INDUCED HYPERTENSION IMPROVES REGIONAL BLOOD-FLOW AND PROTECTS AGAINST INFARCTION DURING FOCAL ISCHEMIA - TIME-COURSE OF CHANGES IN BLOOD-FLOW MEASURED BY LASER-DOPPLER IMAGING

OBJECTIVE: To characterize changes in regional blood flow (rCBF) durin g and after a period of arterial occlusion and determine the effect on rCBF and on the extent of infarction when the mean arterial blood pre ssure is increased during the period of occlusion. METHODS: rCBF in th e middle cerebral artery (MCA) territory of rabbits was monitored usin g laser Doppler perfusion imaging before, during, and after a 1- or 2- hour period of MCA occlusion, and the size of the infarction was asses sed by 2,3,5-triphenyltetrazolamine chloride staining after 2 hours of reperfusion, Test animals, the mean arterial blood pressure of which was increased by 65 mm Hg with intravenous phenylephrine during the is chemia, were compared with control animals that remained normotensive. The laser Doppler perfusion imager (Lisca Developments Co., Linkoping , Sweden) scanned a 3-cm(2) area of cortex with a resolution of 4 mm(2 ) every 15 minutes. RESULTS: MCA occlusion reduced rCBF to 71 +/- 2% o f the control level (n = 24, P < 0.001). Hypertension (HTN) restored r CBF to 84 +/- 3% of the control level (n = 12, P < 0.01), but the HTN- induced improvement diminished with time, so that after 1 hour, there was no longer a significant difference between hypertensive and normot ensive animals. HTN during the MCA occlusion caused a 97% reduction in infarct size (P < 0.05) in the animals subjected to 1 hour of occlusi on but caused only a 45% reduction (P similar to 0.1) in the animals s ubjected tb 2 hours of occlusion. CONCLUSION: This study supports the use of HTN to minimize ischemic injury from short intervals of major i ntracranial vessel occlusion but fails to demonstrate protection when HTN is maintained during occlusions of more than 1 hour.