Pain
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'Diffuse noxious inhibitory controls' or DNIC is the inhibition of multireceptive neurons in the dorsal horn of the spinal cord that results when a noxious stimulus is applied to a region of the body remote from the neuron's excitatory receptive field. Although this phenomenon is well-documented, the behavioral consequences of DNIC are not clear. The present study was undertaken to determine how nocifensor withdrawal reflexes evoked by a noxious stimulus are altered by application of a second noxious stimulus to a distant part of the body. ⋯ When the forepaw or hindpaw was placed in water exceeding 49 degrees C the tail flick reflex to acute noxious radiant heat was inhibited. In contrast, noxious conditioning stimuli, regardless of temperature or location, had no effect on the latency for hindpaw withdrawal evoked by an acute noxious stimulus, but did produce a change in reflex topography from flexion to extension. These results, along with previous research on DNIC, suggest that intense noxious stimuli: (1) inhibit the tail flick reflex via inhibition of multireceptive neurons in the dorsal horn; (2) disinhibit hindpaw extensor motoneurons by inhibiting the activity of multireceptive neurons involved in hindlimb flexion; and (3) reduce pain sensation by inhibiting multireceptive neurons projecting to the brain (see Model in Discussion).
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In view of some recent disagreements about the vocabulary of pain as suggested in the McGill Pain Questionnaire (MPQ), the present study re-examined all MPQ pain descriptors with regard to their appropriateness as descriptors of pain sensation. A sample of 70 undergraduate students (whose first language was English) assigned descriptors to individual sensory subcategories and then rated them in terms of implied intensity of pain. Data were evaluated using three criteria related to the absolute frequency, relative frequency, and unimodality of word assignments to each subcategory. ⋯ These words constitute a parsimonious subset of MPQ descriptors of pain sensation. Such words promise more diagnostic specificity in the assessment of pain. Further research could serve to replicate these findings as part of the ongoing refinement of the MPQ.
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We studied if ethnicity influences patient-controlled analgesia (PCA) for the treatment of post-operative pain. Using a retrospective record review, we examined data from all patients treated with PCA for post-operative pain from January to June 1993. We excluded patients who did not have surgery prior to the prescription of PCA or were not prescribed PCA in the immediate post-operative period. ⋯ While there were no differences in the amount of narcotic self-administered, there were significant differences in the amount of narcotic prescribed among Asians, Blacks, Hispanics, and Whites (F--7,352, P < 0.01). The ethnic differences in prescribed analgesic persisted after controlling for age, gender, pre-operative use of narcotics, pain site, and insurance status. Patient's ethnicity has a greater impact on the amount of narcotic prescribed by the physician than on the amount of narcotic self-administered by the patient.
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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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Randomized Controlled Trial Clinical Trial
Successful treatment of shoulder pain syndrome due to supraspinatus tendinitis with transdermal nitroglycerin. A double blind study.
We have conducted a prospective double blind randomized and placebo controlled clinical study in 20 patients with shoulder pain syndrome caused by supraspinatus tendinitis to determine whether transdermal nitroglycerin (NTG) has analgesic action in this condition. In a randomized manner we used a 5-mg NTG (Nitroplast) patch per day over 3 days or similar placebo patches applied in the most painful area. Patients were evaluated before treatment was initiated and after 24 and 48 h. ⋯ Two patients experienced headache as a side effect 24 h after treatment was started. Patients in the NTG group remained free of symptoms when they were assessed 15 days later. We conclude that NTG is useful in the treatment of shoulder pain syndrome caused by supraspinatus tendinitis and that this treatment could be a useful approach to the management of this common disturbance and probably also in other tendon musculoskeletal disorders.