The neural systems involved in autonomic control and perception of pain are closely coupled, and extensive interactions between these sets of neural structures can be observed. The functional interaction of these systems is an important component of the pain regulatory process. Blood pressure and heart rate are both products of autonomic reactivity, and have been studied to specify the relationship between pain stimuli and autonomic reactions. Heart rate variability (HRV), by contrast, attempts to tease out the relative contributions of sympathetic and parasympathetic activity underlying autonomic reactivity, and therefore bears great potential to study autonomic nervous system (re)activity in experimental pain research.
Tracy, L.M., Jarzock, M.N., Ellis, R.J., Bach, C., Hillecke, T.K., Thayer J.F., & Koenig, J. (2018). Heart rate variability and experimentally induced pain: A replication. Pain Practice, 18(5): 687-689.