Modification of experimental, lower limb ischemic pain with transcutaneous electrical nerve stimulation.

INTRODUCTION

Transcutaneous electrical nerve stimulation (TENS) has been shown to be effective for the reduction of experimentally induced ischemic pain in the upper limb. No studies have been published on the effects of TENS for lower limb ischemic pain.

OBJECTIVES

To investigate the pain-modifying effect of TENS on experimentally induced ischemic pain in the lower limb.

METHODS

A modified Submaximal Effort Tourniquet Test-induced ischemic pain in the nondominant lower limb of 27 healthy volunteers. Each of the participants completed a baseline modified Submaximal Effort Tourniquet Test (No TENS) and 1 of the experimental conditions: either high-frequency TENS (HF-TENS) or placebo TENS (P-TENS). The outcome measures were the time taken (in seconds) for the participants to report pain threshold and pain tolerance. Pain endurance was calculated as the difference between these points. Pain intensity during ischemia was assessed using a numerical rating scale. The McGill Pain Questionnaire recorded participants' retrospective description of 'intolerable' induced pain. The differences in scores between these measures at the baseline and TENS intervention was calculated and used for the analysis.

RESULTS

Paired Student t-tests found significant increases in time to pain tolerance and pain endurance in both the TENS groups (P<0.001 HF-TENS and P<0.05 for P-TENS, respectively). When compared with baseline, time to pain threshold increased significantly only with HF-TENS (P<0.01). The independent Student t-tests detected greater increases in pain threshold, tolerance, and endurance in the HF-TENS group compared with the P-TENS group (P<0.05, 0.002, and 0.003, respectively). Compared with P-TENS, HF-TENS significantly reduced the pain intensity between the fifth and eigth minutes. Both HF-TENS and P-TENS significantly reduced the mean McGill Pain Questionnaire Pain Rating Index scores, but did not show a between-group difference.

CONCLUSIONS

HF-TENS had stronger modifying effects on several aspects of laboratory-induced ischemic pain than did P-TENS. HF-TENS delayed the onset of pain, reduced pain levels, and delayed the onset of extreme pain over a period of several minutes.