Clinical Validation of Intracochlear Pressure as a Method to Characterize the Efficiency of Active Middle Ear Implants in Cadaver Ears

Introduction: Active Middle Ear Implant (AMEI) output can be characterized preclinically in cadaver studies using Laser Doppler vibrometry (LDV) according to ASTM `F2504-05. However, LDV measurements are inadequate for e.g. backward (round window) stimulation. In these cases the measurement of the intracochlear pressure difference (ICPD) is an alternative. Here, we compared output levels calculated from ICPD and LDV and validated results for a first time against clinical data.

Methods: Experiments were performed in ASTM compliant human cadaveric temporal bones (TBs). After acoustic stimulation of the tympanic membrane, the T2 actuator as used in the Cochlear™ Carina® System was coupled to the incus body at controlled static preload. During stimulation stapes footplate (SFP) vibrations and intracochlear pressures in scala tympani and scala vestibule were measured simultaneously. The generated equivalent sound pressure levels were calculated both, based on SFP vibration and ICPD. Bone conduction thresholds and “direct thresholds” measured in patients implanted with this device were used to determine the output level clinically.

Results: The output level measured experimentally in TBs was 90 to 120 eq. dB SPL_FF @1V_RMS. At 5mN loading force LDV data matched clinical data with small deviations (< 6dB below 3 kHz and 9 dB above 4 kHz) while ICPD measurements showed practically no deviation (< 3dB).

Conclusion In incus stimulation actuator output levels calculated from ICPD were similar to output levels based on SFP vibration and to clinical data. Based on our results, ICPD can be used to predict preclinically performance of IMEHDs in cadaver studies.