Adverse Effects of Electrical Energy Applied to the Nervous System

Abstract

Neural prostheses activated by radiofrequency transmission are currently being implanted to treat a variety of clinical problems. It is essential that neither the materials used in these prostheses, particularly the electrodes, nor the stimulus parameters that are employed will cause neural damage. The experiences of investigators engaged in both the experimental laboratory and clinical studies of the effects of electrical stimulation are reported herein.

Histological Alterations Induced by Electrode Implantation and Electrical Stimulation in the Human Brain: A Review

“…Another study in animals reported a more than 10‐fold increased risk to induce a lesion during electrical stimulation with SS compared to Pt‐Ir electrodes (44). SS electrodes corrode at a higher rate compared to Pt‐Ir electrodes both in vitro in a saline solution, as well as in vivo (45–48). The corrosion primarily occurs during electrical stimulation but is also evident in implanted electrodes without electrical stimulation (46).…”

Biomedical engineering specifications for epidural spinal cord stimulation to augment motor performance

“…This is well within the allowable limit according to the assumed damage mechanisms discussed by Brummer and Turner (3). However, the resultant 2 microcoulombs per phase is greater than the 0.45 microcoulombs per phase reported to cause damage when directly applied to brain tissue (4). Of course, for epidural SCS the electrodes are not in direct contact with nervous tissue at all, thus greatly lessening the probability of damage.…”

Postsurgical Pathologies Associated with Intradural Electrical Stimulation in the Central Nervous System: Design Implications for a New Clinical Device

“…Charge-balanced pulses are typically employed during in vivo studies in order to maintain net electrical neutrality within the tissues, and the intercontact impedance provides an important window into the electrophysiological response of the tissues to the applied stimuli. Platinum electrodes are used most commonly, as it has been shown that they are biocompatible, do not elicit a foreign body response, and corrode only over decades thus making their surfaces stable in a fluid environment [57]. Shannon's work [56], for example, coupled all of these factors together to yield an expression for the damage threshold current: $\begin{array}{c}I=\left(\frac{d}{\mathrm{normal2}T}\right)·{\left(\pi ·{\mathrm{normal10}}^k\right)}^{\mathrm{normal1}/\mathrm{normal2}},\end{array}$ where I is the current, d is the diameter of the (disc-shaped) electrode, T is the duration of a single phase of the stimulation cycle, and k is the slope of the log-log plot of the charge density versus charge per phase curve for a given stimulation system and type of tissue.…”

“…We note only that the key histopathologic findings secondary to electrical stimulation of the central nervous system include increased permeability of blood vessels [58], vascular congestion and thrombosis [57, 58], neuronal process swelling and necrosis [57–59], localized gliosis [50], and myelin degeneration [49, 52]. Interestingly, there are also reports in which no significant histopathological findings were found following electrical stimulation [60, 61].…”