title: The ontogeny of cerebrovascular pressure autoregulation in premature infants.
abstract: OBJECTIVE
  To quantify cerebrovascular autoregulation as a function of gestational age (GA) and across the phases of the cardiac cycle.
  
  
  METHODS
  The present study is a hypothesis-generating re-analysis of previously published data. Premature infants (n=179) with a GA range of 23 to 33 weeks were monitored with umbilical artery catheters and transcranial Doppler insonation of the middle cerebral artery for 1-h sessions over the first week of life. Autoregulation was quantified by three methods, as a moving correlation coefficient between: (1) systolic arterial blood pressure (ABP) and systolic cerebral blood flow (CBF) velocity (Sx); (2) mean ABP and mean CBF velocity (Mx); and (3) diastolic ABP and diastolic CBF velocity (Dx). Comparisons of individual and cohort cerebrovascular pressure autoregulation were made across GA for each aspect of the cardiac cycle.
  
  
  RESULTS
  Systolic, mean and diastolic ABP increased with GA (r=0.3, 0.4 and 0.4; P<0.0001). Systolic CBF velocity was pressure-passive in infants with the lowest GA, and Sx decreased with advancing GA (r=-0.3; P<0.001), indicating increased capacity for cerebral autoregulation during systole during development. By contrast, Dx was elevated, indicating dysautoregulation, in all subjects and showed minimal change with advancing GA (r=-0.06; P=0.05). Multivariate analysis confirmed that both GA (P<0.001) and 'effective cerebral perfusion pressure' (ABP minus critical closing pressure (CrCP); P<0.01) were associated with Sx.
  
  
  CONCLUSIONS
  Premature infants have low and usually pressure-passive diastolic CBF velocity. By contrast, the regulation of systolic CBF velocity by pressure autoregulation developed in this cohort between 23 and 33 weeks GA. Elevated effective cerebral perfusion pressure derived from the CrCP was associated with dysautoregulation.
authors.affiliation: Department of Pediatrics, Section of Neonatology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Rhee
authors.affiliation: University of Texas at Houston School of Medicine, Houston, TX, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Fraser
authors.affiliation: Departments of Pediatrics and Anesthesiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kibler
authors.affiliation: Departments of Pediatrics and Anesthesiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Easley
authors.affiliation: Departments of Pediatrics and Anesthesiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Andropoulos
authors.affiliation: Division of Neurosurgery, Addenbrooke's Hospital, Cambridge University, Cambridge, England.
authors.forename: M
authors.initials: M
authors.lastname: Czosnyka
authors.affiliation: Division of Neurosurgery, Addenbrooke's Hospital, Cambridge University, Cambridge, England.
authors.forename: G V
authors.initials: GV
authors.lastname: Varsos
authors.affiliation: Division of Neurosurgery, Addenbrooke's Hospital, Cambridge University, Cambridge, England.
authors.forename: P
authors.initials: P
authors.lastname: Smielewski
authors.affiliation: Department of Cardiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: C G
authors.initials: CG
authors.lastname: Rusin
authors.affiliation: Departments of Pediatrics and Anesthesiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Brady
authors.affiliation: Departments of Pediatrics and Obstetrics and Gynecology, Section of Neonatology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Kaiser
mesh_terms: D001783:Blood Flow Velocity / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005865:Gestational Age; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007234:Infant, Premature / Q000502:physiology*; D020768:Middle Cerebral Artery / Q000502:physiology