DESCRIPTION (provided by applicant): Emerging evidence suggests that otolith organ dysfunction of the vestibular system occurs in Veterans with dizziness and imbalance related to mild traumatic brain injury/blast exposure. It is unclear if standard vestibular rehabilitation is effective for individuals with otolith dysfunction This pilot project is designed to examine the effectiveness of vestibular rehabilitation and a novel treatment approach. The primary function of the vestibular (inner ear balance) system is to maintain gaze and postural stability. The vestibular system is comprised of two types of sensory organs (semicircular canals and otolith organs) with unique contributions to balance. Loss of vestibular function can occur in one or more vestibular sensory organs. Symptoms of vestibular loss include dizziness, postural instability, and/or visual blurring. Moreover, the incidence of falls is greater in individuals with vestibular loss than in healthy individuals of th same age (Herdman et al., 2000). Recent studies suggest that otolith dysfunction is a fairly common finding in individuals with a history of head trauma/blast exposure and/or noise induced hearing loss (Akin & Murnane, 2011; Akin et al., 2012). Therefore, otolith dysfunction may be a significant health concern for the Veteran population, and determining optimal intervention for otolith dysfunction is relevant to VA healthcare. Vestibular Rehabilitation (VR) is the treatment o choice for patients experiencing dizziness, imbalance, and mobility impairments related to vestibular dysfunction. VR typically includes gaze stability exercises, gait and balance training, and general conditioning. Gaze stability exercises are based on the concepts of adaptation and substitution with the goal of facilitating vestibular compensation of the semicircular canal-mediated angular vestibulo-ocular reflex (aVOR). A critical signal to induce adaptation is retinal slip during head movements; thus, adaptation exercises involve head rotation while focusing on a target. Studies of individuals with vestibular dysfunction suggest that VR results in decreased subjective complaints and improved function in many but not all patients (Herdman et al., 2012). Many factors that might influence recovery, such as the involvement of different vestibular sensory organs (semicircular canals versus otolith organs) have not been examined to determine their impact on recovery. Most studies examining the effectiveness of VR have used only tests of VOR function (caloric and rotational tests) that measure hSCC to determine vestibular loss. Thus, little is known about interventions to facilitate vestibular compensation of the otolith organs. Recent studies have demonstrated adaptation following otolith organ stimulation using centrifugation (or linear acceleration). The concept of using centrifugation for otolith adaptation may be similar to using gaze stability exercises for aVOR adaptation. Astronauts who received centrifugation (i.e., off-axis rotation) during in-space flight did not exhibit the typical deconditioning of the otolith-ocular reflex (Buytaert et al., 2013). In a case study, Akin et al. (2013) demonstrated improved symptoms and balance following centrifugation of a patient with chronic unilateral vestibular hypofunction. The purpose of this project is to determine if centrifugation is an effective intervention strategy in the treatment of Veterans with otolith dysfunction. Specific Aim 1 is designed to determine the effect of standard vestibular rehabilitation on otolith dysfunction. Veterans with dizziness/imbalance related to otolith dysfunction will be randomized to a staged intervention of 4 weeks of gaze stability exercises followed by 4 weeks of balance and gait exercises. By providing the intervention in a staged manner we will be able to isolate critical components of rehabilitation of otolith dysfunction. Specific Aim 2 is designed to examine the extent to which centrifugation impacts outcomes for individuals with otolith dysfunction. Veterans with dizziness/imbalance related to otolith dysfunction will be randomized to a staged intervention of 4 weeks of centrifugation (otolith organ stimulation) followed by 4 weeks of balance and gait exercises. Outcome measures of symptom intensity, balance, and gait will be compared.

PUBLIC HEALTH RELEVANCE Relevance of the Proposed Work to the VA Patient Care Mission The goal of this study is to determine the effect of gaze stability exercises versus centrifugation on dizziness and imbalance related to otolith dysfunction. The incidence of dizziness and imbalance increases in populations relevant to VA healthcare: older adults and individuals with noise exposure and traumatic brain injury. Furthermore, preliminary data suggest that otolith dysfunction is a common finding in patients with a history of head trauma/blast exposure or noise induced hearing loss. Successful management of dizziness is critical because dizziness is a major risk factor for falls. An estimate of outpatient costs to the VA in 2001 for fall-related injuries was nearly $3.3 million for the initial visit alone (Luther, 2005). The potential for large economic savings by reducing falls incidence, thus fall-related injuries, is evident. The proposed study is the first step towards developing novel therapeutic approaches to reduce the negative impact of dizziness on Veterans with otolith dysfunction.