Isquemic Pain

Research Report

An Investigation Into the Analgesic Effects of Interferential Currents and Transcutaneous Electrical Nerve Stimulation on Experimentally Induced Ischemic Pain in Otherwise Pain-Free Volunteers
Background and Purpose. Interferential currents (IFC) and transcutaneous electrical nerve stimulation (TENS) are used for pain management. This study compared the analgesic effects ofIFC and TENS on experimentally induced ischemic pain in otherwise pain-free subjects using a modified version of the submaximal-effort tourniquet technique. Subjects. The subjects were 30 volunteers (18 male, 12 female) without known pathology that could cause pain. Their mean age was 33.5 years (SD 9.9, range 21–54). Method. A single-blind, shamcontrolled, parallel-group method was used. Theprimary outcome measure was the change in the self-report of pain intensity during 1 of 3 possible interventions: (1) IFC, (2) TENS, or (3) sham electrotherapy. The IFC and TENS were administered on the forearm, and the sham electrotherapy group received no current output via a dummy stimulator. Results. A 2-way repeated-measures analysis of variance revealed that there was no change in pain intensityduring treatment when all 3 groups were considered together. Further analysis revealed that IFC reduced pain intensity when compared with sham electrotherapy but not when compared only with TENS. Discussion and Conclusion. There were no differences in the magnitude of analgesia between IFC and TENS. Interferential currents reduced pain intensity to a greater extent than sham electrotherapy.[Johnson MI, Tabasam G. An investigation into the analgesic effects of interferential currents and transcutaneous electrical nerve stimulation on experimentally induced ischemic pain in otherwise pain-free volunteers. Phys Ther. 2003;83:208 –223.]

Key Words: Analgesia, Experimentally induced pain, Interferential currents, Submaximal effort tourniquet test, Transcutaneous electrical nerve stimulation.Mark I Johnson, Ghazala Tabasam

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Physical Therapy . Volume 83 . Number 3 . March 2003

ranscutaneous electrical nerve stimulation (TENS) and interferential currents (IFC) are noninvasive, analgesic techniques that are claimed to have an effect.1–5 There is widespread use of TENS throughout health care, and some patients report satisfaction with treatment outcome.1–5 There is anextensive but confusing body of literature on TENS, and systematic reviews have questioned its effectiveness for postoperative pain and labor pain.6 –9 There is some evidence that TENS is beneficial for some forms of chronic pain.9,10 Inadequacies in systematic reviews and in the quality of and appropriateness of randomized controlled trials (RCTs) included in reviews may have contributed, in part, tothe negative findings.11–13 Interferential currents are similar to TENS, although the use of IFC appears to be primarily by physical therapists. Surveys have shown that physical therapists report that they use TENS and IFC regularly.14 –16 The most common use of IFC, we believe, is to relieve pain, although some therapists also report using IFC for the reduction of swelling, the healing of woundsand fractures, and the restoration of function associated with muscle weakness.17,18 These indications mirror information provided in key textbooks on the clinical use of IFC.19 –21 Accep-

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tance of IFC into practice is not based on evidence of effects. Literature on IFC is anecdotal, and some researchers, including ourselves, have questioned the effects of IFC.22–24 Some authors, innonrefereed publications,19 –21 claim that the mechanism of action is different between IFC and TENS. The active element of TENS is biphasic pulsed currents.25–28 In its conventional form, TENS has been shown to selectively activate large-diameter A fibers without concurrently activating small-diameter A and C-fibers or muscle efferents, which leads to inhibition of ongoing activity in second-order...