Threshold, Comfortable Level and Impedance Changes as a Function of Electrode-Modiolar Distance

Abstract

The results support the hypothesis that the relationship between the radial distance of the electrode and the psychophysical measures are influenced by patterns of fibrous tissue growth and individual patient differences, such as etiology and neural survival. Impedance measures for the Nucleus 24 Contour electrode array were higher than the banded electrode array, but this is primarily due to the reduction in electrode surface area. The different outcomes in impedance over time suggest differences in the relative contributions of the components of impedance with the two arrays.

Across-Site Variation in Detection Thresholds and Maximum Comfortable Loudness Levels for Cochlear Implants

“…3). These data are consistent with a more uniform positioning of the CI24M implant against the lateral wall of the scala tympani compared with the CI24R(CS) implant, which may vary in its mediallateral position as suggested by the radiographic data of Saunders et al (2002).…”

“…Other studies have also found small effects of implant type. The difference in mean MP thresholds for CI24M and CI24R(CS) implant groups found by Saunders et al (2002) was 13.8 Cochlear Level units, equivalent to about 2.4 dB. In our study, this difference was 0.8 dB.…”

“…The wide distribution of these values and the considerable overlap in the distributions for the two types of implants suggest that there is a great deal of variability from site to site in the distances between the electrodes and the neurons in both types of implants. For the CI24R(CS) implant, this variability is also evident in the distance between the electrodes and the modiolar core as assessed by analysis of radiographic images (Saunders et al 2002). Another factor that would affect the variability in distance between the stimulated electrodes and the responsive neurons is the large variability in nerve survival patterns that is typically found in deaf ears (Hinojosa and Marion 1983;Nadol 1997).…”

“…These include the medial-lateral position of the electrodes in the scala tympani (Kawano et al 1998;Saunders et al 2002), variation in the pattern of survival of neurons near the electrode array (Hinojosa and Marion 1983;Nadol 1997), and growth of tissue, particularly new dense bone, in the implanted cochlea. Considerable effort is being directed toward increasing the proximity of electrodes to neural tissue, including engineering implants that position electrodes close to the modiolar wall and tissue engineering to increase nerve survival in the implanted cochlea and/or to grow new neural tissue in close proximity to the implant.…”

“…In the CI24M implant, the stimulating electrodes consist of platinum bands that encircle a silicone-rubber carrier. Prior to implantation this implant is straight; when it is inserted into the curved scala tympani, it tends to lie near the lateral wall (Shepherd et al 1985;Kennedy 1987;Saunders et al 2002). In contrast, the CI24R(CS) (Contour) implant has the electrodes positioned on only one side of the silicone-rubber carrier and the carrier is precurved and designed with the intention that, after insertion, the electrodes will lie close to the modiolar wall of the scala tympani Parkinson et al 2002).…”