Abstract
ObjectiveTo analyze intensity-latency functions of intraoperative auditory evoked brainstem responses (ABRs) to stimulation by the Vibrant Soundbridge (VSB) active middle ear implant with respect to coupling efficiency, VSB evoked ABR thresholds, and coupling modality [oval window (OW) placement vs. Incus placement and vs. round window (RW) placement].Study DesignExploratory study.SettingBi-centric study at tertiary referral centers.PatientsTwenty-four patients (10 female, 14 male, mean age: 58 years) who received a VSB.Outcome MeasuresWave-V intensity-latency functions of intraoperative VSB evoked ABRs using a modified audio processor programmed to preoperative bone conduction thresholds for stimulation. Threshold level correction to coupling efficiency and ABR thresholds. Individual plots and exponential function fits.ResultsAfter ABR threshold level correction, the latency functions could be aligned. A large variance of latencies was observed at individual threshold level. Wave-V latency was longest in the Incus placement subgroup (9.73 ms, SD: 1.04) as compared to OW placement subgroup (9.47 ms, SD: 1.05), with the shortest latency in the RW placement subgroup (8.99 ms, SD: 0.68). For increasing stimulation levels, the variance decreased with intensity-latency function slopes converging toward a steady-state (saturation) latency caused by saturation of audio processor (stimulation) gain. Latency saturation was reached at a stimulation level of 50 dB nHL for the OW placement subgroup, 35 dB nHL for the Incus placement subgroup, and 30 dB nHL for the RW placement subgroup. The latency and saturation results indicated decreased dynamic range for RW placement, i.e., reverse stimulation.ConclusionsVSB evoked ABR wave-V intensity-latency function slopes were similar to acoustic stimulation at high stimulation levels with a shift toward longer latencies caused by audio processor signal delay. Saturation of latencies occurred for higher stimulation levels due to saturation of audio processor gain. Thus, the analysis of VSB evoked intensity-latency functions appears to allow for the objective assessment of a patient's individual dynamic range. This can further improve diagnostics as well as intraoperative and postoperative quality control.
Highlights
Active middle ear implants (AMEI) are widely used for hearing rehabilitation in patients with sensorineural, conductive, and mixed hearing loss
For all patients included in the final analysis (n = 22), Vibrant SoundbridgeTM (VSB) evoked auditory brainstem response (ABR) could be measured intraoperatively with mean VSB evoked ABR thresholds (LABR) of 6.2 (SD: 5.6) dB nHL (OW placement), 11.0 (SD: 2.2) dB nHL (Incus placement), and 12.04 (SD: 4.0) dB nHL (RW placement)
Close to the individual LABR, wave-V latency decreased with increasing stimulation level with a slope comparable to that of reference latency data for acoustic stimulation [37,38,39]
Summary
Active middle ear implants (AMEI) are widely used for hearing rehabilitation in patients with sensorineural, conductive, and mixed hearing loss. This has become an appropriate solution for those who cannot be treated with conventional hearing aids due to technical issues such as feedback or sound distortion, or patient related issues like recurrent infections of the auditory canal [1]. The device was originally designed for treatment of sensorineural hearing loss where the only option for vibrational energy transfer was to couple the FMT to the long process of the incus [4]. Coupling to the stapes suprastructure or stapes footplate (OW placement) resulting in stimulation in the natural, normal direction (i.e., perpendicular to the OW) are biomechanically efficient [11].
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