Lower cardiac index levels relate to lower cerebral blood flow in older adults

Apolipoprotein E Genotype Modifies the Association Between Cardiac Output and Cognition in Older Adults

Background

Subtle reductions in cardiac output relate to lower cerebral blood flow, especially in regions where Alzheimer's disease pathology first develops. Apolipoprotein E (APOE)‐ε4 is a genetic susceptibility risk factor for Alzheimer's disease that also moderates vascular damage. This study investigated whether APOE‐ε4 carrier status modifies the cross‐sectional association between cardiac output and cognition.

Methods and Results

Vanderbilt Memory & Aging Project participants free of clinical stroke and dementia (n=306, 73±7 years, 42% female) underwent echocardiography to determine cardiac output (L/min), comprehensive neuropsychological assessment, and venous blood draw to determine APOE genotype and ε4 carrier status. Linear regressions related cardiac output to neuropsychological test performance, adjusting for age, sex, education, race/ethnicity, body surface area, cognitive diagnosis, Framingham Stroke Risk Profile, and APOE‐ε4 status. Main effect models were null (P>0.19). With identical covariates, models were repeated testing a cardiac output×APOE‐ε4 status interaction and again stratified by ε4 carrier status. Cardiac output×APOE‐ε4 status related to naming (β=0.91, P=0.0009), category fluency (β=1.2, P=0.01), information processing speed (β=−5.4, P=0.001), visuospatial skill (β=0.85, P=0.003), and executive function performances (β=0.22, P=0.002). Stratified models suggested that lower cardiac output was associated with worse neuropsychological performances among APOE‐ε4 carriers.

Conclusions

APOE‐ε4 carrier status appears to modify the cross‐sectional association between cardiac output and neuropsychological performance such that lower cardiac output relates to poorer performances among carriers of the ε4 allele. These findings add to increasing evidence that APOE‐ε4 carrier status has important implications for associations between vascular and brain health in aging adults.

Lower total cerebral arterial flow contributes to cognitive performance in multiple sclerosis patients

BACKGROUND

The cognitive performance in multiple sclerosis (MS) patients declines with aging, longer disease duration, and possibly cardiovascular comorbidities.

OBJECTIVES

We investigated whether lower total cerebral arterial blood flow (CABF) measured at the level of the carotid and vertebral arteries may contribute to worse cognitive performance in 132 MS patients and 47 healthy controls.

METHODS

Total CABF was evaluated with extracranial Doppler, whereas structural T2-lesion volume (LV) and gray matter volume (GMV) were measured on 3T MRI. The cognitive performance was assessed by Symbol Digit Modalities Test (SDMT), Brief Visuospatial Memory Test-Revised (BVMT-R), and California Verbal Learning Test-Second Edition (CVLT-II). Analysis of covariance, partial correlation, and regression models were used to test the differences between study groups and cognition/CABF correlations. False discovery rate (FDR)-corrected (Benjamini-Hochberg) p-values (i.e. q-values) less than 0.05 were considered significant.

RESULTS

Association between lower total CABF and the lower cognitive performance was observed only in MS patients (r = 0.318, q < 0.001 and r = 0.244, q = 0.012 for SDMT and BVMT-R, respectively). Lower GMV, higher T2-LV, and CABF were significantly associated with poorer performance on the processing speed measure of SDMT (adjusted R² = 0.295, t-statistics = 2.538, standardized β = 0.203, and q = 0.020), but not with memory tests. Cognitively impaired MS patients had lower total CABF compared to cognitively preserved (884.5 vs 1020.2 mL/min, q = 0.008).

CONCLUSION

Cognitively impaired MS patients presented with lower total CABF. Altered CABF may be a result of reduced metabolic rate and might contribute to abnormal cognitive aging in MS.

Development of a cerebrovascular magnetic resonance imaging biomarker for cognitive aging

OBJECTIVE

Recent availability of amyloid and tau positron emission tomography (PET) has provided us with a unique opportunity to measure the association of systemic vascular health with brain health after accounting for the impact of Alzheimer disease (AD) pathologies. We wanted to quantify early cerebrovascular health-related magnetic resonance imaging brain measures (structure, perfusion, microstructural integrity) and evaluate their utility as a biomarker for cerebrovascular health.

METHODS

We used 2 independent samples (discovery, n = 390; validation, n = 1,035) of individuals, aged ≥ 60 years, along the cognitive continuum with imaging from the population-based sample of Mayo Clinic Study of Aging. We ascertained vascular health by summing up recently existing cardiovascular and metabolic conditions (CMC) from health care records (hypertension, hyperlipidemia, cardiac arrhythmias, coronary artery disease, congestive heart failure, diabetes mellitus, and stroke). Using multiple regression models, we quantified associations between CMC and brain health after accounting for age, sex, education/occupation, and AD burden (from amyloid and tau PET).

RESULTS

Systemic vascular health was associated with medial temporal lobe thinning, widespread cerebral hypoperfusion, and loss of microstructural integrity in several white matter tracts including the corpus callosum and fornix. Further investigations suggested that microstructural integrity of the genu of the corpus callosum was suitable for assessing prodromal cerebrovascular health, had similar distributions in the discovery and independent validation datasets, and predicted cognitive performance above and beyond amyloid deposition.

INTERPRETATION

Systemic vascular health has significant impact on brain structure and function. Quantifying prodromal cerebrovascular health-related brain measures that are independent of AD pathology-related changes has great utility for cognitive aging. Ann Neurol 2018;84:713-724.

Atrial fibrillation, antithrombotic treatment, and cognitive aging: A population-based study

Objective

To examine the association of atrial fibrillation (AF) with cognitive decline and dementia in old age, and to explore the cognitive benefit of antithrombotic treatment in patients with AF.

Methods

This population-based cohort study included 2,685 dementia-free participants from the Swedish National Study on Aging and Care in Kungsholmen, who were regularly examined from 2001–2004 to 2010–2013. AF was ascertained from clinical examination, ECG, and patient registry. Global cognitive function was assessed using the Mini-Mental State Examination. We followed the DSM-IV criteria for the diagnosis of dementia, the NINDS-AIREN (National Institute of Neurological Disorders and Stroke and Association Internationale pour la Recherché et l'Enseignement en Neurosciences) criteria for vascular dementia, and the NINCDS-ADRDA (National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association) criteria for Alzheimer disease. Data were analyzed using multiple linear mixed-effects and Cox regression models.

Results

We identified 243 participants (9.1%) with AF at baseline. During the 9-year follow-up period, 279 participants (11.4%) developed AF and 399 (14.9%) developed dementia. As a time-varying variable, AF was significantly associated with a faster annual Mini-Mental State Examination decline (β coefficient = −0.24, 95% confidence interval [CI]: −0.31 to −0.16) and an increased hazard ratio (HR) of all-cause dementia (HR = 1.40, 95% CI: 1.11–1.77) and vascular and mixed dementia (HR = 1.88, 95% CI: 1.09–3.23), but not Alzheimer disease (HR = 1.33, 95% CI: 0.92–1.94). Among people with either prevalent or incident AF, use of anticoagulant drugs, but not antiplatelet treatment, was associated with a 60% decreased risk of dementia (HR = 0.40, 95% CI: 0.18–0.92).

Conclusion

AF is associated with a faster global cognitive decline and an increased risk of dementia in older people. Use of anticoagulant drugs may reduce dementia risk in patients with AF.

"Exceptional brain aging" without Alzheimer's disease: triggers, accelerators, and the net sum game

Background

As human longevity increases and Alzheimer’s disease (AD) increasingly becomes a significant societal burden, finding pathways or protective factors that facilitate exceptional brain aging without AD pathophysiologies (ADP) will be critical. The goal of this viewpoint is two-fold: 1) to present evidence for “exceptional brain aging” without ADP; and 2) to bring together ideas and observations from the literature and present them as testable hypotheses for biomarker studies to discover protective factors for “exceptional brain aging” without ADP and AD dementia.

Discovering pathways to exceptional aging

There are three testable hypotheses. First, discovering and quantifying links between risk factor(s) and early ADP changes in midlife using longitudinal biomarker studies will be fundamental to understanding why the majority of individuals deviate from normal aging to the AD pathway. Second, a risk factor may have quantifiably greater impact as a trigger and/or accelerator on a specific component of the biomarker cascade (amyloid, tau, neurodegeneration). Finally, and most importantly, while each risk factor may have a different mechanism of action on AD biomarkers, “exceptional aging” and protection against AD dementia will come from “net sum” protection against all components of the biomarker cascade. The knowledge of the mechanism of action of risk factor(s) from hypotheses 1 and 2 will aid in better characterization of their effect on outcomes, identification of subpopulations that would benefit, and the timing at which the risk factor(s) would have the maximal impact. Additionally, hypothesis 3 highlights the importance of multifactorial or multi-domain approaches to “exceptional aging” as well as prevention of AD dementia.

Conclusion

While important strides have been made in identifying risk factors for AD dementia incidence, further efforts are needed to translate these into effective preventive strategies. Using biomarker studies for understanding the mechanism of action, effect size estimation, selection of appropriate end-points, and better subject recruitment based on subpopulation effects are fundamental for better design and success of prevention trials.

Age-dependent changes at the blood-brain barrier. A Comparative structural and functional study in young adult and middle aged rats

Decreased beta-amyloid clearance in Alzheimer's disease and increased blood-brain barrier permeability in aged subjects have been reported in several articles. However, morphological and functional characterization of blood-brain barrier and its membrane transporter activity have not been described in physiological aging yet. The aim of our study was to explore the structural changes in the brain microvessels and possible functional alterations of P-glycoprotein at the blood-brain barrier with aging. Our approach included MR imaging for anatomical orientation in middle aged rats, electronmicroscopy and immunohistochemistry to analyse the alterations at cellular level, dual or triple-probe microdialysis and SPECT to test P-glycoprotein functionality in young and middle aged rats. Our results indicate that the thickness of basal lamina increases, the number of tight junctions decreases and the size of astrocyte endfeet extends with advanced age. On the basis of microdialysis and SPECT results the P-gp function is reduced in old rats. With our multiparametric approach a complex regulation can be suggested which includes elements leading to increased permeability of blood-brain barrier by enhanced paracellular and transcellular transport, and factors working against it. To verify the role of P-gp pumps in brain aging further studies are warranted.

APOE genotype modifies the association between central arterial stiffening and cognition in older adults

Arterial stiffening is associated with cognitive impairment and prodromal Alzheimer's disease. This study tested the interaction between arterial stiffening and an Alzheimer's disease genetic risk factor (apolipoprotein E [APOE] genotype) on cognition among older adults. Vanderbilt Memory & Aging Project participants with normal cognition (n = 162, 72 ± 7 years, 29% APOE-ε4 carrier) and mild cognitive impairment (n = 121, 73 ± 8 years, 42% APOE-ε4 carrier) completed neuropsychological assessment and cardiac MRI to assess aortic stiffening using pulse wave velocity (PWV, m/s). Linear regression models stratified by cognitive diagnosis related aortic PWV × APOE-ε4 status to neuropsychological performances, adjusting for demographic and vascular risk factors. PWV × APOE-ε4 related to poorer performance on measures of lexical retrieval (β = -0.29, p = 0.01), executive function (β = -0.44, p = 0.02), and episodic memory (β = -3.07, p = 0.02). Among participants with higher aortic PWV, APOE-ε4 modified the association between central arterial stiffening and cognition, such that carriers had worse performances than noncarriers. Findings add to a growing body of evidence for APOE-vascular interactions on cognition in older adults and warrant further research into less heart-healthy cohorts where the association between PWV and cognition among older adults might be stronger.

Subclinical Compromise in Cardiac Strain Relates to Lower Cognitive Performances in Older Adults

BACKGROUND

Global longitudinal strain (GLS), reflecting total shortening of the myocardium during the cardiac cycle, has emerged as a more precise myocardial function measure than left ventricular ejection fraction (LVEF). Longitudinal strain may be selectively affected in subclinical heart disease, even in the presence of normal LVEF. This study examines subclinical cardiac dysfunction, assessed by GLS and LVEF, and cognition among older adults.

METHODS AND RESULTS

Vanderbilt Memory and Aging Project participants who were free of clinical dementia, stroke, and heart failure (n=318, 73±7 years, 58% male) completed neuropsychological assessment and cardiac magnetic resonance to quantify GLS and LVEF. Linear regression models related GLS and LVEF to neuropsychological performances, adjusting for age, sex, race/ethnicity, education, Framingham Stroke Risk Profile, cognitive diagnosis, and APOE*ε4 status. Models were repeated with a cardiac×cognitive diagnosis interaction term. Compromised GLS (reflected by higher values) related to worse naming (β=-0.07, P=0.04), visuospatial immediate recall (β=-0.83, P=0.03), visuospatial delayed recall (β=-0.22, P=0.03), and verbal delayed recall (β=-0.11, P=0.007). LVEF did not relate to worse performance on any measure (P>0.18). No diagnostic interactions were observed.

CONCLUSIONS

Our study results are among the first to suggest that compromised GLS relates to worse episodic memory and language performance among older adults who are free of clinical dementia, stroke, and heart failure. Subclinical cardiac dysfunction may correlate with cognitive health in late life, even when LVEF remains normal. The results add to growing evidence that GLS may be a more sensitive and preferred method for quantifying subclinical changes in cardiac function.