Manipulation of transcutaneous electrical nerve stimulation variables has no effect on two models of experimental pain in humans

Two separate studies investigated the hypoalgesic effect of manipulation of Transcutaneous Electrical Nerve Stimulation (TENS) parameters on two models of experimental pain: the Submaximal Effort Tourniquet Technique and cold-presser pain. For the first study, 32 healthy subjects (16 male and 16 female) attended once for the purpose of cold-presser pain induction that involved immersion of the nondominant hand in a water bath at 0 degrees C. Subjects were allocated to Control, Placebo, or 1 of 2 treatment groups (110 or 4-Hz TENS). Pain threshold measurements (time to withdrawal of hand in seconds) were obtained over six standardised cold pain cycles (i.e., two before stimulation onset, three during stimulation, and one cycle after stimulation). In the second study, 48 healthy volunteers (24 male and 24 female) attended on two occasions, 48 h apart, for the purposes of ischaemic pain induction. On the first attendance, baseline data were obtained and on the second, subjects were randomly allocated to Control, Placebo, or one of four treatment groups with different combinations of stimulation frequencies and pulse durations (4 or 110 Hz and 50 or 200 mu s). Measurements of ''current pain intensity'' and ''worst pain experienced'' were obtained via the Visual Analogue Scale (VAS) and the McGill Pain Questionnaire (MPQ), respectively. Analysis of variance performed on both sets of collected data revealed no significant differences between any of the groups, thus indicating no apparent relevance of manipulation of TENS parameters using these models of pain. Several hypotheses are suggested to explain these findings.