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Reducing Artifacts in Intracochlear Pressure Measurements to Study Sound Transmission by Bone Conduction Stimulation in Humans

Borgers, Charlotte*; Fierens, Guy*,†,§; Putzeys, Tristan*,§; van Wieringen, Astrid*; Verhaert, Nicolas*,‡

doi: 10.1097/MAO.0000000000002394
RESEARCH METHODOLOGY
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Hypothesis: Intracochlear pressure (ICP) measurements during bone conduction (BC) stimulation may be affected by motion of the pressure sensor relative to the cochlear promontory bone, demonstrating the need to cement the sensor firmly to the cochlear bone.

Background: ICP is a promising measurement tool for investigating the cochlear drive in BC transmission, but its use is not yet standardized. Previous ICP studies have reported artificially increased pressure due to motion of the sensor relative to the temporal bone. The artifact can be reduced by firmly cementing the sensor to the bone, but this is destructive for the sensor. Previous studies used a custom-made sensor; the use of commercially available sensors, however, is more generic, but also more challenging to combine with the cement. Therefore, the goals of the current study are: firstly, to evaluate a non-destructive cementing method suitable for a commercially available sensor, and secondly, to investigate ICP measurements during BC stimulation in more detail.

Methods: To study the effect of sensor cementing, three fixation conditions were investigated on six fresh-frozen temporal bones: 1) alginate, 2) alginate and dental composite, 3) alginate and dental composite, released from micromanipulators. Pressures in scala tympani and vestibuli were measured simultaneously, while velocity measurements were performed on the cochlear promontory and sensor. The ratio between sensor and promontory bone velocity was computed to quantify the relative motion.

Results: For air conduction stimulation, results were in line with those from previous ICP studies, indicating that baseline measurements were valid and could be used to interpret the results obtained with BC stimulation. Results showed that cementing the sensors and releasing them from the micromanipulators is crucial for valid ICP measurements. When the sensors were only sealed with alginate, the pressure was overestimated, especially at low and mid-frequencies. When the sensors were cemented and held in the micromanipulators, the pressure was underestimated. Compared with the scala tympani measurements, ICP measurements showed a lower scala vestibuli pressure below 1 kHz, and a higher pressure above 1 kHz.

Conclusion: Dental composite is effective as a cement to attach commercially available sensors to the cochlear promontory bone. When sensors are firmly attached, valid ICP measurements can be obtained with BC stimulation.

*Research Group Experimental Oto-rhino-laryngology (ExpORL), Department of Neurosciences, KU Leuven - University of Leuven, Leuven

Cochlear Technology Centre – Mechelen, Mechelen

Department of Otorhinolaryngology, Head and Neck Surgery, University Hospitals Leuven

§Laboratory for Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven - University of Leuven, Heverlee, Belgium

Address correspondence and reprint requests to Charlotte Borgers, M.Sc., Research Group Experimental Oto-rhino-laryngology (ExpORL), Department of Neurosciences, KU Leuven - University of Leuven, 3000, Leuven, Belgium; E-mail: charlotte.borgers@kuleuven.be

Funding sources: This research work is carried out in the frame of IWT Research Project (155047). The last author, N.V. is supported by the Research Foundation Flanders as a senior clinical investigator. T.P. acknowledges support by FWO (12Y6919N). G.F. acknowledges support by VLAIO (HBC.2018.0184).

The authors disclose no conflicts of interest.

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