The Bionics Institute, East Melbourne 3002, Australia. Department of Medical Bionics, University of Melbourne, East Melbourne 3002, Australia.
J Neural Eng. 2017 Aug;14(4):046020. doi: 10.1088/1741-2552/aa7586.
Cochlear implants (CIs) have a limited number of independent stimulation channels due to the highly conductive nature of the fluid-filled cochlea. Attempts to develop highly focused stimulation to improve speech perception in CI users includes the use of simultaneous stimulation via multiple current sources. Focused multipolar (FMP) stimulation is an example of this approach and has been shown to reduce interaction between stimulating channels. However, compared with conventional biphasic current pulses generated from a single current source, FMP is a complex stimulus that includes extended periods of stimulation before charge recovery is achieved, raising questions on whether chronic stimulation with this strategy is safe. The present study evaluated the long-term safety of intracochlear stimulation using FMP in a preclinical animal model of profound deafness.
Six cats were bilaterally implanted with scala tympani electrode arrays two months after deafening, and received continuous unilateral FMP stimulation at levels that evoked a behavioural response for periods of up to 182 d. Electrode impedance, electrically-evoked compound action potentials (ECAPs) and auditory brainstem responses (EABRs) were monitored periodically over the course of the stimulation program from both the stimulated and contralateral control cochleae. On completion of the stimulation program cochleae were examined histologically and the electrode arrays were evaluated for evidence of platinum (Pt) corrosion.
There was no significant difference in electrode impedance between control and chronically stimulated electrodes following long-term FMP stimulation. Moreover, there was no significant difference between ECAP and EABR thresholds evoked from control or stimulated cochleae at either the onset of stimulation or at completion of the stimulation program. Chronic FMP stimulation had no effect on spiral ganglion neuron (SGN) survival when compared with unstimulated control cochleae. Long-term implantation typically evoked a mild foreign body reaction proximal to the electrode array; however stimulated cochleae exhibited a small but statistically significant increase in the tissue response. Finally, there was no evidence of Pt corrosion following long-term FMP stimulation; stimulated electrodes exhibited the same surface features as the unstimulated control electrodes.
Chronic intracochlear FMP stimulation at levels used in the present study did not adversely affect electrically-evoked neural thresholds or SGN survival but evoked a small, benign increase in inflammatory response compared to control ears. Moreover chronic FMP stimulation does not affect the surface of Pt electrodes at suprathreshold stimulus levels. These findings support the safe clinical application of an FMP stimulation strategy.
由于充满液体的耳蜗具有高度导电性，因此耳蜗植入物 (CI) 的独立刺激通道数量有限。尝试开发高度聚焦的刺激以改善 CI 用户的语音感知，包括通过多个电流源同时进行刺激。聚焦多极 (FMP) 刺激就是这种方法的一个例子，并且已经证明可以减少刺激通道之间的相互作用。然而，与来自单个电流源生成的传统双相电流脉冲相比，FMP 是一种复杂的刺激，在达到电荷恢复之前包括延长的刺激期，这引发了关于这种策略的慢性刺激是否安全的问题。本研究在深度耳聋的临床前动物模型中评估了使用 FMP 进行耳蜗内刺激的长期安全性。
在耳聋两个月后，六只猫双侧植入鼓阶电极阵列，并在长达 182 天的时间内接受单侧 FMP 刺激，刺激水平可引起行为反应。在刺激程序的过程中，周期性地监测受刺激和对侧对照耳蜗的电极阻抗、电诱发复合动作电位 (ECAP) 和听觉脑干反应 (EABR)。刺激程序完成后，对耳蜗进行组织学检查，并评估电极阵列是否存在铂 (Pt) 腐蚀的证据。
在长期 FMP 刺激后，对照和慢性刺激电极之间的电极阻抗没有显着差异。此外，在刺激或刺激程序开始时，从对照或受刺激耳蜗诱发的 ECAP 和 EABR 阈值没有差异。与未刺激的对照耳蜗相比，慢性 FMP 刺激对螺旋神经节神经元 (SGN) 存活没有影响。与长期植入相关，通常在电极阵列近端引起轻度异物反应；然而，受刺激的耳蜗表现出组织反应的小但统计学上显著增加。最后，在长期 FMP 刺激后没有发现 Pt 腐蚀的证据；受刺激的电极表现出与未受刺激的对照电极相同的表面特征。
在本研究中使用的水平进行慢性耳蜗内 FMP 刺激不会对电诱发的神经阈值或 SGN 存活产生不利影响，但与对照耳相比，会引起轻微的良性炎症反应增加。此外，在阈上刺激水平下，慢性 FMP 刺激不会影响 Pt 电极的表面。这些发现支持 FMP 刺激策略的安全临床应用。
