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Project

ELVIS: ELectro-VIbrational Stimulation to exploit the full potential of the human cochlea

Cochlear implants (CI) are among the most successful medical implants, showcasing remarkable speech perception capabilities in quiet environments. Nevertheless, for many people with a CI, understanding speech in scenarios involving multiple competing talkers or background noise remains challenging. Recently, one of the promising pathways to further improvement of hearing outcomes with CIs has been to take advantage of the full residual function of the inner ear. A growing group of people has some residual hearing function after implantation. Combining the electrical stimulation by the CI with acoustic stimulation of the residual hearing, i.e. electro-acoustic stimulation (EAS), has been shown to improve speech and music perception. While the clinical benefits of EAS have been proven, the basic understanding of how acoustic stimulation of low-frequency hearing occurs with a CI in place remains limited.

In the doctoral research presented in this thesis, we investigate the long-term impact of a CI on the inner ear mechanics. Moreover, we expand the scope of how to take advantage of the full residual function of the inner ear by proposing an alternative combined stimulation technique: Electro-Vibrational Stimulation (EVS). EVS combines electrical stimulation by the CI with vibrational stimulation by a bone conduction actuator. 

Throughout this doctorate, we approached this aim from three distinct angles, each with its specific methodology. In the first part of this thesis, a histological study in human temporal bones showed that intracochlear fibrosis and neo-ossification were present in all cases at anatomical locations that could impact normal inner ear mechanics. Moreover, cases with acute insertional trauma to the osseous spiral lamina or insertion via a cochleostomy/extended round window approach showed higher proportions of local (fibro-)osseous tissue formation. In the second part, we measured the impact of the most notable histological finding after CI, i.e. round window reinforcement, on the inner ear mechanics with air and bone conduction. This experimental study in human cadaveric specimens indicated that the gradual growth of fibro-osseous tissue over the RW after implantation could cause a delayed loss of residual hearing with air conduction. Bone conduction hearing, in contrast, seems not to be considerably impacted by RW reinforcement. In the third and final part, we evaluated a first EVS prototype in people with a CI and residual low-frequency hearing. The results of this first clinical study are promising, revealing a significant improvement in speech perception in noise with EVS compared to the condition with the CI alone. Even larger effect sizes could be expected with a more individualized fitting and longer adaptation times.

Together, the three parts of this doctoral thesis establish a solid foundation of evidence that EVS is a valuable path worth exploring by future researchers and implant manufacturers.

Date:1 Oct 2020 →  Today
Keywords:Cochlear implantation, Hearing, Bone conduction
Disciplines:Otology
Project type:PhD project