Sijgers Leanne, Röösli Christof, Bertschinger Rahel, Epprecht Lorenz, Veraguth Dorothe, Dalbert Adrian, Huber Alexander, Pfiffner Flurin
Department of Otorhinolaryngology, Head & Neck Surgery, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
Ear Hear. 2025;46(1):83-97. doi: 10.1097/AUD.0000000000001556. Epub 2024 Jul 26.
The inter-phase gap (IPG) offset effect is defined as the dB offset between the linear parts of electrically evoked compound action potential (ECAP) amplitude growth functions for two stimuli differing only in IPG. The method was recently suggested to represent neural health in cochlear implant (CI) users while being unaffected by CI electrode impedances. Hereby, a larger IPG offset effect should reflect better neural health. The aims of the present study were to (1) examine whether the IPG offset effect negatively correlates with the ECAP threshold and the preoperative pure-tone average (PTA) in CI recipients with residual acoustic hearing and (2) investigate the dependency of the IPG offset effect on hair cell survival and intracochlear electrode impedances.
Seventeen adult study participants with residual acoustic hearing at 500 Hz undergoing CI surgery at the University Hospital of Zurich were prospectively enrolled. ECAP thresholds, IPG offset effects, electrocochleography (ECochG) responses to 500 Hz tone bursts, and monopolar electrical impedances were obtained at an apical, middle, and basal electrode set during and between 4 and 12 weeks after CI surgery. Pure-tone audiometry was conducted within 3 weeks before surgery and approximately 6 weeks after surgery. Linear mixed regression analyses and t tests were performed to assess relationships between (changes in) ECAP threshold, IPG offset, impedance, PTA, and ECochG amplitude.
The IPG offset effect positively correlated with the ECAP threshold in intraoperative recordings ( p < 0.001) and did not significantly correlate with the preoperative PTA ( p = 0.999). The IPG offset showed a postoperative decrease for electrode sets that showed an ECochG amplitude drop. This IPG offset decrease was significantly larger than for electrode sets that showed no ECochG amplitude decrease, t (17) = 2.76, p = 0.014. Linear mixed regression analysis showed no systematic effect of electrode impedance changes on the IPG offset effect ( p = 0.263) but suggested a participant-dependent effect of electrode impedance on IPG offset.
The present study results did not reveal the expected relationships between the IPG offset effect and ECAP threshold values or between the IPG offset effect and preoperative acoustic hearing. Changes in electrode impedance did not exhibit a direct impact on the IPG offset effect, although this impact might be individualized among CI recipients. Overall, our findings suggest that the interpretation and application of the IPG offset effect in clinical settings should be approached with caution considering its complex relationships with other cochlear and neural health metrics.
相间间隙（IPG）偏移效应定义为仅在IPG方面不同的两种刺激的电诱发复合动作电位（ECAP）幅度增长函数线性部分之间的分贝偏移。最近有人提出该方法可用于表征人工耳蜗（CI）使用者的神经健康状况，且不受CI电极阻抗的影响。因此，较大的IPG偏移效应应反映更好的神经健康状况。本研究的目的是：（1）研究在有残余听觉的CI接受者中，IPG偏移效应是否与ECAP阈值和术前纯音平均听阈（PTA）呈负相关；（2）研究IPG偏移效应与毛细胞存活及耳蜗内电极阻抗的相关性。
前瞻性纳入了17名在苏黎世大学医院接受CI手术、500Hz时有残余听觉的成年研究参与者。在CI手术后4至12周期间及之后，在顶端、中部和基底电极组测量ECAP阈值、IPG偏移效应、对500Hz短音的电耳蜗图（ECochG）反应以及单极电阻抗。在手术前3周内及手术后约6周进行纯音听力测定。进行线性混合回归分析和t检验，以评估ECAP阈值（变化）、IPG偏移、电阻抗、PTA和ECochG幅度之间的关系。
在术中记录中，IPG偏移效应与ECAP阈值呈正相关（p<0.001），与术前PTA无显著相关性（p = 0.999）。对于ECochG幅度下降的电极组，IPG偏移在术后降低。这种IPG偏移降低显著大于ECochG幅度未降低的电极组，t（17）= 2.76，p = 0.014。线性混合回归分析显示电极阻抗变化对IPG偏移效应无系统性影响（p = 0.263），但提示电极阻抗对IPG偏移存在个体依赖效应。
本研究结果未揭示IPG偏移效应与ECAP阈值之间以及IPG偏移效应与术前听觉之间的预期关系。电极阻抗变化对IPG偏移效应没有直接影响，尽管这种影响在CI接受者中可能存在个体差异。总体而言，我们的研究结果表明，鉴于IPG偏移效应与其他耳蜗和神经健康指标之间的复杂关系，在临床环境中对其进行解释和应用时应谨慎。
