Kiefer Jan, Böhnke Frank, Adunka Oliver, Arnold Wolfgang
Department of Otolaryngology, Klinikum rechts der Isar, Technical University Munich, Ismaninger Strasse 22, D-81675 Munich, Germany.
Hear Res. 2006 Nov;221(1-2):36-43. doi: 10.1016/j.heares.2006.07.013. Epub 2006 Sep 7.
In subjects with remaining low frequency hearing, combined electric-acoustic stimulation (EAS) of the auditory system is a new therapeutic perspective. Intracochlear introduction of a cochlear implant electrode, however, may alter the biomechanical properties of the inner ear and thus affect perception of acoustic stimuli.
Based on histological observations of morphologic changes after cochlear implantation in cadaveric and post mortem studies the effects of basilar membrane (BM) stiffening in the ascending basal and middle turns of the cochlea due to close contact of the BM with the electrode were simulated in a 3D-computational finite element model of the inner ear. To verify our simulated results, pre- and postoperative pure-tone audiograms of 13 subjects with substantial residual hearing, who underwent cochlear implantation, were evaluated.
In the scenario of partial BM-fixation, acoustic energy of middle (2 kHz) and high (6 kHz) frequency was focused basally and apically to the fixed section, increasing BM displacement amplitudes up to 6 dB at a stimulation level of 94 dB (SPL). Lower frequencies were not affected by fixation in the basal and middle turn of the cochlea. In implanted subjects, a small but significant decrease of thresholds was observed at 1.5 kHz, a place in tonotopy adjacent to the tip region of the implanted electrode.
Our model suggests that stiffening of the basilar membrane adjacent to an implanted electrode into the basal and middle cochlear turn did not affect BM movement in the low frequency area. Focussing of acoustic energy may increase perception in regions adjacent to the fixed section. Observations in implanted subjects were concordant with our model predictions. High frequencies, however, should not be amplified in patients using EAS to avoid disturbances in discrimination due to tonotopically incorrect frequency representation.
对于仍保留低频听力的受试者，听觉系统的联合电声刺激（EAS）是一种新的治疗方法。然而，将人工耳蜗电极植入耳蜗内可能会改变内耳的生物力学特性，从而影响对声刺激的感知。
基于尸体和死后研究中人工耳蜗植入后形态学变化的组织学观察，在耳蜗的三维计算有限元模型中模拟了由于基底膜（BM）与电极紧密接触而导致耳蜗基底转和中转基底膜变硬的影响。为了验证我们的模拟结果，对13名有大量残余听力且接受了人工耳蜗植入的受试者的术前和术后纯音听力图进行了评估。
在部分基底膜固定的情况下，中频（2kHz）和高频（6kHz）的声能在基底和顶部聚焦于固定部分，在94dB（声压级）的刺激水平下，基底膜位移幅度增加高达6dB。较低频率不受耳蜗基底转和中转固定的影响。在植入受试者中，在1.5kHz处观察到阈值有小幅但显著的下降，该频率在音调定位上与植入电极的尖端区域相邻。
我们的模型表明，将电极植入耳蜗基底转和中转附近导致的基底膜变硬不会影响低频区域的基底膜运动。声能聚焦可能会增加固定部分附近区域的感知。植入受试者的观察结果与我们的模型预测一致。然而，对于使用EAS的患者，不应放大高频，以避免由于音调定位不正确的频率表示而导致的辨别障碍。
