Duration of Analgesia Induced by Acupuncture-Like TENS on Experimental Heat Pain

Background. Acupuncture-like TENS (AL-TENS) is a treatment modality that can be used to temporarily reduce pain. However, there is no clear data in the literature regarding the specific duration of analgesia induced by AL-TENS. Objectives. To describe and quantify the duration and magnitude of AL-TENS analgesia on experimental heat pain in healthy subjects and verify if the duration or magnitude of analgesia induced by the AL-TENS was influenced by the duration of the application of the AL-TENS (15 versus 30 minutes). Methods. A repeated-measures, intrasubject randomized experimental design was used, where each participant was his/her own control. 22 healthy volunteers underwent heat pain stimulations with a contact thermode before (pretest) and after (posttest) AL-TENS application (15 and 30 minutes). Outcome measures included subjective pain during AL-TENS, duration, and magnitude of AL-TENS-induced analgesia. Results. Survival analysis showed that the median duration of AL-TENS analgesia was 10 minutes following the application of either 15 or 30 minutes of AL-TENS. The magnitude of analgesia following either application was comparable at all points in time ( values > 0.05) and ranged between ？20% and ？36% pain reduction. Conclusion. Only half of the participants still had heat-pain analgesia induced by the AL-TENS at 15 minutes postapplication. 1. Introduction Pain is one of the principal motives to consult a health care professional [1]. Among the analgesic modalities used by rehabilitation professionals, transcutaneous electrical nerve stimulation (TENS) is commonly used, as it is noninvasive, safe, and affordable; it has no undesirable side effects and can be easily administrated in clinical settings as well as by the patients themselves [2]. During or following TENS application, categorized as either Conventional TENS or Acupuncture-like TENS (AL-TENS), analgesia is induced by different pain control mechanisms depending on the parameters used. Parameters for conventional TENS include high-frequency (50–100？Hz), low-intensity (nonpainful paraesthesias) stimulations, and a small pulse width (50–200？μs). On the other hand, AL-TENS parameters include low-frequency (2–10？Hz), high-intensity (above pain threshold) stimulations, and a longer pulse width (100–400？μs). Conventional TENS analgesia is explained by the gate control theory [3, 4], whereas the AL-TENS pain modulation mechanism is explained by descending endogenous opiate system [5]. The later pain modulation mechanism modulates nociceptive transmission by inhibiting ascending nociceptive