The journal of pain : official journal of the American Pain Society
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Randomized Controlled Trial
An investigation into the hypoalgesic effects of high- and low-frequency transcutaneous electrical nerve stimulation (TENS) on experimentally-induced blunt pressure pain in healthy human participants.
Transcutaneous electrical nerve stimulation (TENS) is a noninvasive technique used to reduce pain. It is claimed that TENS frequency is a key determinant of outcome. This study compared TENS delivered at 3 pulses per second (pps) and 80 pps on blunt pressure pain in human participants when TENS intensity was standardized at a strong nonpainful level. Thirty-two pain-free participants completed an experiment in which they received TENS at 3 pps and 80 pps in a crossover fashion. An algometer was used to measure pain threshold for each frequency before and during 20 minutes of TENS. A statistically significant elevation in pain threshold relative to baseline was found for 80 pps when compared to 3 pps after 10 and 20 minutes of TENS (P = .001 and P < .001, respectively). After 20 minutes of TENS, 30 of 32 participants had exceeded a 10N elevation in threshold relative to baseline during 80 pps compared to 19 participants during 3 pps (odds ratio 10.3 (CI, 2.28, 44.78), P = .002). We suggest that the higher rates of impulse generation by TENS at 80 pps resulted in a stronger afferent input to the central nervous system, resulting in stronger segmental inhibition of nociceptive transmission of second-order neurones, in line with the gate control theory of pain. In conclusion, strong nonpainful TENS at 80 pps was superior to 3 pps at increasing pressure-pain threshold in healthy volunteers. We recommend a follow-up study using pain patients. ⋯ This study provides evidence that high frequency TENS at 80 pulses per second increases pain threshold to pressure algometry in healthy participants over and above that seen with low frequency TENS at 3 pulses per second when a strong nonpainful TENS sensation is experienced within the site of experimental pain.
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Sex differences in pain are frequently reported in the literature. However, less is known about possible sex differences in the experience of pain secondary to a disability. The current study explored these issues in persons with limb loss (n = 335, 72% men) who were recruited as part of a postal survey. Participants provided ratings of phantom limb pain (PLP), residual limb pain (RLP), and general pain intensity. Participants also completed measures of pain-related interference, catastrophizing, coping, and beliefs. Results indicated that a greater proportion of males than females (86% vs 77%, respectively) reported the presence of PLP; however, this difference was no longer prominent when cause of limb loss was controlled. No sex differences were found in the presence of RLP, or in average intensity ratings of PLP or RLP. In contrast, females reported greater overall average pain intensity and interference than males. Females also endorsed significantly greater catastrophizing, use of certain pain-coping strategies, and beliefs related to several aspects of pain. This study did not find prominent sex differences in pain specific to limb loss. However, several sex differences in the overall biopsychosocial experience of pain did emerge that are consistent with the broader literature. ⋯ The current study contributes to the literature on sex differences in the experience of pain. Although males and females with limb loss did not significantly differ in their disability-specific pain, sex differences in their broader experience of pain were significant and are worthy of future clinical and empirical attention.
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Using the rat chronic constriction injury (CCI) pain model, we evaluated whether nitrous oxide (N2O), a gas shown to have potent anti-hyperalgesic properties, may alleviate neuropathic pain. Mechanical nociceptive threshold was estimated using the paw pressure vocalization test. Thermal allodynia was challenged by measuring the struggle latency by immersion of the hind paw in a 10 degrees C water bath. A single 50% N2O exposure for 1 hour, 15 minutes not only induced potent anti-nociception during N2O exposure but also provoked a delayed and sustained reduction (37% to 46%) of pain hypersensitivity of the injured hind paw and abolished pain hypersensitivity of the contralateral uninjured hind paw for at least 1 month. Thermal allodynia was completely prevented by a single N2O exposure. A preadministration of naltrexone, which markedly reduced acute N2O-induced anti-nociception, did not affect the persistent reduction of hyperalgesia. The administration of naltrexone in N2O-treated rats, 1 week after the gas exposure, did not induce any effect. This suggests that the long-lasting effect of N2O was not due to its prior acute analgesic effect and was independent of endogenous opioid systems. These data suggest that 50% N2O exposure could be an efficient and safe strategy for alleviating neuropathic pain in a persistent manner. ⋯ Because a single 50% N2O exposure induced a persistent reduction of hyperalgesia-allodynia in a rat neuropathic pain model, clinical trials must be developed for evaluating the N2O effects in patients with neuropathic pain. The ability of N2O to potentiate analgesic effects of other drugs also must be evaluated.