Comparison of Models Associated with Inhibition of Heat Pain Stimuli

The body is able to modulate the experience of pain through various endogenous inhibitory mechanisms.  Two experimental pain protocols have been developed to evaluate the functional status of an individual’s ability to modulate pain. Conditioned pain modulation (CPM) is frequently demonstrated by reductions in pain intensity by a second painful stimulus. Offset analgesia is demonstrated by a reduction in pain intensity approximately ~10s after a slight decrease in stimulus intensity. Objective: This study evaluated whether the efficacy of endogenous pain inhibition produced by offset analgesia and CPM differs in healthy controls and TMD subjects across several days.  It was hypothesized that TMD subjects will demonstrate less pain inhibition compared to healthy controls, and pain inhibition would be stable across several testing sessions in healthy controls compared to TMD subjects. Method: Participants (n=11) underwent a screening visit, which included an exam (Research Diagnostic Criteria, RDC) for TMD. Then, subjects underwent three identical testing sessions that consisted of CPM and offset analgesia paradigms. Focal thermal stimuli were administered by a thermode at the forearm.  For the CPM procedure, the conditioning stimulus included immersion of the foot into a cold-water bath.  Participants instructed to rate pain intensity continuously with a computerized visual analog scale (CoVAS).Result: : Preliminary results to date show that there is no significant group difference in psychological measures. Initial analysis revealed no group differences in pain modulation.  However, indexes of pain inhibition revealed significant difference between the different time points for the offset analgesia (p=.009) and CPM (p=.014)   Pain inhibition was stable over the three testing days.Conclusion: : Based on the current data, no differences were observed between TMD and control subjects. While individuals were classified with TMD by the RDC exam, it is possible that these subjects were not severe enough to be classified as having chronic pain.