Söderqvist Samuel, Sinkkonen Saku T, Sivonen Ville
Department of Otorhinolaryngology - Head and Neck Surgery, Head and Neck Center, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.
Heliyon. 2022 Nov 29;8(12):e11970. doi: 10.1016/j.heliyon.2022.e11970. eCollection 2022 Dec.
A limiting factor of cochlear implant (CI) technology is the electrode-contact overlapping spread of the electrode-generated intracochlear electrical field (EF). While the extent of the spread can be reduced with intracochlear ground electrodes, the stimulation level must be increased to reach similar loudness as with monopolar stimulation utilizing an extracochlear ground. In this study, we investigated the relationship between the monopolar intracochlear EF and the minimum stimulation level required for a measurable neural response assessed with electrically evoked compound action potential (eCAP) thresholds in intraoperative settings. Also, the effect of cochlear diameter on the intracochlear EF was evaluated, as narrower intracochlear EFs were found from larger than smaller cochleae in an earlier study. A total of 171 ears of severely-to-profoundly hearing-impaired patients (ages 0.7-89 years; 42.5 ± 27.8 years, mean ± SD) implanted with a Cochlear Nucleus CI522 or CI622 implant and Slim Straight electrode array or with a Med-El Synchrony implant and Flex 28 electrode array were included in the study. Normal anatomy was established and cochlear diameter was measured for all patients from preoperative imaging. Intraoperative intracochlear EF and eCAP threshold measurements were measured for both Cochlear and Med-El devices with the CIs' back-telemetry options, and EF and eCAP were compared for Cochlear devices. The peak and width of the intracochlear EF correlated with each other ( = 0.46, < 0.001), and both had an inverse relationship with eCAP thresholds ( = -0.41, < 0.001 and = -0.29, < 0.001, respectively). The peak amplitudes of the intracochlear EF increased towards the apical part of the electrode array with both Cochlear ( = 0.97, < 0.001) and Med-El ( = 0.80, = 0.002) devices. The peak amplitudes of the intracochlear EF were shallower across the electrode array in large than in small cochleae ( < 0.05). Our results indicate that the responsiveness of the cochlear nerve is not only dependent on neural health but is also affected by the physical environment of the electrode array, which can be assessed by measuring the intracochlear EF. Further studies are warranted to investigate the detailed characteristics of the intracochlear current spread in CI recipients with varying anatomical features of the cochlea and with electrode arrays with different locations in the scalae or related to the modiolus in the cochleae.
人工耳蜗(CI)技术的一个限制因素是电极产生的耳蜗内电场(EF)的电极接触重叠扩展。虽然使用耳蜗内地电极可以减少扩展范围,但必须提高刺激水平才能达到与使用耳蜗外接地电极的单极刺激相似的响度。在本研究中,我们在术中环境下研究了单极耳蜗内EF与通过电诱发复合动作电位(eCAP)阈值评估的可测量神经反应所需的最低刺激水平之间的关系。此外,评估了耳蜗直径对耳蜗内EF的影响,因为在早期研究中发现,较大耳蜗比较小耳蜗的耳蜗内EF更窄。本研究共纳入171例重度至极重度听力受损患者的耳(年龄0.7 - 89岁;平均±标准差为42.5±27.8岁),这些患者植入了科利耳公司的CI522或CI622植入体及细直电极阵列,或美敦力公司的Synchrony植入体及Flex 28电极阵列。通过术前成像为所有患者建立正常解剖结构并测量耳蜗直径。使用CI的背侧遥测选项对科利耳和美敦力设备进行术中耳蜗内EF和eCAP阈值测量,并对科利耳设备的EF和eCAP进行比较。耳蜗内EF的峰值和宽度相互相关(r = 0.46,P < 0.001),且二者均与eCAP阈值呈负相关(分别为r = -0.41,P < 0.001和r = -0.29,P < 0.001)。使用科利耳(r = 0.97,P < 0.001)和美敦力(r = 0.80,P = 0.002)设备时,耳蜗内EF的峰值幅度均朝着电极阵列的顶部增加。大耳蜗电极阵列上的耳蜗内EF峰值幅度比小耳蜗的更浅(P < 0.05)。我们的结果表明,耳蜗神经的反应性不仅取决于神经健康状况,还受电极阵列物理环境的影响,这可以通过测量耳蜗内EF来评估。有必要进行进一步研究,以调查耳蜗解剖特征不同以及电极阵列在蜗管中位置不同或与耳蜗蜗轴相关的CI接受者耳蜗内电流扩展的详细特征。