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Keywords:

  • Electrical stimulation;
  • pain;
  • sural-gastrocnemius reflex

Objectives

Pain due to peripheral neuropathy is extremely difficult to treat as drugs often become less and less effective over the course of a patient's life. In order to augment such treatments, electrical stimulation has become relatively common, in the form of transcutaneous electrical nerve stimulation, peripheral nerve stimulation, and spinal cord stimulation. Unfortunately, these treatments are only effective in a subset of chronic pain patients.

Materials and Methods

A rabbit sural-gastrocnemius reflex model of pain was used, in which reflex twitches were elicited using 0.3-Hz 100-μs pulses applied to the sural nerve. This stimulation induces a small electromyogram (EMG) twitch recorded from the gastrocnemius with about 1-msec delay. When pain stimuli are applied on the heel of the foot, the amplitude of the reflex-induced EMG response increased by 4.7 ± 2.5-fold (p < 0.005). Sinusoidal stimulation (high-frequency stimulation) was applied (130 Hz) through a tripolar cuff placed distally on the sural nerve to block the C-fiber activity induced by heel pain.

Results

The stimulation paradigm was able to successfully and reversibly block pain signals as measured by the lack of potentiation of the reflex in 100% of the five nerves tested (no significant difference in reflex response, p > 0.5), with thresholds between 500 and 900 μApp.

Conclusions

Complete, reversible block of pain-induced reflex potentiation was obtained in all five nerves tested. This method could be applicable to the control of pain in patients with peripheral neuropathy.