Autonomic response to pain in patients with chronic whiplash associated disorders

Background: Patients with chronic whiplash associated disorders (WAD) demonstrate altered central pain processing and impaired endogenous analgesia. In addition, previous research reported disturbances in the autonomic nervous system and the presence of post-traumatic stress reaction in patients with chronic WAD. The autonomic nervous system, in particular the autonomic stress response, might modulate central pain processing in this population. Objectives: The goal of this study was to compare the autonomic response to acute painful stimuli in patients with chronic WAD and healthy controls and to look for associations between endogenous analgesia and autonomic parameters. Study design: Case-control study. Methods: Thirty patients with chronic WAD and 31 healthy controls were subjected to an experiment evaluating the autonomic nervous system at rest and during experimental painful stimuli. Skin conductance, heart rate, and heart rate variability parameters were monitored continuously during the evaluation of conditioned pain modulation. The paradigm of heterotopic noxious conditioning stimulation was used to assess this conditioned pain modulation effect. Results: The data revealed no difference in autonomic response to pain between chronic WAD and healthy controls. The autonomic response was unrelated to pressure pain thresholds or the effect of conditioned pain modulation in either group. Limitations: The present study only investigates the autonomic response to a stress caused by pain. Conclusion: Results of this study refute autonomic dysfunction in response to pain in patients with chronic WAD. The autonomic nervous system activity or reactivity to acute pain appears unrelated to either pain thresholds or endogenous analgesia in patients with chronic WAD.