. These exercises have been described in detail elsewhere.7 Participants attended VPT twice weekly for 1-hour sessions and were instructed to perform the exercises on a home program basis the other days.

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Statistical Analysis

Group mean pretreatment scores on SOT, MCT, DGI, PT, TA, TF, DVA, and GST were compared with group mean posttreatment scores using a 2-way analysis of variance with standard statistical software (GB-STAT). Significance was defined as P ≤ .01.

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Group mean PT, TA, TF, and DVA values achieved normative or near-normative levels after 4 weeks of VPT. Group mean PT decreased from 43 msec to 27 msec (normal = 20 msec). TF increased from 9 degrees/sec to 13 degrees/sec (normal = 12 degrees/sec). Horizontal TA time decreased from 350 msec to 260 msec, whereas vertical TA time decreased from 360 msec to 280 msec (normal = 250 msec). DVA logMAR loss decreased from 0.33 logMAR right to 0.2 logMAR right; 0.36 logMAR left to 0.2 logMAR left; 0.28 logMAR down to 0.18 logMAR down, and 0.27 logMAR up to 0.18 logMAR up, (normal = 0.20 logMAR or less). However, GST did not return to the normed levels (ie, horizontal GST: 140 degrees/sec left and 144 degrees/sec right; vertical GST: 136 degrees/sec down and 135 degrees/sec up) until completing an additional 4 weeks (ie, 12 weeks total) of VPT. Anecdotally, we noted a return to running 3 miles without symptoms in those soldiers that had normal values of vertical GST at week 12.

SOT test results revealed a reduced vestibular profile (mean CDP SOT score of 58) in participants on initial testing. Similarly, MCT also revealed a significantly higher percentage of prolonged latencies to translation in a portion of our cohort (n = 30) on initial testing. Mean DGI increased from 21 to 23 points at the week 8 test point. Although this was not statistically significant, the DGI tasks that consistently improved were walking with horizontal head motion and with vertical head motion, so we believed the difference to be clinically meaningful. Full performance of the DGI achieving 24 points was attained by all participants after 12 weeks of VPT.

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Vestibular symptoms are the most frequent sequelae of blast-induced mTBI.1 VPT is an important treatment modality for individuals with this diagnosis when the goal is return to duty status. Nevertheless, there is little work objectively documenting the impact of VPT on this group. Previous studies have used clinical measures such as the Glasgow Coma Scale as a general assessment of recovery of consciousness after TBI.8 However, there remains a lack of studies aimed at examining the adequacy of vestibular tests for tracking recovery of vestibular function. Scherer and Schubert9 reinforced the need for “best practice” vestibular assessment for formulation of appropriate VPT treatment strategies. The application of vestibular testing and rehabilitation in individuals with vestibular dysfunction is needed to provide information on objective outcome measures.10 Although we and others have developed VPT procedures that apply a best practice approach for individuals with blast-induced mTBI, these therapies must be customized for the individual based on initial level of function and expected level of recovery.5

Knowledge of the patient's diagnosis and disability is a critical foundation for planning interventions with the goal of return to activities of daily living, work, or sport. The value of the CDP SOT score as a guide for exercise selection and progression has been established;4 and the DGI has been identified as a useful a diagnostic tool.5,11,12 However, these studies have not included individuals with blast-induced mTBI injury, who tend to have a different type of vestibular profile than those tested in previous studies. The blast-induced mTBI population also represents a younger population compared with participants in most previous studies. Similarly, although there are several studies examining the GST as an outcome measure and correlating these scores with postural stability,13–16 the sample sizes were small and were different from our sample of participants with blast-induced mTBI both in terms of vestibular dysfunction and age. Although the entire suite of vestibular-visual-cognitive tests provides valuable information, our data indicate that the vertical GST is the last measure to improve in our population. The utility of this finding in establishing return to military work/duty status is unclear.16 Functional levels that might be considered typical for an older individual with vestibular dysfunction (eg, poststroke) would be unacceptable in a young military population intent on returning to active duty. We recommend that vestibular clinics establish their own normative data sets to establish a basis of comparison to assist return to duty/work status as well as return to physical activity status.17

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In soldiers with mTBI and vestibular disorders caused by blast injuries, many aspects of vestibular-visual-cognitive function recover with VPT. The time course of recovery varies for different aspects of vestibular function. A battery of vestibular-visual-cognitive tests is valuable for establishing initial functional levels and can be used to document improvement. These outcome measures may also be useful to determine return to duty/work status as well as return to physical activity status for military personnel.

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concussion; traumatic brain injury; balance

© 2010 Neurology Section, APTA