Experimentelle Untersuchungen von Kopplungspunkten für einen implantierbaren Sensor im Mittelohr

Introduction

Implantable microphones are crucial for the development of fully implantable hearing systems. A piezoelectric force sensor is well suited for sound recording in the middle ear. The sensitivity and feedback of an implanted actuator such as the Floating Mass Transducer (FMT) of the Vibrant Soundbridge (VSB) depend, among other things, on the type and location of the coupling to the sound conduction chain. The umbo and the incudostapedial joint (ISJ) are well suited as coupling points for the sensor (Leihkauf 2024; Eßinger 2019).

Material and methods

In temporal bone experiments (n=18), the coupling of the sensor at the umbo and in the ISJ was compared. In umbo coupling, the sensor is supported on the promontory using a spacer. The sound transmission from the FMT to the inner ear was measured using a Laser Doppler Vibrometer and served as a reference. The target variables were the sensitivity of the sensor to defined sound pressure in the ear canal (SE) and to the sound generated by the FMT (FB). The ossicular chain was disrupted by removing the incus.

Results

The SE is almost equivalent at both coupling points. In the case of an intact chain, the FB in umbo coupling is up to 10 dB lower than in the ISJ, depending on the frequency. With a broken chain, it is significantly lower and not measurable.

Discussion

In umbo coupling, the sensor shows a higher SE with simultaneously increased FB stability of the overall system. Especially in the case of a completely or partially missing ossicular chain, with 53% a frequent case in VSB patients (Leihkauf 2024), there is no alternative to umbo coupling. The sensor would therefore be well suited for a fully implantable middle ear implant based on the existing VSB and would open up a broad field of application.

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