The effect of haemodilution and hypercapnia on the recovery of cerebral function from experimental focal ischaemia.

The direct cortical response (DCR) and associated local cerebral blood flow was recorded from the primate cerebral cortex during a period of focal ischaemia induced by middle cerebral artery occlusion (MCAO). The DCR was lost when local blood flow fell below 20 ml/100 g/min but began to recover as collateral flow increased. Hypercapnia demonstrated a loss of local vascular reactivity following MCAO, but isovolaemic haemodilution still proved effective in increasing blood flow to these areas. The reduction in blood oxygen content induced by haemodilution did not impair cerebral function but the reduction in whole blood viscosity did exacerbate cerebral susceptibility to hypercapnia-induced intra-cerebral steal.