Mild and moderate hypothermia (alpha-stat) do not impair the coupling between local cerebral blood flow and metabolism in rats

Background and Purpose-The effects of hypothermia on global cerebral blood flow (CBF) and glucose utilization (CGU) have been extensively studied, but less information exists on a local cerebral level. We investigated the eff ects of normothermic and hypothermic anesthesia on local CBF (LCBF) and loc al CGU (LCGU), Methods-Thirty-six rats were anesthetized with isoflurane (1 MAC) and artif icially ventilated to maintain normal Pace, (alpha-stat). Pericranial tempe rature was maintained normothermic (37.5 degrees C, n=12) or was reduced to 35 degrees C (n= 12) or 32 degrees C (n=12), Pericranial temperature was m aintained constant for 60 min until LCBF and LCGU were measured with autora diography, Twelve conscious rats served as normothermic control animals. Results-Normothenmic anesthesia significantly increased mean CBF compared w ith conscious control animals (29%, P<0.05), Mean CBF was reduced to contro l values with mild hypothermia and to 30% below control animals with modera te hypothermia (P<0.05), Normothermic anesthesia reduced mean CGU by 44%. N o additional effects were observed during mild hypothermia. Moderate hypoth ermia resulted in a further reduction in mean CGU (41%, P<0.05). Local anal ysis showed linear relationships between LCBF and LCGU in normothermic cons cious (r=0.93), anesthetized (r=0.92), and both hypothermic groups (35 degr ees C r=0.96, 32 degrees C r=0.96, P<0.05). The LCBF-to-LCCU ratio increase d from 1.5 to 2.5 mL/mu mol during anesthesia (P<0.05), remained at 2.4 mL/ mu mol during mild hypothermia, and decreased during moderate hypothermia ( 2.1 mL/mu mol, P<0.05). Conclusions-Anesthesia and hypothermia induce divergent changes in mean CBF and CGU. However, local analysis demonstrates a well-maintained linear rel ationship between LCBF and LCGU during normothermic and hypothermic anesthe sia.