Investigating the Electrical Properties of Different Cochlear Implants

Abstract

This study characterises and compares electrical properties and current spread across four different makes of cochlear implants with differing electrode designs using a 3D-printed artificial cochlear model. Background: Cochlear implants are currently limited by current spread within the cochlea, which causes low spectral resolution of auditory nerve stimulation. Different cochlear implant makes vary in electrode size, shape, number, and configuration. How these differences affect cochlear implant current spread and function is not well known. Method: Each cochlear implant was inserted into a linear cochlear model containing recording electrodes along its length. Biphasic monopolar stimulation of each implant electrode was carried out, and the resultant waveform and transimpedance matrix (TIM) data obtained from the recording electrodes. This was repeated with each implant rotated 180 degrees in the cochlea model to examine the effects of electrode orientation. Impedance spectroscopy was also carried out at the apex, middle, and base of the model. Results: The four cochlear implants displayed similar TIM profiles and waveforms. One hundred eighty degrees rotation of each cochlear implant made little difference to the TIM profiles. Impedance spectroscopy demonstrated broad similarities in amplitude and phase across the implants, but exhibited differences in certain electrical parameters. Conclusion: Implants with different designs demonstrate similar electrical performance, regardless of electrode size and spacing or electrode array dimension. In addition, rotatory maneuvers during cochlear implantation surgery are unlikely to change implant impedance properties.

The intraoperative relationship between intracochlear electrical field and excitability of the auditory nerve

“…Contrary to an earlier study, where intracochlear EF recordings were similar between different manufacturers ( Swaddiwudhipong et al., 2020 ), in our study the modeled EFs were different between Cochlear and Med-El devices. As the modeling function utilizes EF recordings from non-stimulating electrodes, a greater amount of recording electrodes likely leads to a more accurate estimate of the effective EF.…”

“…Therefore, to make inferences about the effect of the EF on auditory perception, its relationship with psychophysical loudness as well as with patterns of neural activation has been studied. The intracochlear EF seems to be similar between the different manufacturers ( Swaddiwudhipong et al., 2020 ), despite slight differences in the measurement methods. In Cochlear (Sydney, Australia) devices the voltage is recorded for each stimulating and recording electrode pair separately, while in Advanced Bionics (Valencia, CA, USA) and Med-El (Innsbruck, Austria) devices the EF distribution can be recorded simultaneously from all non-stimulated electrode contacts ( Vanpoucke et al., 2004 ).…”

“…The spread of the intracochlear EF is purely a physical measure and can be recorded in saline and from cadavers and plastic cochlea models ( de Rijk et al., 2020 ; Swaddiwudhipong et al., 2020 ). Therefore, to make inferences about the effect of the EF on auditory perception, its relationship with psychophysical loudness as well as with patterns of neural activation has been studied.…”

Transimpedance Matrix Measurements Reliably Detect Electrode Tip Fold-over in Cochlear Implantation

“…Swaddiwudhipong et al (24) recently published a similarity of TIM profiles of different electrode designs across the four main implant companies. These findings indicate that TIM profiles may be generalizable among electrodes and manufacturers and hopefully in short time comparable software will be available for each implant.…”

Models of Cochlea Used in Cochlear Implant Research: A Review

“…For instance, several studies have characterised the electrical properties [32,72] and conducted CI insertion studies [18,75,77] in both fresh-frozen and fixed human cochleae. Furthermore, many electrophysiological and psychoacoustic measures have been developed to test the CI-nerve interface in humans, which include contact impedance and trans-impedance measurements [59,87,138], electrically evoked compound action potentials (eCAPS) [27,41,42], and electrically evoked auditory brainstem responses (eABR) [17,36] which enable the evaluation of CI electrical characteristics (including fibrosis, positioning, and electrical faults), cochlear neural activation patterns, and propagation the CI stimulation to the brain, respectively. However, human studies do not allow us to systematically test numerous parameters in the same experiment, such as electrode position, stimulation parameters, pulse shapes, the geometry of the cochlea, and electrode design, size, and shape, which are much more possible in other models.…”