Pain
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Chronic musculoskeletal conditions are increasingly conceived as involving altered central nervous system processing, and impaired nociceptive flexor reflex (NFR) appears to reflect altered central nervous system processing. The primary objective was to synthesize the evidence for impaired NFR in these conditions. The secondary objective was to evaluate the NFR stimuli parameters employed by reviewed studies. ⋯ The results indicate that there is evidence of central hyperexcitability in people with chronic musculoskeletal pain. Our review also suggests that shorter inter-pulse duration tends to yield smaller variability in NFR threshold. However, further research investigating optimal stimulation parameters is still warranted.
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Comparative Study
A comparison of pain measures in newborn infants after cardiac surgery.
Accurate pain assessment tools to evaluate pain in critically ill neonates in the postoperative period are lacking. Therefore, we compared a number of potentially useful indices of pain in critically ill neonates following cardiac surgery. Eighty-one full-term infants were studied during the first 48 postoperative hours and the following indices were measured: heart rate, mean arterial blood pressure, heart-rate variability, urinary and plasma cortisol, and 4 composite pain measurement scales: Children's and Infants' Postoperative Pain Scale (CHIPPS), CRIES, COMFORT, and Premature Infant Pain Profile (PIPP). ⋯ The factor structure of the COMFORT score revealed that both behavioural and physiological variables account for a significant proportion of the variance (45% and 15%, respectively; P<0.001). Plasma concentrations of cortisol increased postoperatively but urinary cortisol excretion did not change significantly. Of the pain indices studied, the COMFORT score performed best, with both behavioural and physiological components providing significant contributions.
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High-affinity receptors for nerve growth factor (NGF) are found on nociceptors and sympathetic efferents. NGF is known to sensitize nociceptors, increase innervation density, and fire frequency of sympathetic fibers. We explored axonal sensitization of afferent and efferent fibers following intracutaneous injection of NGF in human and pig skin. ⋯ In parallel to the increased pain ratings recorded in humans, activity-dependent slowing of mechano-insensitive nociceptors was reduced by NGF (18.1±2% vs 29±1.4%). In summary, axonal sensitization of nociceptors by NGF could underlie the hyperalgesia to electrical stimulation. Enhanced responses were limited to nociceptors, as no sensitization was found in sympathetic efferent neurons.