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Second Biennial Hearing Aid Research and Development Conference

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September 22-24, 1997
National Institutes of Health
Bethesda, Maryland

Semi-implantable Bone-anchored Hearing Aid for Patients with Sensorineural Hearing Loss

Stefan P. Y. Stenfelt and Bo E. V. HÂkansson, Department of Applied Electronics, Chalmers University of Technology, G–teborg, Sweden, Radi J–nsson, Department of Audiology, Sahlgrenska University Hospital, G–teborg, Sweden, Anders Tjellstr–m, Department of Otolaryngology, Head and Neck Surgery, Sahlgrenska University Hospital, G–teborg, Sweden

The intention of this project is to investigate the possibility to rehabilitate patients with a pure sensorineural hearing loss with an optimized bone-anchored hearing aid (HC-400). This kind of aid is possible to make semi-implantable with the vibrator and electronics in the mastoid part of the temporal bone, and the controls, battery, and microphone on the outside. It is anticipated that a HC-400 hearing aid has some advantages in comparison with a conventional air conduction hearing aid: (1) no effect on the normal air conduction path and the remaining hearing function, (2) no earmould in the canal implying less discomfort; no occlusion effect, less feedback problem and almost no effect on the hearing of the own voice.

Eight patients with symmetrical moderate sensorineural hearing loss, have by means of surgery been equipped with a titanium implant, for attachment of a miniaturized bone-anchored hearing aid. Various amplifier techniques, such as linear and AGC amplifiers, together with different microphones, filters, and vibrators have been evaluated to achieve the best combination for these patients. Together with these technical features, ordinary clinical audiological measurments are performed.

The final HC-400 comprises a directional microphone, a linear amplifier with output limiter and a vibrator with a resonance frequency between 1 and 1.5 kHz. The preliminary results from audiometric tests and questionnaires were positive and hitherto have all showed benefit of the hearing aid. All 8 patients have shown an increase in speech integlibillity and lower hearing thresholds. Three of them have also been equipped with a state of the art air conduction hearing aid. According to audiometric tests, the benefit with the air conduction devices were in the same region as with the HC-400, and these patients prefer to use the air and bone conduction devices interchangeably depending on the sound environment.

Patients with a pure sensorineural hearing loss benefits from an optimized bone-anchored hearing aid, possible to make semi-implantable. In comparison with an air conduction hearing aids the HC-400 were preferred in certain sound environments.

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