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The Hannover Coupler 2.0: Optimization of Coupling between the Floating Mass Transducer and the Round Window
18 April 2018 (online)
The stimulation of the cochlear round window (RW) by the Floating Mass Transducer (FMT) of the Vibrant Soundbridge (MED-EL) still shows large variations in clinical outcomes. In a preceding study improved coupling between the FMT and the RW utilizing the „Hannover Coupler“ FMT prosthesis was shown. Goal of this study was the investigation of an optimized prosthesis (HCv2) and assessing its influence on the FMT-RW coupling.
All experiments were done in fresh human temporal bones. The HCv2 was developed from a preceding prototype in collaboration with MED-EL. The HCv2 contains a FMT-clip with spherical front end (d = 0.5 mm) and has a S-shaped spring at the back end. The spring allows systematic application of static forces (˜0 – 100 mN) between FMT and RW. Stapes footplate (SFP) displacement amplitudes under RW stimulation and under acoustic stimulation were measured by a Laser Doppler vibrometer. Additionally the total harmonic distortion (THD) between 0.5 – 2 kHz and the RW-SFP-transfer function were assessed.
Only temporal bones in compliance to ASTM (F2504 – 05) were included in the analysis (N = 10). With increasing static RW load SFP responses to RW stimulation increased by up to 25 dB at frequencies > 500 Hz. Between 125 – 500 Hz SFP responses decreased with increasing RW force but were still up to 25 dB higher than results shown with the preceding HC. When averaged over speech relevant frequencies (0.5 – 4 kHz) maximal stapes displacements were reached at RW forces ˜15 mN. THDs at that RW load were ≤1.4%.
Optimization of the HC FMT prosthesis resulted in increased SFP responses to RW stimulation especially at frequencies ≤1 kHz.