ELECTROCUTANEOUS NERVE-STIMULATION .2. STIMULUS WAVEFORM SELECTION

The large number of investigations involving the use of electrocutaneous nerve stimulation as a surrogate sensory channel, and for relief of acute and chronic pain, have raised questions about the effect of the stimulus parameters on both nerve excitation and passive tissue heating. The short and long term influence of the stimulus parameters upon nerve stimulation has formerly been described on the basis of clinical studies. The approach taken here was to examine the effects of stimulus parameters using models. For myelinated nerve the Franken-haeuser-Huxley model of Xenopus Laevis was used. The influence of the stimulus parameters on tissue heating was evaluated by the use of a passive model described in the literature. Consideration of electrolytic effects led to the selection of a stimulus with zero net charge flow. The desire for a stimulus that was independent of skin resistance resulted in the investigation of biphasic current waveforms. It was found in this investigation that tissue heating is minimized for all pulse widths if the separation between the positive and negative phase is equal to zero. For zero pulse separation a minimum threshold charge can be found, as the pulse width is varied. For multiple biphasic current pulses, it was found that the threshold charge per pulse decreased with the number of pulses in a train. This effect has also been observed experimentally where it has been termed “quantal stimulation.” © 1979 IEEE