Impaired cerebral autoregulation 24 h after induction of transient unilateral focal ischaemia in the rat

Cerebral blood flow (CBF) and cerebral autoregulation have been investigate d 24 h after transient focal ischaemia in the rat. Cerebral blood flow was measured autoradiographically before and during a moderate hypotensive chal lenge, to test autoregulatory responses, using two CBF tracers, Tc-99m-d,l- hexamethylproyleneamine oxide and C-14-iodoantipyrine, Prior to induced hyp otension, CBF was significantly reduced within areas of infarction; cortex (28 +/- 20 compared with 109 +/- 23 mL/100 g/min contralateral to ischaemic focus, P= 0.001) and caudate (57 +/- 31 compared with 141 +/- 32 mL/100 g/ min contralaterally, P= 0.005). The hypotensive challenge (mean arterial pr essure reduced to 60 mmHg by increasing halothane concentration) did not co mpromise grey matter autoregulation in the contralateral hemisphere; CBF da ta were not significantly different at normotension and during hypotension. However, in the ipsilateral hemisphere, a significant volume of cortex adj acent to the infarct, which exhibited normal flow at normotension, became o ligaemic during the hypotensive challenge (e.g. frontal parietal cortex 109 +/- 15% to 65 +/- 15% Of cerebellar flow, P<0.01). This resulted in a 2.5- fold increase in the volume of cortex which fell below 50% cerebellar flow (39 +/- 34 to 97 +/- 46 mm(3), P=0.003), Moderate hypotension induced a sig nificant reduction in CBF in both ipsilateral and contralateral subcortical white matter (P<0.01). In peri-infarct caudate tissue, CBF was not signifi cantly affected by hypotension. In conclusion, a significant volume of hist ologically normal cortex within the middle cerebral artery territory was fo und to have essentially normal levels of CBF but impaired autoregulatory fu nction at 24 h post-ischaemia.