Pain
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Randomized Controlled Trial Comparative Study Clinical Trial
Fear and anxiety: divergent effects on human pain thresholds.
Animal studies suggest that fear inhibits pain whereas anxiety enhances it; however it is unclear whether these effects generalize to humans. The present study examined the effects of experimentally induced fear and anxiety on radiant heat pain thresholds. Sixty male and female human subjects were randomly assigned to 1 of 3 emotion induction conditions: (1) fear, induced by exposure to three brief shocks; (2) anxiety, elicited by the threat of shock; (3) neutral, with no intervention. ⋯ Pain rating data indicated that participants used consistent subjective criteria to indicate pain thresholds. Both subjective and physiological indicators (skin conductance level, heart rate) confirmed that the treatment conditions produced the targeted emotional states. These results support the view that emotional states modulate human pain reactivity.
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Randomized Controlled Trial Clinical Trial
Relative potency of epidural to intrathecal clonidine differs between acute thermal pain and capsaicin-induced allodynia.
Clonidine is approved in the US for epidural administration in the treatment of intractable neuropathic cancer pain, but is also administered intrathecally for this indication and both epidurally and intrathecally in the treatment of acute, postoperative pain. The purpose of the current study was to estimate the relative potency of clonidine by epidural and intrathecal routes in the treatment of capsaicin-induced hyperalgesia and allodynia as a model of central hypersensitivity and of noxious heat as a model of acute pain. Twenty-four healthy volunteers were randomized to receive either intrathecal clonidine (75, 150, or 300 micrograms) or epidural clonidine (150, 300, or 600 micrograms) and rated pain from a Peltier-controlled thermode at a lumbar, thoracic, and cervical dermatomal site before and after drug administration. ⋯ For acute thermal pain, intrathecal clonidine produced a dose-dependent analgesia with a lumbar>thoracic>cervical gradient, whereas only one dose of epidural clonidine reduced thermal pain and this was at the thoracic testing site. In contrast, the potency of clonidine to reduce capsaicin-induced allodynia was similar between the two routes of injection, and for hyperalgesia, clonidine was only slightly more potent after intrathecal than epidural injection. These data support clinical studies from non-comparative trials and suggest there is a >6-fold potency ratio of intrathecal:epidural administration of clonidine for acute pain, but a <2-fold potency ratio for these routes for mechanical hypersensitivity.