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-pressor pain. For the first study, 32 healthy subjects (16 male and 16 female) attended once for the purpose of cold-pressor pain induction that involved immersion of the nondominant hand in a water bath at 0°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 μs). 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.
Rehabilitation Sciences Research Group, Schools of Biomedical Sciences and *Health Sciences, University of Ulster at Jordanstown, County Antrim, Northern Ireland
Manuscript submitted December 8, 1995; 1st revision received March 27, 1996; 2nd revision received June 18, 1996; accepted for publication August 6, 1996.
Address correspondence and reprint requests to Dr. D. M. Walsh at Rehabilitation Sciences Research Group, School of Health Sciences, University of Ulster at Jordanstown, County Antrim BT37 0QB, Northern Ireland.