Introduction:
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.
Methods:
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.
Results:
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%.
Conclusion:
Optimization of the HC FMT prosthesis resulted in increased SFP responses to RW stimulation
especially at frequencies ≤1 kHz.
