Lo J, Bester C, Collins A, Newbold C, Hampson A, Chambers S, Eastwood H, O'Leary S
Department of Otolaryngology, University of Melbourne, Melbourne, VIC, Australia.
Department of Otolaryngology, University of Melbourne, Melbourne, VIC, Australia; Royal Victorian Eye and Ear Hospital, Melbourne, VIC, Australia.
Hear Res. 2018 Feb;358:50-58. doi: 10.1016/j.heares.2017.11.001. Epub 2017 Nov 9.
To preserve residual hearing, techniques for monitoring and reducing the effects of trauma during cochlear implant surgery are being developed. This study examines the relationships between intraoperative recordings (electrode insertion force and electrocochleography), trauma, and hearing loss after cochlear implantation. The study also evaluated the efficacy of intravenous steroids for reducing hearing loss after implantation. Thirty-two normal-hearing guinea pigs were randomly implanted with electrode arrays of differing stiffness ('hard' or 'soft'). These arrays used an intracochlear electrode to record electrode insertion force and electrocochleography responses to a multi-frequency acoustic stimulus during implantation. Additionally, sub-cohorts of animals were administered intravenous saline ('control') or dexamethasone ('steroid') prior to surgery. Subsequent hearing loss was assessed using electrocochleography recordings from the round window membrane prior to surgery and 4 weeks after implantation. After 4 weeks, cochleae were harvested and imaged with thin sheet laser imaging microscopy. After 4 weeks, compound action potential (CAP) thresholds did not differ between steroid and control groups. The CAP amplitude at low-mid frequencies decreased after implantation with a hard electrode, an effect which was partly negated by administering steroids. A decrease in the 'intraoperative' CAP amplitude preceded the reporting of insertion resistance by the surgeon by 5.94 s (±4.03 s SEM). Intraoperative CAP declines were also correlated with higher grades of trauma (r = 0.56, p < 0.01) and greater hearing loss (r = 0.56, p < 0.01). This relationship was not repeated with intraoperative cochlear microphonics. A rise in intraoperative force, which preceded the reporting of resistance by 0.71 s (±0.15 s SEM), was correlated with trauma (r = 0.400, p = 0.04) but not hearing loss (r = 0.297, p = 0.27). Preserving intraoperative CAP amplitudes during implantation was predictive of an atraumatic insertion and reduced post-implantation hearing loss. A rise in force usually preceded the reporting of resistance, although by less than 1 s. These results suggest that intraoperative CAPs may offer a more robust feedback mechanism for improving hearing preservation rates than cochlear microphonic and electrode insertion force recordings, especially considering the rapid changes in insertion force and relatively slow human reaction times. Pre-operative steroids were effective in reversing loss of CAP amplitude with hard electrodes and evoked by lower frequency tones, which suggests a possible role in reducing synaptopathy.
为了保留残余听力，正在研发用于监测和减少人工耳蜗植入手术期间创伤影响的技术。本研究探讨了术中记录（电极插入力和电蜗描记术）、创伤与人工耳蜗植入后听力损失之间的关系。该研究还评估了静脉注射类固醇对减少植入后听力损失的疗效。32只听力正常的豚鼠被随机植入不同硬度（“硬”或“软”）的电极阵列。这些阵列使用耳蜗内电极在植入过程中记录电极插入力和对多频声刺激的电蜗描记术反应。此外，在手术前，将动物亚组分别给予静脉注射生理盐水（“对照组”）或地塞米松（“类固醇组”）。使用手术前和植入后4周圆窗膜的电蜗描记术记录来评估随后的听力损失。4周后，取出耳蜗并用薄片激光成像显微镜成像。4周后，类固醇组和对照组之间的复合动作电位（CAP）阈值没有差异。植入硬电极后，中低频的CAP幅度下降，而给予类固醇可部分抵消这种影响。外科医生报告插入阻力前5.94秒（±4.03秒标准误），“术中”CAP幅度就开始下降。术中CAP下降也与更高等级的创伤（r = 0.56，p < 0.01）和更大的听力损失（r = 0.56，p < 0.01）相关。术中耳蜗微音电位则未出现这种关系。术中力的增加比报告阻力提前0.71秒（±0.15秒标准误），与创伤相关（r = 0.400，p = 0.04），但与听力损失无关（r = 0.
