The Qualitative Hyperalgesia Profile: A New Metric to Assess ChronicPost-Thoracotomy Pain

摘要

Thoracotomy often results in chronic pain, characterized by resting pain and elevated mechano-sensitivity. Thispaper defines complex behavioral responses to tactile stimulation in rats after thoracotomy, shown to be reversiblyrelieved by systemic morphine, in order to develop a novel qualitative “pain” score. A deep incision and 1 hour of ribretraction in male Sprague-Dawley rats resulted in reduced threshold and a change in the locus of greatest tactile (vonFrey filament) sensitivity, from the lower back to a more rostral location around the wound site, and extending bilaterally.The fraction of rats showing nocifensive responses to mild stimulation (10 gm) increased after thoracotomy (from a preoperativevalue of 0/10 to 8/10 at 10 days post-op), and the average threshold decreased correspondingly, from 15 gm to~4 gm. The nature of the nocifensive responses to tactile stimulation, composed pre-operatively only of no response(Grade 0) or brief contractions of the local subcutaneous muscles (Grade I), changed markedly after thoracotomy, with theappearance of new behaviors including a brisk lateral “escape” movement and/or a 180o rotation of the trunk (bothincluded as Grade II), and whole body shuddering, and scratching and squealing (Grade III). Systemic morphine (2.5mg/kg, i.p.) transiently raised the threshold for response and reduced the frequency of Grade II and III responses,supporting the interpretation that these represent pain. The findings support the development of a Qualitative HyperalgesicProfile to assess the complex behavior that indicates a central integration of hyperalgesia.