REGIONAL HETEROGENEITY OF CEREBRAL BLOOD-FLOW RESPONSE TO GRADED VOLUME-CONTROLLED HEMORRHAGE

Objective: Of the animal models of human hemorrhagic shock, the volume -controlled hemorrhage model appears to come closer to the clinical si tuation than the commonly used pressure-controlled model, since the vo lume-controlled model allows regulatory adjustment of blood pressure. The effects of volume-controlled hemorrhage on local cerebral blood fl ow (LCBF) of conscious animals are not known, The present study invest igates specific reaction patterns of LCBF in comparison to mean cerebr al blood flow (CBF) during graded volume-controlled hemorrhagic shock in conscious rats. Methods: Conscious, spontaneously breathing, and mi nimally restrained rats were subjected to different degrees of volume- controlled hemorrhage (taking either 25, 30, 35, or 40 ml arterial blo od/kg body weight (b.w.). Thirty minutes after the completion of blood taking, LCBF was determined during hemorrhagic hypovolemia using the autoradiographic iodo (C-14) antipyrine method. A group of untreated r ats (no hemorrhage) served as controls. LCBF was determined in 34 defi ned brain structures and mean CBF was calculated. Results: During less severe hemorrhage (25 and 30 ml/kg b.w.) mean CBF was significantly h igher than in the control group (+19% and +25%), During severe hemorrh age (35 and 40 ml/kg b.w.) mean CBF remained unchanged compared to the control values, although significant increases in LCBF could be detec ted in many of the brain structures analyzed (maximum +44%). The mean coefficient of variation of CBF was increased, indicating a larger het erogeneity of LCBF values at shed blood volumes of 35 and 40 ml/kg b.w . Conclusions: A comprehensive and novel description of the local dist ribution of CBF during graded volume-controlled hemorrhage in consciou s rats shows unexpected increases in LCBF and mean CBE This ''hypovole mic cerebral hyperemia'' might be caused by endogenous hemodilution, t hus main taining the blood supply to the brain during hypovolemic shoc k.