Hypertension-related cognitive decline: is the time right for intervention studies?

The importance of lowering blood pressure in hypertensive subjects is well known but the relationship between hypertension and cognitive function has been a subject of considerable controversy. Cross-sectional studies investigating the relationship between blood pressure and cognition have shown conflicting relationships whilst the majority of longitudinal studies have demonstrated elevated blood pressure to be associated with cognitive decline. Randomised studies have demonstrated heterogeneous and sometimes conflicting effects of blood pressure lowering on cognitive function and suggested reasons include multiple mechanisms by which hypertension affects the brain, the variety of cognitive instruments used for assessment and differences in antihypertensive treatments. Chronic hypertension accelerates arteriosclerotic changes in the brain with a disproportionate effect on subcortical circuits associated with cerebral small vessel disease. Randomised clinical trials assessing the cognitive consequences of blood pressure reduction in people with small vessel disease are lacking and many of the existing controversies on the cognitive consequences of blood pressure lowering, especially in older people, arise from the design limitations of studies. This article describes the methodological issues in designing such a trial and the results of a pilot evaluation to see if careful selection of subjects and measurements would make undertaking intervention studies feasible. Given the predicted upswing in people with cognitive impairments, the time is right for randomised clinical trials with specific cognitive end-points to examine the relationship between cognitive function and hypertension and guide practice.