Objective estimation of frequency-specific pure-tone hearing thresholds following bone-conduction hearing aid stimulation.

Patients suffering from conductive or mixed hearing loss may benefit from bone-conduction hearing systems (BAHS). The amount of amplification provided by the hearing system is selected based on the individual's sensorineural frequency-specific threshold. With patients who are not able to provide thresholds behaviorally, such as young children, objective methods are required to estimate the unaided and aided hearing threshold and thus the success of the hearing system fitting. In a prospective study with ten adult Baha softband users, aided and unaided frequency-specific thresholds were estimated. Aided thresholds to tone bursts via Baha stimulation were obtained behaviorally and electrophysiologically using cortical auditory evoked potentials (CAEPs) and were compared to pure-tone thresholds using routine clinical audiometry. For all stimulation frequencies, the frequency-specific electrophysiological and behavioral hearing thresholds measured with Baha stimulation were highly correlated and not different. Increased thresholds were observed only with the 0.5 kHz Baha stimulation as compared to the pure-tone audiogram. Objective measurement of frequency-specific hearing thresholds with CAEPs is applicable to BAHS users.

Auditory brainstem and cortical potentials following bone-anchored hearing aid stimulation.

Patients suffering from conductive or mixed hearing loss and Single-Sided Deafness may benefit from implantable hearing devices relying on bone conducted auditory stimulation. However, with only passively cooperative patients, objective methods are needed to estimate the aided and unaided pure-tone audiogram. This study focuses on the feasibility aspect of an electrophysiological determination of the hearing thresholds with bone-anchored hearing aid stimulation. Therefore, 10 normal-hearing subjects were provided with a Baha Intenso (Cochlear Ltd.) which was temporarily connected to the Baha Softband (Cochlear Ltd.). Auditory evoked potentials were measured by auditory stimulation paradigm used in clinical routine. The amplitudes, latencies, and thresholds of the resulting auditory brainstem responses (ABR) and the cortically evoked responses (CAEP) were correlated with the respective responses without the use of the Baha Intenso. The recording of ABR and CAEP by delivering the stimuli to the Baha results in response waveforms which are comparable to those evoked by earphone stimulation and appears appropriate to be measured using the Baha Intenso as stimulator. At the ABR recordings a stimulus artifact at higher stimulation levels and a constant latency shift caused by the Baha Intenso has to be considered. The CAEP recording appeared promising as a frequency specific objective method to approve the fitting of bone-anchored hearing aids. At all measurements, the ABR and CAEP thresholds seem to be consistent with the normal hearing of the investigated participants. Thus, a recording of auditory evoked potentials using a Baha is in general possible if specific limitations are considered.