Effectiveness of non-invasive vagus nerve stimulation vs heart rate variability biofeedback interventions for chronic pain conditions: A systematic review

Objectives Autonomic regulation has been identified as a potential regulator of pain via vagal nerve mediation, assessed through heart rate variability (HRV). Non-invasive vagal nerve stimulation (nVNS) and heart rate variability biofeedback (HRVB) have been proposed to modulate pain. A limited number of studies compare nVNS and HRVB in persons with chronic pain conditions. This systematic review compared interventions of nVNS and HRVB in adults with long-standing pain conditions. Methods PubMed, MEDLINE, CINAHL, SPORTDiscus, Google Scholar, and Cochrane library were used to retrieve the randomized controlled trials for this review between the years 2010 and 2023. Search terms included chronic pain, fibromyalgia, headache, migraine, vagus nerve stimulation, biofeedback, HRV, pain assessment, pain, and transcutaneous. Results Ten full-text articles of 1,474 identified were selected for full qualitative synthesis, with a combined population of 813 subjects. There were n = 763 subjects in studies of nVNS and n = 50 subjects for HRVB. Six of the nine nVNS studies looked at headache disorders and migraines ( n = 603), with two investigating effects on fibromyalgia symptoms ( n = 138) and one the effects on chronic low back pain ( n = 22). Of the nVNS studies, three demonstrated significant results in episode frequency, six in pain intensity (PI) reduction, and three in reduced medication use. The HRVB study showed statistically significant findings for reduced PI, depression scores, and increased HRV coherence. Conclusion Moderate to high-quality evidence suggests that nVNS is beneficial in reducing headache frequency and is well-tolerated, indicating it might be an alternative intervention to medication. HRVB interventions are beneficial in reducing pain, depression scores, use of non-steroidal anti-inflammatory medication, and in increasing HRV coherence ratio. HRVB and nVNS appear to show clinical benefits for chronic pain conditions; however, insufficient literature exists to support either approach.