title: Evoked pain analgesia in chronic pelvic pain patients using respiratory-gated auricular vagal afferent nerve stimulation.
abstract: OBJECTIVE
  Previous vagus nerve stimulation (VNS) studies have demonstrated antinociceptive effects, and recent noninvasive approaches, termed transcutaneous-vagus nerve stimulation (t-VNS), have utilized stimulation of the auricular branch of the vagus nerve in the ear. The dorsal medullary vagal system operates in tune with respiration, and we propose that supplying vagal afferent stimulation gated to the exhalation phase of respiration can optimize t-VNS.
  
  
  METHODS
  Counterbalanced, crossover study.
  
  
  METHODS
  Patients with chronic pelvic pain (CPP) due to endometriosis in a specialty pain clinic. INTERVENTIONS/OUTCOMES: We evaluated evoked pain analgesia for respiratory-gated auricular vagal afferent nerve stimulation (RAVANS) compared with nonvagal auricular stimulation (NVAS). RAVANS and NVAS were evaluated in separate sessions spaced at least 1 week apart. Outcome measures included deep-tissue pain intensity, temporal summation of pain, and anxiety ratings, which were assessed at baseline, during active stimulation, immediately following stimulation, and 15 minutes after stimulus cessation.
  
  
  RESULTS
  RAVANS demonstrated a trend for reduced evoked pain intensity and temporal summation of mechanical pain, and significantly reduced anxiety in N = 15 CPP patients, compared with NVAS, with moderate to large effect sizes (η(2) > 0.2).
  
  
  CONCLUSIONS
  Chronic pain disorders such as CPP are in great need of effective, nonpharmacological options for treatment. RAVANS produced promising antinociceptive effects for quantitative sensory testing (QST) outcomes reflective of the noted hyperalgesia and central sensitization in this patient population. Future studies should evaluate longer-term application of RAVANS to examine its effects on both QST outcomes and clinical pain.
authors.affiliation: Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA. vitaly@nmr.mgh.harvard.edu
authors.forename: Vitaly
authors.initials: V
authors.lastname: Napadow
authors.forename: Robert R
authors.initials: RR
authors.lastname: Edwards
authors.forename: Christine M
authors.initials: CM
authors.lastname: Cahalan
authors.forename: George
authors.initials: G
authors.lastname: Mensing
authors.forename: Seth
authors.initials: S
authors.lastname: Greenbaum
authors.forename: Assia
authors.initials: A
authors.lastname: Valovska
authors.forename: Ang
authors.initials: A
authors.lastname: Li
authors.forename: Jieun
authors.initials: J
authors.lastname: Kim
authors.forename: Yumi
authors.initials: Y
authors.lastname: Maeda
authors.forename: Kyungmo
authors.initials: K
authors.lastname: Park
authors.forename: Ajay D
authors.initials: AD
authors.lastname: Wasan
mesh_terms: D000328:Adult; D059350:Chronic Pain / Q000209:etiology / Q000628:therapy*; D018592:Cross-Over Studies; D004715:Endometriosis / Q000150:complications; D045853:Exhalation / Q000502:physiology; D005260:Female; D006801:Humans; D008875:Middle Aged; D017699:Pelvic Pain / Q000209:etiology / Q000628:therapy*; D010865:Pilot Projects; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods*; D055536:Vagus Nerve Stimulation / Q000379:methods*; D055815:Young Adult