Pain
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Randomized Controlled Trial Clinical Trial
Effect of adrenergic receptor activation on post-herpetic neuralgia pain and sensory disturbances.
Patients with acute herpes zoster, and to a lesser extent post-herpetic neuralgia (PHN), have been reported to respond to local anesthetic blockade of the sympathetic nervous system. In animal models of nerve injury, local injection of adrenergic agonists after nerve injury, but not before, excites nociceptors. In some patients with chronic neuropathic pain, local application of norepinephrine evokes pain. ⋯ After injection of the adrenergic agonist into PHN skin, both overall PHN pain and allodynia severity were significantly greater than after saline injection, peaking at 10-15 min post-injection. Even when PHN has been present for years, adrenergic receptor stimulation in PHN skin increases pain, most likely through direct activation of C-nociceptors in the painful skin. Increased allodynia is most likely mediated centrally and driven by the increase in C-nociceptor input.
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Injection of formalin in the rat hindpaw produces two phases of nociceptive behavior. Although it is generally agreed that the first phase results from direct chemical activation of nociceptive primary afferent fibers, the factors that contribute to the second phase are not established. In the present study, we monitored the expression of the c-fos protein to evaluate whether the pattern of activity of dorsal horn neurons differs as a result of ongoing afferent activity during the two phases. ⋯ We did not observe further significant decreases when both remifentanil and lidocaine, or bupivacaine and lidocaine were injected (69.7% and 74.6%, respectively). Our results not only provide strong evidence that activity during the second phase is necessary for maintaining the maximal expression of c-fos in the spinal cord, but also reveal significant regional differences in the central patterns of activity generated during the two phases. These results also confirm our previous reports that c-fos expression is not eliminated when the behavioral manifestation of the noxious stimulus is completely blocked.
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Clinical Trial
Quantification of local and referred muscle pain in humans after sequential i.m. injections of hypertonic saline.
The aim of the present study was to test (1) whether muscle pain is influenced by temporal and spatial summation, and (2) whether sequential noxious muscle stimuli applied at hourly interstimulus-intervals could produce an increased sensation of pain due to central hyperexcitability. In the study eleven healthy men were exposed to computer-controlled intramuscular infusion of saline (5%) given over 20 s in m. tibialis anterior (m. TA). ⋯ The infusion given 4 h after the sequential infusions tended to produce an increase in the referred pain area and in the pain intensity. In all three experiments significant correlations were found between the VAS peak and the size of the local (R = 0.64, P < 0.0001, n = 231) and referred (R = 0.47, P < 0.0001, n = 231) pain areas. Based on the above results it can be concluded that experimental muscle pain is influenced by temporal and spatial summation.
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Intramuscular injection of hypertonic saline is a good model to study human muscle pain (Kellgren 1938). The present study concerns the intramuscular (i.m.) pain mediators in saline-induced muscle pain. In experiment 1, the diffusion of infused hypertonic and isotonic saline (0.5 ml) in m. tibialis anterior was illustrated by magnetic resonance imaging (MRI) in one subject. ⋯ The i.m. pressure was not different during the infusions of hypertonic and isotonic saline but was increased between the infusions of hypertonic saline. This study has shown that i.m. infusion of hypertonic saline produced a saline-pool, causing the i.m. pressure to increase. Possibly, pain activation and cessation are related to increased intramuscular sodium and potassium content respectively.
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Clinical Trial
The effects of distraction on exercise and cold pressor tolerance for chronic low back pain sufferers.
Distraction has been found to be effective for the attenuation of experimental and acute clinical pain but its efficacy for chronic pain management remains unclear. There are even some suggestions that distraction may be a counterproductive strategy for chronic pain sufferers. In this study we found that a word shadowing distraction task increased the ability of a group of 12 female and eight male chronic low back pain (CLBP) sufferers to carry out a brief (maximum 300 s) step-up exercise that temporarily increased their pain (P < 0.05). ⋯ Interestingly, the same distraction task did not increase the cold pressor (CP) tolerance time for the CLBP group but produced a 26% increase in tolerance time for a pain-free control group consisting of nine females and nine males (P < 0.05). Also, performance on the distraction task during the CP was worse for the CLBP group than the controls (P < 0.05). Although these findings should be interpreted cautiously because of the parameters of the experiment, they do suggest that distraction is a potentially useful technique to assist chronic pain sufferers.