title: Heart rate variability after acute traumatic brain injury in children.
abstract: OBJECTIVE
  To evaluate heart rate variability (HRV) by power spectral analysis of heart rate and its relationship to intracranial pressure (ICP), cerebral perfusion pressure (CPP), and outcomes in children with acute traumatic head injury.
  
  
  METHODS
  Prospective, case series.
  
  
  METHODS
  Pediatric intensive care unit in a level II trauma center/children's hospital.
  
  
  METHODS
  Fifteen critically ill children with documented acute traumatic brain injury and four control subjects.
  
  
  METHODS
  None.
  
  
  RESULTS
  The normalized total power from 0.04 to 0.15 Hz was used to quantify low-frequency HRV and from 0.15 to 0.40 Hz to quantify high-frequency HRV. The ratio of low- to high-frequency (LF/HF) power was used as a measure of sympathetic modulation of heart rate. The power spectral data from the 5-min samples were averaged over each hour of data collection, and an hourly LF/HF ratio was obtained based on a 60-min electrocardiogram collection (twelve 5-min segments). The daily mean LF/HF ratio was calculated from the hourly LF/HF measurements. We found no linear correlation between the LF/HF ratio and either ICP or CPP (p = NS). There was a significant decrease in the LF/HF ratio when the intracranial pressure was >30 mm Hg (p < .001) or the cerebral perfusion pressure was <40 mm Hg (p < .001). Children with a Glasgow Coma Scale score of 3-4 had a lower LF/HF ratio compared with those who had a Glasgow Coma Scale score of 5-8 (p < .005). Patients who progressed to brain death had a markedly lower LF/HF ratio (p < .001), with a significant decrease after the first 4 hrs of hospitalization. Patients with more favorable outcomes had significantly higher LF/HF ratios.
  
  
  CONCLUSIONS
  Our findings suggest that an ICP of >30 mm Hg or a CPP of <40 mm Hg may be associated with marked autonomic dysfunction and poor outcome. We speculate that HRV power spectral analysis may be a useful adjunct in determining the severity of neurologic insult and the prognosis for recovery in children. The LF/HF ratio may be helpful not only in identifying those patients who will progress to brain death but also in predicting which patients will have favorable outcomes.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Biswas
authors.forename: W A
authors.initials: WA
authors.lastname: Scott
authors.forename: J F
authors.initials: JF
authors.lastname: Sommerauer
authors.forename: P M
authors.initials: PM
authors.lastname: Luckett
mesh_terms: D000208:Acute Disease; D000367:Age Factors; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000209:etiology*; D001341:Autonomic Nervous System / Q000503:physiopathology; D001926:Brain Death; D001930:Brain Injuries / Q000150:complications* / Q000503:physiopathology*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004562:Electrocardiography; D005260:Female; D005583:Fourier Analysis; D015600:Glasgow Coma Scale; D023261:Glasgow Outcome Scale; D006339:Heart Rate; D006801:Humans; D007223:Infant; D007427:Intracranial Pressure; D008297:Male; D008991:Monitoring, Physiologic; D011379:Prognosis; D011446:Prospective Studies; D012815:Signal Processing, Computer-Assisted; D016019:Survival Analysis; D013997:Time Factors; D016896:Treatment Outcome