The journal of pain : official journal of the American Pain Society
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Although nonnoxious, high-frequency electrical stimulation applied segmentally (ie, conventional transcutaneous electrical nerve stimulation [TENS]) has been proposed to modulate pain, the mechanisms underlying analgesia remain poorly understood. To further elucidate how TENS modulates pain, we examined evoked responses to noxious thermal stimuli after the induction of sensitization using capsaicin in healthy volunteers. We hypothesized that sensitization caused by capsaicin application would unmask TENS analgesia, which could not be detected in the absence of sensitization. Forty-nine healthy subjects took part in a series of experiments. The experiments comprised the application of topical capsaicin (.075%) on the left hand in the C6 dermatome, varying the location of TENS (segmental, left C6 dermatome, vs extrasegmental, right shoulder), and assessing rating of perception (numeric rating scale: 0-10) and evoked potentials to noxious contact heat stimuli. The extrasegmental site was included as a control condition because previous studies indicate no analgesic effect to remote conventional TENS. Conventional TENS had no significant effect on rating or sensory evoked potentials in subjects untreated with capsaicin. However, segmental TENS applied in conjunction with capsaicin significantly reduced sensation to noxious thermal stimuli following a 60-minute period of sensitization. ⋯ The study indicates that sensitization with capsaicin unmasks the analgesic effect of conventional TENS on perception of noxious contact heat stimuli. Our findings indicate that TENS may be interacting segmentally to modulate distinct aspects of sensitization, which in turn results in analgesia to thermal stimulation.
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The Mediating Role of Acceptance in Multidisciplinary Cognitive-Behavioral Therapy for Chronic Pain.
Cognitive-behavioral therapy (CBT) is the most frequently delivered psychological intervention for adults with chronic pain. The treatment yields modest effect sizes, and the mechanisms of action remain understudied and unclear. Efforts are needed to identify treatment mediators that could be used to refine CBT and improve outcomes. The primary aim of this study was to investigate whether pain-related acceptance, from the psychological flexibility model, mediates changes in outcome over time in a CBT-based treatment program. This includes comparing how this variable relates to 3 other variables posited as potential mediators in standard CBT: life control, affective distress, and social support. Participants attended a 5-week outpatient multidisciplinary program with self-report data collected at assessment, posttreatment, and 12-month follow-up. Multilevel structural equation modeling was used to test for mediation in relation to 3 outcomes: pain interference, pain intensity, and depression. Results indicate that effect sizes for the treatment were within the ranges reported in the CBT for pain literature. Pain-related acceptance was not related to pain intensity, which is in line with past empirical evidence and the treatment objectives in acceptance and commitment therapy. Otherwise, pain-related acceptance was the strongest mediator across the different indices of outcome. Accumulated results like these suggest that acceptance of pain may be a general mechanism by which CBT-based treatments achieve improvements in functioning. More specific targeting of pain-related acceptance in treatment may lead to further improvements in outcome. ⋯ Potential mediators of outcome in a CBT-based treatment for adult chronic pain were investigated using multilevel structural equation modeling. The results highlight the role of pain-related acceptance as an important treatment process even when not explicitly targeted during treatment. These data may help clinicians and researchers better understand processes of change and improve the choice and development of treatment methods.
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This analysis examined the influence of quantifiable parameters of daily sleep continuity, primarily sleep duration and sleep fragmentation, on daily pain in adults with sickle cell disease. Seventy-five adults with sickle cell disease completed baseline psychosocial measures and daily morning (sleep) and evening (pain) diaries over a 3-month period. Mixed-effect modeling was used to examine daily between- and within-subjects effects of sleep continuity parameters on pain, as well as the synergistic effect of sleep fragmentation and sleep duration on pain. Results revealed that nights of shorter sleep duration and time in bed, increased fragmentation, and less efficient sleep (relative to one's own mean) were followed by days of greater pain severity. Further, the analgesic benefit of longer sleep duration was attenuated when sleep fragmentation was elevated. These results suggest that both the separate and combined effects of sleep duration and fragmentation should be considered in evaluating pain in adults with sickle cell disease. ⋯ Subjective parameters of sleep continuity (eg, sleep duration, fragmentation, and efficiency) predict clinical pain in individuals with sickle cell disease. Additionally, sleep duration should not be considered in isolation, and its association with pain may be qualified by sleep fragmentation. Research and practice should include assessments of both when addressing pain severity.
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Parametric statistical methods are common in human pain research. They require normally distributed data, but this assumption is rarely tested. The current study analyzes the appropriateness of parametric testing for outcomes from the cold pressor test (CPT), a common human experimental pain test. We systematically reviewed published CPT studies to quantify how often researchers test for normality and how often they use parametric versus nonparametric tests. We then measured the normality of CPT data from 7 independent small to medium cohorts and 1 study of >10,000 subjects. We then examined the ability of 2 common mathematical transformations to normalize our skewed data sets. Lastly, we performed Monte Carlo simulations on a representative data set to compare the statistical power of the parametric t-test versus the nonparametric Wilcoxon Mann-Whitney test. We found that only 39% of published CPT studies (47/122) mentioned checking data distribution, yet 72% (88/122) used parametric statistics. Furthermore, among our 8 data sets, CPT outcomes were virtually always nonnormally distributed, and mathematical transformations were largely ineffective in normalizing them. The simulations demonstrated that the nonparametric Wilcoxon Mann-Whitney test had greater statistical power than the parametric t-test for all scenarios tested: For small effect sizes, the Wilcoxon Mann-Whitney test had up to 300% more power. ⋯ These results demonstrate that parametric analyses of CPT data are routine but incorrect and that they likely increase the chances of failing to detect significant between-group differences. They suggest that nonparametric analyses become standard for CPT studies and that assumptions of normality be routinely tested for other types of pain outcomes as well.
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Pain among older adults is common and generally associated with high levels of functional disability. Despite its important role in elders' pain experiences, perceived (formal) social support (PSS) has shown inconsistent effects on their functional autonomy. This suggests a moderator role of 2 recently conceptualized functions of PSS: perceived promotion of dependence versus autonomy. The present study aimed at revising and further validating the Formal Social Support for Autonomy and Dependence in Pain Inventory (FSSADI_PAIN), which measures these 2 PSS functions among institutionalized elders in pain. Two hundred fifty older adults (mean age = 81.36 years, 75.2% women) completed the revised FSSADI_PAIN along with measures of physical functioning (ie, Medical Outcome Study Short Form-36) and informal PSS (ie, Social Support Scale of Medical Outcomes Study). Confirmatory factor analyses showed a good fit for a 2-factor structure: 1) perceived promotion of autonomy (n = 4 items; α = .89), and 2) perceived promotion of dependence (n = 4 items; α = .85). The revised FSSADI_PAIN showed good content, discriminant, and criterion-related validity; it discriminated the PSS of male and female older adults and also of elders with different levels of physical functioning. In conclusion, the revised FSSADI_PAIN is an innovative, valid, and reliable tool that allows us to assess 2 important functions of PSS, which may play a relevant role in the prevention and reduction of pain-related physical disability and functional dependence among institutionalized older adults. ⋯ This article presents a revised version of the FSSADI_PAIN that assesses elders' perceived promotion of functional autonomy/dependence as 2 independent functions of perceived social support. This measure may contribute to future research on the role of close interpersonal contexts on the promotion of active aging among elders with chronic pain.