title: Neurally mediated cardiac syncope: autonomic modulation after normal saline infusion.
abstract: OBJECTIVE
  This study assessed the heart variability response to orthostatic stress during tilt table testing before and after normal saline administration.
  
  
  BACKGROUND
  The efficacy of sodium chloride and mineralocortoid in the treatment of neurally mediated cardiac syncope is attributed to intravascular volume expansion; however, their modulation of autonomic nervous system activity has not been evaluated.
  
  
  METHODS
  Heart rate variability analysis was performed on 12 adolescents with a history of syncope or presyncope (mean age 15.2+/-0.7 years) during tilt table testing. Subjects were upright 80 degrees for 30 min or until syncope. After normal saline administration, the patient was returned upright for 30 min. Heart rate variability analysis data were analyzed by an autoregression model (Burg method).
  
  
  RESULTS
  All subjects reproducibly developed syncope during control tilt table testing; median time to syncope was 9.4+/-2.1 min. After normal saline infusion, none of the subjects developed syncope after 30 min upright. In the control tilt, there was an initial increase followed by a progressive decrease in low frequency power until syncope. Repeat tilt after normal saline administration demonstrates that low frequency power increased but the magnitude of initial change was blunted when compared with control. In addition, low frequency power increased during normal saline tilt sequence compared with the control tilt, during which it decreased.
  
  
  CONCLUSIONS
  Normal saline blunted low frequency power stimulation and prevented paradoxical low frequency power (sympathetic) withdrawal. Increasing intravascular volume with normal saline alters autonomic responses that may trigger neurally mediated syncope reflexes.
authors.affiliation: Department of Cardiology, Children's National Medical Center, Washington, DC 20010, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Burklow
authors.forename: J P
authors.initials: JP
authors.lastname: Moak
authors.forename: J J
authors.initials: JJ
authors.lastname: Bailey
authors.forename: F T
authors.initials: FT
authors.lastname: Makhlouf
mesh_terms: D000293:Adolescent; D001341:Autonomic Nervous System / Q000503:physiopathology*; D001794:Blood Pressure; D001810:Blood Volume / Q000187:drug effects / Q000502:physiology*; D002648:Child; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D015203:Reproducibility of Results; D012965:Sodium Chloride / Q000008:administration & dosage*; D013575:Syncope / Q000503:physiopathology*; D018667:Tilt-Table Test
chemical_list: D012965:Sodium Chloride