Uncoupling of cerebral blood flow and metabolism after cerebral contusion in the rat

Positron emission tomography scans of patients with head injuries often sho w discrete areas of increased F-18- fluorodeoxyglucose uptake ("hot spots") when performed hours to days after the initial ictus. Using quantitative a utoradiographic methods, the authors have investigated whether cerebral blo od flow and glucose metabolism are uncoupled 2 hours after controlled head injury in an animal model, and whether any "hot spots" are accompanied by c hanges in cerebral glucose concentration. Experiments were performed on 18 anesthetized, ventilated (1.5% halothane in 2:1 nitrous oxide:oxygen) Sprag ue-Dawley rats weighing 300 to 330 g. A burr hole was made over the left pa rietal cortex, and all animals received a piston impact on the intact dura (2 mm in diameter, 2.0 m/sec, 2 mm in depth). All animals remained anesthet ized and ventilated for a further 2 hours, after which quantitative autorad iography was used to determine either (1) local cerebral blood flow (LCBF) using C-14-iodoantipyrine, (2) local cerebral glucose utilization (LCGU) us ing C-14-deoxyglucose, or (3) local cerebral glucose content (LCGC) using C -14-methylglucose. Local CBF, LCGU, and LCGC were measured in five regions adjacent to the contusion, and values then were normalized on the contralat eral cortex. Normalized LCBF, LCGU, or LCGC varied in parallel in ipsilater al cortex (no change) and in the ischemic core of the contusion (reduced). However, there were marked changes in the patterns observed in the boundary zone (within 1 mm of the contusion). In all six rats used for LCGU measure ment, there were discrete areas of high metabolism, whereas in all six rats used for LCBF measurement, flow was universally depressed in the boundary zone. Of the six rats used for LCGC determination, there was a discrete are a of high signal in only one. The authors conclude that there are discrete areas of uncoupling of cerebral blood flow and metabolism after head injury within 2 hours of cerebral contusion in the rat that cannot be explained b y changes in cerebral glucose content in the majority of animals.