The effect of acute-experimental pain models on offset analgesia

Background: Offset analgesia (OA) is characterized by a disproportionately large decrease in pain perception after a slight decrease in noxious stimulation. In patients with ongoing pain, this response is reduced. The effect is pronounced in painful body areas. The influence of acute pain has not been sufficiently investigated. The aim of this study was to investigate the influence of two experimental acute pain models, measured within the area of acute pain and on the non-affected opposite side, thereby considering the possible somatotopic nature of OA. Methods: Healthy, pain-free volunteers (n = 75) were randomly assigned to one of three groups (cold water, exercise and control group). The ‘cold water group’ immersed one hand into cold water for 3 min (Cold Pressor Task), while the ‘exercise group’ performed an isometric grip exercise for 3 min. There was no manipulation in the control group. Each experimental pain stimulus was performed at both (dominant, non-dominant) forearms. The individualized OA paradigm consisted of offset and constant temperature trials. Offset analgesia was measured immediately before, during and after the experimental pain stimuli. Results: A significant difference in OA was shown during experimental pain when compared to the control condition (exercise vs. control: p < 0.001, cold vs. control: p = 0.001), with no difference between the experimental conditions (p > 0.05). Immediately following the pain stimulation, results were marginally non-significant (p = 0.05). Conclusions: Experimental painful stimulation reduced OA. This result should be interpreted with caution due to potential influences of conditioned pain modulation or exercise-induced hypoalgesia as well as possible floor effects. Significance: Temporal contrast of pain perception is inhibited in acute pain states. This study showed that reduced offset analgesia is observed when pain is experimentally induced using noxious cold and exercise stimuli.