title: Critical cerebral perfusion pressure at high intracranial pressure measured by induced cerebrovascular and intracranial pressure reactivity.
abstract: OBJECTIVE
  The lower limit of cerebral blood flow autoregulation is the critical cerebral perfusion pressure at which cerebral blood flow begins to fall. It is important that cerebral perfusion pressure be maintained above this level to ensure adequate cerebral blood flow, especially in patients with high intracranial pressure. However, the critical cerebral perfusion pressure of 50 mm Hg, obtained by decreasing mean arterial pressure, differs from the value of 30 mm Hg, obtained by increasing intracranial pressure, which we previously showed was due to microvascular shunt flow maintenance of a falsely high cerebral blood flow. The present study shows that the critical cerebral perfusion pressure, measured by increasing intracranial pressure to decrease cerebral perfusion pressure, is inaccurate but accurately determined by dopamine-induced dynamic intracranial pressure reactivity and cerebrovascular reactivity.
  
  
  METHODS
  Cerebral perfusion pressure was decreased either by increasing intracranial pressure or decreasing mean arterial pressure and the critical cerebral perfusion pressure by both methods compared. Cortical Doppler flux, intracranial pressure, and mean arterial pressure were monitored throughout the study. At each cerebral perfusion pressure, we measured microvascular RBC flow velocity, blood-brain barrier integrity (transcapillary dye extravasation), and tissue oxygenation (reduced nicotinamide adenine dinucleotide) in the cerebral cortex of rats using in vivo two-photon laser scanning microscopy.
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  Male Sprague-Dawley rats.
  
  
  METHODS
  At each cerebral perfusion pressure, dopamine-induced arterial pressure transients (~10 mm Hg, ~45 s duration) were used to measure induced intracranial pressure reactivity (Δ intracranial pressure/Δ mean arterial pressure) and induced cerebrovascular reactivity (Δ cerebral blood flow/Δ mean arterial pressure).
  
  
  RESULTS
  At a normal cerebral perfusion pressure of 70 mm Hg, 10 mm Hg mean arterial pressure pulses had no effect on intracranial pressure or cerebral blood flow (induced intracranial pressure reactivity = -0.03 ± 0.07 and induced cerebrovascular reactivity = -0.02 ± 0.09), reflecting intact autoregulation. Decreasing cerebral perfusion pressure to 50 mm Hg by increasing intracranial pressure increased induced intracranial pressure reactivity and induced cerebrovascular reactivity to 0.24 ± 0.09 and 0.31 ± 0.13, respectively, reflecting impaired autoregulation (p < 0.05). By static cerebral blood flow, the first significant decrease in cerebral blood flow occurred at a cerebral perfusion pressure of 30 mm Hg (0.71 ± 0.08, p < 0.05).
  
  
  CONCLUSIONS
  Critical cerebral perfusion pressure of 50 mm Hg was accurately determined by induced intracranial pressure reactivity and induced cerebrovascular reactivity, whereas the static method failed.
authors.affiliation: 1Department of Neurosurgery, University of New Mexico School of Medicine, Albuquerque, NM. 2Biomedical Research and Integrative Neuroimaging Center, University of New Mexico School of Medicine, Albuquerque, NM. 3Department of Internal Medicine, Xiangya Hospital, Central South University, Changsha, Hunan, China.
authors.forename: Denis E
authors.initials: DE
authors.lastname: Bragin
authors.forename: Gloria L
authors.initials: GL
authors.lastname: Statom
authors.forename: Howard
authors.initials: H
authors.lastname: Yonas
authors.forename: Xingping
authors.initials: X
authors.lastname: Dai
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Nemoto
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D001812:Blood-Brain Barrier / Q000378:metabolism*; D001831:Body Temperature; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004298:Dopamine / Q000494:pharmacology; D006706:Homeostasis / Q000502:physiology*; D019586:Intracranial Hypertension / Q000503:physiopathology*; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D018613:Microscopy, Confocal; D009243:NAD / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D009243:NAD; D004298:Dopamine