Controlled round-window stimulation in human temporal bones yielding reproducible and functionally relevant stapedial...

Area of Science:

• Otoacoustic emissions
• Biomedical engineering
• Cochlear implant technology

Background:

• Round window (RW) stimulation is crucial for auditory prostheses, but clinical outcomes vary significantly.
• The precise mechanical influence of RW stimulation on the cochlea is not fully understood.
• Existing studies show high variability, necessitating controlled investigations.

Purpose of the Study:

• To identify optimal conditions for effective and reproducible round window (RW) stimulation.
• To investigate the mechanical coupling between an actuator and the RW membrane.
• To determine the impact of RW membrane pretension on stimulation efficacy.

Main Methods:

• Utilized eight human temporal bones for controlled mechanical stimulation of the RW membrane.
• Employed piezoelectric stack actuators with specific tip geometries for stimulation.
• Implemented a two-stage positioning protocol for precise actuator placement and vibration measurement.

Main Results:

• Achieved reproducible measurements of stimulus vibration at the RW and stapes footplate displacement.
• Determined an average displacement ratio of 0.089 up to 1.2 kHz with optimal coupling.
• Identified 90-μm RW membrane pretension as essential for optimum and reproducible stimulation.

Conclusions:

• Precise actuator coupling and RW membrane pretension are critical for successful round window stimulation.
• Inter-patient variability in RW stimulation effectiveness likely stems from coupling success, not anatomical differences.
• Findings support the equal-volume displacement hypothesis under specific conditions.