Transcutaneous electrical nerve stimulation: A microneurographic and perceptual study

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Abstract
The peripheral physiological mechanisms involved in transcutaneous electrical nerve stimulation (TENS) for the suppression of pain were examined by assessing pain perception in 14 healthy volunteers and microneurography in 8 humans. For pain suppressing stimulation, ring electrodes and stimulators capable of producing rectangular, sine wave, triangular and hybrid wave forms were used. Pain was induced with electrical stimuli on the distal phalanx of the middle finger. TENS with rectangular, sine wave and triangular pulses activated mainly A.beta. and some A.delta. fibers. Pain suppressing capacity of different wave forms used was the same and achieved with stimuli close to the threshold for pain. Pain was most effectively diminished when noxious and pain suppressing stimuli were applied to the same finger: this effect was smaller with the 2 stimuli on neighboring fingers, and very weak when pain suppressing stimulus was applied to the contralateral hand. Increases in stimulus frequency resulted in an increased and variable latency and intermittent blocking of those spike components which were near theshold at low frequency stimulation. This was apparently due to local changes in excitation threshold. In surface-recorded averaged electroneurograms this effect was seen as amplitude decrement and increased response duration, but was not due to impulse transmission failure in A.delta. fibers as seen microneurographically. On continuous high frequency stimulation the intensity of sensation elicited diminished, although there was no change in the microneurogram. The peripheral contribution to the analgesic effects of TENS seems unimportant.

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