Day-by-day blood pressure variability: cause or consequence of vascular brain injury?

D ementia represents an important public health issue in developed countries because of increasing longevity of the elderly population. 1 Cerebral damage is mediated by changes in cerebral vasculature affecting both large and small vessels. 2 The microvascular disease results in chronic ischemic changes affecting the white matter, which in the long run can lead to cognitive alterations, which may progress to overt vas-cular dementia. 2 It is thus important to identify and counterbalance the risk factors for cognitive decline at a population level. Although high midlife blood pressure (BP) is associated with an increased risk of late-life dementia, 3,4 the pathophysiol-ogy of the relationship between elevated BP and low cognition remains unclear. In particular, it is uncertain whether, to preserve cognition, it is better not only to lower the mean BP level but also to achieve a more stable BP. Both high and, especially in the elderly, low BP have been linked to cognitive decline and dementia. 5 Patients with hypertension may be especially vulnerable to swings of pressure including episodes of hypo-tension, because in elderly persons with chronic hypertension, the shift of cerebral autoregulation toward higher BP levels makes the brain more exposed to hypoperfusion. 6 BP variability (BPV) increases with age, and recent studies have reported an association between long-term BPV and silent cerebral lesions, in particular white matter hyperintensities. 7 Of note, the association of BPV with poorer outcome was found in subjects with higher as well as in those with lower BP levels. 7 In a cohort of 6506 elderly individuals followed-up for 8 years, Alpérovitch et al 8 found that an increase of 1 SD in the coefficient of variation of BP measured on 3 visits was associated with a 10% increased risk of dementia. BP measured out of office predicts cardiovascular outcomes better than traditional BP measured by the doctor. In addition it allows for an easy and detailed assessment of BPV, which may have relevant implications for the clinical evaluation of patients with hypertension. Clinical studies have shown that short-term BPV evaluated from 24-hour ambulatory monitoring was associated with white matter hyperintensities and silent infarcts. 9 A cross-sectional association with short-term BPV has been found also for cognitive function, especially in elderly hypertensives with no history of cerebrovascular disease. 10 The relationship between cognitive function and home BP is less known. Self-measured BP is a better predictor of car-diovascular outcomes than office …