Association of visit-to-visit variability in blood pressure with cognitive function in old age: prospective cohort study

Visit-to-visit blood pressure variability and dementia

Visit-to-visit blood pressure variability has been shown to be an independent risk factor for stroke and cognitive impairment. However, the underlying mechanisms are not fully understood. Artery remodeling and silent cerebral injury are suggested to be involved in the relationship between visit-to-visit blood pressure variability and cognitive impairment. The present review article summarizes the recent literature on these topics. Here we review visit-to-visit blood pressure variability, artery remodeling, silent cerebral injury and an issue regarding the impact of these components on dementia including Alzheimer's disease.

Higher Visit-to-Visit Low-Density Lipoprotein Cholesterol Variability Is Associated With Lower Cognitive Performance, Lower Cerebral Blood Flow, and Greater White Matter Hyperintensity Load in Older Subjects

Background:

Recently, it was shown that intraindividual variation in low-density lipoprotein cholesterol (LDL-C) predicts both cerebrovascular and cardiovascular events. We aimed to examine whether this extends to cognitive function and examined possible pathways using a magnetic resonance imaging substudy.

Methods:

We investigated the association between LDL-C variability and 4 cognitive domains at month 30 in 4428 participants of PROSPER (PROspective Study of Pravastatin in the Elderly at Risk). Additionally, we assessed the association of LDL-C variability with neuroimaging outcomes in a subset of 535 participants. LDL-C variability was defined as the intraindividual standard deviation over 4 postbaseline LDL-C measurements, and all analyses were adjusted for mean LDL-C levels and cardiovascular risk factors.

Results:

Higher LDL-C variability was associated with lower cognitive function in both the placebo and pravastatin treatment arms. Associations were present for selective attention ( P =0.017 and P =0.11, respectively), processing speed ( P =0.20 and P =0.029), and memory (immediate recall, P =0.002 and P =0.006; delayed recall, P =0.001 and P ≤0.001). Furthermore, higher LDL-C variability was associated with lower cerebral blood flow in both trial arms ( P =0.031 and P =0.050) and with greater white matter hyperintensity load in the pravastatin arm ( P =0.046). No evidence was found for interaction between LDL-C variability and pravastatin treatment for both cognitive and magnetic resonance imaging outcomes.

Conclusions:

We found that higher visit-to-visit variability in LDL-C, independently of mean LDL-C levels and statin treatment, is associated with lower cognitive performance, lower cerebral blood flow, and greater white matter hyperintensity load.

Evaluation of the Use of Home Blood Pressure Measurement Using Mobile Phone-Assisted Technology: The iVitality Proof-of-Principle Study

Background

Mobile phone-assisted technologies provide the opportunity to optimize the feasibility of long-term blood pressure (BP) monitoring at home, with the potential of large-scale data collection.

Objective

In this proof-of-principle study, we evaluated the feasibility of home BP monitoring using mobile phone-assisted technology, by investigating (1) the association between study center and home BP measurements; (2) adherence to reminders on the mobile phone to perform home BP measurements; and (3) referrals, treatment consequences and BP reduction after a raised home BP was diagnosed.

Methods

We used iVitality, a research platform that comprises a Website, a mobile phone-based app, and health sensors, to measure BP and several other health characteristics during a 6-month period. BP was measured twice at baseline at the study center. Home BP was measured on 4 days during the first week, and thereafter, at semimonthly or monthly intervals, for which participants received reminders on their mobile phone. In the monthly protocol, measurements were performed during 2 consecutive days. In the semimonthly protocol, BP was measured at 1 day.

Results

We included 151 participants (mean age [standard deviation] 57.3 [5.3] years). BP measured at the study center was systematically higher when compared with home BP measurements (mean difference systolic BP [standard error] 8.72 [1.08] and diastolic BP 5.81 [0.68] mm Hg, respectively). Correlation of study center and home measurements of BP was high (R=0.72 for systolic BP and 0.72 for diastolic BP, both P<.001). Adherence was better in participants measuring semimonthly (71.4%) compared with participants performing monthly measurements (64.3%, P=.008). During the study, 41 (27.2%) participants were referred to their general practitioner because of a high BP. Referred participants had a decrease in their BP during follow-up (mean difference final and initial [standard error] −5.29 [1.92] for systolic BP and −2.93 [1.08] for diastolic BP, both P<.05).

Conclusion

Mobile phone-assisted technology is a reliable and promising method with good adherence to measure BP at home during a 6-month period. This provides a possibility for implementation in large-scale studies and can potentially contribute to BP reduction.

Visit-to-Visit Variability in Blood Pressure Is Related to Late-Life Cognitive Decline

The association between visit-to-visit variability of blood pressure (BP) and cognitive decline over time remains incompletely understood in a general population of older adults. We assessed the hypothesis that higher visit-to-visit variability in BP, but not mean BP, would be associated with faster decline in cognitive function among community-dwelling older adults. This prospective cohort study comprised 976 adults who had 3 or 4 visits with BP measurements as part of the China Health and Nutrition Survey from 1991, up to their first cognitive tests, and completed cognitive screening tests at ≥2 visits in 1997, 2000, or 2004. Visit-to-visit BP variability was expressed as the SD, coefficient of variation, or as the variation independent of mean BP across visits conducted at a mean interval of 3.2 years. Mean (SD) age at the first cognitive test was 64 (6) years. Using multivariable-adjusted linear mixed-effects models, we found higher visit-to-visit variability in systolic BP, but not mean systolic BP, was associated with a faster decline of cognitive function (adjusted mean difference [95% confidence interval] for high versus low tertile of SD variability: standardized composite scores -0.038 standard units (SU)/y [-0.066 to -0.009] and verbal memory -0.041 SU/y [-0.075 to -0.008]). Higher visit-to-visit variability in diastolic BP was associated with a faster decline of cognitive function, independent of mean diastolic BP, among adults aged 55 to 64 years but not those ≥65 years. Our results suggest that higher long-term BP visit-to-visit variability is associated with a faster rate of cognitive decline among older adults.

Blood Pressure Lowering Medication, Visit-to-Visit Blood Pressure Variability, and Cognitive Function in Old Age

BACKGROUND

Visit-to-visit blood pressure (BP) variability is associated with cognitive impairment. We assessed to what extent the association between BP variability and cognitive impairment is mediated by the association of BP lowering medication (BPLM) with both BP variability and cognition.

METHODS

We studied 5,606 participants from the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER). BP was measured every 3 months during 3.2 years; BP variability was defined as the SD of BP measurements during follow-up. Cognitive function was assessed at baseline and during follow-up using the Stroop test, Letter-Digit Coding test, and immediate and delayed Picture-Word Learning tests. Multivariate regression models were used with and without adjustments for BPLM to calculate the percentage to which BPLM mediated the association between BP variability and cognition.

RESULTS

Participants taking calcium antagonists had a higher score in baseline Letter-Digit Coding test (mean difference (95% confidence interval (CI) 0.45 (0.06; 0.88). Participants taking beta-blockers had a steeper decline in Stroop test (additional change per year (95% CI) 0.40 (0.09; 0.70) and Letter-Digit Coding test (0.08 (-0.15; -0.02)). Furthermore, a steeper decline in Stroop test was found in participants taking renin-angiotensin system (RAS) inhibitors (0.50 (0.16; 0.85). Systolic BP variability was higher in participants taking beta-blockers and RAS inhibitors (mean difference in systolic BP variability in mm Hg (95% CI) 0.75 (0.45; 1.04) and 1.37 (1.04; 1.71) respectively). Participants taking diuretics, calcium antagonists, and RAS inhibitors had a higher diastolic BP variability (mean difference in diastolic BP variability in mm Hg (95% CI) 0.27 (0.04; 0.49), 0.37 (0.12; 0.62) and 0.65 (0.37; 0.93) SD, respectively). Beta estimates remained essentially the same when we adjusted for BPLM in the association of BP variability with cognitive function.

CONCLUSIONS

The association between BP variability and cognitive impairment was not mediated by BPLM.

Effect of orthostatic hypotension on sustained attention in patients with autonomic failure

INTRODUCTION

Orthostatic hypotension has been associated with impaired cognitive function, but cognitive function during orthostatic hypotension has hardly been studied. We studied the effect of orthostatic hypotension, induced by head-up tilt (HUT), on sustained attention in patients with autonomic failure.

METHODS

We studied the sustained attention to response task (SART) in the supine position and during HUT in 10 patients with autonomic failure and 10 age-matched and sex-matched controls. To avoid syncope, the tilting angle was tailored to patients to reach a stable systolic blood pressure below 100 mm Hg. Controls were all tilted at an angle of 60°. Cerebral blood flow velocity, blood pressure and heart rate were measured continuously.

RESULTS

In patients, systolic blood pressure was 61.4 mm Hg lower during HUT than in the supine position (p<0.001). Patients did not make more SART errors during HUT than in the supine position (-1.3 errors, p=0.3). Controls made 2.3 fewer errors during SART in the HUT position compared to the supine position (p=0.020). SART performance led to an increase in systolic blood pressure (+11.8 mm Hg, p=0.018) and diastolic blood pressure (+5.8 mm Hg, p=0.017) during SART in the HUT position, as well as to a trend towards increased cerebral blood flow velocity (+3.8 m/s, p=0.101).

DISCUSSION

Orthostatic hypotension in patients with autonomic failure was not associated with impaired sustained attention. This might partly be explained by the observation that SART performance led to a blood pressure increase. Moreover, the upright position was associated with better performance in controls and, to a lesser extent, also in patients.

Molecular mechanism of aggravation of hypertensive organ damages by short-term blood pressure variability

There is increasing evidence that not only the elevation of systolic and diastolic blood pressure (BP) but also the increase in BP variability (or fluctuation) are associated with hypertensive organ damages and the morbidity and mortality of cerebrovascular and cardiovascular events. However, the molecular mechanism whereby the increase in BP variability aggravates hypertensive organ damages remains unknown. Thus, we created a rat chronic model of a combination of hypertension and large BP variability by performing bilateral sino-aortic denervation in spontaneously hypertensive rat. A series of our studies using this model revealed that large BP variability induces chronic myocardial inflammation by activating local angiotensin II and mineralocorticoid receptor systems and thereby aggravates cardiac hypertrophy and myocardial fibrosis, leading to systolic dysfunction, in hypertensive hearts. In addition, large BP variability induces the aggravation of arteriolosclerotic changes and ischemic cortical fibrosis in hypertensive kidney via local angiotensin II system.

Visit-to-visit blood pressure variability in Alzheimer disease

The aim of this study was to evaluate visit-to-visit blood pressure (BP) variability in a cohort of patients with Alzheimer disease (AD) and healthy controls. Patients with clinically diagnosed mild or moderate AD and cognitively normal controls matched for age and sex were recruited and followed up for 6 months. To characterize the BP status of each individual, mean, maximum and minimum values, SD, and coefficient of variation were obtained for both systolic BP (SBP) and diastolic BP (DBP). Seventy AD patients and 140 controls were enrolled. No meaningful differences were found in prevalence or treatments of various vascular risk factors. AD patients had higher maximum and lower minimum values and greater SD and coefficient of variation of both SBP and DBP. Group differences in mean values were significant only for SBP. In the multiple logistic regression analysis, adjusted for confounding variables, all the indices related to BP variability were significantly associated with AD. Our results show that AD patients have a greater variability of both SBP and DBP in comparison with age-matched cognitive normal controls, suggesting potential implication in the pathogenesis or progression of the disease.

Biological correlates of blood pressure variability in elderly at high risk of cardiovascular disease

BACKGROUND

Visit-to-visit variability in blood pressure is an independent predictor of cardiovascular disease. This study investigates biological correlates of intra-individual variability in blood pressure in older persons.

METHODS

Nested observational study within the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) among 3,794 male and female participants (range 70-82 years) with a history of, or risk factors for cardiovascular disease. Individual visit-to-visit variability in systolic and diastolic blood pressure and pulse pressure (expressed as 1 SD in mm Hg) was assessed using nine measurements over 2 years. Correlates of higher visit-to-visit variability were examined at baseline, including markers of inflammation, endothelial function, renal function and glucose homeostasis.

RESULTS

Over the first 2 years, the mean intra-individual variability (1 SD) was 14.4mm Hg for systolic blood pressure, 7.7mm Hg for diastolic blood pressure, and 12.6mm Hg for pulse pressure. After multivariate adjustment a higher level of interleukin-6 at baseline was consistently associated with higher intra-individual variability of blood pressure, including systolic, diastolic, and pulse pressure. Markers of endothelial function (Von Willebrand factor, tissue plasminogen activator), renal function (glomerular filtration rate) and glucose homeostasis (blood glucose, homeostatic model assessment index) were not or to a minor extent associated with blood pressure variability.

CONCLUSION

In an elderly population at risk of cardiovascular disease, inflammation (as evidenced by higher levels of interleukin-6) is associated with higher intra-individual variability in systolic, diastolic, and pulse pressure.

Heart failure and Alzheimer's disease

It has recently been proposed that heart failure is a risk factor for Alzheimer's disease. Decreased cerebral blood flow and neurohormonal activation due to heart failure may contribute to the dysfunction of the neurovascular unit and cause an energy crisis in neurons. This leads to the impaired clearance of amyloid beta and hyperphosphorylation of tau protein, resulting in the formation of amyloid beta plaques and neurofibrillary tangles. In this article, we will summarize the current understanding of the relationship between heart failure and Alzheimer's disease based on epidemiological studies, brain imaging research, pathological findings and the use of animal models. The importance of atherosclerosis, myocardial infarction, atrial fibrillation, blood pressure and valve disease as well as the effect of relevant medications will be discussed.

The diagnosis and management of mild cognitive impairment: a clinical review

IMPORTANCE

Cognitive decline is a common and feared aspect of aging. Mild cognitive impairment (MCI) is defined as the symptomatic predementia stage on the continuum of cognitive decline, characterized by objective impairment in cognition that is not severe enough to require help with usual activities of daily living.

OBJECTIVE

To present evidence on the diagnosis, treatment, and prognosis of MCI and to provide physicians with an evidence-based framework for caring for older patients with MCI and their caregivers.

EVIDENCE ACQUISITION

We searched PubMed for English-language articles in peer-reviewed journals and the Cochrane Library database from inception through July 2014. Relevant references from retrieved articles were also evaluated.

FINDINGS

The prevalence of MCI in adults aged 65 years and older is 10% to 20%; risk increases with age and men appear to be at higher risk than women. In older patients with MCI, clinicians should consider depression, polypharmacy, and uncontrolled cardiovascular risk factors, all of which may increase risk for cognitive impairment and other negative outcomes. Currently, no medications have proven effective for MCI; treatments and interventions should be aimed at reducing cardiovascular risk factors and prevention of stroke. Aerobic exercise, mental activity, and social engagement may help decrease risk of further cognitive decline. Although patients with MCI are at greater risk for developing dementia compared with the general population, there is currently substantial variation in risk estimates (from <5% to 20% annual conversion rates), depending on the population studied. Current research targets improving early detection and treatment of MCI, particularly in patients at high risk for progression to dementia.

CONCLUSIONS AND RELEVANCE

Cognitive decline and MCI have important implications for patients and their families and will require that primary care clinicians be skilled in identifying and managing this common disorder as the number of older adults increases in coming decades. Current evidence supports aerobic exercise, mental activity, and cardiovascular risk factor control in patients with MCI.

Modeling metabolic syndrome and its association with cognition: the Northern Manhattan study

Metabolic syndrome (MetS) is a clustering of vascular risk factors and is associated with increased risk of cardiovascular disease. Less is known about the relationship between MetS and cognition. We examined component vascular risk factors of MetS as correlates of different cognitive domains. The Northern Manhattan Study (NOMAS) includes 1290 stroke-free participants from a largely Hispanic multi-ethnic urban community. We used structural equation modeling (SEM) to model latent variables of MetS, assessed at baseline and an average of 10 years later, at which time participants also underwent a full cognitive battery. The two four-factor models, of the metabolic syndrome (blood pressure, lipid levels, obesity, and fasting glucose) and of cognition (language, executive function, psychomotor, and memory), were each well supported (CFI=0.97 and CFI=0.95, respectively). When the two models were combined, the correlation between metabolic syndrome and cognition was -.31. Among the metabolic syndrome components, only blood pressure uniquely predicted all four cognitive domains. After adjusting for age, gender, race/ethnicity, education, smoking, alcohol, and risk factor treatment variables, blood pressure remained a significant correlate of all domains except memory. In this stroke-free race/ethnically diverse community-based cohort, MetS was associated with cognitive function suggesting that MetS and its components may be important predictors of cognitive outcomes. After adjusting for sociodemographic and vascular risk factors, blood pressure was the strongest correlate of cognitive performance. Findings suggest MetS, and in particular blood pressure, may represent markers of vascular or neurodegenerative damage in aging populations.

Long-term blood pressure variability throughout young adulthood and cognitive function in midlife: the Coronary Artery Risk Development in Young Adults (CARDIA) study

Whether long-term blood pressure (BP) variability throughout young adulthood is associated with cognitive function in midlife remains uncertain. Using data from the Coronary Artery Risk Development in Young Adults (CARDIA), which recruited healthy young adults aged 18 to 30 years (mean age, 25 years) at baseline (Y(0)), we assessed BP variability by SD and average real variability (ARV) for 25 years (8 visits). Cognitive function was assessed with the Digit Symbol Substitution Test (psychomotor speed test), the Rey Auditory Verbal Learning Test (verbal memory test), and the modified Stroop test (executive function test) at follow-up (Y(25)). At the Y(25) examination, participants (n=2326) had a mean age of 50.4 years, 43% were men, and 40% were black. In multivariable-adjusted linear regression models, higher ARV(SBP), ARV(DBP), and SD(DBP) were significantly associated with lower scores of Digit Symbol Substitution Test (β [SE]: -0.025 [0.006], -0.029 [0.007], and -0.029 [0.007], respectively; all P<0.001) and Rey Auditory Verbal Learning Test (β [SE]: -0.016 [0.006], -0.021 [0.007], and -0.019 [0.007], respectively; all P<0.05) after adjustment for demographic and clinical characteristics and with cumulative exposure to BP through Y(0) to Y(25). Neither SDBP nor ARV(BP) was associated with the Stroop score. The associations between ARV(BP) or SD(BP) and each cognitive function test were similar between blacks and whites except for 1 significant interaction between race and SDS(BP) on the Digit Symbol Substitution Test (P<0.05). Long-term BP variability for 25 years beginning in young adulthood was associated with worse psychomotor speed and verbal memory tests in midlife, independent of cumulative exposure to BP during follow-up.

Measurement-to-measurement blood pressure variability is related to cognitive performance: the Maine Syracuse study

The objective was to investigate the association between variability in blood pressure (BP) and cognitive function for sitting, standing, and reclining BP values and variability derived from all 15 measures. In previous studies, only sitting BP values have been examined, and only a few cognitive measures have been used. A secondary objective was to examine associations between BP variability and cognitive performance in hypertensive individuals stratified by treatment success. Cross-sectional analyses were performed on 972 participants of the Maine Syracuse Study for whom 15 serial BP clinic measures (5 sitting, 5 recumbent, and 5 standing) were obtained before testing of cognitive performance. Using all 15 measures, higher variability in systolic and diastolic BP was associated with poorer performance on multiple measures of cognitive performance, independent of demographic factors, cardiovascular risk factors, and pulse pressure. When sitting, reclining, and standing systolic BP values were compared, only variability in standing BP was related to measures of cognitive performance. However, for diastolic BP, variability in all 3 positions was related to cognitive performance. Mean BP values were weaker predictors of cognition. Furthermore, higher overall variability in both systolic and diastolic BP was associated with poorer cognitive performance in unsuccessfully treated hypertensive individuals (with BP ≥140/90 mm Hg), but these associations were not evident in those with controlled hypertension.

Cognitive impairment and risk of future stroke: a systematic review and meta-analysis

BACKGROUND

Several studies have assessed the link between cognitive impairment and risk of future stroke, but results have been inconsistent. We conducted a systematic review and meta-analysis of cohort studies to determine the association between cognitive impairment and risk of future stroke.

METHODS

We searched MEDLINE and Embase (1966 to November 2013) and conducted a manual search of bibliographies of relevant retrieved articles and reviews. We included cohort studies that reported multivariable adjusted relative risks and 95% confidence intervals or standard errors for stroke with respect to baseline cognitive impairment.

RESULTS

We identified 18 cohort studies (total 121 879 participants) and 7799 stroke events. Pooled analysis of results from all studies showed that stroke risk increased among patients with cognitive impairment at baseline (relative risk [RR] 1.39, 95% confidence interval [CI] 1.24-1.56). The results were similar when we restricted the analysis to studies that used a widely adopted definition of cognitive impairment (i.e., Mini-Mental State Examination score < 25 or nearest equivalent) (RR 1.64, 95% CI 1.46-1.84). Cognitive impairment at baseline was also associated with an increased risk of fatal stroke (RR 1.68, 95% CI 1.21-2.33) and ischemic stroke (RR 1.65, 95% CI 1.41-1.93).

INTERPRETATION

Baseline cognitive impairment was associated with a significantly higher risk of future stroke, especially ischemic and fatal stroke.

Day-to-day variability in home blood pressure is associated with cognitive decline: the Ohasama study

Although an association between high blood pressure and cognitive decline has been reported, no studies have investigated the association between home blood pressure and cognitive decline. Home blood pressure measurements can also provide day-to-day blood pressure variability calculated as the within-participant SD. The objectives of this prospective study were to clarify whether home blood pressure has a stronger predictive power for cognitive decline than conventional blood pressure and to compare the predictive power of the averaged home blood pressure with day-to-day home blood pressure variability for cognitive decline. Of 485 participants (mean age, 63 years) who did not have cognitive decline (defined as Mini-Mental State Examination score, <24) initially, 46 developed cognitive decline after a median follow-up of 7.8 years. Each 1-SD increase in the home systolic blood pressure value showed a significant association with cognitive decline (odds ratio, 1.48; P=0.03). However, conventional systolic blood pressure was not significantly associated with cognitive decline (odds ratio, 1.24; P=0.2). The day-to-day variability in systolic blood pressure was significantly associated with cognitive decline after including home systolic blood pressure in the same model (odds ratio, 1.51; P=0.02), whereas the odds ratio of home systolic blood pressure remained positive, but it was not significant. Home blood pressure measurements can be useful for predicting future cognitive decline because they can provide information not only on blood pressure values but also on day-to-day blood pressure variability.

Blood pressure, internal carotid artery flow parameters, and age-related white matter hyperintensities

White matter hyperintensities (WMH) are associated with hypertension. We examined interactions among blood pressure (BP), internal carotid artery (ICA) flow velocity parameters, and WMH. We obtained BP measurements from 694 community-dwelling subjects at mean ages 69.6 (±0.8) years and again at 72.6 (±0.7) years, plus brain MRI and ICA ultrasound at age 73±1 years. Diastolic and mean BP decreased and pulse pressure increased, but systolic BP did not change between 70 and 73 years. Multiple linear regression, corrected for vascular disease and risk factors, showed that WMH at the age of 73 years were associated with history of hypertension (β=0.13; P<0.001) and with BP at the age of 70 years (systolic β=0.08, mean β=0.09, diastolic β=0.08; all P<0.05); similar but attenuated associations were seen for BP at the age of 73 years. Lower diastolic BP and higher pulse pressure were associated with higher ICA pulsatility index at the age 73 years (diastolic BP age 70 years: standardized β=-0.24, P<0.001; pulse pressure age 70 years: β=0.19, P<0.001). WMH were associated with higher ICA pulsatility index (β=0.13; P=0.002) after adjusting for BP and correction for multiple testing. Therefore, falling diastolic BP and increased pulse pressure are associated with increased ICA pulsatility index, which in turn is associated with WMH. This suggests that hypertension and WMH may either associate indirectly because hypertension increases arterial stiffness that leads to WMH over time, or coassociate through advancing age and stiffer vessels, or both. Reducing vascular stiffness may reduce WMH progression and should be tested in randomized trials, in addition to testing antihypertensive therapy.