title: Heart rate non linear dynamics in patients with persistent vegetative state: a preliminary report.
abstract: OBJECTIVE
  This study evaluated the hypothesis that neural networks derangement in patients with a vegetative state (VS) may cause an alteration of heart rate (HR) non-linear pattern.
  
  
  METHODS
  Fifteen consecutive patients with a persistent VS and 15 matched healthy control subjects were included in the study. A 6-hour continuous electrocardiographic recording was used for the time series analysis measuring the occurrence time of the intervals between consecutive normal sinus heart beats (RR' intervals). Parameters evaluating linear and non-linear HR variability were studied. Approximate Entropy (ApEn), a non-linear parameter that quantifies the unpredictability of fluctuations in an instantaneous HR time series, was calculated from the average values of time series with fixed input variables.
  
  
  RESULTS
  All linear parameters, with the only exception being the percentage of RR' intervals that were by at least 50 ms different from the previous interval (0.56, SD = 1.31 vs 10.35, SD = 12.58; p = 0.005) were similar in patients and in healthy control subjects. Mean ApEn values (0.68, SD = 0.24 vs 1.10, SD = 0.16; p = 0.0001) were lower in patients than in healthy control subjects.
  
  
  CONCLUSIONS
  The findings support the hypothesis that derangement of neural networks may cause a reduction of non-linear behaviour in HR such as ApEn.
authors.affiliation: Istituto San Raffaele - Tosinvest Sanità, Post-Coma Intensive and Rehabilitation Care Unit, Cassino, Italy. marco.sara@sanraffaele.it
authors.forename: Marco
authors.initials: M
authors.lastname: Sarà
authors.forename: Fabio
authors.initials: F
authors.lastname: Sebastiano
authors.forename: Simona
authors.initials: S
authors.lastname: Sacco
authors.forename: Francesca
authors.initials: F
authors.lastname: Pistoia
authors.forename: Paolo
authors.initials: P
authors.lastname: Onorati
authors.forename: Giorgio
authors.initials: G
authors.lastname: Albertini
authors.forename: Antonio
authors.initials: A
authors.lastname: Carolei
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000502:physiology*; D017711:Nonlinear Dynamics; D018458:Persistent Vegetative State / Q000503:physiopathology*