The influence of stimulus control on the effects of transcutaneous electrical nerve stimulation (TENS) on experimental ischaemic pain

Kirk, Kerry Alicia (1998). The influence of stimulus control on the effects of transcutaneous electrical nerve stimulation (TENS) on experimental ischaemic pain. PhD thesis The Open University.



A review of the relevant literature suggested a number of unresolved issues in the most efficacious use of TENS for pain-relief including the degree of control and the frequency of TENS. The study investigated the influence of giving subjects control of the TENS stimulus on reported pain intensity and unpleasantness during experimental ischaemic pain induction of the arm. The pain induction and assessment procedures were established during an initial series of three experiments. Subjects in these and the subsequent experiments were healthy female student volunteers from Queen Margaret College. A further series of experiments investigated the influence of control of the TENS intensity on VAS scores of pain intensity and unpleasantness. When used, TENS (symmetrical biphasic current; pulse duration 200ýts; intensity `just perceptible') was applied for the 15 minutes prior to cuff inflation and during the 15 minutes of pain induction (electrodes placed over Erb's point and lateral to C6/7). The first TENS experiment investigated the. influence of three different conditions (experimenter controlling TENS intensity; subject controlling TENS intensity; no TENS) using high frequency (100Hz) TENS. All subjects (n=12) were randomly exposed to the three testing conditions using a repeated measures design. A 2-way ANOVA with repeated measures on both factors showed no statistically significant effects (p>_0.05) on either VAS pain intensity or unpleasantness scores. The procedure was repeated with different subjects (n=12) using low frequency (5Hz) TENS. The results showed that mean pain scores were statistically significantly lower (p<_0.05) in the subject control condition than in the other two conditions (experimenter control and no TENS). A final experiment (n=12) compared VAS pain intensity and unpleasantness scores between the three conditions of, subject controlling 100Hz TENS, subject controlling 5Hz TENS and no TENS. The results demonstrated a trend for the 5Hz TENS condition to give lower mean pain scores than the other two conditions with both intensity (p=0.239) and unpleasantness scores (p=0.110). From the results and discussion it was suggested that the pain-relieving benefit of TENS was enhanced when the subjects were given control of the current intensity, especially when using low frequency TENS. The clinical implications of the results are discussed.

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