Utilizing Electrocochleography as a Microphone for Fully Implantable Cochlear Implants.

Current cochlear implants (CIs) are semi-implantable devices with an externally worn sound processor that hosts the microphone and sound processor. A fully implantable device, however, would ultimately be desirable as it would be of great benefit to recipients. While some prototypes have been designed and used in a few select cases, one main stumbling block is the sound input. Specifically, subdermal implantable microphone technology has been poised with physiologic issues such as sound distortion and signal attenuation under the skin. Here we propose an alternative method that utilizes a physiologic response composed of an electrical field generated by the sensory cells of the inner ear to serve as a sound source microphone for fully implantable hearing technology such as CIs. Electrophysiological results obtained from 14 participants (adult and pediatric) document the feasibility of capturing speech properties within the electrocochleography (ECochG) response. Degradation of formant properties of the stimuli /da/ and /ba/ are evaluated across various degrees of hearing loss. Preliminary results suggest proof-of-concept of using the ECochG response as a microphone is feasible to capture vital properties of speech. However, further signal processing refinement is needed in addition to utilization of an intracochlear recording location to likely improve signal fidelity.

Intra-Cochlear Electrocochleography During Cochear Implant Electrode Insertion Is Predictive of Final Scalar Location.

HYPOTHESIS: Electrocochleography (ECochG) patterns observed during cochlear implant (CI) electrode insertion may provide information about scalar location of the electrode array. BACKGROUND: Conventional CI surgery is performed without actively monitoring auditory function and potential damage to intracochlear structures. The central hypothesis of this study was that ECochG obtained directly through the CI may be used to estimate intracochlear electrode position and, ultimately, residual hearing preservation. METHODS: Intracochlear ECochG was performed on 32 patients across 3 different implant centers. During electrode insertion, a 50-ms tone burst stimulus (500 Hz) was delivered at 110 dB SPL. The ECochG response was monitored from the apical-most electrode. The amplitude and phase changes of the first harmonic were imported into an algorithm in an attempt to predict the intracochlear electrode location (scala tympani [ST], translocation from ST to scala vestibuli [SV], or interaction with basilar membrane). Anatomic electrode position was verified using postoperative computed tomography (CT) with image processing. RESULTS: CT analysis confirmed 25 electrodes with ST position and 7 electrode arrays translocating from ST into SV. The ECochG algorithm correctly estimated electrode position in 26 (82%) of 32 subjects while 6 (18%) electrodes were wrongly identified as translocated (sensitivity = 100%, specificity = 77%, positive predictive value = 54%, and a negative predictive value = 100%). Greater hearing loss was observed postoperatively in participants with translocated electrode arrays (36 ±â€Š15 dB) when compared with isolated ST insertions (28 ±â€Š20 dB HL). This result, however, was not significant (p = 0.789). CONCLUSION: Intracochlear ECochG may provide information about CI electrode location and hearing preservation.

Real-Time Intracochlear Electrocochleography Obtained Directly Through a Cochlear Implant.

HYPOTHESIS: Utilizing the cochlear implant to record electrophysiologic responses during device placement is a feasible and efficacious technique for monitoring near real-time cochlear physiology during and following electrode insertion. BACKGROUND: Minimizing intracochlear trauma during cochlear implantation has emerged as a highly researched area to help improve patient performance. Currently, conventional cochlear implant technology allows for the recording of electrically evoked compound action potentials (eCAPs). Acoustically evoked potentials may be more sensitive in detecting physiologic changes occurring as a result of electrode insertion. Electrocochleography obtained from within the cochlea allows hair cell and neural response monitoring along the cochlear spiral at locations where changes most likely would occur. METHODS: Intracochlear electrocochleography (ECochG) was recorded from the cochlear implant during surgery in 14 subjects. A long acquisition time (54.5 ms), capable of measuring potentials from the low frequency-serving apical region of the cochlea (125 and 500 Hz) was employed. Two distinct intracochlear processing methods were used and compared in obtaining electrophysiologic data. RESULTS: Measureable intracochlear ECochG responses were obtained from all 14 participants. The 1st harmonic distortions (cochlear microphonic and auditory nerve neurophonic) generally increased steadily with electrode insertion. Electrode and frequency scan following insertion revealed that response amplitude varied based on location of recording electrode and frequency of stimulation. Exquisite sensitivity to manipulation during round window muscle packing was demonstrated. CONCLUSION: Intracochlear ECochG recorded from the electrode array of the cochlear implant is a highly feasible technique that sheds light on cochlear micromechanics during cochlear implant electrode placement.