(478) Testing a Novel Piezoelectric Middle-Ear Microphone in Sheep

Introduction: We have designed a novel middle-ear implantable microphone for fully implantable cochlear implants, which has performed well in cadaveric human temporal bones. In this study we tested the middle-ear microphone in sheep temporal bones in preparation for future live-sheep trials.

Methods: Temporal bones from three cadaveric fresh but previously frozen Hampshire sheep heads were surgically prepared with an extended facial recess approach preserving the facial nerve. The piezoelectric middle-ear microphone was secured in a micromanipulator with the sensing region interfacing the convex portion of the manubrium close to the umbo within the middle-ear cavity. Open-field single-tone stimuli from 1-20 kHz at 60-90 dB SPL were presented and measured with a reference microphone at the ear canal. Simultaneously, we measured the middle-ear microphone’s output in volts via a custom-made amplifier and manubrium velocity via a laser Doppler vibrometer through the ear canal.

Results: Measured middle-ear microphone output that sensed the manubrium motion was more than 30 dB above the noise level at 60 dB SPL stimulus across all frequencies. The measured output behaved linearly across the tested range of stimulus sound pressure.

Conclusions: The middle-ear microphone can be inserted with preservation of the facial nerve in Hampshire sheep. The middle-ear microphone has good signal-to-noise ratio and behaves linearly across a dynamic range of input sound pressure levels for all frequencies. These results suggest that Hampshire sheep will be suitable for future in vivo large-animal trials of our middle-ear microphone and potentially other types of middle-ear implants.