A double-blind investigation of the hypoalgesic effects of transcutaneous electrical nerve stimulation upon experimentally induced ischaemic pain

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Abstract
The hypoalgesic effect of transcutaneous electrical nerve stimulation (TENS) at 2 different frequencies was assessed under double-blind conditions using a standardised form of the submaximum effort tourniquet technique. For the purpose of pain induction, 32 healthy naive female subjects attended on 2 occasions, the first during which baseline data were obtained and the second during which the women were randomly allocated to 1 of 4 groups: Control, Placebo, TENS-1 (110 Hz) or TENS-2 (4 Hz). In the treatment groups, 2 hydrogel electrodes were positioned over Erb's point and lateral to C6 and C7 vertebral spines. A TENS machine was applied for 10 min before the cuff was inflated and remained on for the duration of the pain procedure (12 min). Pain was measured using visual analogue scales (VAS) and the McGill Pain Questionnaire (MPQ) to assess ‘current pain intensity’ and ‘worst pain experienced’, respectively. Analysis of VAS scores showed significant differences between groups (ANOVA, P = 0.02), with the TENS-2 group showing a greater hypoalgesic effect than the other groups. One-factor ANOVA showed no significant differences in MPQ scores between groups. The results of this study have provided evidence of the hypoalgesic effects of TENS upon experimental ischaemic pain which were found to be frequency specific with the lower frequency used here (4 Hz) demonstrating the only significant effect.