Optimized Signal Analysis to Quantify the Non-Linear Behaviour of the Electrically Evoked Vestibulo-Ocular Reflex in Patients with a Vestibular Implant

Dmitrii Starkov*, Maksim Pleshkov, Nils Guinand, Angélica Pérez Fornos, Maurizio Ranieri, Samuel Cavuscens, Joost Johannes Antonius Stultiens, Elke Maria Johanna Devocht, Herman Kingma, Raymond van de Berg

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

INTRODUCTION: Different eye movement analysis algorithms are used in vestibular implant research to quantify the electrically evoked vestibulo-ocular reflex (eVOR). Often, standard techniques are used as applied for quantification of the natural VOR in healthy subjects and patients with vestibular loss. However, in previous research, it was observed that the morphology of the VOR and eVOR may differ substantially. In this study, it was investigated if the analysis techniques for eVOR need to be adapted to optimize a truthful quantification of the eVOR (VOR gain, orientation of the VOR axis, asymmetry, and phase shift).

METHODS: "Natural" VOR responses were obtained in six age-matched healthy subjects, and eVOR responses were obtained in eight bilateral-vestibulopathy patients fitted with a vestibular implant. Three conditions were tested: "nVOR" 1-Hz sinusoidal whole-body rotations of healthy subjects in a rotatory chair, "eVOR" 1-Hz sinusoidal electrical vestibular implant stimulation without whole-body rotations in bilateral-vestibulopathy patients, and "dVOR" 1-Hz sinusoidal whole-body rotations in bilateral-vestibulopathy patients using the chair-mounted gyroscope output to drive the electrical vestibular implant stimulation (therefore also in sync 1 Hz sinusoidal). VOR outcomes were determined from the obtained VOR responses, using three different eye movement analysis paradigms: (1) peak eye velocity detection using the raw eye traces; (2) peak eye velocity detection using full-cycle sine fitting of eye traces; (3) peak eye velocity detection using half-cycle sine fitting of eye traces.

RESULTS: The type of eye movement analysis algorithm significantly influenced VOR outcomes, especially regarding the VOR gain and asymmetry of the eVOR in bilateral-vestibulopathy patients fitted with a vestibular implant. Full-cycle fitting lowered VOR gain in the eVOR condition (mean difference: 0.14 ± 0.06 95% CI, p = 0.018). Half-cycle fitting lowered VOR gain in the dVOR condition (mean difference: 0.08 ± 0.04 95% CI, p = 0.009). In the eVOR condition, half-cycle fitting was able to demonstrate the asymmetry between the excitatory and inhibitory phases of stimulation in comparison with the full-cycle fitting (mean difference: 0.19 ± 0.12 95% CI, p = 0.024). The VOR axis and phase shift did not differ significantly between eye movement analysis algorithms. In healthy subjects, no clinically significant effect of eye movement analysis algorithms on VOR outcomes was observed.

CONCLUSION: For the analysis of the eVOR, the excitatory and inhibitory phases of stimulation should be analysed separately due to the inherent asymmetry of the eVOR. A half-cycle fitting method can be used as a more accurate alternative for the analysis of the full-cycle traces.

Original languageEnglish
Pages (from-to)458-468
Number of pages11
JournalAudiology and Neurotology
Volume27
Issue number6
Early online date11 Jul 2022
DOIs
Publication statusPublished - Nov 2022

Keywords

  • BALANCE
  • Bilateral vestibular areflexia
  • Bilateral vestibulopathy
  • CRITERIA
  • Eye movement analysis algorithm
  • Neural prosthesis
  • Signal fitting
  • Vestibular implant
  • Vestibular prosthesis
  • Vestibulo-ocular reflex

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