title: Investigation of heart rate and blood pressure variability, baroreflex sensitivity, and approximate entropy in acute brain injury patients.
abstract: OBJECTIVE
  The purpose of the study was to investigate longitudinally over time heart rate (HR) and blood pressure variability and baroreflex sensitivity in acute brain injury patients and relate them with the severity of neurologic dysfunction and outcome.
  
  
  METHODS
  Data from 20 brain injured patients due to multiple causes and treated in the intensive care unit were used, with HR and blood pressure recorded from monitors and analyzed on a daily basis. We performed power spectral analysis estimating low frequencies (LF: 0.04-0.15 Hz), high frequencies (HF: 0.15-0.4 Hz), and their ratio and calculated the approximate entropy, which assesses periodicity within a signal and transfer function (TF), that estimates baroreflex sensitivity. Heart rate variance was considered as a measure of HR variability.
  
  
  RESULTS
  Nonsurvivors (brain dead) had lower approximate entropy (0.65 +/- 0.24 vs 0.84 +/- 0.26, P < .05) and lower variance mean values (0.48 +/- 0.54 vs 1.29 +/- 0.42 ms(2)/Hz, P < .01), lower LF and HF minimum values (0.31 +/- 0.88 vs 1.11 +/- 0.46, P < .01; and 0.27 +/- 0.42 vs 0.86 +/- 0.30, P < .01, respectively), lower LF/HF (0.22 +/- 0.29 vs 0.62 +/- 0.28, P < .01), and lower TF mean values (0.43 +/- 0.29 vs 1.11 +/- 0.74, P < .05) during their whole stay in the intensive care unit in relation with survivors. The mean variance (P < .05), mean TF (P < .05), and mean LF/HF (P < .05) were significantly successful in separating survivors from nonsurvivors.
  
  
  CONCLUSIONS
  We conclude that in acute brain injury patients, low variability, low baroreflex sensitivity, and sustained decrease in LF/HF of HR signals are linked with a high mortality rate.
authors: Department of Anesthesiology and Intensive Care Medicine, Intensive Care Unit, AHEPA Teaching Hospital, Thessaloniki, Greece.
authors: Vasilios
authors: V
authors: Papaioannou
authors: Maria
authors: M
authors: Giannakou
authors: Nikos
authors: N
authors: Maglaveras
authors: Efthymios
authors: E
authors: Sofianos
authors: Maria
authors: M
authors: Giala
mesh_terms: D000368:Aged; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D001930:Brain Injuries / Q000175:diagnosis* / Q000503:physiopathology*; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D011379:Prognosis; D012720:Severity of Illness Index