Access Type

Open Access Dissertation

Date of Award

January 2020

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Otolaryngology, Head and Neck Surgery

First Advisor

Anthony T. Cacace

Abstract

The purpose of this study was to evaluate the feasibility of developing a novel approach of otolith assessment in humans. This approach used vestibular short-latency evoked potentials (VsEP) to evaluate some fundamental characteristics of VsEP responses in healthy young adults. Currently, measures for direct assessment of the otoliths are non-existent, as vestibular evoked myogenic potentials (VEMPs) rely on neck muscle contraction for cVEMPs or are a reflection of the vestibulo-ocular reflex (VOR) for oVEMPs, rather than the otoliths themselves (Fujimoto, Suzuki, Kinoshita, Egami, Sugasawa, & Iwasaki, 2018).

Stimuli consisted of bone-conducted vibrations elicited by a specialized vibrator (Bruel & Kjaer, model 4810; B&K mini-shaker) attached to a power amplifier (B&K, model 2718) that causes linear acceleration movements of the skull. Standard reusable surface electrodes with the reference electrode placed on the forehead (Fpz), ground placed on the mastoid process of left ear (M2), and a (Lilly or Sanabel) wick electrode (placed as on the left tympanic membrane) were used to record early electrical activity (4ms). Data was collected and analyzed from 11 healthy young adults (6 males and 5 females) ranging in age from 19-39 years (mean: 23.1 years; SD: 6.9 years) who met the inclusion criteria for testing. Audiometric thresholds were tested to ensure normal hearing sensitivity (0.25-8 kHz; <25 dB HL, bilaterally).

A general analysis of the VsEPs was conducted through visual inspection of the waveforms and statistical analyses of the VsEP responses. The statistical analyses consisted of a series of one-way ANOVAs with repeated measures which included stimulus frequency (500 and 1000 Hz), intensity (115, 105, 95, & 85 dB SPL), along with masked (100, 90, & 80 dB HL) and unmasked conditions.

VsEPs appear to be promising due to the simplicity of the test and ease of analysis - looking at waveforms without requiring active participation from participants. It would be necessary to complete testing on additional healthy participants to ensure that there continues to remain a consistency across all VsEP conditions regardless of participant; as this study showed, no large outliers were found across results for any of the participants tested in this study. It would also be beneficial to assess additional VsEP parameters (e.g., contralateral masking, additional stimulus and masking levels, varying durations, etc) in known individuals with specific otolith dysfunction to see if able to find such consistency across disordered group in the future before this assessment will be translatable into a clinical setting.

Results of this study indicate that the amplitudes of the VsEPs are significantly impacted (p<.05) by the intensity of the stimulus, regardless of the frequency tested, with the higher intensity having higher mean amplitudes than the lower intensities tested. On the other hand, the VsEP latencies remained consistent, regardless of the different frequencies, stimulus intensity, and masker levels assessed.

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