INDUCED CURRENT CONSTRAINTS AND CAPACITIVE EFFECTS IN INDUCTIVE NERVE-STIMULATION

A number of studies have reported in vivo and in vitro stimulation of nerves by means of induced currents. We have found that purely inductive stimulation of the frog sciatic nerve and gastrocnemius muscle using unshielded or shielded whole toroids could not be achieved with techniques and EMF intensities and durations consistent with those reported by other investigators. In those instances where stimulation was achieved, our findings suggest that it resulted from capacitive coupling between unshielded toroids and a nerve/grounding electrode. Maximum primary voltages ranged up to 80 V. Corresponding secondary EMF's and pulse durations were as much as 5 V and 100 μS, respectively, in different experiments. Stimulating capacitive current densities near the nerve were estimated to be in the range of 100 to 400 mA/cm2, while maximum induced current densities were estimated to be in the range of 10 to 30 mA/cm2 for the same pulse duration. © 1990 IEEE