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Does the stress response system reacts different to pain in patients with chronic whiplash?

Ever had a car accident? Did you feel the rush of stress on that moment? A whiplash accident is often the result of a car accident and causes a lot of physical and psychological stress. It might even cause a post-traumatic stress reaction and this stress reaction is related with a poor long-term recovery in whiplash patients. A disturbed stress system is not the only possible consequence after a whiplash accident, also dysfunctions of the pain system are often present. More specifically patients with a chronic whiplash have a hypersensitive nervous system and a dysfunctional internal pain inhibitory mechanism. Are these effects on the stress system and the pain system unrelated or are they components of one integrated system?
To answer this question, we examined the stress response to a physical stressor (i.e. pain). Patients with a chronic whiplash and healthy controls were subjected to an experiment to evaluate pain thresholds and pain inhibition. Meanwhile their autonomic functions (skin conductance, heart rate and heart rate variability parameters) were continuously registered, to measure the autonomic response to acute pain. We found that both patients with a chronic whiplash and healthy controls had an autonomic response to the acute pain. But we did not find any difference in this response in whiplash patients compared to healthy controls. This indicates that chronic WAD patients and healthy controls show similar patterns of autonomic response to a painful stimulus. Furthermore, there was no relation between the pain thresholds, pain inhibition and the autonomic parameters. Yet, whiplash patients who also suffered from post-traumatic stress reaction had a reduced autonomic reactivity to pain. Our most interesting observation is that chronic whiplash patients do not show a distinctive autonomic stress response to acute pain. On the contrary chronic whiplash patients have a similar response as healthy controls. With this, also at rest the autonomic activity was similar. It seems that patients with chronic whiplash have normal autonomic activity and reactivity to acute pain. Except for a subgroup experiencing post-traumatic stress, who showed a blunted stress reaction. This suggests that a disturbance in the autonomic nervous system is not a general feature in chronic whiplash, but instead might be a trait of a subgroup experiencing a prolonged state of stress after the impact event.

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Margot De Kooning is a doctoral researcher at the Vrije Universiteit Brussel (Belgium) and the University of Antwerp (Belgium). She is interested in the role of central mechanism and there interaction in chronic unexplained pain. She focuses on the stress response system, pain-motor interactions and sensorimotor integration and pain processing mechanisms in patients with whiplash associated disorders.