The purpose of this project is to determine the effects of mild traumatic brain injury and blast exposure on the inner ear balance and central nervous systems.
The goal of this project is to determine the effects of mild traumatic brain injury (mTBI) and blast exposure on the vestibular system and CNS. Dizziness and balance disorders are common symptoms associated with mTBI or head injury. Numerous studies have provided significant evidence that mTBI or head injury can cause damage to the vestibular system; however, most have limited the vestibular evaluation to assessment of horizontal semicircular canal function. Recently, methods have been developed to assess otolith function, and there is some evidence that head injury may affect the otolith organs to a greater degree than the semicircular canals. mTBI has been called the signature condition of Veterans returning from Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF), and the cause is often related to blast exposure from improvised explosive devices, mortars or rocket-propelled grenades. Some investigators have presumed that dizziness and balance disorders following blast exposure are related to CNS damage caused by the TBI rather than the pressure wave from the blast injury. Thus, most research has focused on the vestibular consequences of TBI (or head injury), and there is limited data on the effects of blast exposure on vestibular function or balance. Recently, magnetic resonance imaging techniques have been developed that may allow for testing the assumption that the symptoms of dizziness or imbalance related to head injury or blast exposure are often due to central vestibular or CNS involvement. Specific aims of this project are to determine the effect of mTBI and blast exposure on (1) peripheral vestibular system function (specifically, horizontal semicircular canal function, and otolith organ function), (2) central vestibular/CNS function, (3) postural stability, and (4) dizziness-related quality of life. Four subject groups will include Veterans complaining of dizziness/imbalance with (1) a history of blast exposure, (2) with mTBI, (3) with blast exposure and mTBI, and (4) a control group. Each subject will undergo tests of horizontal semicircular canal function (caloric and rotary chair), tests of otolith function (vestibular evoked myogenic potentials, subjective visual vertical), central vestibular function/CNS function (ocular motor tests, diffusion tensor and susceptibility weighting imaging), gait and balance testing, and the Dizziness Handicap Inventory.
Study Type
OBSERVATIONAL
Enrollment
140
Mountain Home VA Medical Center James H. Quillen VA Medical Center, Mountain Home, TN
Mountain Home, Tennessee, United States
Peripheral Vestibular Function (Vestibulo-ocular Reflex/Semicircular Canal): Caloric Weakness
The caloric weakness was determined using monothermal warm inter-ear difference (MWIED) which was calculated as: (\|RW\| - \|LW\| )/( \|RW\| + \|LW\|) x 100, where RW = the maximum slow phase velocity (SPV) of nystagmus induced by warm water irrigation in the right ear and LW = the maximum SPV of nystagmus induced by warm water irrigation in the left ear. For participants with MWIED \> 10, then cool caloric irrigation was also performed and caloric weakness was determined using a bithermal inter-ear difference (BIED) calculated as: (\|RW\| + \|RC\|) - (\|LW\| + \|LC\|) / (\|RW\| + \|RC\| + \|LW\| + \|LC\|) x 100, where RC = maximum SPV of nystagmus induced by cool water irrigation in the right ear and LC = maximum SPV of nystagmus induced by cool water irrigation in the left ear.
Time frame: up to 30 minutes
Rotary Chair Slow Harmonic Acceleration (SHA) Gain
Rotary chair slow harmonic acceleration (SHA) vestibulo-ocular reflex (VOR) gain at 0.01 Hz was used as a measure of peripheral vestibular function (VOR/horizontal semicircular canal). VOR gain is defined as the ratio of the slow component velocity eye movement (output) to the velocity of the head movement (input).
Time frame: up to 30 minutes
Peripheral Vestibular Function (Saccular-collic Pathway): Cervical Vestibular Evoked Potential (cVEMP)
Air-conducted cervical vestibular evoked potential (cVEMP) inter-ear amplitude asymmetry ratio was used as a measure of otolith organ function (saccular-collic pathway). Inter-ear amplitude asymmetry ratio was calculated as: \[(\|L\_P1-N1\| - \|R\_P1-N1\|)/ (\|L\_P1-N1\| + \|R\_P1-N1\|)\] x100, where L\_P1-N1 = peak-to-peak cVEMP amplitude of the left side and R\_P1-N1 = peak-to-peak cVEMP amplitude of the right side. The amplitudes were calculated from cVEMP responses at a stimulus intensity of 120 dB peakSPL. The criterion for abnormal cVEMP was defined as an absent cVEMP or a corrected cVEMP amplitude asymmetry ratio greater than or equal to 40%, either of which would indicate a unilateral vestibular loss. A bilateral vestibular loss was indicated by absent cVEMPs bilaterally.
Time frame: Up to 30 minutes
This platform is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional.
Rotary Chair Slow Harmonic Acceleration (SHA) Phase
Rotary chair slow harmonic acceleration (SHA) vestibulo-ocular reflex (VOR) phase at 0.01 Hz was used as a measure of peripheral vestibular function (VOR/horizontal semicircular canal). The phase is the timing difference between the velocity of head movement and the slow-phase eye velocity. This parameter is normalized for a full cycle of a sinusoid (360 degrees) and presented in an angular unit of degrees rather than a unit of time. For perfectly compensatory eye movements the phase is 0 degrees, meaning there is no difference between the actual eye velocity and the ideal VOR (by convention, degrees is added to the phase so that the comparison is based on the ideal VOR responses instead of the actual head motion).
Time frame: Up to 30 minutes (SHA phase is obtained simultaneously with SHA gain)
Peripheral Vestibular Function (Utricular-ocular Pathway): Ocular Vestibular Evoked Potential (oVEMP)
Bone-conducted ocular vestibular evoked potential (oVEMP) inter-ear amplitude asymmetry ratio was used as a measure of otolith organ function (utricular-ocular pathway). Inter-ear amplitude asymmetry ratio was calculated as: \[(\|L\_N1-P1\| - \|R\_N1-P1\|)/ (\|L\_N1-P1\| + \|R\_N1-P1\|)\] x100, where L\_N1-P1 = peak-to-peak oVEMP amplitude of the left eye/right ear and R\_N1-P1 = peak-to-peak oVEMP amplitude of the right eye/left ear. The oVEMP is a contralateral response; therefore, recordings from the left eye reflect the response of the right ear and vice versa. The amplitudes were calculated from oVEMP responses at a stimulus intensity of 155 dB peakFL. The criterion for abnormal oVEMP was defined as an absent oVEMP or a corrected oVEMP amplitude asymmetry ratio greater than or equal to 40%, either of which would indicate a unilateral vestibular loss. A bilateral vestibular loss was indicated by absent oVEMPs bilaterally.
Time frame: Up to 20 minutes
Central Vestibular/Central Nervous System (CNS) Function: Visual Fixation Suppression
Visual fixation suppression was used as a measure of central vestibular/CNS function. Visual fixation suppression is a measure of vestibulo-ocular reflex (VOR) gain obtained during visual fixation at 0.16 Hz slow harmonic acceleration on the rotary chair. VOR gain was defined as the ratio of the slow component velocity eye movement (output) to the velocity of the head movement (input). Visual fixation suppression was considered normal if VOR gain is suppressed \> 50% with visual fixation compared to no fixation.
Time frame: 1 minute
Postural Stability: Sensory Organization Test (SOT)
This measure is the composite equilibrium score from six conditions of the sensory organization test obtained with the Neurocom Equitest. Results of the SOT were calculated based on maximum peak-to-peak anterior-posterior sway expressed as an equilibrium score ranging from 0 to 100, with 0 indicating loss of balance (i.e., required support of harness, took a step, touched walls for support or opened eyes in eyes closed conditions) and 100 indicating perfect stability. The outcome measure was the equilibrium composite score and was calculated by the software as the weighted average of the equilibrium scores for the six conditions. For ages 18-59 years, the normative value (mean - 1.67 SD) for the composite score is at least 70 (NeuroCom, 2011).
Time frame: Up to 20 minutes
Dizziness Handicap Inventory
The Dizziness Handicap Inventory (DHI) was used as a quality of life measure.The DHI measures the subject's self-perceived dizziness. The scale has 25 questions with 3 possible answers each: "Yes" = 4 points, "Sometimes" = 2 points, and "No" = 0 points. The minimum number of points that a subject can score is 0 and the maximum number of points is 100. The subject's self-perceived dizziness is reported as a percentage with a range of 0-100%, and is calculated by: subject's total number of points/maximum number of points (100) x 100%. The higher the score on the DHI, the worse a patient's self-perceived dizziness.
Time frame: Up to 10 minutes