Dynamic Current Focusing: A Novel Approach to Loudness Coding in Cochlear Implants
Dynamic Current Focusing: A Novel Approach to Loudness Coding in Cochlear Implants
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DOI：
10.1097/aud.0000000000000593
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发表时间：
2019-01-01
期刊：
影响因子：
3.7
通讯作者：
Frijns, Johan H. M.
中科院分区：
文献类型：
--
作者：
de Jong, Monique A. M.;Briaire, Jeroen J.;Frijns, Johan H. M.
目的：为了提高频谱分辨率和语音清晰度，已经提出了几种电流聚焦方法，通过减少脑内电流扩散来增加空间选择性。例如，三极刺激将电流施加到中央电极，并使用两个侧翼电极作为返回路径，从而产生较窄的脑内电场，因此与单极（MP）刺激相比增加了光谱分辨率。然而，需要更多的电流，并且在一些患者中，特别是具有高电极阻抗的患者，由于顺应性限制，不能支持完全响度增长。本研究描述和分析了一种新的响度编码方法，该方法使用阈值附近的三极刺激，并逐渐扩大激励（通过降低补偿系数σ），以增加响度，而不需要增加总电流。假设这种动态电流聚焦（DCF）策略增加了空间选择性，特别是在较低响度水平下，同时在较高响度水平下保持最大选择性，而不会达到合规限制。设计：11名患有语后听力损失的成人人工耳蜗植入者，至少有9个月的经验他们的HiRes90 K植入物被选为参与本研究。使用他们自己的临床程序（安装在Harmony处理器上）评估噪声中语音清晰度（荷兰矩阵句子测试）、45和65 dB处的频谱涟漪辨别力和时间调制检测阈值的基线性能。随后，DCF策略被安装在研究Harmony处理器上。阈值水平用σ = 0.8确定，这意味着80%的电流返回到侧翼电极，剩余的20%返回到脑外接地电极。而不是增加整体脉冲幅度，西格玛降低，以确定最舒适的响度。经过2至3小时的适应研究策略，同样的心理物理措施采取。结果：在45分贝，平均频谱涟漪分数显着改善，从2.4波纹每倍频程与他们的临床计划，以3.74波纹每倍频程与DCF策略（p = 0.016）。11名参与者中有8名的频谱分辨率提高到65 dB。然而，在更高的呈现水平下，没有观察到DCF和MP之间的显著差异。对于MP和DCF策略，噪声中的语音和时间调制检测阈值都是相等的。主观上，2名参与者更喜欢DCF策略而不是他们自己的临床计划，2名参与者更喜欢他们自己的策略，而大多数参与者没有偏好。电池寿命减少，范围从1.5到4小时。结论：DCF策略在较低的响度水平下提供了更好的频谱分辨率，但在语音测试中表现相同。这些结果需要更长的适应期来研究长期结果，并评估涟漪测试中的结果是否会转移到言语得分。进一步的研究，例如，关于拟合规则和降低功耗，是必要的，使DCF策略适合于常规临床应用。
Objectives: In an attempt to improve spectral resolution and speech intelligibility, several current focusing methods have been proposed to increase spatial selectivity by decreasing intracochlear current spread. For example, tripolar stimulation administers current to a central electrode and uses the two flanking electrodes as the return pathway, creating a narrower intracochlear electrical field and hence increases spectral resolution when compared with monopolar (MP) stimulation. However, more current is required, and in some patients, specifically the ones with high electrode impedances, full loudness growth cannot be supported because of compliance limits. The present study describes and analyses a new loudness encoding approach that uses tripolar stimulation near threshold and gradually broadens the excitation (by decreasing compensation coefficient sigma) to increase loudness without the need to increase overall current. It is hypothesized that this dynamic current focusing (DCF) strategy increases spatial selectivity, especially at lower loudness levels, while maintaining maximum selectivity at higher loudness levels, without reaching compliance limits.Design: Eleven adult cochlear implant recipients with postlingual hearing loss, with at least 9 months of experience with their HiRes90K implant, were selected to participate in this study. Baseline performance regarding speech intelligibility in noise (Dutch matrix sentence test), spectral ripple discrimination at 45 and 65 dB, and temporal modulation detection thresholds were assessed using their own clinical program, fitted on a Harmony processor. Subsequently, the DCF strategy was fitted on a research Harmony processor. Threshold levels were determined with sigma = 0.8, which means 80% of current is returned to the flanking electrodes and the remaining 20% to the extracochlear ground electrode. Instead of increasing overall pulse magnitude, sigma was decreased to determine most comfortable loudness. After 2 to 3hr of adaptation to the research strategy, the same psychophysical measures were taken.Results: At 45 dB, average spectral ripple scores improved significantly from 2.4 ripples per octave with their clinical program to 3.74 ripples per octave with the DCF strategy (p = 0.016). Eight out of 11 participants had an improved spectral resolution at 65 dB. Nevertheless, no significant difference between DCF and MP was observed at higher presentation levels. Both speech-in-noise and temporal modulation detection thresholds were equal for MP and DCF strategies. Subjectively, 2 participants preferred the DCF strategy over their own clinical program, 2 preferred their own strategy, while the majority of the participants had no preference. Battery life was decreased and ranged from 1.5 to 4hr.Conclusions: The DCF strategy gives better spectral resolution, at lower loudness levels, but equal performance on speech tests. These outcomes warrant for a longer adaptation period to study long-term outcomes and evaluate if the outcomes in the ripple tests transfer to the speech scores. Further research, for example, with respect to fitting rules and reduction of power consumption, is necessary to make the DCF strategy suitable for routine clinical application.