Negative affect moderates the effect of respiratory gated vagal nerve stimulation on pain severity in patients with chronic low back pain

Chronic low back pain (CLBP) is the leading cause of disability in the United States. There is considerable interest in the development of safe, effective, nonpharmacological approaches to managing CLBP. Respiratory-gated electrical stimulation of the somatosensory vagal afferent receptors in the ear (RAVANS), has been shown to reduce chronic pelvic pain and migraine headache pain. Further, there is evidence to suggest that the benefits of RAVANS are enhanced when paired with mindful meditation. The purpose of the current study was to examine the effects of RAVANS on pain sensitivity and back pain severity among patients with CLBP. Nineteen adults (mean age =54) with CLBP who had previous mindfulness meditation training participated. Participants attended two laboratory sessions. During each session, they completed brief quantitative sensory testing (QST) including punctate pain ratings (PPR) and pressure pain thresholds (PPT) and rated their back pain severity. Participants then completed a 28-minute stimulation session paired with a mindfulness of breath meditation. During one visit, participants received RAVANS stimulation and during the other, they received sham stimulation. Session order was randomized. Following stimulation, participants repeated QST and provided pain ratings. Results of 2 (treatment: RAVANS vs Sham) X 2 (time: pre- vs. post-stimulation) RMANOVAS indicated that, regardless of treatment condition, PPT increased while PPR and back pain severity decreased post-stimulation. Greater negative affect (e.g., depression and anxiety) was associated with greater improvement in backpain in the RAVANS condition and less improvement in the sham condition. Greater mindfulness was associated with greater improvement in back pain in the sham condition, ut not the RAVANS condition. This suggests that the analgesic effects of mindfulness meditation may have overshadowed any effect of RAVANS stimulation, especially given the brief duration and single session design. Moreover, patients with more negative affect may be more likely to benefit from RAVANS.