Time Between Implantation and Electrode Array Design Inform Electrode Impedance Dynamics and Cochlear Immunity 2309163

Abstract Introduction Cochlear implantation (CI) outcomes can be limited due to immune-mediated foreign body responses. Previous research outlined the potential role of immunological memory in sequentially-implanted patients. Time between sequential CI and electrode array design may inform these relationships on the basis of possible long-lived memory cell decay and differential insertion trauma (thought to be greater with perimodiolar arrays), respectively. Using electrode impedance as a proxy for fibrosis, we hypothesize that longer time between CI leads to smaller increases and that perimodiolar arrays lead to higher increases in electrode impedance for the second CI. Methods Retrospective data for 79 subjects with sequential bilateral implants were obtained from the University of Iowa cohort. 12-month impedances (averaged across electrodes 5-22) were calculated and analyzed by time elapsed between implantation (six month increments) and electrode array design. Results 12-month average impedances in the first and second implant were positively correlated across all time groupings. Correlations demonstrated a bimodal strength variation across these groupings (0-6m, 0.6211; 6-12m, 0.5556; 12-18m, 0.0233; 18-24m, 0.9220; 24-30m, 0.5379; 30+m, 0.1067). A significant difference in 12 month average impedance in first versus second implant was found in perimodiolar arrays (p = 0.0020, (-936,-220Ω)) but not lateral wall arrays (p = 0.9148, (-808, 894Ω)). Conclusion Significant increases in electrode impedance were seen in perimodiolar, not lateral wall, arrays. This may be a function of differential tissue trauma upon insertion. Bimodal correlation strength variation seen in electrode impedances by implant sequence and time between CI may elucidate dynamics informing initial trauma versus delayed immunologic response with subsequent taper, though sample size is small. Further research is warranted to more fully characterize findings. Funding Source P50DC000242, R01DC018488, T35HL007485, and a Carver College of Medicine Summer Research Fellowship Topic Categories Neuroimmunology (NEUR)