PET STUDY OF CHANGES IN LOCAL BRAIN HEMODYNAMICS AND OXYGEN-METABOLISM AFTER UNILATERAL MIDDLE CEREBRAL-ARTERY OCCLUSION IN BABOONS

Local cerebral hemodynamics and oxygen metabolism were measured by pos itron emission tomography (PET) with the oxygen-15 (O-15) steady-state method in baboons, immediately before (T0), 1 (T1), and 3-4 (T2) h af ter permanent middle cerebral artery occlusion (MCAO). At T1, there wa s a marked fall in both cerebral blood flow (CBF) and the CBF/cerebral blood volume (CBV) ratio in the occluded territory; these changes wer e sustained at T2, indicating stable reduction in cerebral perfusion p ressure and lack of spontaneous reperfusion within this time range. Co mpared with pre-occlusion conditions, the oxygen extraction fraction ( OEF) in the occluded territory was elevated at both T1 and T2, indicat ive of a persistent oligemia/ischemia for up to 3 h after MCAO. At T2, however, this OEF increase had lessened, concomitantly with a decline in cerebral metabolic rate of oxygen (CMRO2). This impairment of oxid ative metabolism occurred earlier in the deep, compared with the corti cal, MCA territories; in the latter, the CMRO, was essentially preserv ed at T1 and only moderately reduced at T2, possibly suggesting prolon ged viability. Finally, no significant changes in CBF or CMRO2 were ob served in the contralateral MCA territory in this time range after MCA O. Despite methodological limitations (mainly partial volume effects r elated to PET imaging, which may have resulted in an underestimation o f true changes and an overlooking of heterogeneous changes) our study demonstrates the feasibility of the combined PET-MCAO paradigm in babo ons; this experimental approach should be valuable in investigating th e pathophysiology and therapy of acute stroke.