Endogenous pain inhibition is unrelated to autonomic responses in acute whiplash-associated disorders

Abstract

Abstract-Patients with acute whiplash-associated disorder (WAD) demonstrate an inefficient endogenous pain inhibition and may experience a dysfunction in autonomic nervous system reactivity to pain. This study compared the autonomic response to painful stimuli between patients with acute and chronic WAD and healthy controls. In addition, the role of the autonomic nervous system for explaining inefficient endogenous pain inhibition was examined in acute WAD. Seventeen patients with acute WAD, 30 patients with chronic WAD, and 31 healthy controls participated in an experiment evaluating the autonomic nervous system at rest and during painful stimuli. Skin conductance and heart rate variability (HRV) parameters were monitored continuously during conditioned pain modulation. A significant autonomic response to pain was present for skin conductance and two HRV parameters in all experimental groups. There was an interaction effect in the skin conductance response to pain but not in HRV responses in any of the groups. In patients with acute WAD, no significant correlations were present between pain, pressure pain thresholds, pain inhibition, and any of the autonomic parameters. This study refutes autonomic dysfunction at rest and in response to pain in acute WAD. The dysfunctional conditioned pain modulation appears unrelated to autonomic responses to pain.

Patients with Impaired Descending Nociceptive Inhibitory System Present Altered Cardiac Vagal Control at Rest

“…study that also did not observe differences between the parasympathetic cardiac modulation at rest in patients with acute and chronic pain after a whiplash injury (30). Painful stimuli and many pain conditions are related to enhancing of sympathetic activity (30,(33)(34)(35)(36). Indeed, the use of beta-blockade decreased pain intensity (33) and noradrenaline injection increased it (37).…”

“…The deterioration of the cardiac parasympathetic regulation of the patients with impaired DNIS may be related to the central nervous system function modifica-tions. In patients with a whiplash injury, no association was observed between the parasympathetic branch and the CPM, although it was observed that patients with chronic injury showed correlations between HRV variables and the impairment of the endogenous analgesia (30). Data from neuroimaging studies demonstrate that chronic pain is associated with anatomical and functional modifications in different brain areas (31).…”

Stress and Sensitization in Chronic Pain

“…One normally finds that pain to the test stimulus is less when applied along with another pain stimulus than when presented alone. The reduced efficacy of CPM has been found in several patient populations including fibromyalgia, irritable bowel syndrome (IBS), temporomandibular disorder (TMD), and whiplash-associated disorders (Wijk & Veldhuijzen, 2010;De Kooning et al, 2015;Kennedy et al, 2016).…”

Relationships of abdominal pain, reports to visceral and temperature pain sensitivity, conditioned pain modulation, and heart rate variability in irritable bowel syndrome

“…There is some evidence that ANS balance influences the endogenous inhibitory pain network in individuals with chronic pain conditions . One non‐invasive approach to assessing ANS activity is heart rate variability (HRV).…”

“…There is some evidence that ANS balance influences the endogenous inhibitory pain network in individuals with chronic pain conditions. [15][16][17] One non-invasive approach to assessing ANS activity is heart rate variability (HRV). Heart rate variability is a measure of the heart period variability based on within-subject statistical or time-series summarization of sequences of measured normal RR intervals.…”