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Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 197-219.

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Background: The otoliths act as gravito-inertial force sensors and contribute to the perception of spatial orientation. The perception of gravitational vertical can be assessed by asking a subject to adjust a light bar to the vertical. Prior to clinical use of the SVV (subjective visual vertical) test, normative data and test-retest reliability must be established. Purpose: To obtain normative data and d etermine the test-retest reliability for the SVV test performed in static and dynamic test conditions. Research Design: A descriptive design was used to obtain normative data. Study Sample: Twenty-four young adults with no history of neurological disease, middle-ear pathology, open or closed head injury, cervical injury, or audiovestibular disorder participated in the study. Data Collection and Analysis: The SVV angle was measured in the static position and in three dynamic conditions: (1) on-axis clockwise (CW) rotation, (2) off-axis CW rotation of right ear, and (3) off-axis CW rotation of left ear. Results: In young healthy individuals, the SVV was Conclusions: The normative data obtained in this study may be useful in identifying patients with chronic utricular dysfunction. We recommend the use of difference angles (on-axis SVV ‐ off-axis SVV) to remove baseline bias and decrease the variability of the SVV angles for the off-axis conditions.

Despite our understanding of the impact of noise-induced damage to the auditory system, much less is known about the impact of noise exposure on the vestibular system. In this article, we review the anatomical, physiological, and functional evidence for noise-induced damage to peripheral and central vestibular structures. Morphological studies in several animal models have demonstrated cellular damage throughout the peripheral vestibular system and particularly in the otolith organs; however, there is a paucity of data on the effect of noise exposure on human vestibular end organs. Physiological studies have corroborated morphological studies by demonstrating disruption across vestibular pathways with otolith-mediated pathways impacted more than semicircular canal-mediated pathways. Similar to the temporary threshold shifts observed in the auditory system, physiological studies in animals have suggested a capacity for recovery following noise-induced vestibular damage. Human studies have demonstrated that diminished sacculo-collic responses are related to the severity of noise-induced hearing loss, and dose-dependent vestibular deficits following noise exposure have been corroborated in animal models. Further work is needed to better understand the physiological and functional consequences of noise-induced vestibular impairment in animals and humans.

Young adults are more likely to suffer blast injury and traumatic brain injury (TBI) than other age groups. This article reviews the literature on the vestibular consequences of blast exposure and TBI and concussion. In addition, the vestibular test findings obtained from 31 veterans with a history of blast exposure and/or mild TBI are presented. The authors discuss loss of horizontal semicircular canal function and postural instability related to head injury. Preliminary data suggest the novel theory that otolith organs are uniquely vulnerable to head injury and blast exposure.