Spatio-temporal Dynamics of Perfusion during Transient Focal Ischemia: Sequential Experimental PET in Cats
Objective: We studied the temporal evolution of regional dysfunction in transient focal ischemia using sequential positron emission tomography (PET), with special emphasis on postischemic hyperperfusion. Methods: Cerebral blood flow (CBF), oxygen metabolism (CMRO2 ), and oxygen extraction (OEF) were repeatedly measured before and up to 24 hours after 60 min middle cerebral artery (MCA) occlusion in 16 halothane anesthetized cats. PET results were compared to final histopathologic outcome. Results: In all animals, CBF decreased in the ischemic territory below 45% of preischemic controls. Recirculation was partially successful in 3 cats, and hypoperfused regions persisted resulting in gross infarction. 3 major types of hyperperfusion evolved in the other cats: 1. In 5 cats, hyperperfusion covering large parts of the MCA territory persisted throughout the experiment. During ischemia, CBF reduction was severe, and OEF increases were restricted to the surrounding of subsequently hyperperfused regions. At the final stage, large infarcts were observed. 2. In 6 cats, hyperperfusion was transient and often followed by hypoperfusion in parts of previously hyperperfused regions. During MCA occlusion, CBF reduction was more gradual, and OEF elevations covered not only the surroundings but partially also subsequently hyperperfused zones. Infarcts were normally restricted to the center of hyperperfused regions, or did not develop. 3. In 2 cats, hyperperfused regions grew progressively over time. In this type, CBF reduction was also more gradual, OEF increases were widely distributed in the ischemic territory, and infarcts were small. Conclusion: Sequential experimental PET revealed variable spatio-temporal patterns of postischemic perfusion following transient MCAO in cats. Regions with continued hyperperfusion have a particularly bad outcome, as have those with continued incomplete recirculation. Transient postischemic hyperperfusion, however, may be beneficial in zones with subcritical CBF reduction or spontaneous partial reperfusion during the ischemic episode.