Induced current constraints and capacitance effects in inductive nerve stimulation

It is found tha purely inductive stimulation of the frog sciatic nerve and gastrocnemius muscle using unshielded or shielded whole toroids cannot be achieved with techniques and electromotive force (EMF) intensities and durations consistent with previously published reports. In the instances where stimulation is achieved, the findings suggest that it results from capacitive coupling between unshielded toroids and a nerve/grounding electrode. Maximum primary voltages range up to 80 V. Corresponding secondary EMFs and pulse durations are as much as 5 V and 100 mu s, respectively, in different experiments. Stimulating capacitive current densities near the nerve are estimated to be in the range of 100 to 400 mA/cm ², while maximum induced current densities are estimated to be in the range of 10 to 30 mA/cm ² for the same pulse duration.