The journal of pain : official journal of the American Pain Society
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There is emerging evidence of altered pain signal processing as a likely underlying mechanism in chronic lateral epicondylalgia (LE), yet this remains to be assessed. Furthermore, it has been proposed that neurodynamic tests reflect nociceptive withdrawal responses. Therefore, the objective was to improve our understanding of spinal cord excitability as measured by nociceptive flexion reflex (NFR) threshold in chronic LE with and without a positive neurodynamic test. NFR threshold, pain-free grip, and pressure pain threshold were measured in 30 LE participants and 31 healthy controls. Test of neural tissue involvement (using upper limb neural tension, radial bias) was used to differentiate LE participants with or without a positive neurodynamic test. There were significant differences in NFR threshold between the control and LE with or without a positive neurodynamic test (F[2,54] = 5.68, P = .006), after adjusting for age, sex, pain rating at NFR threshold, and reflex size (NFR interval peak z score). The mean differences (95% confidence interval) in NFR threshold between the control and LE with or without a positive neurodynamic test were 3.74 mA (.637, 6.84) and 3.38 mA (.0245, 6.74) respectively. ⋯ The results suggest evidence of spinal cord hyperexcitability, particularly sensory hypersensitivity, in LE with or without a positive neurodynamic test. Our data appear to support the hypothesis that continued peripheral afferent stimulation results in facilitation of nociceptive pathways in this patient population.
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The impact of pain early in life is a salient issue for sickle cell disease (SCD), a genetic condition characterized by painful vaso-occlusive episodes (VOEs) that can begin in the first year of life and persist into adulthood. This study examined the effects of age and pain history (age of onset and frequency of recent VOEs) on acute procedural pain in children with SCD. Endothelin-1, a vaso-active peptide released during VOEs and acute tissue injury, and its precursor, Big Endothelin, were explored as markers of pain sensitization and vaso-occlusion. Sixty-one children with SCD (ages 2 to 18) underwent venipuncture at routine health visits. Procedural pain was assessed via child and caregiver reports and observational distress. Pain history was assessed using retrospective chart review. Three primary results were found: 1) younger age was associated with greater procedural pain across pain outcomes; 2) higher frequency of VOEs was associated with greater procedural pain based on observational distress (regardless of age); and 3) age was found to moderate the relationship between VOEs and procedural pain for child-reported pain and observational distress for children 5 years of age and older. Associations between the endothelin variables and pain prior to venipuncture were also observed. ⋯ For children with SCD, the child's age and recent pain history should be considered in procedural pain management. The endothelin system may be involved in preprocedure pain, but additional research is needed to understand the role of endothelins in pain sensitization.
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Persistent stressors associated with sociodemographic disadvantage exert a physiologic toll, labeled "allostatic load," that contributes to disparities in some health conditions. We investigated the contribution of allostatic load to pain prevalence in U.S. adults. Interviews with 14,184 adults in the 1999-2004 National Health and Nutrition Examination Survey asked about severe headache, pain that lasted >24 hours, and widespread pain. Ten biomarkers of allostatic load were quantified from blood (glycated hemoglobin), serum (C-reactive protein, homocysteine, cholesterol, triglycerides), urine (creatinine, albumin), and physical measurements (body mass index, systolic and diastolic blood pressure). Log-binomial regression models estimated prevalence ratios (PRs) and 95% confidence intervals (95% CIs). Prevalence ranged from 3.4% for widespread pain to 26.9% for pain >24 hours. After adjustment for demographic characteristics, low income was associated with greater prevalence of pain >24 hours (PR = 1.65, 95% CI = 1.49, 1.83), severe headache (PR = 2.05, 95% CI = 1.68, 2.50), and widespread pain (PR = 3.67, 95% CI = 2.56, 5.27). Racial/ethnic minorities had lower prevalence of all 3 pain conditions than non-Hispanic whites. While greater allostatic load was associated with elevated prevalence of pain, allostatic load did not meaningfully attenuate PRs associated with income or race/ethnicity. We conclude that greater pain prevalence among low-income groups is not explained by greater allostatic load. ⋯ In U.S. adults, pain occurs more frequently in lower-income groups, although the relationship is not attributable to their experience of greater allostatic load. While allostatic load contributes to population variation in pain, other etiologic mechanisms contributing to pain are needed to account for income disparities in pain.
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Evoked potentials (EPs) to radiant or contact heat pain stimuli reflect the synchronization of brain activity to noxious inputs. However, we do not know how they relate to conscious awareness (AW) of a sensation. In healthy volunteers, we determined the time of AW for thermal noxious and non-noxious sensory inputs and examined its correlation to parametric measures of vertex EPs. Subjects had to report the position of the hand of a Libet's clock at the moment they perceived either a laser or a thermode stimulus. AW was determined after subtracting the position of the clock hand at the moment of stimulus delivery from the one reported by the subject, in ms. Subjects estimated AW in all single trials, including those in which no EPs could be identified. Mean AW was estimated earlier than the corresponding EP latency for both types and intensities of stimuli. There was a weak but significant negative correlation of AW to EPs amplitude, which was higher than the correlation of AW to EPs latency. Our results indicate that the timing of AW is influenced by the subjective relevance of sensory inputs. This feature could be used for the analysis of cognitive aspects of pain processing. ⋯ This article presents a way to measure the subjective awareness of the sensation induced by a noxious heat stimulus, either radiant or contact, in healthy human subjects. This method could be used for the analysis of cognitive aspects of pain processing.
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While self-pain motivates protective behaviors and self-oriented feelings, the perception of others' pain often motivates concern and prosocial behaviors toward the person suffering. The conflicting consequences of these 2 states raise the question of how pain is perceived in others when one is actually in pain. Two conflicting hypotheses could predict the interaction between these 2 signals: the threat value of pain hypothesis and the shared-representation model of pain empathy. Here, we asked 33 healthy volunteers exposed to acute experimental pain to judge the intensity of the pain felt by models expressing different levels of pain in video clips. Results showed that compared to a control warm stimulus, a stimulus causing self-pain increased the perception of others' pain for clips depicting male pain expressions but decreased the perceived intensity of female high pain expressions in both male and female participants. These results show that one's own pain state influences the perception of pain in others and that the gender of the person observed influences this interaction. ⋯ By documenting the effects of self-pain on pain perception in others, this study provides a better understanding of the shared mechanisms between self-pain and others' pain processing. It could ultimately provide clues as to how the health status of health care professionals could affect their ability to assess their patients' pain.