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Free keywords:
cerebral infarction; cerebral ischemia; focal; glutamates; intracranial pressure; perfusion; tomography; emission computed; cats
Abstract:
Copyright 2002 American Heart Association, Inc.
Abstract:
Background and Purpose-To study the putative role and predictive significance of glutamate elevation in space- occupying ischemic stroke. we investigated the correlation between perfusional disturbances and glutamate alterations in a transient ischemia model in cats that is susceptible to secondary deterioration after reperfusion. Methods-In 10 halothane-anesthetized cats, the left middle cerebral artery was occluded for 3 hours, followed by 6 hours of reperfusion. Laser-Doppler flowmetry (LDF) probes, microdialysis/high- performance liquid chromatography, and pressure sensors measured simultaneously regional cerebral blood flow (CBF), extracellular amino acids, mean arterial blood pressure, and intracranial pressure, respectively. Cerebral perfusion pressure (CPP) was calculated. In complementary experiments (n=2), regional CBF was assessed by sequential positron emission tomography. Results-Middle cerebral artery occlusion reduced LDF-measured CBF in all animals to <25% of control. In 5 of 10 cats, glutamate rose approximately 30-fold during ischemia. LDF-measured CBF and glutamate primarily recovered after reperfusion. Glutamate rose again in the late reperfusion phase, when CPP decreased to <60 mm Hg, and symptoms of transtentorial herniation were recognized. Positron emission tomography revealed ischemic thresholds of 15 to 20 mL/100 g per minute for secondary deterioration. In the other 5 cats, ischemic elevation of glutamate was significantly smaller. and signs of secondary deterioration were not recognized. Conclusions-Glutamate determinations during ischemia predict fatal outcome, as do intracranial pressure and CPP measurements during early reperfusion. Secondary amino acid elevation during reperfusion is presumably caused by a drastic decrease of CPP to <50 mm Hg in the final stage of space-occupying, malignant focal ischemia. At this stage, a further progression of injury due to increased glutamate may be irrelevant with respect to fatal outcome.
