[An implantable hearing aid for inner ear hearing loss. Short-term implantation of microphone and transducer]

Abstract

A microphone constructed for implantation in the posterior wall of the auditory canal and a piezoelectric transducer serving as the main components of an implantable hearing aid were temporally implanted in five patients during middle ear surgery under local anesthesia. The microphone was positioned beneath the skin of the auditory canal such that it completely covered the microphone membrane. The vibratory element of the transducer was coupled to the malleus in four patients with normal ossicular chains and directly to the stapes in one patient with missing incus. The microphone and transducer were electrically connected with an external battery-driven signal amplifier. Speech material and music were presented in the operation room at a sound level of 65 dB SPL under free-field conditions. The patients had to estimate the quality of speech, music, and their own voice as well as the effects of bone-conducting noises. All patients were able to hear with the system. An intraoperative talk without vision contact was possible without any problems, as was understanding of numerals ("Freiburger Zahlentest"). Perception of music was judged as "clear and undistorted with all broadband component." The estimation was also valid for one patient with a sensorineural hearing loss. One patient declared the music to be "a little of unnatural." Bone-conducted sound was estimated as normal in two patients, better than without an implant in one patient with sensorineural hearing loss, and "somewhat metallic" in another patient. Hearing the own voice was considered "normal" in two cases "monotonous" in one case, and "a little bit roaring" in another case. An amplification factor that can be technically realized in an implantable hearing aid was necessary for one of the patients with sensorineural hearing loss to perceive music at a pleasant volume. On the basis of this study, essential requirements for the construction of a fully implantable hearing aid are fulfilled.