Pain
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Clinical Trial Controlled Clinical Trial
The effect of Ketamine on stimulation of primary and secondary hyperalgesic areas induced by capsaicin--a double-blind, placebo-controlled, human experimental study.
The non-competitive NMDA-antagonist, Ketamine, was infused (i.v.) in healthy volunteers to study the effect on central excitability with the presence of cutaneous hyperalgesia. Hyperalgesia was established experimentally on the dorsum of the foot by topical application of capsaicin (1%). Different thermal and mechanical conditioning stimuli were applied to the primary and secondary hyperalgesic areas to modulate the central nociceptive excitability monitored by the nociceptive reflex. ⋯ Ketamine caused an increase in the summation threshold compared to the placebo treatment. In conclusion, these results demonstrate that (1) summation of activity in non-nociceptive and nociceptive afferents occurs under hyperalgesic conditions and, (2) this summation can be inhibited by NMDA-antagonists. Therefore, the study shows an apparent involvement of NMDA-receptors in some of the central mechanisms underlying secondary hyperalgesia.
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Heat pain threshold is commonly considered to be an 'absolute' value, which is not dependent on the area stimulated. In contrast, suprathreshold heat pain sensation has been shown to be highly dependent on the area stimulated, with considerable spatial summation demonstrated both within and between dermatomes. The present study sought to reevaluate two major issues: (a) Whether nociceptive thresholds are, indeed, independent of stimulation area. (b) Whether the spatial summation of suprathreshold heat pain sensation is independent of threshold changes. ⋯ Furthermore, when using a stimulus configuration in which stimulation area was increased without changing nociceptive threshold, no spatial summation of perceived pain intensity was seen. Our results suggest that the spatial summation of perceived heat pain intensity can be attributed to reduced heat pain threshold. Furthermore, our findings stress the importance of determining pain thresholds in studies examining the psychophysics of suprathreshold noxious stimuli.
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Unrelieved cancer pain remains a significant problem worldwide. Patients receive inadequate analgesia for a variety of complex and multifactorial reasons. Limited availability of opioids secondary to concerns about potential diversion of these medications for illicit use and poor compliance with oral regimens are significant factors in many countries. ⋯ Varying the thickness, diameter, and number of implants provides flexibility in the release rate and duration of release. This implantable opioid delivery device could provide a sustained subcutaneous infusion of hydromorphone to patient with cancer pain in developed and developing nations without pumps, catheters, or extensive outpatient support services. In addition, it should improve compliance and reduce concern regarding illicit diversion of opioids.
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The objective of this study was to describe the health care utilization and prospective predictors of high-cost primary-care back pain patients. In the primary-care clinics of a large, staff model health maintenance organization in western Washington State, 1059 subjects were selected from consecutive patients presenting for back pain. The design was a 1-year prospective cohort study. ⋯ A minority of primary-care back pain patients accounted for a majority of health-care costs. Patients with high back pain costs accounted for more back pain-related health-care utilization than did patients with high total costs. Factors predicting subsequent high costs suggest behavioral interventions targeting dysfunction, pain persistence, and depression may reduce health-care utilization and prevent accumulation of high health-care costs among primary-care back pain patients.
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Randomized Controlled Trial Clinical Trial
Topical capsaicin selectively attenuates heat pain and A delta fiber-mediated laser-evoked potentials.
Cutaneous stimulation with CO2 laser pulses activates A delta of nociceptive afferents and evokes late cerebral potentials (LEPs), the amplitude of which correlates parametrically with the perceived magnitude estimation of laser pulses. Capsaicin is known to desensitize the nociceptive terminals of C fibers. In this double-blind, vehicle-controlled experiment, we tested the hypothesis that topical capsaicin would inactivate A delta afferents and lead to an attenuation of the LEPs. ⋯ It indicated that topical capsaicin caused a definite functional and reversible inactivation of A delta nociceptive afferent transmission. The decline in the magnitude estimation of laser pulses concomitantly with the attenuation of LEP amplitudes supports the hypothesis that some A delta afferents mediate noxious heat in humans. These findings demonstrate the usefulness of LEP in the physiological evaluation of nociceptive pathways and its potential usefulness in objectively documenting the effect of pharmacological treatment on pain perception.