Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill, NC.
Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Chapel Hill, NC.
Ear Hear. 2019 Jul/Aug;40(4):833-848. doi: 10.1097/AUD.0000000000000659.
Electrocochleography (ECochG) obtained through a cochlear implant (CI) is increasingly being tested as an intraoperative monitor during implantation with the goal of reducing surgical trauma. Reducing trauma should aid in preserving residual hearing and improve speech perception overall. The purpose of this study was to characterize intracochlear ECochG responses throughout insertion in a range of array types and, when applicable, relate these measures to hearing preservation. The ECochG signal in cochlear implant subjects is complex, consisting of hair cell and neural generators with differing distributions depending on the etiology and history of hearing loss. Consequently, a focus was to observe and characterize response changes as an electrode advances.
In 36 human subjects, responses to 90 dB nHL tone bursts were recorded both at the round window (RW) and then through the apical contact of the CI as the array advanced into the cochlea. The specific setup used a sterile clip in the surgical field, attached to the ground of the implant with a software-controlled short to the apical contact. The end of the clip was then connected to standard audiometric recording equipment. The stimuli were 500 Hz tone bursts at 90 dB nHL. Audiometry for cases with intended hearing preservation (12/36 subjects) was correlated with intraoperative recordings.
Successful intracochlear recordings were obtained in 28 subjects. For the eight unsuccessful cases, the clip introduced excessive line noise, which saturated the amplifier. Among the successful subjects, the initial intracochlear response was a median 5.8 dB larger than the response at the RW. Throughout insertion, modiolar arrays showed median response drops after stylet removal while in lateral wall arrays the maximal median response magnitude was typically at the deepest insertion depth. Four main patterns of response magnitude were seen: increases > 5 dB (12/28), steady responses within 5 dB (4/28), drops > 5 dB (from the initial response) at shallow insertion depths (< 15 mm deep, 7/28), or drops > 5 dB occurring at deeper depths (5/28). Hearing preservation, defined as < 80 dB threshold at 250 Hz, was successful in 9/12 subjects. In these subjects, an intracochlear loss of response magnitude afforded a prediction model with poor sensitivity and specificity, which improved when phase, latency, and proportion of neural components was considered. The change in hearing thresholds across cases was significantly correlated with various measures of the absolute magnitudes of response, including RW response, starting response, maximal response, and final responses (p's < 0.05, minimum of 0.0001 for the maximal response, r's > 0.57, maximum of 0.80 for the maximal response).
Monitoring the cochlea with intracochlear ECochG during cochlear implantation is feasible, and patterns of response vary by device type. Changes in magnitude alone did not account for hearing preservation rates, but considerations of phase, latency, and neural contribution can help to interpret the changes seen and improve sensitivity and specificity. The correlation between the absolute magnitude obtained either before or during insertion of the ECochG and the hearing threshold changes suggest that cochlear health, which varies by subject, plays an important role.
通过耳蜗植入物（CI）获得的电 Cochleography（ECochG）越来越多地被用作植入过程中的术中监测手段，目的是减少手术创伤。减少创伤应该有助于保留残余听力并整体提高言语感知能力。本研究的目的是描述在一系列数组类型中插入过程中整个耳蜗内的 ECochG 反应，并在适用的情况下将这些测量结果与听力保护相关联。耳蜗植入物受试者的 ECochG 信号很复杂，由毛细胞和神经发生器组成，其分布因听力损失的病因和病史而异。因此，我们关注的是观察和描述电极前进时的响应变化。
在 36 名人类受试者中，通过在圆形窗口（RW）记录 90dB nHL 纯音爆发的反应，然后通过 CI 的顶端接触记录反应，同时数组向耳蜗内推进。具体设置使用手术现场的无菌夹，通过软件控制将夹与植入物的接地短接，然后将夹的末端连接到标准听力记录设备。刺激是 90dB nHL 的 500Hz 纯音爆发。对有听力保护意向的病例（12/36 例受试者）进行听力测试，并与术中记录相关联。
在 28 名受试者中成功获得了整个耳蜗内的记录。对于 8 个不成功的病例，夹引入了过多的线路噪声，使放大器饱和。在成功的受试者中，最初的整个耳蜗内反应比 RW 处的反应平均大 5.8dB。在整个插入过程中，去除导丝后，中鼻甲数组的反应幅度中位数下降，而在侧壁数组中，最大的中位数反应幅度通常在最深的插入深度。观察到四种主要的反应幅度模式：增加>5dB（12/28）、在 5dB 以内稳定响应（4/28）、在较浅的插入深度（<15mm 深，7/28）处初始反应下降>5dB 或在较深的深度处下降>5dB（5/28）。听力保护定义为 250Hz 时阈值<80dB，在 12/12 例受试者中成功。在这些受试者中，反应幅度的变化提供了一个预测模型，其敏感性和特异性较差，当考虑相位、潜伏期和神经成分比例时，敏感性和特异性有所提高。病例之间的听力阈值变化与反应幅度的各种绝对测量值显著相关，包括 RW 反应、起始反应、最大反应和最终反应（p<0.05，最大反应的最小为 0.0001，r>0.57，最大反应的最大为 0.80）。
在耳蜗植入过程中使用整个耳蜗内的 ECochG 监测耳蜗是可行的，并且反应模式因设备类型而异。幅度的变化本身并不能解释听力保护率，但考虑相位、潜伏期和神经贡献可以帮助解释所观察到的变化，并提高敏感性和特异性。在插入 ECochG 之前或期间获得的绝对幅度与听力阈值变化之间的相关性表明，受试者之间的耳蜗健康状况差异很大，这对听力保护很重要。
