Department of Otolaryngology, University of Colorado School of Medicine, Aurora, Colorado, USA.
Cochlear Boulder LLC, Boulder, Colorado, USA.
Ear Hear. 2019 May/Jun;40(3):725-731. doi: 10.1097/AUD.0000000000000655.
Active middle ear implants (AMEI) have been used to treat hearing loss in patients for whom conventional hearing aids are unsuccessful for varied biologic or personal reasons. Several studies have discussed feedback as a potential complication of AMEI usage, though the feedback pathway is not well understood. While reverse propagation of an acoustic signal through the ossicular chain and tympanic membrane constitutes an air-conducted source of feedback, the implanted nature of the device microphone near the mastoid cortex suggests that bone conduction pathways may potentially be another significant factor. This study examines the relative contributions of potential sources of feedback during stimulation with an AMEI.
Four fresh-frozen, hemi-sectioned, human cadaver specimens were prepared with a mastoid antrostomy and atticotomy to visualize the posterior incus body. A Carina active middle ear implant actuator (Cochlear Ltd., Boulder, CO) was coupled to the incus by two means: (1) a stereotactic arm mounted independently of the specimen and (2) a fixation bracket anchored directly to the mastoid cortical bone. The actuator was driven with pure-tone frequencies in 1/4 octave steps from 500 to 6000 Hz. Acoustic sound intensity in the ear canal was measured with a probe tube microphone (Bruel & Kjær, Nærum, Denmark). Bone-conducted vibration was quantified with a single-axis laser Doppler vibrometer (Polytec Inc., Irvine, CA) from both a piece of reflective tape placed on the skin overlying the mastoid and a bone-anchored titanium screw and pedestal (Cochlear Ltd., Centennial, CO) implanted in the cortical mastoid bone.
Microphone measurements revealed ear-canal pressures of 60-89 dB SPL, peaking in the frequency range below 2 kHz. Peak LDV measurements were greatest on the mastoid bone (0.32-0.79 mm/s with mounting bracket and 0.21-0.36 mm/s with the stereotactic suspension); peak measurements on the skin ranged from 0.05 to 0.15 mm/s with the bracket and 0.03 to 0.13 mm/s with stereotactic suspension.
AMEI produce both air- and bone-conducted signals of adequate strength to be detected by the implanted device microphone, potentially resulting in reamplification. Understanding the relative contribution of these sources may play an important role in the development of targeted mitigation algorithms, as well as surgical techniques emphasizing acoustic isolation.
主动中耳植入物（AMEI）已被用于治疗因各种生物学或个人原因而对传统助听器无效的患者的听力损失。有几项研究讨论了反馈作为 AMEI 使用的潜在并发症，尽管反馈途径尚不清楚。虽然声信号通过听小骨链和鼓膜的反向传播构成了空气传导反馈的源，但设备麦克风植入在乳突皮质附近表明骨导途径可能是另一个重要因素。本研究检查了在 AMEI 刺激过程中潜在反馈源的相对贡献。
四个新鲜冷冻的半剖人体标本准备了乳突造口术和鼓室切开术，以可视化后镫骨体。卡丽娜主动中耳植入物执行器（Cochlear Ltd.，博尔德，CO）通过两种方式与镫骨连接：（1）通过与标本独立安装的立体定向臂；（2）直接固定在乳突皮质骨上的固定支架。执行器用纯音在 1/4 倍频程中从 500 到 6000 Hz 进行驱动。耳道中的声强用探针管麦克风（Bruel & Kjær，Nærum，丹麦）进行测量。通过放置在覆盖乳突皮肤的一块反射带上的单轴激光多普勒测振仪（Polytec Inc.，Irvine，CA）和植入皮质乳突骨中的骨锚钛螺钉和底座（Cochlear Ltd.，Centennial，CO），定量测量骨导振动。
麦克风测量显示耳道压力为 60-89 dB SPL，在低于 2 kHz 的频率范围内达到峰值。在乳突骨上测量到的最大 LDV 峰值（使用安装支架时为 0.32-0.79 mm/s，使用立体定向悬架时为 0.21-0.36 mm/s）；使用支架时，皮肤的峰值测量范围为 0.05 至 0.15 mm/s，使用立体定向悬架时为 0.03 至 0.13 mm/s。
AMEI 产生的空气和骨导信号强度足以被植入设备麦克风检测到，这可能导致再放大。了解这些源的相对贡献可能在开发有针对性的缓解算法以及强调声学隔离的手术技术方面发挥重要作用。
