title: Central hypervolemia with hemodilution impairs dynamic cerebral autoregulation.
abstract: BACKGROUND
  Frequent changes in the perioperative central blood volume could affect cerebral autoregulation through alterations in sympathetic nerve activity, cardiac output, blood viscosity, and cerebral vasomotor tone. However, the effect of dynamic cerebral autoregulation has not been studied during acute wide-ranging changes in central blood volume, especially with respect to central hypervolemia with hemodilution.
  
  
  METHODS
  We evaluated dynamic cerebral autoregulation during central hypovolemia and central hypervolemia with hemodilution using spectral and transfer function analysis between mean arterial blood pressure (MBP) and cerebral blood flow (CBF) velocity variability in 12 individuals. Rapid changes in central blood volume were achieved using two levels of lower body negative pressure (-15 and -30 mm Hg) and two discrete infusions of normal saline (15 mL/kg and total 30 mL/kg). We then estimated changes in central blood volume as central venous pressure (CVP) and/or cardiac output using impedance cardiography.
  
  
  RESULTS
  Steady-state CBF velocity and cardiac output decreased at -30 mm Hg lower body negative pressure (changes of CVP approximately -4 mm Hg) or were increased by each saline infusion (changes of CVP 4-6 mm Hg), without a significant change in MBP. However, transfer function gain (magnitude of transfer) between MBP and CBF velocity variability significantly increased only after saline infusion, suggesting an increased magnitude of transfer from MBP oscillations to CBF fluctuations during central hypervolemia with hemodilution.
  
  
  CONCLUSIONS
  Our results suggest that, although steady-state CBF velocity changes under both central hypervolemia and hypovolemia, only hypervolemic hemodilution impairs dynamic cerebral autoregulation.
authors.affiliation: Department of Hygiene and Space Medicine, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Iwasaki
authors.forename: Ken
authors.initials: K
authors.lastname: Aoki
authors.forename: Shigeki
authors.initials: S
authors.lastname: Shibata
authors.forename: Jitsu
authors.initials: J
authors.lastname: Kato
authors.forename: Setsuro
authors.initials: S
authors.lastname: Ogawa
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D001810:Blood Volume / Q000502:physiology*; D001921:Brain / Q000098:blood supply* / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D006438:Hemodilution / Q000009:adverse effects / Q000379:methods*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male