Correlation of Electrical Impedance and Evoked Potentials With Properties of the Electrode Interface Using in Situ Block-Face Imaging of the Rat Pelvic Nerve.

Abstract

Electrical stimulation is an emerging therapy for urologic disorders. The interface between electrode and neural tissue is a critical region of interest given it affects thresholds of neural activation. Measures of electrode impedance are used clinically to estimate tissue fibrosis at the interface; however, the relationship between impedance and fibrosis is not well defined.This study aimed to assess the relationship between interface tissue fibrosis and nerve distance from electrode surface with measurements of impedance and evoked thresholds using a chronic model of visceral nerve implantation.An extraneural four-platinum electrode array was implanted on the rat (N = 14) pelvic nerve and measured common ground impedance, transimpedance, and electrically evoked neural thresholds during two weeks of implantation. A novel serial block-face staining and imaging technique was used to assess the electrode-nerve interface in situ.Analysis revealed no significant correlations between impedance or neural threshold and fibrotic tissue area (p > 0.05). Proximal electrodes 1 and 2 were significantly further away from neural tissue than were distal electrodes 3 and 4 (p < 0.011). Despite this, there were no differences in neural thresholds among electrode configurations (p > 0.05).Measurements of electrode impedance and neural thresholds indicate the presence but not the absolute amount of interface tissue fibrosis. Understanding the dynamics of the nerve-electrode interface is essential for designing suitable peripheral nerve electrode arrays and informing on stimulation parameters to advance the future clinical use of pelvic nerve stimulation as a neuromodulation therapy in urologic disorders.