Objective: High blood pressure is common in acute stroke and is associated independently with poor outcome. Lowering blood pressure might improve outcome, provided it does not reduce cerebral blood flow in the presence of dysfunctional cerebral autoregulation.
Methods: We performed a systematic review of clinical controlled trials that administered antihypertensive agents within 7 days of ischaemic stroke and measured cerebral blood flow or cerebral blood flow velocity.
Results: From 74 identified publications, 11 trials met the criteria. A variety of antihypertensive agents were used: angiotensin-converting enzyme inhibitors (three trials), angiotensin-receptor antagonists (one), calcium antagonists (five), diuretics (one) and nitrates (two). The trials' median quality score was 2.5/5, and the studies used single photon emission computed tomography (five trials), xenon-computed tomography (three) and positron emission tomography (one) for determining cerebral blood flow, and transcranial Doppler (six) for measuring flow velocity. Analysis of randomized controlled trials revealed no alteration in cerebral blood flow for any antihypertensive agent. Nonrandomized trials that assessed blood flow before and after administration of the agents showed an increase in blood flow for calcium channel blockers (standardized mean difference 0.43, 95% confidence interval 0.01-0.85).
Conclusion: There are few quality studies assessing the effect of antihypertensive agents on cerebral blood flow and flow velocity, and variability in reporting make meta-analysis difficult. However, there is little existing evidence that antihypertensive agents reduce cerebral blood flow in spite of their effects on lowering blood pressure.