Investigating the Effects of Artificial Baroreflex Stimulation on Pain Perception: A Comparative Study in Healthy Participants and Individuals with Chronic Low Back Pain

The autonomic nervous system (ANS) and pain exhibit a reciprocal relationship, whereupon acute pain triggers ANS responses, while resting ANS activity can influence pain perception. Nociceptive signalling can also be altered by "top-down" processes occurring in the brain, brainstem, and spinal cord, known as descending modulation. By employing the Conditioned Pain Modulation (CPM) paradigm, our previous study revealed a connection between reduced low-frequency heart rate variability (HRV) and CPM. Chronic pain patients often experience both ANS dysregulation and impaired CPM. Baroreceptors, which contribute to blood pressure and HRV regulation, may play a significant role in this relationship, but their involvement in pain perception and their functioning in chronic pain have not been sufficiently explored. In this study, we combined artificial baroreceptor stimulation in both pressure pain and CPM paradigms, seeking to explore the role of baroreceptors in pain perception and descending modulation. 22 patients with chronic low back pain (CLBP) and 29 healthy controls (HC) took part in this study. We identified a relationship between baroreflex functioning and perception of pressure pain, finding differential modulation of pressure pain between diagnostic groups. Specifically, HC participants perceived less pain in response to baroreflex activation, whereas CLBP patients exhibited increased pain sensitivity. CPM scores were associated with baseline measures of baroreflex efficiency in both patients and controls. Our data support the importance of the baroreflex in chronic pain and a possible mechanism of dysregulation involving the interaction between the autonomic nervous system and descending pain modulation.