Steady State Membrane Potential and Sodium Current Changes during High Frequency Electrical Nerve Stimulation

Nerve injuries found in previous studies need to be explained with appropriate simulation studies. This study employed an axonal model based on the Frankenhaeuser-Huxley (FH) equations to investigate the changes of membrane potentials and sodium currents during high frequency (HF) electrical stimulation. The HF electrical stimulation induced continuously changing high-amplitude membrane responses different from the normal action potentials (APs). The phenomena of steady state depolarization and hyper polarization were observed at relatively low (1 kHz) and high (10 kHz) frequency HF currents respectively, for which overall inward and outward sodium fluxes occurred. Although only inward sodium flux occurred at low amplitude (1 mA) HF current, both inward and outward sodium fluxes were observed at high amplitude (5 mA) HF current. Higher frequencies (10 kHz) of HF currents caused more inward sodium fluxes and had bigger inward-to-outward ratio values. The results suggested the existence of an optimal HF frequency for HF electrical nerve stimulation. Successful verification of this would promote the design of safe HF electrical nerve stimulation protocols.