Active Middle Ear Implant Evoked Auditory Brainstem Response Intensity-Latency Characteristics

Area of Science:

• Neuroscience
• Audiology
• Biomedical Engineering

Background:

• The Vibrant Soundbridge (VSB) is an active middle ear implant used for hearing restoration.
• Intraoperative auditory evoked brainstem responses (ABRs) are crucial for assessing auditory pathway function during surgery.
• Understanding the relationship between stimulation intensity and latency in VSB-evoked ABRs is key for optimizing device performance.

Purpose of the Study:

• To analyze the intensity-latency functions of intraoperative VSB-evoked ABRs.
• To investigate the influence of coupling efficiency, VSB-evoked ABR thresholds, and coupling modality (oval window, incus, round window) on these functions.
• To correlate findings with coupling modality and assess the dynamic range of the VSB implant.

Main Methods:

• A bi-centric exploratory study involving 24 patients implanted with a VSB.
• Measurement of Wave-V intensity-latency functions of intraoperative VSB-evoked ABRs using a modified audio processor.
• Analysis of individual plots and exponential function fits after threshold level correction to coupling efficiency and ABR thresholds.

Main Results:

• Wave-V latency varied significantly across coupling modalities, with the shortest latency observed in the round window (RW) placement subgroup.
• Latency saturation occurred at different stimulation levels depending on the placement (OW, Incus, RW), indicating varying dynamic ranges.
• The RW placement subgroup showed a decreased dynamic range, suggesting reverse stimulation.

Conclusions:

• VSB-evoked ABR intensity-latency functions resemble acoustic stimulation at high levels, with longer latencies due to signal delay.
• Latency saturation is attributed to audio processor gain saturation.
• Analysis of these functions enables objective assessment of individual dynamic range, potentially improving diagnostics and quality control.