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Objective: A decrease in intracochlear electrocochleographic (ECochG) amplitude during cochlear implantation has been associated with poorer postoperative hearing preservation in several short-term studies. Here, we relate the stability of ECochG during surgery to hearing preservation at 3- and 12-months. Methods: Patients with hearing ≤80-dB HL at 500 Hz were implanted with a slim-straight electrode array. ECochG responses to short, high-intensity, 500-Hz pure tones of alternating polarity were recorded continuously from the apical-most electrode during implantation. No feedback was provided to the surgeon. ECochG amplitude was derived from the difference response, and implantations classified by the presence (“ECochG drop”) or absence (“no drop”) of a ≥30% reduction in ECochG amplitude during insertion. Residual hearing (relative and absolute) was reported against the ECochG class. Results: ECochG was recorded from 109 patients. Of these, interpretable ECochG signals were recorded from 95. Sixty-six of 95 patients had an ECochG drop during implantation. Patients with an ECochG drop had poorer preoperative hearing above 1000 Hz. Hearing preservation (in decibels, relative to preoperative levels and functionally) was significantly poorer at 250-, 500-, and 1000-Hz at 3 months in patients exhibiting an ECochG drop. Twelve-month outcomes were available from 85 patients, with significantly poorer functional hearing, and greater relative and absolute hearing loss from 250 to 1000 Hz, when an ECochG drop had been encountered. Conclusion: Patients exhibiting ECochG drops during implantation had significantly poorer hearing preservation 12 months later. These observational outcomes support the future development of surgical interventions responsive to real-time intracochlear ECochG. Early intervention to an ECochG drop could potentially lead to prolonged improvements in hearing preservation.

Objective: Lay the groundwork for using electrocochleography (ECochG) as a measure of cochlear health, by characterizing typical patterns of the ECochG response observed across the electrode array in cochlear implant recipients with residual hearing.Methods: ECochG was measured immediately after electrode insertion in 45 cochlear implant recipients with residual hearing. The Cochlear Response Telemetry system was used to record ECochG across the electrode array, in response to 100- or 110-dB SPL pure tones at 0.5-kHz, presented at 14 per second and with alternating polarities. Hair cell activity, as the cochlear microphonic (CM), was estimated by taking the difference (DIF) of the two polarities. Neural activity, as the auditory nerve neurophonic (ANN), was estimated by taking the sum (SUM) of the two polarities. Prior work in humans and animal studies suggested that the expected ECochG pattern in response to a 0.5-kHz pure tone is an apical-peak in CM amplitude and latency.Results: The most prevalent pattern was a peak in the DIF amplitude near the most apical electrode, with a prolongation of latency toward the electrode tip; this was found in 21/39 individuals with successful ECochG recordings. The 21 apical-peak recipients had the best low-frequency hearing. A low amplitude, long-latency DIF response that remained relatively constant across the electrode array was found in 10/39 individuals, in a group with the poorest low- and high-frequency hearing. A third, previously undescribed, pattern occurred in 8/39 participants, with mid-electrode peaks in DIF amplitude. These recipients had the best high-frequency hearing and a progressive prolongation of DIF latency around the mid-electrode peaks consistent with the presence of discrete populations of hair cells.Conclusions: The presence of distinct patterns of the ECochG response with relationships to pre-operative hearing levels supports the notion that ECochG across the electrode array functions as a measure of cochlear health.

Objectives: Real-time electrocochleography (ECochG) has been used as a monitoring tool during cochlear implantation (CI), whereby, amplitude drops have been correlated with postoperative acoustic hearing results. However, no consensus has been reached as to how a single event of an amplitude drop should be characterized. The aim of this study was to identify ECochG events that predict loss of hearing 1 month after surgery. Design: Fifty-five patients were included in this prospective cohort study. Real-time ECochG measurements were performed during CI electrode insertion. Single ECochG events were characterized according to their amplitude loss and slope steepness. Results: Using receiver operating characteristic analyses, the most efficient cut-off criterion for a relative hearing loss of 25% was an amplitude loss of 61% at a fixed slope steepness of 0.2 µV/sec. Three-quarters of our population had at least one such event during implantation. Most events occurred shortly before full insertion. With increasing number of events, median residual hearing thresholds deteriorated for all frequencies. Larger amplitude drops trended toward worse hearing preservation. Signal recovery after an ECochG event could not be correlated to acoustic hearing outcomes. Conclusions: Our data suggest that amplitude drops exceeding 61% of the ongoing signal at a slope steepness of 0.2 µV/sec are correlated with worse acoustic hearing preservation. Clearly defined ECochG events have the potential to guide surgeons during CI in the future. This is essential if a fully automated data analysis is to be employed or benchmarking undertaken.

Aim: To obtain direct evidence for the cochlear travelling wave in humans by performing electrocochleography from within the cochlea in subjects implanted with an auditory prosthesis. Background: Sound induces a travelling wave that propagates along the basilar membrane, exhibiting cochleotopic tuning with a frequency-dependent phase delay. To date, evoked potentials and psychophysical experiments have supported the presence of the travelling wave in humans, but direct measurements have not been made. Methods: Electrical potentials in response to rarefaction and condensation acoustic tone bursts were recorded from multiple sites along the human cochlea, directly from a cochlear implant electrode during, and immediately after, its insertion. These recordings were made from individuals with residual hearing. Results: Electrocochleography was recorded from 11 intracochlear electrodes in 7 ears from 6 subjects, with detectable responses on all electrodes in 5 ears. Cochleotopic tuning and frequency-dependent phase delay of the cochlear microphonic were demonstrated. The response latencies were slightly shorter than those anticipated which we attribute to the subjects' hearing loss. Conclusions: Direct evidence for the travelling wave was observed. Electrocochleography from cochlear implant electrodes provides site-specific information on hair cell and neural function of the cochlea with potential diagnostic value.

Objectives/Hypothesis: Spikes in cochlear implant impedance are associated with inner ear pathology after implantation. Here, we correlate these spikes with episodes of hearing loss and/or vertigo, with a comparison between lateral wall and peri-modiolar electrode arrays. Methods: Seven hundred seventy recipients of Cochlear's slim-straight, lateral wall electrode (CI422), or peri-modiolar (CI512) electrode were investigated for impedance spikes. Impedance fluctuations were defined as a median rise of ≥ 4 kΩ across all intracochlear electrodes from baseline measurements taken 2 weeks after switch-on. Medical records were analyzed from 189 of the 770 patients. Results: The slim straight, lateral wall electrode was found to spike in impedance at a significantly higher rate than the peri-modiolar array (17% vs 12%). The peri-modiolar electrode tended to spike in impedance earlier than the slim-straight electrode. Impedance spikes were found to significantly correlate with medical events (hearing loss, vertigo, or tinnitus). Overall, in the “spike” group, 42 of 75 patients (56%) demonstrated a clinical event during the impedance spike, whereas 26 of 114 patients (22%) of the “non-spike” group had a clinical event. This significant difference existed with both implant types. Conclusion: These results demonstrate a small, but significant increase in impedance spikes in lateral wall electrodes, and support the relationship between spikes in cochlear implant impedances and postoperative inner-ear events, including the loss of residual hearing and vertigo. Monitoring cochlear implant impedance may be a method for early detection, and so the prevention, of these events in the future.

Cochlear implantation has successfully restored the perception of hearing for nearly 200 thousand profoundly deaf adults and children. More recently, implant candidature has expanded to include those with considerable natural hearing which, when preserved, provides an improved hearing experience in noisy environments. But more than half of these patients lose this natural hearing soon after implantation. To reduce this burden, biosensing technologies are emerging that provide feedback on the quality of surgery. Here we report clinical findings on a new intra-operative measurement of electrical impedance (4-point impedance) which, when elevated, is associated with high rates of postoperative hearing loss and vestibular dysfunction. In vivo and in vitro data presented suggest that elevated 4-point impedance is likely due to the presence of blood within the cochlea rather than its geometry. Four-point impedance is a new marker for the detection of cochlear injury causing bleeding, that may be incorporated into intraoperative monitoring protocols during CI surgery. The preservation of cochlear structure and residual functional hearing has become the standard of care for cochlear implantation (CI). Hearing preservation is important to facilitate combined electrical and acoustic stimulation of the cochlea, as this improves speech recognition in noise and music appreciation 1-4. Cochlear structural preservation will ensure that the ear is ready for future, regenerative therapies 5,6. Structural and functional preservation of the cochlea depends not only upon the electrode design, but also the surgery. Electrodes must be introduced into the cochlea without causing injury. Until recently, technologies have not existed to guide the surgeon during the implant procedure; the operation has been conducted "blind" without the provision of feedback. Over recent years, we and others have begun to monitor cochlear function during cochlear implantation 7-10 , using the CI's own electrodes to monitor the electrophysiological response of the ear to acoustic stimulation. This technique, known as electrocochleography, has provided valuable information to guide surgeons during the operation; if the electrophysiological response is preserved during surgery, residual hearing is better after implantation 7-10. This paper is motivated by a desire to increase the scope of intraoperative monitoring during CI surgery. Current methods allow real-time detection of cochlear dysfunction, but these do not assess cochlear injury directly. Here we report on a method that has this potential. We have monitored "four-point" electrical impedance (4PI) from the implant's intracochlear electrodes during CI surgery. This impedance measurement is acquired by passing current between two outer electrodes whilst the voltage (from which the impedance may be inferred) is measured between two inner electrodes (Fig. 1A). The method is believed to assess the bulk impedance between the two inner electrodes, and has been used to differentiate between tissue and fluid ...

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