Simulation of fiber conduction block using high frequency alternative current with asymmetric biphasic waveform and its mechanism of action

Abstract

Introduction: High Frequency Alternating Currents is a safe, reversible and selective method for nerve conduction block that has been under study during the last decade as a treatment for the diseases involving abnormal neural impulses. However, reducing the stimulus amplitude, and the undesired onset response, as well as optimizing the stimulus parameters for more effective block is still under study. In this article, simulation of the electrical stimulation of neural fibers is used to study the efficiency of the asymmetric biphasic waveforms in inducing the block condition, and to investigate its mechanism of action. Materials and Methods: Computer simulations were carried out based on a detailed model of mammalian peripheral nerve fibers. Electrical stimulation of a 51-node axon with two point-source electrodes was simulated, one for inducing conduction block, and the other for applying a test stimulus. Asymmetric biphasic waveform was applied and the neural responses including the block phenomena and its mechanism were studied. Results: High frequency stimulation induces three different responses in the fiber, based on its amplitude and position related to the electrode: no excitation, repetitive excitation and block. The proposed waveform provides lower block thresholds and by increasing the asymmetry of the waveform, the net charge required to induce conduction block was significantly reduced in comparison with the sine and symmetric rectangular waveforms. The stimulation increases the average membrane voltage and this is higher when asymmetric waveform is used which can explain the higher efficiency of this waveform for inducing conduction block. Conclusion: Lower thresholds for the proposed waveform is very important in clinical use of the high frequency alternating currents due to higher efficiency of the stimulation, lower power consumption of the stimulator, and lower side effects of the stimulation, and can be considered as a step towards the clinical use of high frequency stimulations. Keywords: High Frequency Alternating Current, Asymmetric Rectangular Waveform, Nerve Conduction Block, Computer Simulation