Characterization of changes in electroencephalographic markers associated with transient cerebral ischemia

This study characterized and contrasted the electroencephalographic (EEG) effects of ischemia using two rodent models of global transient cerebral ischemia. Male Sprague-Dawley rats were surgically prepared for cortical EEG recordings and for induction of ischemia either by the four-artery occlusion (4AO-M) or the centrifugation (Cent-M) models of ischemia.; The first part of the study assessed the effects of 15 minutes of occlusion by the 4AO-M presented as a continuous exposure or as thirty 30-second occlusions followed by 30-second reperfusions. An increase in total EEG power and a shift toward slower EEG frequencies were observed in both groups, but was more pronounced in the 15-minute group. A subgroup of the continuous occlusion group developed an isoelectric EEG pattern approximately five minutes into the ischemic exposure.; The second part of the study contrasted the EEG effects of ischemia produced by the two models. An increase in total EEG power and a shift toward slower EEG frequencies were observed in both models. Physical stresses exerted on the lower body and possible "draining" of cerebral blood during centrifugation are proposed as contributing to greater EEG effects observed in the Cent-M.; The third part of the study examined the effects of ischemia on EEG and circle of Willis pressure in the 4AO-M and cortical intra-parenchymal pressure in the Cent-M. Pressures in both models were decreased during ischemia and occasionally elevated above baseline during reperfusion. Relative changes were most pronounced in the Cent-M where many animals experiencing the pressure overshoot also demonstrated a rapid onset brief isoelectric EEG event.; The results of the present study show that ischemia is associated with specific changes in EEG, namely increased total power and shifts toward slower EEG frequencies or, in some animals, isoelectric EEG. These changes were more pronounced under conditions of continuous ischemia than conditions of interrupted ischemia. It was further shown that ischemia was associated with falls in either circle of Willis or cortical intra-parenchymal pressures. Lastly, it was observed that the changes already mentioned were more pronounced in the Cent-M than in the 4AO-M.