Influence of hypotension and hypotensive technique on the area of profound reduction in cerebral blood flow during focal cerebral ischaemia in the rat.

We have studied the effect of induced hypotension on reduction in regional cerebral blood flow (CBF) during middle cerebral artery occlusion (MCAO). Rats were anaesthetized with 2% isoflurane. MCAO was performed during four conditions: normotension (mean arterial pressure (MAP) 107 (SD 15) mm Hg); hypovolaemic hypotension (blood withdrawn to reduce MAP to 43 (2) mm Hg); nitroprusside (SNP) hypotension (MAP reduced to 45 (3) mm Hg); isoflurane hypotension (MAP reduced to 44 (3) mm Hg with 3.5 (0.48)% isoflurane). Hypotension was established before MCAO and was maintained for 10 min, at which time the dimension of the brain areas with zero CBF was determined autoradiographically. All hypotensive regimens were associated with significantly larger areas of extreme CBF reduction. In a coronal section at the centre of the MCA distribution, the area with zero CBF (expressed as a percentage of the area of the entire coronal section) was: normotension 4.7 (4.5)%; hypovolaemic hypotension 10.1 (2.8)%; nitroprusside hypotension 13.5 (2.0)%; and isoflurane hypotension 11.8 (3.9)%. There were no differences between the three hypotensive regimens. The data indicate that, when focal cerebral ischaemia occurs during hypotension (MAP 45 mm Hg) induced by any of the three regimens evaluated, extreme CBF reduction occurs over larger areas than are observed during normotension. These data confirm the importance of arterial pressure as a determinant of collateral flow during focal cerebral ischaemia.