Axonal blocking and injuring responses caused by asymmetric high frequency electrical stimulations of frog's sciatic nerve

High frequency (HF) electrical stimulations have proven to be able to block nerve conductions, which would have widespread potential clinical applications. However, some studies demonstrated that the HF blocking stimulus of short duration of 5 s could also cause long lasting injuries to neural conductions. Further revelations of the effects of various kinds of HF stimulus on nerve's conduction would provide more insights into the possible underlying mechanisms and directions towards designing more safe and efficacious HF waveforms. This study investigated the blocking and injuring effects of the asymmetric HF currents on neural conductions on bullfrog's sciatic nerves. The used stimulus included the 5 s low frequency (10 Hz) pulse train to generate control and test compound action potentials (CAPs) and the 5 s HF asymmetric currents to block the CAPs conduction. The asymmetric HF waveforms were characterized by various frequencies (F=1, 2, or 5 kHz) and anode-to-cathode pulse width ratios (r=1, 2, or 3), and the first cathode pulse had a constant width of 0.05 ms. The parameters of blocking rates (BR) and injuring rates (IR) were measured to identify the possible effects. The results demonstrated that the HF currents of relatively high F (5 kHz) and low r (1 and 2) might be useful for achieving nerve conduction blockades of relatively high blocking rates and low injury rates.