[Active electronic hearing implants for middle and inner ear hearing loss--a new era in ear surgery. II: Current state of developments]

Abstract

Active hearing implants have been developed to varying degrees for conductive hearing loss as well as for sensorineural hearing loss. Implants for conductive hearing loss match impedance transformation by the middle ear. They will be referred to as ITI (impedance transformation implants). Three partial ITIs have been developed for routine clinical use: the Swedish transcutaneous BAHA, the American subcutaneous AUDIANT, and the Japanese P-MEI. Of greater importance with respect to the number of patients are electronic implants for sensorineural hearing loss. These implants are designed to replace parts of the function of the cochlea amplifier (CA). Therefore, in this study, they will be called CAI (cochlea amplifier implant). The CAI consist of four parts: (1) transducer, (2) microphone, (3) control unit, and (4) battery. A CAI for routine clinical use does not yet exist. Two transducer principles have thus far been developed for use in CAIs: the electromagnetic (EM) and the piezoelectric (PE) principle. Most of the transducers that have been described are EM transducers. The American Maniglia implant and the American floating mass transducer have been tested in humans. Both belong to the category of high energy consuming (HEC) implants with a limited frequency range that does not contain the whole speech spectrum. This is in contrast to the Canadian electromagnetic Fredrickson-HEC implant which is capable of transmitting broad band signals of up to 10 kHz. All ot he HEC-EM transducers lack an implantable microphone and an implantable battery. The German CAI, one of the piezoelectrical implants, was recently implanted acutely in humans. It consists of a piezoelectrical, ossicle coupled, low energy consuming (LEC) transducer, as well as an implantable microphone. It allows a broadband signal of up to 10 kHz, yet at a considerably lower level of energy.