Recent studies have established that kilohertz frequency alternating current (KHFAC) nerve conduction block possesses several desirable clinical characteristics. Normally, KHFAC manifests within small time lapses and can rapidly be reversed, where conduction returns to the nerve fibers within a few seconds. KHFAC offers the prospect of arresting undesirable motor, sensory and autonomic nerve activity, with focal and temporal precision, without having generalized side effects. In the existing literature plethora, it has been clearly elucidated that several animal species, possess nerves that can recover conduction within seconds after the cessation of KHFAC, when administered for a duration less than 5-10 minutes. Such studies have outlined three distinct types of nerve recovery: immediate, fast and slow recovery, as characterized by measure of motor nerve conduction block using two simulating electrodes: one placed proximal and the other distal. Unfortunately, the action potentials generated at the distal stimulating electrode do not pass the KHFAC region and only pass through a short region of untreated nerve before reaching the same neuromuscular junction.
Recently, a team of researchers Case Western Reserve University in Cleveland investigated the effect of repeated and prolonged application of KHFAC on rat sciatic nerve with bipolar platinum electrodes. In addition, the researchers hoped to further cross-examine the carry-over block effect systematically. Their work is currently published in the research journal, Journal of Neural Engineering.
It was observed that conduction recovery times were notably affected by the cumulative duration of KHFAC application. Again, they noted that the peak stimulated muscle force returned to pre-block levels instantly after cessation of KHFAC delivery when applied for not longer than 15min. Startlingly, the muscles fell significantly but recovered to near pre-block levels for cumulative stimulus of 50 ± 20min, for the tested On/Off times and frequencies. Conduction was also noted to recover in two phases: an initial fast one, followed by a slower phase. Finally, no permanent conduction block was seen at the end of the observation period during the experiment.
The Kevin Kilgore et al study has presented three categories of nerve response to prolonged KHFAC conduction block depending on the rate at which normal nerve conduction is restored following the cessation of KHFAC delivery. It has been seen that with KHFAC applied repeatedly for durations of 1–30min, with intervals of 1–30min, the carry-over block effect becomes reversible and does not appear to induce permanent change in nerve conduction. Altogether, this carry-over block effect may be exploited to provide continuous conduction block in peripheral nerves without continuous application of KHFAC.
Narendra Bhadra, Emily Foldes, Tina Vrabec, Kevin Kilgore, Niloy Bhadra. Temporary persistence of conduction block after prolonged kilohertz frequency alternating current on rat sciatic nerve. J. Neural Eng. 15 (2018) 016012 (9pp)Go To J. Neural Eng