Effects of different vestibular implant stimulation paradigms on balance and gait variability in people with severe bilateral vestibulopathy: a triple-blinded randomised cross-over study

ObjectivesThe vestibular implant is a neuroprosthesis that may offer a promising treatment for patients with severe bilateral vestibulopathy (BVP). This study explored the impact of different vestibular stimulation modes on gait and balance outcomes. It was expected that stimulation modes incorporating head motion-modulated input (modes A and B) would result in more favourable gait and balance outcomes compared to non-modulated baseline stimulation or no stimulation. MethodsThe VertiGo! trial is a randomized controlled crossover study. The trial includes nine participants with severe BVP who received a vestibular implant. In this triple-blinded sub-study, balance and gait variability were assessed during four testing weeks, the first providing a reference (no stimulation) followed by three weeks each with four days of stimulation: (A) baseline stimulation with head motion-modulation; (B) reduced baseline stimulation with head motion-modulation, and (C) baseline stimulation without modulation. Participants walked at different walking speeds (0.6, 0.8, and 1.0m/s) on an instrumented treadmill integrated in a 6-degree of freedom motion platform. Different walking conditions were evaluated (unperturbed, three levels of mediolateral platform sway and darkness). Coefficients of variation of spatiotemporal step parameters were analysed using 3D motion capture. Participants also completed the Mini-Balance Evaluation Systems Test (Mini-BESTest) once during the reference week and twice (day 1 and day 4) of each stimulation period. ResultsThere were no clear indications across the participants that stimulation modes A and B (compared to either mode C or no stimulation) were uniformly beneficial for either step time CoV after three days of stimulation or Mini-BESTest scores after four days of stimulation (though some individuals did demonstrate this pattern). Mini-BESTest scores significantly improved between day one and day four of stimulation. ConclusionsFour days of VCI stimulation appears to affect gait variability and balance (as measured by the Mini-BESTest) but effects vary between individuals and no consistent effect of stimulation mode across participants and walking conditions was found. Balance improved from day one to day four of stimulation (without a significant learning effect over all seven clinical balance assessments), indicating the importance of habituation to vestibular implant stimulation before beneficial functional outcomes can be expected.