gms | German Medical Science

Introduction. Several treatment alternatives are currently available for patients suffering from mixed hearing loss. These include power hearing aids (PHAs), bone conduction implants (BCIs) and active middle-ear implants (AMEIs). Otologists have the difficult task of selecting one of multiple devices with partially overlapping indications. The availability of objective and well-defined treatment selection guidance based on the capability of different devices in relation to the patient's audiological needs is, therefore, of the utmost importance. This study gathers evidence for device capabilities in terms of maximum power output (MPO) from technical specifications and published tests.

Methods. MPO was obtained for PHAs and BCIs from the datasheets provided by the manufacturers. Actuator efficiencies of AMEIs were extracted from all publications reporting on laser Doppler vibrometry measurements with AMEIs in temporal bones. Only AMEI publications compliant with the ASTM [1] standard or the extended criteria from Rosowski et al. [2] were selected for data on actuator efficiencies. Conversion from stapes displacement/velocity to equivalent sound pressure level was performed using an internal reference (i.e., the middle ear transfer function) when available or, otherwise, using the ASTM reference. Whenever more than one publication was available for a given condition, the corresponding grand mean of the actuator efficiency was computed as an average weighted by the sample sizes of the publications. The MPOs of the different combinations of AMEI model and coupling variant were derived from the respective actuator efficiencies and maximum electrical outputs of the AMEIs.

Results. In mixed hearing loss with mobile stapes, MPO of the Cochlear™ Carina^® AMEI with coupling to the stapes head with the CliP àWengen extension is 123–136 dB SPLFF eq., and of the MED-EL Vibrant Soundbridge^® (VSB) AMEI with coupling to the stapes head with the CliP coupler is 102–147 dB SPLFF eq. For cases with an immobile stapes, MPO of the Carina AMEI with coupling to the round window (RW) with the 0.5-mm ball extension is 85–121 dB SPLFF eq., and of the VSB AMEI coupled to the RW with interposed connective tissue is 86–104 dB SPLFF eq. The MPO of the Cochlear Baha^® 5 SuperPower BCI is 43–96 dB SPLFF. In sensorineural hearing loss, MPO of the Carina AMEI with coupling to the incus body without an extension is 110–122 dB SPLFF eq. and of the VSB AMEI with coupling to the long process of the incus with the classic coupler is 82–111 dB SPLFF eq. The average MPO of two power hearing aids (GN ReSound™ Enzo™ and Phonak Naída™ Q UP) is 100–135 dB SPLFF.

Conclusion. It is already available a wealth of data on MPO of several hearing device types. These data are key to the establishment of consensual, objective treatment selection guidance. Further research should be directed to confirming that the resulting selection guidance does indeed optimize clinical outcomes.