The journal of pain : official journal of the American Pain Society
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The aim of this study was to investigate the predictive value of exercise-induced hypoalgesia (EIH) profile on pain intensity induced by nerve injury in a rat model. EIH was tested by evaluating the percentage of withdrawal responses to a train of 30 mechanical stimuli on the hind paw before and after 180 seconds of exercise on a rotating rod. The rats were grouped into low, medium, and high EIH based on their reduction in the percentage of withdrawal responses before and after exercise. Rats from each group then underwent left sciatic nerve constriction injury. Mechanical allodynia, mechanical hyperalgesia, and heat allodynia were assessed in the affected and contralateral hind paws prior to and 3 and 7 days following the procedure. The low EIH rats demonstrated increased hypersensitivity at baseline and developed significantly more severe heat allodynia, mechanical allodynia, and hyperalgesia 3 and 7 days following the injury compared to the medium and high EIH rats. Moreover, the low EIH rats developed contralateral heat allodynia following the injury. The EIH of habituated and nonhabituated rats was compared to study the role of stress on the hypoalgesic effect. No significant differences were found between the habituated and nonhabituated rats at baseline and 1 and 5 minutes after the exercise. ⋯ EIH profile was found to be predictive of pain severity following nerve injury. It may suggest that selected patients with faulty pain modulation are at risk for developing chronic pain following injury or surgical procedures. EIH may represent a preoperative means to detect this predisposition and enable proactive management.
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Morphine and fentanyl produce antinociception in part by binding to mu-opioid receptors in the periaqueductal gray (PAG). The present study tested the hypothesis that the PAG also contributes to the antinociceptive effects of other commonly used opioids (oxycodone, methadone, and buprenorphine). Microinjection of high doses of oxycodone (32-188 μg/.4 μL) into the ventrolateral PAG of the rat produced a dose-dependent increase in hot plate latency. This antinociception was evident within 5 minutes and nearly gone by 30 minutes. In contrast, no antinociception was evident following microinjection of methadone or buprenorphine into the ventrolateral PAG despite use of a wide range of doses and test times. Antinociception was evident following subsequent microinjection of morphine into the same injection sites or following systemic administration of buprenorphine, demonstrating that the injections sites and drugs could support antinociception. Antinociception to systemic, but not PAG, administration of buprenorphine occurred in both male and female rats. These and previous data demonstrate that the mu-opioid receptor signaling pathway for antinociception in the PAG is selectively activated by some commonly used opioids (eg, morphine, fentanyl, and oxycodone) but not others (eg, methadone or buprenorphine). The fact that methadone and buprenorphine produce antinociception following systemic administration demonstrates that mu-opioid receptor signaling varies depending on location in the nervous system. ⋯ This study demonstrates that the PAG contributes to the antinociceptive effects of some commonly used opioids (morphine, fentanyl, and oxycodone) but not others (methadone or buprenorphine). Such functional selectivity in PAG-mediated opioid antinociception helps explain why the analgesic profile of opioids is so variable.
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Military personnel returning from conflicts in Iraq and Afghanistan often endorse pain and posttraumatic stress disorder (PTSD) symptoms, either separately or concurrently. Associations between pain and PTSD symptoms may be further complicated by blast exposure from explosive munitions. Although many studies have reported on the prevalence and disability associated with polytraumatic injuries following combat, less is known about symptom maintenance over time. Accordingly, this study examined longitudinal interactive models of co-occurring pain and PTSD symptoms in a sample of 209 military personnel (mean age = 27.4 years, standard deviation = 7.6) who experienced combat-related blast exposure. Autoregressive cross-lagged analysis examined longitudinal associations between self-reported pain and PTSD symptoms over a 1-year period. The best-fitting covariate model indicated that pain and PTSD were significantly associated with one another across all assessment periods, χ² (3) = 3.66, P = .30, Tucker-Lewis index = .98, comparative fit index = 1.00, root mean squared error of approximation = .03. PTSD symptoms had a particularly strong influence on subsequent pain symptoms. The relationship between pain and PTSD symptoms is related to older age, race, and traumatic brain injury characteristics. Results further the understanding of complex injuries among military personnel and highlight the need for comprehensive assessment and rehabilitation efforts addressing the interdependence of pain and co-occurring mental health conditions. ⋯ This longitudinal study demonstrates that pain and PTSD symptoms strongly influence one another and interact across time. These findings have the potential to inform the integrative assessment and treatment of military personnel with polytrauma injuries and who are at risk for persistent deployment-related disorders.
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Electronic and information technologies are increasingly being used to assess pain. This study aims to 1) introduce Painometer, a smartphone app that helps users to assess pain intensity, and 2) report on its usability (ie, user performance and satisfaction) and acceptability (ie, the willingness to use it) when it is made available to health care professionals and nonprofessionals. Painometer includes 4 well-known pain intensity scales: the Faces Pain Scale-Revised, the numerical rating scale-11, the Coloured Analogue Scale, and the visual analog scale. Scores reported with these scales, when used in their traditional format, have shown to be valid and reliable. The app was tested in a sample of 24 health care professionals and 30 nonprofessionals. Two iterative usability cycles were conducted with a qualitative usability testing approach and a semistructured interview. The participants had an average of 10 years' experience in using computers. The domains measured were ease of use, errors in usage, most popular characteristics, suggested changes, and acceptability. Adding instructions and changing format and layout details solved the usability problems reported in cycle 1. No further problems were reported in cycle 2. Painometer has been found to be a useful, user-friendly app that may help to improve the accuracy of pain intensity assessment. ⋯ Painometer, a smartphone app to assess pain intensity, shows good usability and acceptability properties when used by health care professionals and nonprofessionals.