An Examination of the Potential for Autonomic Nervous System Responses and Postural Sway to Serve as Indicators of Visual-Vestibular Mismatch

Abstract

Background. Although treatments for dizziness as a result of visual-vestibular mismatch (VVM) exist, the lack of prognostic information about this population affects the quality of their rehabilitation care. Despite numerous studies showing that individuals presenting with non-specific dizziness are likely to have VVM, and despite VVM being recognized by to the international classification of vestibular disorders by the Bárány Society, it remains unknown how prevalent this condition is. The VVM diagnostic questionnaire has not yet been generally accepted as a useful tool for diagnosis. There are inadequate criteria for prescribed vestibular rehabilitation for individuals with VVM, and little evidence to support the selection of treatment programs among this population. Treatment outcomes are not particularly successful because of a lack of guidelines. Studies have been performed that address dizziness severity, but no reliable biometric measurement has been developed yet. A potential measure of VVM could be responses of the autonomic nervous system (ANS) during vestibulo-visual challenges given the anatomical relationship between the vestibular system and the ANS. Individuals with both peripheral and central vestibular dysfunction exhibit symptoms and signs of autonomic dysfunction as a result of vestibulo-autonomic interactions. Moreover, changes in postural sway are a tangible indicator of the balance during any disturbance to the vestibular system. In this dissertation the use of measures of electrodermal activity (EDA) of the ANS and postural acceleration are explored in vestibular migraine (VM) individuals both with and without VVM. Purpose. The aims of this dissertation were to examine, in VM adults: 1) the presence of VVM and visual dependency in individuals presenting with complaints of dizziness using the VVM questionnaire and the Rod and Frame protocol, respectively; 2) the potential of EDA activity and postural responses to differentiate between VM and healthy individuals when accommodating for postural instability and visual-vestibular conflict; and 3) the effect of exposure to different visual contexts of VR environments on EDA phasic and tonic responses and postural responses in identified VM adults with VVM. Participants. Seventy-four participants with dizziness were enrolled in Aim 1 (70% female, mean age 45.4 ± 14.8 years), and a total of 45 participants (23 healthy, 45.5% female, mean age 34± 9 years) and (22 VM adults, 61% female, mean age 34.4 ± 8, including 12 VM adults with VVM, 77% female, mean age 34±9) were enrolled in the experimental studies for Aims 2 and 3. Methods. In Aim 1, the VVM questionnaire and the Rod and Frame protocol were used to test the presence of VVM and visual dependency, respectively. In Aims 2 and 3, a Shimmer 3 IMU sensor accelerometer was used to assess trunk acceleration in the anterior-posterior, medial-lateral, and vertical directions with different VR environments (STREET and SPACE). EDA measurements were assessed with a wireless wearable Shimmer 3 GSR+. Clinical measures of dizziness and mobility were concurrently tested. A linear mixed model was used to examine the effect of VM with and without VVM on standing balance and EDA activity. Results. The presence of VVM, headache, and visual dependency demonstrated a strong association. EDA activity and postural acceleration significantly differed between VM and healthy individuals. Specific subjective reporting tools, including ABC, VSS-SF, VVAS, and DHI, were reliable for distinguishing between VM and healthy individuals. Lastly, VM individuals with VVM exhibited significantly greater NPL of trunk accelerations in the vertical plane than VM individuals without VVM with the STREET environment compared to the SPACE environment. Conclusion. VVM and visual dependency could be risk factors for developing vestibular migraine and should be included in the examination protocol of those populations. Combining measures of EDA and trunk acceleration may provide objective measures of the severity of dizziness related to VVM. Results of this dissertation suggest that the use of EDA measures combined with NPL-Vert could provide potential neurophysiological biomarkers in identifying VVM in adults with vestibular migraines. Further, the correlation between the characteristics of the visual environment and the subjective dizziness outcome measure may contribute to establishing a threshold-tolerance basis for designing a vestibular rehabilitation program that will more precisely target symptom severity.