Medicine (RMH) - Theses
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ItemAn examination of different modes of TENS treatment upon experimental pain perception( 1998)Transcutaneous electrical nerve stimulation or TENS has been the subject of extensive research over the past 30 years, yet relatively little consensus exists with respect to optimal stimulation parameters which consistently produce pain relief or the mechanisms underlying its analgesic actions. A high degree of TENS response variability has led to the institution of different modes of treatment which vary in their featured operating parameters, proposed mechanism( s) of action and efficacy in clinical situations. Much attention has focused on conventional (high frequency flow intensity) forms of stimulation and, to date, little attempt has been made to systematically compare alternative modes of TENS, especially high intensity applications. Moreover, the lack of a well-circumscribed set of effective analgesic parameters coupled with the distinct physical sensation produced by TENS treatment, has made it difficult to devise suitable placebo protocols. The first series of experiments (1-6) examined the importance of TENS frequency and intensity in the modulation of experimental pain perception. In all cases where submaximal intensity TENS was applied to healthy skin, no overall analgesic effect was detected, regardless of the frequency of application. However, submaximal stimulation did successfully modulate hyperalgesia induced by capsaicin treatment, especially within the primary site of pain, although spontaneous pain sensations were not systematically altered. In contrast, maximal intensity TENS was successful in producing significant elevations in laser-evoked pain and reductions in spontaneous pain with application periods as brief as five minutes, at both high and low frequency. This TENS protocol also proved efficacious in transforming so-called TENS "nonresponders" into consistent "'responders". The second series of experiments (7-8) examined the potential for improvement in current "dead-battery" TENS placebo methods and investigated the role of A-β afferents in mediating TENS analgesia. Given that maximal intensity applications provide the most profound changes in experimental pain, clinically-irrelevant parameters of low frequency and low intensity were investigated as a potential placebo alternative. It was found that such parameters produced discernible muscular contractions but wielded little influence on laser pain thresholds which was reinforced when tested against active, high intensity TENS. Furthermore, preferential A-β fibre compression blockade produced the most significant attenuation of maximal TENS response, suggesting that the maximal recruitment and activation of A-β afferent fibres is vital for TENS-induced pain relief. Altogether, these findings indicate that stimulation intensity is the most important parameter consideration for TENS modulation of experimentally-induced pain. Moreover, the peripheral contribution of A-β afferents is essential for TENS analgesia, even at parameters not envisioned by the original Gate Control Theory.