title: Oxygen delivery at high blood viscosity and decreased arterial oxygen content to brains of conscious rats.
abstract: We addressed the question to which extent cerebral blood flow (CBF) is maintained when, in addition to a high blood viscosity (Bvis) arterial oxygen content (CaO2) is gradually decreased. CaO2) was decreased by hemodilution to hematocrits (Hct) of 30, 22, 19, and 15% in two groups. One group received blood replacement (BR) only and served as the control. The second group received an additional high viscosity solution of polyvinylpyrrolidone (BR/PVP). Bvis was reduced in the BR group and was doubled in the BR/PVP. Despite different Bvis, CBF did not differ between BR and BR/PVP rats at Hct values of 30 and 22%, indicating a complete vascular compensation of the increased Bvis at decreased CaO2. At an Hct of 19%, local cerebral blood flow (LCBF) in some brain structures was lower in BR/PVP rats than in BR rats. At the lowest Hct of 15%, LCBF of 15 brain structures and mean CBF were reduced in BR/PVP. The resulting decrease in cerebral oxygen delivery in the BR/PVP group indicates a global loss of vascular compensation. We concluded that vasodilating mechanisms compensated for Bvis increases thereby maintaining constant cerebral oxygen delivery. Compensatory mechanisms were exhausted at a Hct of 19% and lower as indicated by the reduction of CBF and cerebral oxygen delivery.
authors.affiliation: Faculty of Clinical Medicine, Department of Anesthesiology, Mannheim D-68067, Heidelberg, Germany. freebel@msn.com
authors.forename: A
authors.initials: A
authors.lastname: Rebel
authors.forename: C
authors.initials: C
authors.lastname: Lenz
authors.forename: H
authors.initials: H
authors.lastname: Krieter
authors.forename: K F
authors.initials: KF
authors.lastname: Waschke
authors.forename: K
authors.initials: K
authors.lastname: Van Ackern
authors.forename: W
authors.initials: W
authors.lastname: Kuschinsky
mesh_terms: D000818:Animals; D000983:Antipyrine / Q000031:analogs & derivatives*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D001809:Blood Viscosity / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000098:blood supply* / Q000187:drug effects / Q000378:metabolism*; D002536:Cerebral Arteries / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology; D006400:Hematocrit; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D011205:Povidone / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014851:Wakefulness
chemical_list: C077842:polyvinylpolypyrrolidone; D011205:Povidone; D010100:Oxygen; D000983:Antipyrine; C008135:iodoantipyrine