Comparison of frequency and time domain methods of assessment of cerebral autoregulation in traumatic brain injury

Xiuyun Liu*, Marek Czosnyka, Joseph Donnelly, Karol P. Budohoski, Georgios V. Varsos, Nathalie Nasr, Kenneth Martin Brady, Matthias Reinhard, Peter J. Hutchinson, Peter Smielewski

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


The impulse response (IR)-based autoregulation index (ARI) allows for continuous monitoring of cerebral autoregulation using spontaneous fluctuations of arterial blood pressure (ABP) and cerebral flow velocity (FV). We compared three methods of autoregulation assessment in 288 traumatic brain injury (TBI) patients managed in the Neurocritical Care Unit: (1) IR-based ARI; (2) transfer function (TF) phase, gain, and coherence; and (3) mean flow index (Mx). Autoregulation index was calculated using the TF estimation (Welch method) and classified according to the original Tiecks' model. Mx was calculated as a correlation coefficient between 10-second averages of ABP and FV using a moving 300-second data window. Transfer function phase, gain, and coherence were extracted in the very low frequency (VLF, 0 to 0.05 Hz) and low frequency (LF, 0.05 to 0.15 Hz) bandwidths. We studied the relationship between these parameters and also compared them with patients' Glasgow outcome score. The calculations were performed using both cerebral perfusion pressure (CPP; suffix 'c') as input and ABP (suffix 'a'). The result showed a significant relationship between ARI and Mx when using either ABP (r=-0.38, P<0.001) or CPP (r=-0.404, P<0.001) as input. Transfer function phase and coherence-a were significantly correlated with ARI-a and ARI-c (P<0.05). Only ARI-a, ARI-c, Mx-a, Mx-c, and phase-c were significantly correlated with patients' outcome, with Mx-c showing the strongest association.

Original languageEnglish (US)
Pages (from-to)248-256
Number of pages9
JournalJournal of Cerebral Blood Flow and Metabolism
Issue number2
StatePublished - Feb 2 2015


  • cerebral autoregulation index
  • mean flow index
  • transcranial doppler
  • transfer function analysis

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology
  • Cardiology and Cardiovascular Medicine


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