Helmstaedter Victor, Lenarz Thomas, Erfurt Peter, Kral Andrej, Baumhoff Peter
Department of Otolaryngology, Hannover Medical School, Hannover, Germany.
Cluster of Excellence "Hearing 4 All" (DFG EXC 1077), Hannover, Germany.
Ear Hear. 2018 Jul/Aug;39(4):687-700. doi: 10.1097/AUD.0000000000000526.
For the increasing number of cochlear implantations in subjects with residual hearing, hearing preservation, and thus the prevention of implantation trauma, is crucial. A method for monitoring the intracochlear position of a cochlear implant (CI) and early indication of imminent cochlear trauma would help to assist the surgeon to achieve this goal. The aim of this study was to evaluate the reliability of the different electric components recorded by an intracochlear electrocochleography (ECochG) as markers for the cochleotopic position of a CI. The measurements were made directly from the CI, combining intrasurgical diagnostics with the therapeutical use of the CI, thus, turning the CI into a "theragnostic probe."
Intracochlear ECochGs were measured in 10 Dunkin Hartley guinea pigs of either sex, with normal auditory brainstem response thresholds. All subjects were fully implanted (4 to 5 mm) with a custom six contact CI. The ECochG was recorded simultaneously from all six contacts with monopolar configuration (retroauricular reference electrode). The gross ECochG signal was filtered off-line to separate three of its main components: compound action potential, cochlear microphonic, and summating potential (SP). Additionally, five cochleae were harvested and histologically processed to access the spatial position of the CI contacts. Both ECochG data and histological reconstructions of the electrode position were fitted with the Greenwood function to verify the reliability of the deduced cochleotopic position of the CI.
SPs could be used as suitable markers for the frequency position of the recording electrode with an accuracy of ±1/4 octave in the functioning cochlea, verified by histology. Cochlear microphonics showed a dependency on electrode position but were less reliable as positional markers. Compound action potentials were not suitable for CI position information but were sensitive to "cochlear health" (e.g., insertion trauma).
SPs directly recorded from the contacts of a CI during surgery can be used to access the intracochlear frequency position of the CI. Using SP monitoring, implantation may be stopped before penetrating functioning cochlear regions. If the technique was similarly effective in humans, it could prevent implantation trauma and increase hearing preservation during CI surgery. Diagnostic hardware and software for recording biological signals with a CI without filter limitations might be a valuable add-on to the portfolios of CI manufacturers.
对于残余听力患者人工耳蜗植入数量的不断增加，听力保留以及预防植入创伤至关重要。一种监测人工耳蜗（CI）在耳蜗内位置并早期提示即将发生的耳蜗创伤的方法，将有助于外科医生实现这一目标。本研究的目的是评估通过耳蜗内电耳蜗图（ECochG）记录的不同电成分作为CI耳蜗定位标记的可靠性。测量是直接从CI进行的，将术中诊断与CI的治疗用途相结合，从而将CI转变为“治疗诊断探针”。
对10只听觉脑干反应阈值正常、雌雄不限的Dunkin Hartley豚鼠进行耳蜗内ECochG测量。所有受试动物均完全植入（4至5毫米）定制的六触点CI。采用单极配置（耳后参考电极）同时从所有六个触点记录ECochG。对总的ECochG信号进行离线滤波，以分离其三个主要成分：复合动作电位、耳蜗微音电位和总和电位（SP）。另外，收获五只耳蜗并进行组织学处理，以确定CI触点的空间位置。将ECochG数据和电极位置的组织学重建与格林伍德函数拟合，以验证推导的CI耳蜗定位的可靠性。
通过组织学验证，在功能正常的耳蜗中，SP可作为记录电极频率位置的合适标记，精度为±1/4倍频程。耳蜗微音电位显示出对电极位置的依赖性，但作为位置标记不太可靠。复合动作电位不适用于CI位置信息，但对“耳蜗健康”（如插入创伤）敏感。
术中直接从CI触点记录的SP可用于确定CI在耳蜗内的频率位置。通过监测SP，可在穿透功能正常的耳蜗区域之前停止植入。如果该技术在人类中同样有效，则可预防植入创伤并提高CI手术期间的听力保留率。用于记录无滤波限制的CI生物信号的诊断硬件和软件可能是CI制造商产品组合中有价值的附加组件。
