title: Relationship of vascular wall tension and autoregulation following traumatic brain injury.
abstract: BACKGROUND
  The vascular wall tension (WT) of small cerebral vessels can be quantitatively estimated through the concept of critical closing pressure (CrCP), which denotes the lower limit of arterial blood pressure (ABP), below which small cerebral arterial vessels collapse and blood flow ceases. WT can be expressed as the difference between CrCP and intracranial pressure (ICP) and represent active vasomotor tone. In this study, we investigated the association of WT and CrCP with autoregulation and outcome of a large group of patients after traumatic brain injury (TBI).
  
  
  METHODS
  We retrospectively analysed recordings of ABP, ICP and transcranial Doppler (TCD) blood flow velocity from 280 TBI patients (median age: 29 years; interquartile range: 20-43). CrCP and WT were calculated using the cerebrovascular impedance methodology. Autoregulation was assessed based on TCD-based indices, Mx and ARI.
  
  
  RESULTS
  Low values of WT were found to be associated with an impaired autoregulatory capacity, signified by its correlation to FV-based indices Mx (R = -0.138; p = 0.021) and ARI (R = 0.118; p = 0.048). No relationship could be established between CrCP and any of the autoregulatory indices. Neither CrCP nor WT was found to correlate with outcome.
  
  
  CONCLUSIONS
  Impaired autoregulation was found to be associated with a lower WT supporting the role of vasoparalysis in the loss of autoregulatory capacity. In contrast, no links between CrCP and autoregulation could be identified.
authors.affiliation: Division of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Hills Road, Cambridge, CB2 0QQ, UK, gv249@cam.ac.uk.
authors.forename: Georgios V
authors.initials: GV
authors.lastname: Varsos
authors.forename: Karol P
authors.initials: KP
authors.lastname: Budohoski
authors.forename: Angelos G
authors.initials: AG
authors.lastname: Kolias
authors.forename: Xiuyun
authors.initials: X
authors.lastname: Liu
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.forename: Vassilis G
authors.initials: VG
authors.lastname: Varsos
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hutchinson
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001930:Brain Injuries / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002536:Cerebral Arteries / Q000503:physiopathology*; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult