24-hour Ambulatory Blood Pressure, Cognitive Performance, and Cerebral Microbleeds in the Elderly

Introduction: Multiple studies suggest a role for blood pressure (BP) variability and nocturnal BP dipping in the development of cerebrovascular disease and cognitive impairment. We analyzed cross-sectional data from a cohort of 90+ year-olds to test the hypothesis that BP variables are associated with cognitive function and cerebral microbleeds (CMB). Methods: Study subjects were 121 participants (mean age = 93 years, 63% female) in The 90+ Study, a study of aging in individuals aged 90 years and older from a California retirement community. Participants were given a neuropsychological test battery to determine cognitive status. All subjects underwent 24-hour ambulatory BP measurement with a automatic device. MRI scans were available for 26 participants. Over three time frames (24-hour, daytime, nighttime) and separately for SBP and DBP, we represented BP by mean, minimum, maximum, standard deviation (SD), coefficient of variation, average real variability, percentage of high measurements (≥140 mmHg for SBP and ≥90 mmHg for DBP), percentage of low measurements (<90 mmHg for SBP and <60 mmHg for DBP), and nocturnal dip (% change of mean night BP from mean day BP). Differences in means of BP variables between groups based on cognitive status (normal vs cognitively impaired not demented (CIND)/demented) and presence/absence of CMB were tested using t-tests. Results: Cognitive status was normal in 97 subjects, CIND/demented in 24. Mean nocturnal dips (both SBP and DBP) differed significantly between the two groups, with normal participants having on average greater dip levels (6.6 vs 1.3, p=0.006 for SBP and 11 vs 4.4, p=0.002 for DBP). No other BP variable showed a large or significant difference. Greater nocturnal dips were also related to better performance on cognitive test scores related to language, recent memory, and visual-spatial ability. MRI findings showed subjects with CMB (n=18) had higher SD of daytime SBP than those without (n=8) (20 vs 16, p=0.03)