In-situ sensitivity of a totally-implantable microphone.

One of the key components of fully-implantable hearing devices is the implantable microphone. A crucial parameter when characterizing implantable microphones is the acoustic sensitivity, as it is one of the input parameters for the fitting algorithm and influences the achievable gain. The aim of our study was to investigate the sensitivity of an implanted subcutaneous microphone over time to answer two research questions: (1) How does the sensitivity change once the microphone is implanted under the skin (pre-op versus in-situ)? and (2) How does the sensitivity change from short-term to mid-term? We have measured the in-situ microphone sensitivity in three subjects implanted with a fully-implantable active middle ear implant from 2 weeks up to 20 weeks after implantation with a research software. The microphone sensitivity changed after implantation with clinically relevant changes around the resonance frequency of the microphone. Based on our results, it is essential to measure the in-situ microphone sensitivity at the time of initial fitting of the implant. Once implanted no clinically relevant changes in the microphone sensitivity were observed over time, with a clear decrease in variability over time.