Alteration of the relative vibration of the round window membrane after implantation of a direct acoustic cochlear implant

Abstract

Objective: Subjects implanted with a Direct Acoustic Cochlear Implant (DACI) show improvements in their bone conduction (BC) thresholds after surgery. We hypothesised that a new pathway for BC sound is created via the DACI. The aim of this study was to investigate the contribution of this pathway to the cochlear response via measurements of the promontory and round window membrane (RWM) velocities while stimulating with a conventional bone conductor.

Design: This study was a cadaver head study with a repeated measures study design.

Study Sample: Eight ears of five fresh-frozen cadaveric whole heads were investigated in this trial.

Results: After DACI implantation the promontory and RWM velocities did not change significantly in the frequency range 0.5–2 kHz when the DACI was switched off.

Conclusions: No significant changes in the relative vibration magnitude of the RWM after DACI implantation were observed. The improvements in BC thresholds seen in patients implanted with a DACI very likely have their origin in the changed impedance at the oval window after DACI surgery leading to a more efficient contribution from the inner ear components to BC sound.

Keywords:

• Direct Acoustic Cochlear Implant
• bone conduction
• otosclerosis
• middle ear
• mixed hearing loss
• round window
• stapes surgery
• relative round window velocity

Acknowledgements

We would like to thank Charlotte Borgers for organising the bonding material and for her help during the cadaver head sessions and Joris Walraevens for the technical input.

Disclosure statement

No potential conflict of interest was reported by the authors.