title: Pre-operative baroreflex sensitivity and efferent cardiac parasympathetic activity are correlated with post-operative pain.
abstract: BACKGROUND
  A maladaptation of the autonomic nervous system may been seen in patients with chronic pain that includes persistent changes in the autonomic tone, increased heart rate, and reduced heart rate variability and baroreflex sensitivity. Baroreflex sensitivity and acute pain intensity have been reported to be inversely correlated. However, it is unknown whether the same correlation applies with regard to post-operative pain. In the present study, autonomic function was measured in patients scheduled for minor hand surgery and correlated with early and persistent pain after the procedure. Thus, the cause (autonomic imbalance) was present before the effect (post-operative pain). Our primary hypothesis was that a lower level of pre-operative baroreflex sensitivity is correlated with increased early post-operative pain.
  
  
  METHODS
  There were 30 patients included and scheduled for open carpal tunnel surgery. Baroreflex sensitivity and heart rate variability were measured before surgery. Efferent cardiac parasympathetic activity was estimated by power spectral analysis of heart rate variability. Post-operative pain was recorded daily for 6 weeks (early post-operative pain) and for 1 week 1 year after surgery (persistent post-operative pain).
  
  
  RESULTS
  Pre-operative baroreflex sensitivity correlated negatively with early (P=0.05) and persistent (P=0.04) post-operative pain. Efferent cardiac parasympathetic activity correlated negatively with early (P=0.03) but not persistent post-operative pain (P=0.12).
  
  
  CONCLUSIONS
  The findings suggest that a low pre-operative level of baroreflex sensitivity is associated with higher post-operative pain intensity. To our knowledge, this is the first study to show the correlation between baroreflex sensitivity and post-operative pain.
authors.affiliation: Danish Pain Research Center, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: R
authors.initials: R
authors.lastname: Nielsen
authors.forename: L
authors.initials: L
authors.lastname: Nikolajsen
authors.forename: K
authors.initials: K
authors.lastname: Krøner
authors.forename: H
authors.initials: H
authors.lastname: Mølgaard
authors.forename: L
authors.initials: L
authors.lastname: Vase
authors.forename: T S
authors.initials: TS
authors.lastname: Jensen
authors.forename: A J
authors.initials: AJ
authors.lastname: Terkelsen
mesh_terms: D000328:Adult; D000368:Aged; D001342:Autonomic Nervous System Diseases / Q000503:physiopathology*; D017704:Baroreflex; D001794:Blood Pressure; D002349:Carpal Tunnel Syndrome / Q000601:surgery; D005260:Female; D006321:Heart / Q000294:innervation* / Q000503:physiopathology; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D010149:Postoperative Pain / Q000453:epidemiology* / Q000503:physiopathology; D055815:Young Adult