TITLE: AUTONOMIC NERVOUS SYSTEM CHANGES IN INDIVIDUALS WITH CHRONIC PAIN: A SYSTEMATIC REVIEW OF THE LITERATURE

BACKGROUND AND AIMS: Treatment of chronic pain has placed enormous economic burden on the global healthcare system. Autonomic nervous system (ANS) dysregulation is suggested to be a biomarker of stress and overall health, and is correlated to chronic pain. One measure of ANS dysregulation is heart rate variability (HRV), and diminished HRV can strongly and independently predict adverse future prognosis. While an association between HRV and all-cause mortality has been demonstrated, cheaper and quicker measurements of heart rate (HR) and blood pressure (BP) have been less investigated. The aim of this review was to investigate the relationship between HR or BP and chronic pain conditions.

METHODS: Searches in multiple databases were performed including PubMed, Ovid, Google Scholar, and CINAHL from September 2003 through February 2019 and included clinical trials (with or without randomization), systematic reviews, and meta-analyses. Inclusion criteria was preregistered though PROSPERO.

RESULTS: Abnormalities in HR and BP were present in a wide variety of chronic pain conditions, although at varying degrees and inconsistently. The changes were sometimes present at rest and sometimes in response to physical or cognitive effort or stress. 

CONCLUSIONS: These findings suggest that chronic pain conditions may result in dysregulation of the ANS. Valid measurement of HRV is typically confined to cumbersome ECG equipment or expensive wearable devices. HR and BP may provide quicker and less expensive ways of measuring this dysregulation, but further research is needed to determine HR and BP are valid measures in those with chronic pain conditions.