title: Pulsatile intracranial pressure and cerebral autoregulation after traumatic brain injury.
abstract: BACKGROUND
  Strong correlation between mean intracranial pressure (ICP) and its pulse wave amplitude (AMP) has been demonstrated in different clinical scenarios. We investigated the relationship between invasive mean arterial blood pressure (ABP) and AMP to explore its potential role as a descriptor of cerebrovascular pressure reactivity after traumatic brain injury (TBI).
  
  
  METHODS
  We retrospectively analyzed data of patients suffering from TBI with brain monitoring. Transcranial Doppler blood flow velocity, ABP, ICP were recorded digitally. Cerebral perfusion pressure (CPP) and AMP were derived. A new index-pressure-amplitude index (PAx)-was calculated as the Pearson correlation between (averaged over 10 s intervals) ABP and AMP with a 5 min long moving average window. The previously introduced transcranial Doppler-based autoregulation index Mx was evaluated in a similar way, as the moving correlation between blood flow velocity and CPP. The clinical outcome was assessed after 6 months using the Glasgow outcome score.
  
  
  RESULTS
  293 patients were studied. The mean PAx was -0.09 (standard deviation 0.21). This negative value indicates that, on average, an increase in ABP causes a decrease in AMP and vice versa. PAx correlated strong with Mx (R                            (2) = 0.46, P < 0.0002). PAx also correlated with age (R                            (2) = 0.18, P < 0.05). PAx was found to have as good predictive outcome value (area under curve 0.71, P < 0.001) as Mx (area under curve 0.69, P < 0.001).
  
  
  CONCLUSIONS
  We demonstrated significant correlation between the known cerebral autoregulation index Mx and PAx. This new index of cerebrovascular pressure reactivity using ICP pulse wave information showed to have a strong association with outcome in TBI patients.
authors.affiliation: Neurosurgical Unit, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK. iperdany@hotmail.com
authors.forename: D K
authors.initials: DK
authors.lastname: Radolovich
authors.forename: M J H
authors.initials: MJ
authors.lastname: Aries
authors.forename: G
authors.initials: G
authors.lastname: Castellani
authors.forename: A
authors.initials: A
authors.lastname: Corona
authors.forename: A
authors.initials: A
authors.lastname: Lavinio
authors.forename: P
authors.initials: P
authors.lastname: Smielewski
authors.forename: J D
authors.initials: JD
authors.lastname: Pickard
authors.forename: M
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D015924:Blood Pressure Monitors; D001930:Brain Injuries / Q000401:mortality / Q000503:physiopathology* / Q000534:rehabilitation; D015331:Cohort Studies; D004739:England; D005260:Female; D023261:Glasgow Outcome Scale; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007362:Intensive Care Units; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011673:Pulsatile Flow / Q000502:physiology; D012016:Reference Values; D012047:Rehabilitation Centers; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D012984:Software; D015996:Survival Rate; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult