Intraoperative adjustments to optimize active middle ear implant performance

Abstract

Conclusion: After initial contact of the active middle ear implant (AMEI) on the incus, significant increases in device performance can be achieved intraoperatively without affecting residual hearing by additional static loading of the incus with 62 μm (quarter turn) to 125 μm (half turn) increments via an adjustment screw. Objectives: To assess the performance gains of driving the incus with an AMEI under increasing static loads in cadaveric temporal bones. Methods: Incus drive efficacy was assessed using laser Doppler velocimetry measurements of stapes velocities over a frequency range of 0.25 to 8 kHz. Results were compared to stapes velocities following acoustic stimulation via insert earphone. Maximum equivalent ear canal sound pressure level (L_Emax) and residual hearing loss after initial loading of the AMEI (first contact) were compared in each temporal bone. Additional increases in incus load were induced by turning an adjustment screw in quarter turn steps, corresponding to 62 μm increments per step. L_Emaxand residual hearing loss were reassessed after each step. For each temporal bone, experiments were repeated for three different AMEIs. Results: On average across bones, incus stimulation upon initial contact produced an L_Emaxof 125, 127, and 121 dB SPL and residual hearing losses of –2, –1, and –1 dB with respect to unloaded, unaided conditions for the three AMEIs, respectively. Across bones and transducers, increasing static transducer load by incrementing the AMEI up to 125 μm significantly improved performance without affecting residual hearing loss. Loading beyond 125 μm (half turn) did not improve performance but significantly increased residual hearing loss.

Keywords::

• Laser Doppler velocimetry
• human cadaveric temporal bone
• loading

Acknowledgments

We would like to acknowledge the technical and material support provided by Laurent Badih, Brian Conn, and Jim Easter of Otologics LLC, Boulder, CO, USA. We appreciate the assistance of Dr. Michael Hall in constructing the custom experimental equipment (with support by NIH grant P30 NS041854-05). This study was supported in part by an Otologics LLC educational grant (H.A.J. and D.J.T.) and Department of Physiology and Biophysics funds (D.J.T.).

Declaration of interest: Partial funding for these experiments was provided by an education grant from Otologics LLC (Boulder, CO, USA).