title: Dysautonomia after severe traumatic brain injury: evidence of persisting overresponsiveness to afferent stimuli.
abstract: OBJECTIVE
  To differentiate between dysautonomic and nondysautonomic subjects with acquired brain injury by measuring sympathetic reactivity after a nociceptive clinical procedure and to determine the utility of heart rate variability as an indicator of sympathetic overresponsivity in dysautonomic subjects.
  
  
  METHODS
  This case-controlled study recruited subjects with acquired brain injury (mean, 5 yrs postinjury) attending a hospital-based outpatient clinic, comprising seven dysautonomic subjects with traumatic brain injury, eight nondysautonomic traumatic brain injury subjects, and 11 nondysautonomic subjects with nontraumatic acquired brain injury. Sympathetic reactivity after nociceptive stimuli (limb assessment and botulinum toxin injection for spasticity management) was compared among groups.
  
  
  RESULTS
  Sympathetic overactivity in dysautonomic subjects was evident across all physiologic parameters, whereas nondysautonomic subjects demonstrated limited reactivity. Heart rate variability measures of the balance between sympathetic and parasympathetic cardiac control showed a significant elevation in response to nociceptive stimuli, a response not observed in either nondysautonomic group. This sympathetic overactivity showed a normalizing tendency with increasing time postinjury.
  
  
  CONCLUSIONS
  This study found persistent sympathetic overactivity in response to nociceptive stimuli in dysautonomic subjects (mean, 5 yrs postinjury). This significantly extends the duration over which such sympathetic overactivity has been quantified in this group, contributing to the accumulating empirical evidence that dysautonomic paroxysms result from sympathetic overresponsiveness. Given that sympathetic overactivity has now been observed from day 7 through 5 yrs postinjury, quantitative evaluation of patients for overresponsiveness to stimuli should be added to current diagnostic procedures at all stages of recovery.
authors.affiliation: Brain Injury Rehabilitation Service, Westmead Hospital, New South Wales, Australia.
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Baguley
authors.forename: Roxana E
authors.initials: RE
authors.lastname: Heriseanu
authors.forename: Melissa T
authors.initials: MT
authors.lastname: Nott
authors.forename: Jenny
authors.initials: J
authors.lastname: Chapman
authors.forename: Joseph
authors.initials: J
authors.lastname: Sandanam
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology; D001930:Brain Injuries / Q000150:complications*; D016022:Case-Control Studies; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology; D054969:Primary Dysautonomias / Q000209:etiology / Q000503:physiopathology*; D055815:Young Adult