Leblans Marc, Sismono Fergio, Vanpoucke Filiep, van Dinther Joost, Lerut Bob, Kuhweide Rudolf, Offeciers Erwin, Zarowski Andrzej
European Institute For ORL, GZA Sint-Augustinus, Antwerp, Belgium.
European Institute For ORL, GZA Sint-Augustinus, Antwerp, Belgium.
Hear Res. 2022 Dec;426:108563. doi: 10.1016/j.heares.2022.108563. Epub 2022 Jun 21.
Measurement of the complex electrical impedance of the electrode contacts can provide new insights into the factors playing a role in the preservation of residual hearing with cochlear implants (CIs). However, unraveling the contributions related to the different phenomena from impedance data necessitates more advanced measurement and analysis techniques. The present study explores a new impedance measurement option recently included into the cochlear-implant programming software and aims to contribute to a more solid basis for the clinical use of impedance measures as a biomarker for fibrous tissue formation. Twenty adult CI-recipients were followed from surgery until 1 year after implantation by means of Electrode Voltage Telemetry (EVT), also called Electric Field Imaging or TransImpedance-Matrix measurement, and a 4-point technique for probing the voltage between adjacent electrode contacts. The data were compared to the electrode location derived from computed tomography, and to the device usage log. Using our impedance model for electrical stimulation of the cochlea, the polarization impedance related the electrode-tissue interface was determined, and the bulk impedance (access resistance) was split into a near-field and a far-field component. On average, the polarization impedance increased abruptly after surgery, indicating a strong passivation of the electrode contacts before cochlear-implant initiation. Its initial rise resolved almost completely soon after device switchon (2-4 weeks). The gradual increase of the access resistance mainly happened during the first 40 days on a time scale very similar to that observed in a guinea-pig study correlating impedance changes to fibrous tissue growth. The higher increase towards the round window is consistent with the higher amount of tissue observed in histological animal studies close to the electrode entry point. While the initial changes were due to the near-field resistance, the far-field resistance began to rise only after one month for half of the study group, once the near-field component had reached its critical value. This suggests indeed fibrosis initiating near the electrode contacts and spreading thereafter farther away. The near-field resistance positively correlated to device usage. EVT data allow for a further decomposition of the impedance at a cochlear-implant electrode, yielding a more detailed description of the postoperative intracochlear phenomena, such as fibrosis.
测量电极触点的复电阻抗可为深入了解人工耳蜗（CI）保留残余听力的相关因素提供新的视角。然而，要从阻抗数据中解析出与不同现象相关的贡献，需要更先进的测量和分析技术。本研究探索了一种最近纳入人工耳蜗编程软件的新阻抗测量方法，旨在为将阻抗测量作为纤维组织形成生物标志物的临床应用奠定更坚实的基础。通过电极电压遥测（EVT，也称为电场成像或跨阻抗矩阵测量）以及一种用于探测相邻电极触点之间电压的四点技术，对20名成年人工耳蜗植入者从手术开始直至植入后1年进行了跟踪研究。将这些数据与计算机断层扫描得出的电极位置以及设备使用记录进行了比较。使用我们用于耳蜗电刺激的阻抗模型，确定了与电极 - 组织界面相关的极化阻抗，并将体阻抗（接入电阻）分为近场和远场分量。平均而言，极化阻抗在术后急剧增加，表明在人工耳蜗启动前电极触点发生了强烈的钝化。其初始上升在设备开启后不久（2 - 4周）几乎完全消退。接入电阻的逐渐增加主要发生在最初的40天内，时间尺度与在豚鼠研究中观察到的将阻抗变化与纤维组织生长相关联的时间尺度非常相似。朝向圆窗方向更高的增加与在组织学动物研究中靠近电极入口点观察到的更多组织量一致。虽然初始变化是由于近场电阻引起的，但对于一半的研究组，远场电阻仅在一个月后才开始上升，此时近场分量已达到其临界值。这确实表明纤维化在电极触点附近开始并随后向更远的地方扩散。近场电阻与设备使用呈正相关。EVT数据允许对人工耳蜗电极处的阻抗进行进一步分解，从而更详细地描述术后耳蜗内现象，如纤维化。
