The nondeafened guinea pig model was utilized in this study to assess the functional and morphologic effects of cochlear implantation and electrical stimulation. Auditory brainstem responses (ABRs) were recorded prior to and following intrascalar implantation of a 3M-House cochlear electrode (n = 41 ears), as well as after electrical stimulation (n = 23 ears). The experimental population was divided into the following groups according to implantation and stimulation parameters: 200 μA for 3 hours (group I); 200 μA for 24 hours (group II); 400 μA for 3 hours (group III); implanted, but not stimulated (group IV); and nonimplanted, not stimulated ears (group V). Of those cochleae that sustained the trauma of implantation, 32 percent had no detectable ABR to 110 dB SPL clicks, while only 7 percent additionally failed to respond to 130 dB SPL clicks. No significant difference (one-way ANOVA with repeated measures at the 95 percent confidence limit) could be detected when comparing those ears that retained ABRs according to experimental grouping.
Morphologic analysis was performed on 29 cochleae. Spiral ganglion “packing densities” were not found to be significantly different among the groups (ANOVA). The status of the organ of Corti was significantly better in groups II and V in comparison to the other groups (Kruskal-Wallis test with pairwise comparisons, p < 0.05); there was no discernible dose-response relationship. Morphologic and electrophysiologic changes correlated with insertion trauma and infection rather than with electrical stimulation at the levels tested in this study. Future research will attempt to develop a computer algorithm that can quantify cochlear morphologic changes in response to implantation and electrical stimulation to improve the analysis of these effects.
1Georgetown University Medical Center, 3800 Reservoir Road, N.W., Washington, D.C.
2Naval Medical Research Institute, Bethesda, Maryland
3Food and Drug Administration, Center for Devices and Radiological Health, Rockville, Maryland
4Reprint requests: A. Julianna Gulya, M.D., Georgetown University Medical Center, 3800 Reservoir Road, N.W., Washington, DC 20007
Presented in part at the Midwinter Meeting of the Association for Research in Otolaryngology, St. Petersburg, Florida, February, 1990.
Acknowledgments: The authors wish to express their appreciation of Petty Officers J. Velasquez and D. Lehman, U.S. Navy, for technical assistance.