Both sympathetic and parasympathetic nervous systems are involved in regulating pain states. The activity of these systems seems to become disturbed in states of chronic pain. This disruption in autonomic balance can be measured through the assessment of heart rate variability (HRV), that is, the variability of the interval between consecutive heart beats. However, there is yet to be a systematic evaluation of the body of literature concerning HRV across several chronic pain conditions. Moreover, modern meta-analytical techniques have never been used to validate and consolidate the extent to which HRV may be decreased in chronic pain. Following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement guidelines, this study systematically evaluated and critically appraised the literature concerning HRV in people living with chronic pain. After screening 17,350 sources, 51 studies evaluating HRV in a chronic pain group met the inclusion criteria. Twenty-six moderate-high quality studies were included in quantitative meta-analyses. On average, the quality of studies was moderate. There were 6 frequency-domain and time-domain measures of HRV across a broad range of chronic pain conditions. High heterogeneity aside, pooled results from the meta-analyses reflected a consistent, moderate-to-large effect of decreased high-frequency HRV in chronic pain, implicating a decrease in parasympathetic activation. These effects were heavily influenced by fibromyalgia studies. Future research would benefit from wider use of standardised definitions of measurement, and also investigating the synergistic changes in pain state and HRV throughout the development and implementation of mechanism-based treatments for chronic pain.

Lower resting vagally mediated heart rate variability (HRV) is thought to reflect poorer function of the neurophysiological pathways underlying emotion regulation (ER) and thus, poorer ER abilities. Sex differences in resting HRV exists such that women typically exhibit higher resting HRV than men. It is proposed that greater HRV in women reflects compensation for greater negative affect such as anxiety and depression. However, research has not yet investigated how the association between resting HRV and every day perceived difficulties in ER may be moderated by sex. The current study sought to test this in a sample of 362 young participants (207 females, mean age of 19). Resting HRV was assessed during a 5-min baseline period using an electrocardiogram. Participants then completed the 36-item Difficulties in Emotion Regulation Scale (DERS) designed to evaluate participant's daily difficulties in ER. Controlling for several covariates, sex significantly moderated the relationship between resting HRV and ER difficulties, such that women showed a much stronger relationship compared with men. Specifically, women with lower HRV reported greater difficulties in ER compared with men with lower HRV, whereas women with higher HRV reported slightly lesser difficulties in ER compared with all men. Overall, this study supports a deeper understanding of how neurophysiological differences in ER between men and women-as indexed by resting HRV-may contribute to how effectively individuals regulate their emotions on a day-to-day basis, with implications for well-being. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Over the past 20 years, our understanding of social factors on pain experience has increased. Edwards et al observed that the presence of a friend resulted in an increased pain threshold and tolerance to experimentally induced pain (cold pressor test and pressure algometry). Having a male friend present had the most prominent effect on male participants' reporting of pain. However, the effects of psychosocial traits known to effect pain experience (eg, catastrophising) were not considered.