Intracellular sodium concentration and membrane potential oscillation in axonal conduction block induced by high-frequency biphasic stimulation.

Objective. A new axonal conduction model was used to analyze the interaction between intracellular sodium concentration and membrane potential oscillation in axonal conduction block induced by high-frequency (kHz) biphasic stimulation (HFBS). Approach. The model includes intracellular and extracellular sodium and potassium concentrations and ion pumps. First, the HFBS (1 kHz, 5.4 mA) was applied for a duration (59.4 s) long enough to produce an axonal conduction block after terminating the stimulation, i.e. a post-stimulation block. Then, the intensity of HFBS was reduced to a lower level for 4 s to determine if the axonal conduction block could be maintained. Main results. The block duration was shortened from 1363 ms to 5 ms as the reduced HFBS intensity was increased from 0 mA to 4.1 mA. The block was maintained for the entire tested period (4000 ms) if the reduced intensity was above 4.2 mA. At the low intensity (<4.2 mA) the membrane potential oscillation disrupted the post-stimulation block caused by the increased intracellular sodium concentration, while at the high intensity (>4.2 mA) the membrane potential oscillation was strong enough to maintain the block and further increased the intracellular sodium concentration. Significance. This study indicates a possibility to develop a new nerve block method to reduce the HFBS intensity, which can extend the battery life for an implantable nerve stimulator in clinical applications to block pain of peripheral origin.