Pain
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Clinical Trial
Electrical stimulation of motor cortex for pain control: a combined PET-scan and electrophysiological study.
Although electrical stimulation of the precentral gyrus (MCS) is emerging as a promising technique for pain control, its mechanisms of action remain obscure, and its application largely empirical. Using positron emission tomography (PET) we studied regional changes in cerebral flood flow (rCBF) in 10 patients undergoing motor cortex stimulation for pain control, seven of whom also underwent somatosensory evoked potentials and nociceptive spinal reflex recordings. The most significant MCS-related increase in rCBF concerned the ventral-lateral thalamus, probably reflecting cortico-thalamic connections from motor areas. ⋯ A model of MCS action is proposed, whereby activation of thalamic nuclei directly connected with motor and premotor cortices would entail a cascade of synaptic events in pain-related structures receiving afferents from these nuclei, including the medial thalamus, anterior cingulate and upper brainstem. MCS could influence the affective-emotional component of chronic pain by way of cingulate/orbitofrontal activation, and lead to descending inhibition of pain impulses by activation of the brainstem, also suggested by attenuation of spinal flexion reflexes. In contrast, the hypothesis of somatosensory cortex activation by MCS could not be confirmed by our results.
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Following pediatric eye surgery, visual scales for assessment of recovery are inadequate due to impairment of vision. A tactile scale (TaS) was therefore developed and tested in a pilot-trial. Fifty children, 23 girls and 27 boys undergoing different types of ophthalmic surgery used TaS to rate postoperative pain and nausea. ⋯ The mean ratings of pain by TaS were significantly (P<0.05, General Linear Model followed by Dunnett's t-test) lower up to 3 h after the administration of analgesics compared to ratings before analgesics were given, indicating that ratings by TaS were related to the children's actual level of pain. Nausea and/or vomiting was common and was reported or recorded in 28 children (56%). After further validation, TaS may be a useful tool for assessment of postoperative pain and efficacy of given treatments in children and adults, not only after eye procedures, but also following other types of surgery.
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The psychophysical responses to noxious cold stimulation of the skin in normal human subjects are not well understood. Continuous pain ratings with the visual analogue scale is an important method to assess these responses. In this study, we addressed several important issues about the parameters with which stimuli are delivered: the type of skin stimulated, the rate with which the stimulus temperature decreases, and the dimension of the pain rated by subjects. ⋯ The McGill Pain Questionnaire (MPQ) was used to assess the quality of cold-evoked pain. Supra-threshold stimuli (34 degrees C base) were delivered at 0.5, 1 or 2 degrees C/s to 2 degrees C, held for 20s and returned to baseline at 9 degrees C/s. These studies revealed: (1) Cold thresholds, measured with MOL, were lower (i.e. occurred at higher absolute temperatures) for the hairy skin of the dorso-lateral hand compared to the glabrous skin of the thenar eminence. (2) A similar pattern was evident for cold induced pain thresholds with MOL at 1.5 degrees C/s and with intensity and affect VAS scales at 0.5 and 1 degrees C/s. (3) Exponents for supra-threshold ratings fit to power functions were larger for the glabrous skin site than the hairy skin site regardless of cooling rate or dimension of pain measured. (4) All pain indices were higher for slower cooling rates. (5) No significant differences were found in the pain indices for pain ratings of intensity and affect. (6) A substantial proportion of subjects chose words representing paradoxical heat with the MPQ. (7) Painful paradoxical heat sensations occurred most often during cooling, while innocuous warm sensations mainly occurred during the rewarming phase.
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Recent studies suggest that peripheral morphine may represent a valuable treatment in inflammatory painful diseases. This study examined effects of intraplantar morphine against noxious pressure and paw edema in rats with repeated acute inflammation induced by two carrageenin injections 7 days apart. This model mimics at least partly some aspects of recurrent inflammatory pain encountered in the clinical situation. ⋯ The intraplantar injection of morphine (100 and 150 microg) produced a transient increase in the volume of inflamed hindpaw, not reversible by intraplantar naloxone methiodide (40 microg). Pretreatment with intraplantar morphine had no effect on reduction of vocalization thresholds to paw pressure and edema related to a second ipsilateral injection of carrageenin 7 days later. These findings suggest that peripheral morphine may be useful for the clinical management of acute inflammatory pain rather than in recurrent inflammatory painful situations.