TNS-evoked long loop effects.

Local analgesia can be produced by transcutaneous electrical stimulation of peripheral nerves. This is used in the treatment of chronic pain states. Its clinical effectiveness depends on two points; namely (1) the stimulation has to be perceptible, and (2) paresthesias elicited by TNS must be localized in the area of pain. To verify this in healthy subjects we produced an experimental pain by radiant heating of the skin and tested the analgesic effect of TNS. TNS stimuli parameters (duration, amplitude and frequency) were determined so that double blind conditions were given. Stimulation with small rectangular pulses showed the best analgesic effect especially at a stimulation rate of 100 Hz. The stimulation of various nerves showed that most of the analgesic effects depend on spinal level mechanisms but probably long loop effects are involved.