Background: This study examined electrical bioimpedance as a biomarker for intracochlear tissue changes after cochlear implant surgery, comparing monopolar, three-point, and four-point impedance measurements over time and evaluating different measurement systems and approaches. Methods: Impedance measurements were obtained from 21 participants during surgery and at four postoperative stages. Monopolar impedances were recorded using the Bionic Ear Data Collection System (BEDCS) and the Active Insertion Monitoring (AIM) system. Three- and four-point impedances were recorded directly using BEDCS, and indirect three-point impedances were additionally derived from Electrical Field Imaging matrices recorded using BEDCS or AIM. Results: There was an 11% relative error between monopolar measurements from BEDCS and AIM and a 25% discrepancy between direct and indirect three-point measurements. Despite this, direct and indirect measurements from both systems were useful for tracking postoperative impedance shifts. Three- and four-point measurements showed a strong relationship both during and after surgery. Our results suggest that three- and four-point measurements are more specific than monopolar impedances in capturing localized tissue changes. Conclusions: Three- and four-point impedance measurements are potential markers of intracochlear tissue changes over time. While direct three-point impedance measurements offer higher accuracy, indirect measurements provide a feasible alternative for monitoring intracochlear changes in clinical settings lacking the option of direct measurements.

Background: Cochlear implant (CI) electrode insertion can change the mechanical state of the ear whereby wideband tympanometry absorbance (WBTA) may serve as a sensitive tool to monitor these mechanical changes of the peripheral auditory pathway after CI surgery. In WBTA, the amount of acoustic energy reflected by the tympanic membrane is assessed over a wide frequency range from 226 Hz to 8000 Hz. The objective of this study was to monitor changes in WBTA in CI recipients before and after surgery. Methods: Following otoscopy, WBTA measurements were conducted twice in both ears of 38 standard CI recipients before and in the range of 4 to 15 weeks after CI implantation. Changes from pre- to postoperative absorbance patterns were compared for the implanted as well as the contralateral control ear for six different frequencies (500 Hz, 750 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz). Furthermore, the influence of the time point of the measurement, surgical access, electrode type, sex and side of the implantation were assessed for the implanted and the control ear in a linear mixed model. Results: A significant decrease in WBTA could be observed in the implanted ear when compared with the contralateral control ear for 750 Hz (p < 0.01) and 1000 Hz (p < 0.05). The typical two-peak pattern of WBTA measurements was seen in both ears preoperatively but changed to a one-peak pattern in the newly implanted ear. The linear mixed model showed that not only the cochlear implantation in general but also the insertion through the round window compared to the cochleostomy leads to a decreased absorbance at 750 and 1000 Hz. Conclusions: With WBTA, we were able to detect mechanical changes of the acoustical pathway after CI surgery. The implantation of a CI led to decreased absorbance in the lower frequencies and the two-peak pattern was shifted to a one-peak pattern. The result of the linear mixed model indicates that WBTA can detect mechanical changes due to cochlear implantation not only in the middle ear but also in the inner ear.

This study compared outcomes of two electrophysiological measures, electrocochleography (ECochG) and panoramic electrically-evoked compound action potential (PECAP), and two psychophysical measures, temporal and electrode discrimination test (TED) and spectrotemporal two-octave bandpass modulation test (STM), in cochlear implant (CI) listeners. The aim was to investigate whether tonotopic regions showing poorer performance on the acoustic STM test also exhibit reduced peripheral integrity (ECochG and PECAP) or diminished modulation encoding abilities at the electrode level (TED). Twenty-seven Advanced Bionics CI candidates were prospectively enrolled prior to CI surgery. ECochG and PECAP recordings were obtained from all intracochlear electrodes intraoperatively and three months post-implantation, respectively. TED was measured via direct electrode stimulation six months post-implantation, and the STM test was conducted with CI-processed acoustic stimulation one year after surgery. All measures were obtained or averaged across four tonotopic regions. After adjusting for region-specific CI-processing differences, linear mixed model analyses showed significantly poorer STM performance in the worst-performing region compared with the other three regions (p < 0.001). TED values were also significantly worse in this region (p < 0.01), whereas ECochG and PECAP values did not differ significantly between the worst region on the STM test and the remaining regions. These findings demonstrate that while electrophysiological and psychophysical measures each provide valuable, spatially specific information, they capture distinct physiological and perceptual aspects of auditory processing. This highlights the need to investigating which measure, or combination of measures, can best guide individualized CI programming adjustments by identifying suboptimal performing tonotopic regions.

Background: Various representations exist in the literature to visualize electrocochleography (ECochG) recordings along the basilar membrane (BM). This lack of generalization complicates comparisons within and between cochlear implant (CI) users, as well as between publications. This study synthesized the visual representations available in the literature via a systematic review and provides a novel approach to visualize ECochG data in CI users. Methods: A systematic review was conducted within PubMed and EMBASE to evaluate studies investigating ECochG and CI. Figures that visualized ECochG responses were selected and analyzed. A novel visualization of individual ECochG data, the ZH-ECochG Bode plot (ZH = Zurich), was devised, and the recordings from three CI recipients were used to demonstrate and assess the new framework. Results: Within the database search, 74 articles with a total of 115 figures met the inclusion criteria. Analysis revealed various types of representations using different axes; their advantages were incorporated into the novel visualization framework. The ZH-ECochG Bode plot visualizes the amplitude and phase of the ECochG recordings along the different tonotopic regions and angular insertion depths of the recording sites. The graph includes the pre- and postoperative audiograms to enable a comparison of ECochG responses with the audiometric profile, and allows different measurements to be shown in the same graph. Conclusions: The ZH-ECochG Bode plot provides a generalized visual representation of ECochG data, using well-defined axes. This will facilitate the investigation of the complex ECochG potentials generated along the BM and allows for better comparisons of ECochG recordings within and among CI users and publications. The scripts used to construct the ZH-ECochG Bode plot are provided by the authors.

Spectrotemporal modulation tests probe spectral and temporal resolution in cochlear implant (CI) users. This study investigated how carrier type and bandpass modulations influenced modulation detection performance. Nineteen CI users performed a reaction-time task involving the detection of spectral (0.25–2 cycles/octave) and/or temporal (4–16 Hz) modulations embedded in a broadband carrier. Carriers were either (1) a complex tone composed of 87 random-phase sinusoids spaced linearly at 100 Hz and weighted by a pink spectrum or (2) pink noise. Surprisingly, stimuli with dense spectral modulations were more readily detected when paired with the complex tone carrier. In contrast, the pink noise carrier yielded the expected low-pass spectral modulation transfer function profile. Electrodogram simulations based on CI sound processing strategies suggest that using a complex tone carrier with more closely spaced, logarithmically arranged tones may reduce unintended cues, such as spectral aliasing. Additionally, 2-octave limited bandwidth stimuli with a fixed temporal modulation rate (4 Hz) and spectral densities ranging from 0–2 cycles/octave were tested within broadband pink noise, centered at frequencies from 500 to 4000 Hz. Detection sensitivity was lowest at 500 Hz—a result supported by electrodograms—suggesting potential device processing limitations for spectrotemporal modulations at apical electrode sites.

Objectives: Intracochlear electrocochleography (ECochG) in cochlear implant (CI) recipients is a potential tool for monitoring cochlear function during and after electrode array (EA) insertion. However, mechanisms underlying ECochG amplitude variations along the cochlear duct, and their significance for hearing preservation (HP), remain unclear. Therefore, a longitudinal study was conducted to monitor maximum ECochG amplitude and its tonotopic location from EA insertion to 1 yr postimplantation. It was hypothesized that changes in maximum amplitude (>30%) and/or shifts in its location (>1 octave) across timepoints reflect intracochlear alterations associated with residual hearing changes. Design: ECochG recordings were obtained in 80 adult CI recipients with measurable residual hearing. For Contour Advance (CI612) and Slim Straight (CI622) arrays (Cochlear Ltd.), recordings were taken from every second intracochlear electrode. For HiFocus SlimJ and MidScala arrays (Advanced Bionics LLC), recordings were obtained from all electrodes. Measurements were conducted at four timepoints: (1) intraoperatively, during EA insertion (Intraop1), (2) intraoperatively, immediately after full insertion (Intraop2), (3) approximately 7 wk after surgery (Postop1), and (4) approximately 1 yr after surgery (Postop2). 500 Hz tone bursts were used for acoustic stimulation and the magnitude of the difference between responses to alternating-polarity stimuli was analyzed. Tonotopic electrode locations were determined from postoperative cone beam computed tomography scans. Pure-tone audiograms were obtained preoperatively and at approximately 7 wk and 1 yr postoperatively. HP was determined using the HEARRING group formula. Results: Maximum ECochG amplitudes remained largely stable intraoperatively, with no significant difference between Intraop1 and Intraop2 in complete-case analysis (n = 44). In contrast, a significant decrease in maximum amplitude was observed between Intraop2 and Postop1 ( p < 0.001). Participants with >30% amplitude reduction between the 2 intraoperative recordings (Intraop1 versus Intraop2) did not differ significantly in HP from those with stable amplitudes. However, those showing a >30% reduction in the early postoperative period (Intraop2 versus Postop1) showed significantly lower HP ( p = 0.028). Nonapical peak location during Intraop1 occurred in 41% of the cases, although tonotopic location of the maximum peak during insertion monitoring (Intraop1) did not show a relationship with HP. Tonotopic location shifts of the maximum amplitude (>1 octave) were observed in a small subset of cases between consecutive recordings up to Postop2. However, peak location changes (apical, basal, stable) were not associated with significant differences in HP. Conclusions: Our results suggest that nonapical peak patterns are not necessarily markers of insertion trauma and may instead reflect variability in cochlear integrity (e.g., dead regions). Peak location during insertion monitoring was not associated with postoperative HP, and both maximum amplitude and tonotopic peak location remained stable intraoperatively. In contrast, early postoperative reductions in ECochG amplitude were common and associated with HP, highlighting the need to investigate strategies to minimize early intracochlear reactions. Overall, the study demonstrates the value of ECochG for monitoring intracochlear processes over time.