Longitudinal Changes in Cerebral Blood Flow in the Older Hypertensive Brain

Baseline Blood Pressure Was Associated with Hemispheric Cerebral Blood Flow in Acute Small Subcortical Infarcts

INTRODUCTION

While increased baseline blood pressure (BP) is a prevalent comorbidity in the acute phase of ischemic stroke, the association between baseline BP and the state of hemispheric perfusion in patients with acute small subcortical infarcts (SSIs) has not been studied in detail. The aim of this study was to investigate the relationship between baseline BP and hemispheric cerebral blood flow (CBF) in acute SSIs.

METHODS

This retrospective study included 101 patients with acute SSIs. Baseline hemispheric CBF was assessed through co-registration of baseline CT perfusion imaging and follow-up diffusion-weighted imaging. The association between baseline BP, CBF, and different cerebral small vessel disease (CSVD) biomarkers was assessed.

RESULTS

Baseline systolic BP (SBP) and diastolic BP (DBP) were negatively associated with contralateral hemispheric CBF after multivariate-adjusted linear analysis (SBP: β = -0.001, 95% CI: -0.002 to 0.000, p = 0.030; DBP: β = -0.002, 95% CI: -0.003∼0.001, p = 0.006). Among other CSVD biomarkers, the presence of any cerebral microbleeds showed a significant association with lower CBF in the contralateral hemisphere of the infarct lesion (r = -0.270, p = 0.035).

CONCLUSION

In patients with acute SSIs, increased baseline BP was associated with reduced CBF in the contralateral hemisphere of the infarct lesion, which probably could be interpreted by the exacerbation of the CSVD burden, suggesting a potential mechanistic link between BP autoregulation dysfunction and the aggravation of neurovascular impairment in SSIs.

The association of regional cerebral blood flow and glucose metabolism in normative ageing and insulin resistance

Rising rates of insulin resistance and an ageing population are set to exact an increasing toll on individuals and society. Here we examine the contribution of age and insulin resistance to the association of cerebral blood flow and glucose metabolism; both critical process in the supply of energy for the brain. Thirty-four younger (20-42 years) and 41 older (66-86 years) healthy adults underwent a simultaneous resting state MR/PET scan, including arterial spin labelling. Rates of cerebral blood flow and glucose metabolism were derived using a functional atlas of 100 brain regions. Older adults had lower cerebral blood flow than younger adults in 95 regions, reducing to 36 regions after controlling for cortical atrophy and blood pressure. Lower cerebral blood flow was also associated with worse working memory and slower reaction time in tasks requiring cognitive flexibility and response inhibition. Younger and older insulin sensitive adults showed small, negative correlations between relatively high rates of regional cerebral blood flow and glucose metabolism. This pattern was inverted in insulin resistant older adults, who showed hypoperfusion and hypometabolism across the cortex, and a positive correlation. In insulin resistant younger adults, the association showed inversion to positive correlations, although not to the extent seen in older adults. Our findings suggest that the normal course of ageing and insulin resistance alter the rates of and associations between cerebral blood flow and glucose metabolism. They underscore the criticality of insulin sensitivity to brain health across the adult lifespan.

Hypertension: Causes and Consequences of Circadian Rhythms in Blood Pressure

Hypertension is extremely common, affecting approximately 1 in every 2 adults globally. Chronic hypertension is the leading modifiable risk factor for cardiovascular disease and premature mortality worldwide. Despite considerable efforts to define mechanisms that underlie hypertension, a potentially major component of the disease, the role of circadian biology has been relatively overlooked in both preclinical models and humans. Although the presence of daily and circadian patterns has been observed from the level of the genome to the whole organism, the functional and structural impact of biological rhythms, including mechanisms such as circadian misalignment, remains relatively poorly defined. Here, we review the impact of daily rhythms and circadian systems in regulating blood pressure and the onset, progression, and consequences of hypertension. There is an emphasis on the impact of circadian biology in relation to vascular disease and end-organ effects that, individually or in combination, contribute to complex phenotypes such as cognitive decline and the loss of cardiac and brain health. Despite effective treatment options for some individuals, control of blood pressure remains inadequate in a substantial portion of the hypertensive population. Greater insight into circadian biology may form a foundation for novel and more widely effective molecular therapies or interventions to help in the prevention, treatment, and management of hypertension and its related pathophysiology.

Effects of a brief HIIT intervention on cognitive performance in older women

Cardiorespiratory fitness (CRF) mitigates age-related decline in cognition and brain volume. Little is known, however, about the effects of high-intensity interval training (HIIT) on cognitive aging and the relationship between HIIT, cognition, hippocampal subfield volumes, and cerebral oxygen extraction fraction (OEF). Older sedentary women participated in an 8-week HIIT intervention. We conducted cognitive assessments, fitness assessments (VO2max), MRI scans: asymmetric spin echo oxygen extraction fraction (ASE-OEF), high-resolution multiple image co-registration and averaging (HR-MICRA) imaging, and transcranial Doppler ultrasonography before and after the intervention. VO2max increased from baseline (M = 19.36, SD = 2.84) to follow-up (M = 23.25, SD = 3.61), Z =  - 2.93, p < .001, r = 0.63. Composite cognitive (Z =  - 2.05, p = 0.041), language (Z =  - 2.19, p = 0.028), and visuospatial memory (Z =  - 2.22, p = 0.026), z-scores increased significantly. Hippocampal subfield volumes CA1 and CA3 dentate gyrus and subiculum decreased non-significantly (all p > 0.05); whereas a significant decrease in CA2 (Z =  - 2.045, p = 0.041, r = 0.436) from baseline (M = 29.51; SD = 24.50) to follow-up (M = 24.50; SD = 13.38) was observed. Right hemisphere gray matter was correlated with language z-scores (p = 0.025; r = 0.679). The subiculum was correlated with attention (p = 0.047; r = 0.618) and verbal memory (p = 0.020; r = 0.700). The OEF and CBF were unchanged at follow-up (all p > .05). Although we observed cognitive improvements following 8 weeks of our HIIT intervention, they were not explained by hippocampal, OEF, or CBF changes.

Pulse pressure and APOE ε4 dose interact to affect cerebral blood flow in older adults without dementia

This study assessed whether the effect of vascular risk on cerebral blood flow (CBF) varies by gene dose of apolipoprotein (APOE) ε4 alleles. 144 older adults without dementia from the Alzheimer's Disease Neuroimaging Initiative underwent arterial spin labeling and T1-weighted MRI, APOE genotyping, fluorodeoxyglucose positron emission tomography (FDG-PET), lumbar puncture, and blood pressure (BP) assessment. Vascular risk was assessed using pulse pressure (systolic BP - diastolic BP). CBF was examined in six AD-vulnerable regions: entorhinal cortex, hippocampus, inferior temporal cortex, inferior parietal cortex, rostral middle frontal gyrus, and medial orbitofrontal cortex. Linear regressions tested the interaction between APOE ε4 dose and pulse pressure on CBF in each region, adjusting for age, sex, cognitive classification, antihypertensive medication use, FDG-PET, reference CBF region, and AD biomarker positivity. There was a significant interaction between pulse pressure and APOE ɛ4 dose on CBF in the entorhinal cortex, hippocampus, and inferior parietal cortex, such that higher pulse pressure was associated with lower CBF only among ε4 homozygous participants. These findings demonstrate that the association between pulse pressure and regional CBF differs by APOE ε4 dose, suggesting that targeting modifiable vascular risk factors may be particularly important for those genetically at risk for AD.

A novel 5-stage visual rating scale for global arterial spin labeling perfusion assessment in the brain: Simplifying evaluation for clinical implementation

Objectives

The aim of this study was to develop and validate a visual rating scale for evaluating global arterial spin labeling (ASL) perfusion changes in the brain, with potential applications in a variety of conditions that impact general brain blood supply and perfusion.

Methods

We employed a five-stage scale (0 being normal and 4 indicating the most severe perfusion decline) to assess 156 patients using a 3D pulsed ASL technique. Three radiologists independently reviewed the images, and inter-rater reliability of the visual rating scale was evaluated.

Results

The ASL stages showed a consistent distribution among the patients. The inter-rater reliability among the three radiologists, as measured by the Intraclass Correlation Coefficient (ICC), was 0.982.

Conclusion

Our findings suggest that this visual rating scale can be effectively implemented in everyday practice to evaluate global perfusion changes in the context of cardiovascular diseases, cerebrovascular diseases, cerebral small vessel disease, and other conditions that alter brain vascularization and perfusion. Further research is needed to explore the full range of clinical applications and to refine the scale for optimal utility.

The Clinical Relevance of Autonomic Dysfunction, Cerebral Hemodynamics, and Sleep Interactions in Individuals Living With SCI

A myriad of physiological impairments is seen in individuals after a spinal cord injury (SCI). These include altered autonomic function, cerebral hemodynamics, and sleep. These physiological systems are interconnected and likely insidiously interact leading to secondary complications. These impairments negatively influence quality of life. A comprehensive review of these systems, and their interplay, may improve clinical treatment and the rehabilitation plan of individuals living with SCI. Thus, these physiological measures should receive more clinical consideration. This special communication introduces the under investigated autonomic dysfunction, cerebral hemodynamics, and sleep disorders in people with SCI to stakeholders involved in SCI rehabilitation. We also discuss the linkage between autonomic dysfunction, cerebral hemodynamics, and sleep disorders and some secondary outcomes are discussed. Recent evidence is synthesized to make clinical recommendations on the assessment and potential management of important autonomic, cerebral hemodynamics, and sleep-related dysfunction in people with SCI. Finally, a few recommendations for clinicians and researchers are provided.

TAK1 Improves Cognitive Function via Suppressing RIPK1-Driven Neuronal Apoptosis and Necroptosis in Rats with Chronic Hypertension

Chronic hypertension is a major risk factor for cognitive impairment, which can promote neuroinflammation and neuronal loss in the central nervous system. Transforming growth factor β-activated kinase 1 (TAK1) is a key molecular component in determining cell fate and can be activated by inflammatory cytokines. This study aimed to investigate the role of TAK1 in mediating neuronal survival in the cerebral cortex and hippocampus under chronic hypertensive conditions. To that end, we used stroke-prone renovascular hypertension rats (RHRSP) as chronic hypertension models. Adeno-associated virus (AAV) designed to overexpress or knock down TAK1 expression were injected into the lateral ventricles of rats and the subsequent effects on cognitive function and neuronal survival under chronic hypertensive conditions were assessed. We found that, TAK1 knockdown in RHRSP markedly increased neuronal apoptosis and necroptosis and induced cognitive impairment, which could be reversed by Nec-1s, an inhibitor of receptor interacting protein kinase 1 (RIPK1). In contrast, overexpression of TAK1 in RHRSP significantly suppressed neuronal apoptosis and necroptosis and improved cognitive function. Further knockdown of TAK1 in sham-operated rats received similar phenotype with RHRSP. The results have been verified in vitro. In this study, we provide in vivo and in vitro evidence that TAK1 improves cognitive function by suppressing RIPK1-driven neuronal apoptosis and necroptosis in rats with chronic hypertension.

Imbalance of thalamic metabolites in an experimental model of hypertension: role of bergamot polyphenols

Cerebral metabolites are associated with different physiological and pathological processes in brain tissue. Among them, the concentrations of N-acetylaspartate (NAA) and choline-containing compounds (Cho) in the thalamic region are recognized and analyzed as important predictive markers of brain impairment. The relationship among hypertension, modulation of brain metabolite levels and cerebral diseases is of recent investigation, leaving many unanswered questions regarding the origin and consequences of the metabolic damage caused in grey and white matter during hypertension. Here we provide evidence for the influence of hypertension on NAA and Cho ratios in hypertensive rat thalamus and how the use of natural occurring compounds ameliorates the balance of thalamic metabolites.

Hippocampal connectivity and memory decline in cognitively intact APOE ε4 carriers

INTRODUCTION

Resting-state functional magnetic resonance imaging (fMRI) graph theory may help detect subtle functional connectivity changes affecting memory prior to impairment.

METHODS

Cognitively normal apolipoprotein E (APOE) ε4 carriers/noncarriers underwent longitudinal cognitive assessment and one-time MRI. The relationship of left/right hippocampal connectivity and memory trajectory were compared between carriers/noncarriers.

RESULTS

Steepness of verbal memory decline correlated with decreased connectivity in the left hippocampus, only among APOE ε4 carriers. Right hippocampal metrics were not correlated with memory and there were no significant correlations in the noncarriers. Verbal memory decline correlated with left hippocampal volume loss for both carriers and noncarriers, with no other significant volumetric findings.

DISCUSSION

Findings support early hippocampal dysfunction in intact carriers, the AD disconnection hypothesis, and left hippocampal dysfunction earlier than the right. Combining lateralized graph theoretical metrics with a sensitive measure of memory trajectory allowed for detection of early-stage changes in APOE ε4 carriers before symptoms of mild cognitive impairment are present.

HIGHLIGHTS

Graph theory connectivity detects preclinical hippocampal changes in APOE ε4 carriers. The AD disconnection hypothesis was supported in unimpaired APOE ε4 carriers. Hippocampal dysfunction starts asymmetrically on the left.

Hypertensive Adults Exhibit Lower Myelin Content: A Multicomponent Relaxometry and Diffusion Magnetic Resonance Imaging Study

BACKGROUND

It is unknown whether hypertension plays any role in cerebral myelination. To fill this knowledge gap, we studied 90 cognitively unimpaired adults, age range 40 to 94 years, who are participants in the Baltimore Longitudinal Study of Aging and the Genetic and Epigenetic Signatures of Translational Aging Laboratory Testing to look for potential associations between hypertension and cerebral myelin content across 14 white matter brain regions.

METHODS

Myelin content was probed using our advanced multicomponent magnetic resonance relaxometry method of myelin water fraction, a direct and specific magnetic resonance imaging measure of myelin content, and longitudinal and transverse relaxation rates (R1 and R2), 2 highly sensitive magnetic resonance imaging metrics of myelin content. We also applied diffusion tensor imaging magnetic resonance imaging to measure fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity values, which are metrics of cerebral microstructural tissue integrity, to provide context with previous magnetic resonance imaging findings.

RESULTS

After adjustment of age, sex, systolic blood pressure, smoking status, diabetes status, and cholesterol level, our results indicated that participants with hypertension exhibited lower myelin water fraction, fractional anisotropy, R1 and R2 values and higher mean diffusivity, radial diffusivity, and axial diffusivity values, indicating lower myelin content and higher impairment to the brain microstructure. These associations were significant across several white matter regions, particularly in the corpus callosum, fronto-occipital fasciculus, temporal lobes, internal capsules, and corona radiata.

CONCLUSIONS

These original findings suggest a direct association between myelin content and hypertension and form the basis for further investigations including longitudinal assessments of this relationship.

Ambient RNAs removal of cortex-specific snRNA-seq reveals Apoe+ microglia/macrophage after deeper cerebral hypoperfusion in mice

BACKGROUND

Ambient RNAs contamination in single-nuclei RNA sequencing (snRNA-seq) is a challenging problem, but the consequences of ambient RNAs contamination of damaged and/or diseased tissues are poorly understood. Cognitive impairments and white/gray matter injuries are characteristic of deeper cerebral hypoperfusion mouse models induced by bilateral carotid artery stenosis (BCAS), but the molecular mechanisms still need to be further explored. More importantly, the BCAS mice can also offer an excellent model to examine the signatures of ambient RNAs contamination in damaged tissues when performing snRNA-seq.

METHODS

After the sham and BCAS mice were established, cortex-specific single-nuclei libraries were constructed. Single-nuclei transcriptomes were described informatically by the R package Seurat, and ambient RNA markers of were identified in each library. Then, after removing ambient RNAs in each sample using the in silico approaches, the combination of CellBender and subcluster cleaning, single-nuclei transcriptomes were reconstructed. Next, the comparison of ambient RNA contamination was performed using irGSEA analysis before and after the in silico approaches. Finally, further bioinformatic analyses were performed.

RESULTS

The ambient RNAs are more predominant in the BCAS group than the sham group. The contamination mainly originated from damaged neuronal nuclei, but could be reduced largely using the in silico approaches. The integrative analysis of cortex-specific snRNA-seq data and the published bulk transcriptome revealed that microglia and other immune cells were the primary effectors. In the sequential microglia/immune subgroups analysis, the subgroup of Apoe⁺ MG/Mac (microglia/macrophages) was identified. Interestingly, this subgroup mainly participated in the pathways of lipid metabolism, associated with the phagocytosis of cell debris.

CONCLUSIONS

Taken together, our current study unravels the features of ambient RNAs in snRNA-seq datasets under diseased conditions, and the in silico approaches can effectively eliminate the incorrected cell annotation and following misleading analysis. In the future, snRNA-seq data analysis should be carefully revisited, and ambient RNAs removal needs to be taken into consideration, especially for those diseased tissues. To our best knowledge, our study also offers the first cortex-specific snRNA-seq data of deeper cerebral hypoperfusion, which provides with novel therapeutic targets.

The effects of a moderate physical activity intervention on physical fitness and cognition in healthy elderly with low levels of physical activity: a randomized controlled trial

BACKGROUND

Increasing physical activity is one of the most promising and challenging interventions to delay or prevent cognitive decline and dementia.

METHODS

We conducted a randomized controlled trial to assess the effects of a physical activity intervention, aimed at increasing step count, in elderly with low levels of physical activity on measures of strength, balance, aerobic capacity, and cognition. Participants were assigned to 9 months of exercise counseling or active control.

RESULTS

The intention-to-treat analyses show that the intervention, compared to control, increases the level of physical activity, but has no significant effect on physical fitness and cognition. Those who increased their physical activity with 35% or more show significant improvements in aerobic capacity, gait speed, verbal memory, executive functioning, and global cognition, compared to those who did not achieve a 35% increase.

LIMITATIONS

The number of participants that achieved the intended improvement was lower than expected.

CONCLUSION

Responder analyses suggest an improvement of physical fitness and cognition in those who achieved an increase in physical activity of at least 35%.

TRIAL REGISTRATION

The trial protocol is registered at the Dutch Trial Register NL5675, August 1, 2016.

Hypertension, Neurovascular Dysfunction, and Cognitive Impairment

Hypertension affects a significant proportion of the adult and aging population and represents an important risk factor for vascular cognitive impairment and late-life dementia. Chronic high blood pressure continuously challenges the structural and functional integrity of the cerebral vasculature, leading to microvascular rarefaction and dysfunction, and neurovascular uncoupling that typically impairs cerebral blood supply. Hypertension disrupts blood-brain barrier integrity, promotes neuroinflammation, and may contribute to amyloid deposition and Alzheimer pathology. The mechanisms underlying these harmful effects are still a focus of investigation, but studies in animal models have provided significant molecular and cellular mechanistic insights. Remaining questions relate to whether adequate treatment of hypertension may prevent deterioration of cognitive function, the threshold for blood pressure treatment, and the most effective antihypertensive drugs. Recent advances in neurovascular biology, advanced brain imaging, and detection of subtle behavioral phenotypes have begun to provide insights into these critical issues. Importantly, a parallel analysis of these parameters in animal models and humans is feasible, making it possible to foster translational advancements. In this review, we provide a critical evaluation of the evidence available in experimental models and humans to examine the progress made and identify remaining gaps in knowledge.

Investigating changes in blood-cerebrospinal fluid barrier function in a rat model of chronic hypertension using non-invasive magnetic resonance imaging

Chronic hypertension is a major risk factor for the development of neurodegenerative disease, yet the etiology of hypertension-driven neurodegeneration remains poorly understood. Forming a unique interface between the systemic circulation and the brain, the blood-cerebrospinal fluid barrier (BCSFB) at the choroid plexus (CP) has been proposed as a key site of vulnerability to hypertension that may initiate downstream neurodegenerative processes. However, our ability to understand BCSFB's role in pathological processes has, to date, been restricted by a lack of non-invasive functional measurement techniques. In this work, we apply a novel Blood-Cerebrospinal Fluid Barrier Arterial Spin Labeling (BCSFB-ASL) Magnetic resonance imaging (MRI) approach with the aim of detecting possible derangement of BCSFB function in the Spontaneous Hypertensive Rat (SHR) model using a non-invasive, translational technique. SHRs displayed a 36% reduction in BCSFB-mediated labeled arterial water delivery into ventricular cerebrospinal fluid (CSF), relative to normotensive controls, indicative of down-regulated choroid plexus function. This was concomitant with additional changes in brain fluid biomarkers, namely ventriculomegaly and changes in CSF composition, as measured by T1 lengthening. However, cortical cerebral blood flow (CBF) measurements, an imaging biomarker of cerebrovascular health, revealed no measurable change between the groups. Here, we provide the first demonstration of BCSFB-ASL in the rat brain, enabling non-invasive assessment of BCSFB function in healthy and hypertensive rats. Our data highlights the potential for BCSFB-ASL to serve as a sensitive early biomarker for hypertension-driven neurodegeneration, in addition to investigating the mechanisms relating hypertension to neurodegenerative outcomes.

Sex-specific longitudinal association between baseline physical activity level and cognitive decline in Chinese over 45 years old: Evidence from the China health and retirement longitudinal study

OBJECTIVES

To examine whether sex-specific associations between baseline PA level and follow up cognitive performance in Chinese subjects exist from the China Health and Retirement Longitudinal study (CHARLS).

METHOD

A total of 3395 adults aged 45 or old from the CHARLS were used for analysis. The combined scores of measurements of mental status and verbal episodic memory were utilized for assessing cognitive function at baseline in 2011 and the follow-up survey in 2015. Baseline PA level was quantified as the total PA score. Multiple linear regression and logistic regression models were used to examine the association between baseline PA status and global cognitive function and cognitive domains.

RESULTS

In the female subjects (n = 1748), compared with individuals of PA level in the lower tertile, those grouped into the upper tertile had the lowest risk of global cognitive decline [odds ratio (OR) =0.273, 95% confidence interval (CI) =0.077-0.960; p = 0.043] and verbal episodic memory decline [OR)=0.257, 95% CI =0.066-1.003; p = 0.051] from 2011 to 2015. However, no significant associations were observed in the male subjects (n = 1647).

CONCLUSION

In the female subjects, higher PA level was associated with reduced risk of cognitive decline within 4 years, this might be associated with reduced decline of verbal episodic memory. Our findings confirmed that female sex would positively affect the association between PA levels and cognitive decline.

The effect of endovascular baroreflex amplification on central sympathetic nerve circuits and cerebral blood flow in patients with resistant hypertension: A functional MRI study

BACKGROUND

Endovascular baroreflex amplification (EVBA) by implantation of the MobiusHD is hypothesized to lower blood pressure by decreasing sympathetic activity through the mechanism of the baroreflex. In the present exploratory study we investigated the impact of MobiusHD implantation on central sympathetic nerve circuits and cerebral blood flow (CBF) in patients with resistant hypertension.

MATERIALS AND METHODS

In thirteen patients, we performed blood oxygenation level-dependent functional magnetic resonance imaging (BOLD fMRI) at rest and during Valsalva maneuvers, before and 3 months after EVBA. Data were analyzed using a whole-brain approach and a brainstem-specific analysis. CBF was assessed using arterial spin labeling MRI.

RESULTS

Resting-state fMRI analysis did not reveal significant differences in functional connectivity at 3 months after EVBA. For the Valsalva maneuver data, the whole-brain fMRI analysis revealed significantly increased activation in the posterior and anterior cingulate, the insular cortex, the precuneus, the left thalamus and the anterior cerebellum. The brainstem-specific fMRI analysis showed a significant increase in BOLD activity in the right midbrain 3 months after EVBA. Mean gray matter CBF (partial volume corrected) decreased significantly from 48.9 (9.9) ml/100 gr/min at baseline to 43.4 (13.0) ml/100 gr/min (p = 0.02) at 3 months.

CONCLUSIONS

This first fMRI pilot study in patients with resistant hypertension treated with EVBA showed a significant increase in BOLD activity during the Valsalva maneuver in brain regions related to sympathetic activity. No notable signal intensity changes were observed in brain areas involved in the baroreflex circuit. Future randomized controlled studies are needed to investigate whether the observed changes are directly caused by EVBA.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov, identifier: NCT02827032.

Deeper cerebral hypoperfusion leads to spatial cognitive impairment in mice

BACKGROUND

Vascular cognitive impairment (VCI) is the second-leading cause of dementia worldwide, which is caused by cerebrovascular diseases or relevant risk factors. However, there are no appropriate animal models, which can be used to study changes of neuropathology in the human VCI. To better understand the development of VCI, we modified three mouse models of chronical vascular diseases, and further compared the advantage and disadvantage of these models. We hope to establish a more suitable mouse model mimicking VCI in human beings.

METHODS

Adult male C57/BL6 mice (n=98) were used and animals underwent transient bilateral common carotid arteries occlusion (tBCCAO), or bilateral common carotid artery stenosis (BCAS), or right unilateral common carotid artery occlusion, respectively. Haemodynamic changes of surface cerebral blood flow (CBF) were examined up to 4 weeks. Spatial cognitive impairment was evaluated to determine the consequence of chronic cerebral ischaemia.

RESULTS

These mouse models showed different extents of CBF reduction and spatial reference memory impairment from 1 week up to 4 weeks postoperation compared with the control group (p<0.05). We found that (1) bilaterally ligation of common carotid artery caused decrease of 90% CBF in C57/BL6 mice (p<0.05) and caused acute instead of prolonged impairment of spatial reference memory (p<0.05); (2) unilateral ligation of common carotid artery did not cause severe ipsilateral ischaemia as seen in the tBCCAO mice and caused minor but significant spatial reference memory disturbance (p<0.05); and (3) 20% decrease in the bilateral CBF did not cause spatial reference memory impairment 4 weeks postoperation (p>0.05), while 30% decrease in bilateral or unilateral CBF led to significant memory disturbance in mice (p<0.05).

CONCLUSION

We demonstrated that BCAS using 0.16/0.18 mm microcoils is an alternative VCI mouse model when studying the mechanism and developing therapy of VCI.

Mediation of the APOE Associations With Cognition Through Cerebral Blood Flow: The CIBL Study

Background

The ε4 allele of the apolipoprotein E (APOE) gene is a strong genetic risk factor for aging-related cognitive decline. However, the causal connection between ε4 alleles and cognition is not well understood. The objective of this study was to identify the roles of cerebral blood flow (CBF) in cognitive-related brain areas in mediating the associations of APOE with cognition.

Methods

The multiple linear regression analyses were conducted on 369 subjects (mean age of 68.8 years; 62.9% of women; 29.3% of APOE ε4 allele carriers). Causal mediation analyses with 5,000 bootstrapped iterations were conducted to explore the mediation effects.

Result

APOE ε4 allele was negatively associated with cognition (P < 0.05) and CBF in the amygdala, hippocampus, middle temporal gyrus, posterior cingulate, and precuneus (all P < 0.05). The effect of the APOE genotype on cognition was partly mediated by the above CBF (all P < 0.05).

Conclusion

CBF partially mediates the potential links between APOE genotype and cognition. Overall, the APOE ε4 allele may lead to a dysregulation of the vascular structure and function with reduced cerebral perfusion, which in turn leads to cognitive impairment.

Association of blood pressure with brain structure in youth with and without bipolar disorder

BACKGROUND

We previously found that blood pressure (BP) is elevated, and associated with poorer neurocognition, in youth with bipolar disorder (BD). While higher BP is associated with smaller brain structure in adults, studies have not examined this topic in BD or youth.

METHODS

Participants were 154 youth, ages 13-20 (n = 81 BD, n = 73 HC). Structural magnetic resonance imaging and diastolic (DBP), and systolic (SBP) pressure were obtained. Region of interest (ROI; anterior cingulate cortex [ACC], insular cortex, hippocampus) and vertex-wise analyses controlling for age, sex, body-mass-index, and intracranial volume investigated BP-neurostructural associations; a group-by-BP interaction was also assessed.

RESULTS

In ROI analyses, higher DBP in the overall sample was associated with smaller insular cortex area (β=-0.18 p = 0.007) and was associated with smaller ACC area to a significantly greater extent in HC vs. BD (β=-0.14 p = 0.015). In vertex-wise analyses, higher DBP and SBP were associated with smaller area and volume in the insular cortex, frontal, parietal, and temporal regions in the overall sample. Additionally, higher SBP was associated with greater thickness in temporal and parietal regions. Finally, higher SBP was associated with smaller area and volume in frontal, parietal, and temporal regions to a significantly greater extent in BD vs. HC.

LIMITATIONS

Cross-sectional design, single assessment of BP.

CONCLUSION

BP is associated with brain structure in youth, with variability related to structural phenotype (volume vs. thickness) and psychiatric diagnosis (BD vs. HC). Future studies evaluating temporality of these findings, and the association of BP changes on brain structure in youth, are warranted.

Tracer kinetic assessment of blood-brain barrier leakage and blood volume in cerebral small vessel disease: Associations with disease burden and vascular risk factors

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Permeability surface area (PS) was higher, even in normal appearing tissue.

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PS was higher in patients with more white matter hyperintensities.

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Tissue damage affecting vascular surface area may affect how we interpret tracer kinetic results.

Subtle blood–brain barrier (BBB) permeability increases have been shown in small vessel disease (SVD) using various analysis methods. Following recent consensus recommendations, we used Patlak tracer kinetic analysis, considered optimal in low permeability states, to quantify permeability-surface area product (PS), a BBB leakage estimate, and blood plasma volume (v_P) in 201 patients with SVD who underwent dynamic contrast-enhanced MRI scans. We ran multivariable regression models with a quantitative or qualitative metric of white matter hyperintensity (WMH) severity, demographic and vascular risk factors. PS increased with WMH severity in grey (B = 0.15, Confidence Interval (CI): [0.001,0.299], p = 0.049) and normal-appearing white matter (B = 0.015, CI: [−0.008,0.308], p = 0.062). Patients with more severe WMH had lower v_P in WMH (B = -0.088, CI: [−0.138,-0.039], p < 0.001), but higher v_P in normal-appearing white matter (B = 0.031, CI: [−0.004,0.065], p = 0.082). PS and v_P were lower at older ages in WMH, grey and white matter. We conclude higher PS in normal-appearing tissue with more severe WMH suggests impaired BBB integrity beyond visible lesions indicating that the microvasculature is compromised in normal-appearing white matter and WMH. BBB dysfunction is an important mechanism in SVD, but associations with clinical variables are complex and underlying damage affecting vascular surface area may alter interpretation of tracer kinetic results.

Capillary function progressively deteriorates in prodromal Alzheimer's disease: A longitudinal MRI perfusion study

Cardiovascular risk factors are associated with the development of Alzheimer's disease (AD), and increasing evidence suggests that cerebral microvascular dysfunction plays a vital role in the disease progression. Using magnetic resonance imaging, we investigated the two-year changes of the cerebral microvascular blood flow in 11 mild cognitively impaired (MCI) patients with prodromal AD compared to 12 MCI patients without evidence of AD and 10 cognitively intact age-matched controls. The pAD-MCI patients displayed widespread deterioration in microvascular cerebral perfusion associated with capillary dysfunction. No such changes were observed in the other two groups, suggesting that the dysfunction in capillary perfusion is linked to the AD pathophysiology. The observed capillary dysfunction may limit local oxygenation in AD leading to downstream β-amyloid aggregation, tau hyperphosphorylation, neuroinflammation and neuronal dysfunction. The findings are in agreement with the capillary dysfunction hypothesis of AD, suggesting that increasing heterogeneity of capillary blood flow is a primary pathological event in AD.

Changes in cerebral arterial pulsatility and hippocampal volume: a transcranial doppler ultrasonography study

The physiological mechanisms of age-related cognitive decline remain unclear, in no small part due to the lack of longitudinal studies. Extant longitudinal studies focused on gross neuroanatomy and diffusion properties of the brain. We present herein a longitudinal analysis of changes in arterial pulsatility - a proxy for arterial stiffness - in two major cerebral arteries, middle cerebral and vertebral. We found that pulsatility increased in some participants over a relatively short period and these increases were associated with hippocampal shrinkage. Higher baseline pulsatility was associated with lower scores on a test of fluid intelligence at follow-up. This is the first longitudinal evidence of an association between increase in cerebral arterial stiffness over time and regional shrinkage.

Impact of sex and APOE ε4 on age-related cerebral perfusion trajectories in cognitively asymptomatic middle-aged and older adults: A longitudinal study

Cerebral hypoperfusion is thought to contribute to cognitive decline in Alzheimer's disease, but the natural trajectory of cerebral perfusion in cognitively healthy adults has not been well-studied. This longitudinal study is consisted of 950 participants (40-89 years), who were cognitively unimpaired at their first visit. We investigated the age-related changes in cerebral perfusion, and their associations with APOE-genotype, biological sex, and cardiometabolic measurements. During the follow-up period (range 0.13-8.24 years), increasing age was significantly associated with decreasing cerebral perfusion, in total gray-matter (β=-1.43), hippocampus (-1.25), superior frontal gyrus (-1.70), middle frontal gyrus (-1.99), posterior cingulate (-2.46), and precuneus (-2.14), with all P-values < 0.01. Compared with male-ɛ4 carriers, female-ɛ4 carriers showed a faster decline in global and regional cerebral perfusion with increasing age, whereas the age-related decline in cerebral perfusion was similar between male- and female-ɛ4 non-carriers. Worse cardiometabolic profile (i.e., increased blood pressure, body mass index, total cholesterol, and blood glucose) was associated with lower cerebral perfusion at all the visits. When time-varying cardiometabolic measurements were adjusted in the model, the synergistic effect of sex and APOE-ɛ4 on age-related cerebral perfusion-trajectories became largely attenuated. Our findings demonstrate that APOE-genotype and sex interactively impact cerebral perfusion-trajectories in mid- to late-life. This effect may be partially explained by cardiometabolic alterations.

Hemodynamic and structural brain measures in high and low sedentary older adults

Due to its cardiovascular effects sedentary behaviour might impact cerebrovascular function in the long term, affecting cerebrovascular regulatory mechanisms and perfusion levels. Consequently this could underly potential structural brain abnormalities associated with cognitive decline. We therefore assessed the association between sedentary behaviour and brain measures of cerebrovascular perfusion and structural abnormalities in community-dwelling older adults. Using accelerometery (GENEActiv) data from The Irish Longitudinal Study on Ageing (TILDA) we categorised individuals by low- and high-sedentary behaviour (≤8 vs >8 hours/day). We examined prefrontal haemoglobin oxygenation levels using Near-Infrared Spectroscopy during rest and after an orthostatic challenge in 718 individuals (66 ± 8 years, 52% female). Global grey matter cerebral blood flow, total grey and white matter volume, total and subfield hippocampal volumes, cortical thickness, and white matter hyperintensities were measured using arterial spin labelling, T1, and FLAIR MRI in 86 individuals (72 ± 6 years, 55% female). While no differences in prefrontal or global cerebral hemodynamics were found between groups, high-sedentary individuals showed lower hippocampal volumes and increased white matter hyperintensities compared to their low-sedentary counterparts. Since these structural cerebral abnormalities are associated with cognitive decline and Alzheimer's disease, future work exploring the causal pathways underlying these differences is needed.

Age-specific cerebral haemodynamic effects of early blood pressure lowering after transient ischaemic attack and non-disabling stroke

INTRODUCTION

There is limited knowledge of the effects of blood pressure (BP) lowering on cerebral haemodynamics after transient ischaemic attack (TIA) and non-disabling stroke, particularly at older ages. We aimed to evaluate changes in transcranial Doppler (TCD) haemodynamic indices in patients undergoing early blood pressure lowering after TIA/non-disabling stroke, irrespective of age.

PATIENTS AND METHODS

Among consecutive eligible patients attending a rapid-access clinic with suspected TIA/non-disabling stroke and no evidence of extra/intracranial stenosis, hypertensive ones underwent intensive BP-lowering guided by daily home telemetric blood pressure monitoring (HBPM). Clinic-based BP, HBPM, End-tidal CO2 and bilateral middle cerebral artery (MCA) velocity on TCD were compared in the acute setting versus one-month follow-up; changes were stratified by baseline hypertension (clinic-BP≥140/90) and by age (<65, 65-79 and ≥80).

RESULTS

In 697 patients with repeated TCD measures, mean/SD baseline systolic-BP (145.0/21.3 mmHg) was reduced by an average of 11.3/19.9 mmHg (p < 0.0001) at one-month (133.7/17.4 mmHg), driven by patients hypertensive at baseline (systolic-BP change = -19.0/19.2 mmHg, p < 0.001; vs -0.5/15.4, p = 0.62 in normotensives). Compared with baseline, a significant change was observed at one-month only in mean/SD MCA end diastolic velocity (EDV) (0.77/7.26 cm/s, p = 0.005) and in resistance index (RI) (-0.005/0.051, p = 0.016), driven by hypertensive patients (mean/SD EDV change: 1.145/6.96 cm/s p = 0.001, RI change -0.007/0.06, p = 0.014). Findings were similar at all ages (EDV change - ptrend=0.357; RI change - ptrend=0.225), including 117 patients aged ≥80. EDV and RI changes were largest in 100 patients with clinic systolic-BP decrease ≥30 mmHg (mean/SD EDV change = 2.49/7.47 cm/s, p = 0.001; RI change -0.024/0.063, p < 0.0001).

CONCLUSION

There was no evidence of worsening of TCD haemodynamic indices associated with BP-lowering soon after TIA/non-disabling stroke, irrespective of age and degree of BP reduction. In fact, EDV increase and RI decrease observed after treatment of hypertensive patients suggest a decrease in distal vascular resistance.

Disease Burden Affects Aging Brain Function

BACKGROUND

Most older adults live with multiple chronic disease conditions, yet the effect of multiple diseases on brain function remains unclear.

METHODS

We examine the relationship between disease multimorbidity and brain activity using regional cerebral blood flow (rCBF) 15O-water PET scans from 97 cognitively normal participants (mean baseline age 76.5) in the Baltimore Longitudinal Study of Aging (BLSA). Multimorbidity index scores, generated from the presence of 13 health conditions, were correlated with PET data at baseline and in longitudinal change (n=74) over 5.05 (2.74 SD) years.

RESULTS

At baseline, voxel-based analysis showed that higher multimorbidity scores were associated with lower relative activity in orbitofrontal, superior frontal, temporal pole and parahippocampal regions, and greater activity in lateral temporal, occipital and cerebellar regions. Examination of the individual health conditions comprising the index score showed hypertension and chronic kidney disease individually contributed to the overall multimorbidity pattern of altered activity. Longitudinally, both increases and decreases in activity were seen in relation to increasing multimorbidity over time. These associations were identified in orbitofrontal, lateral temporal, brainstem, and cerebellar areas.

CONCLUSION

Together, these results show that greater multimorbidity is associated with widespread areas of altered brain activity, supporting a link between health and changes in aging brain function.

Development of a protocol to assess within-subject, regional white matter hyperintensity changes in aging and dementia

BACKGROUND

White matter hyperintensities (WMH), associated with both dementia risk and progression, can individually progress, remain stable, or even regress influencing cognitive decline related to specific cerebrovascular-risks. This study details the development and validation of a registration protocol to assess regional, within-subject, longitudinal WMH changes (ΔWMH) that is currently lacking in the field.

NEW METHOD

3D-FLAIR images (baseline and one-year-visit) were used for protocol development and validation. The method was validated by assessing the correlation between forward and reverse longitudinal registration, and between summated regional progression-regression volumes and Global ΔWMH. The clinical relevance of growth-regression ΔWMH were explored in relation to an executive function test.

RESULTS

MRI scans for 79 participants (73.5 ± 8.8 years) were used in this study. Global ΔWMH vs. summated regional progression-regression volumes were highly associated (r2 = 0.90; p-value < 0.001). Bi-directional registration validated the registration method (r2 = 0.999; p-value < 0.001). Growth and regression, but not overall ΔWMH, were associated with one-year declines in performance on Trial-Making-Test-B.

COMPARISON WITH EXISTING METHOD(S)

This method presents a unique registration protocol for maximum tissue alignment, demonstrating three distinct patterns of longitudinal within-subject ΔWMH (stable, growth and regression).

CONCLUSIONS

These data detail the development and validation of a registration protocol for use in assessing within-subject, voxel-level alterations in WMH volume. The methods developed for registration and intensity correction of longitudinal within-subject FLAIR images allow regional and within-lesion characterization of longitudinal ΔWMH. Assessing the impact of associated cerebrovascular-risks and longitudinal clinical changes in relation to dynamic regional ΔWMH is needed in future studies.

Urinary sodium and potassium excretion and cerebrovascular health: a multimodal imaging study

PURPOSE

Dietary sodium and potassium intake are associated with stroke, but the potential mechanisms are unclear. We aimed to study the association between sodium and potassium intake and subclinical cerebrovascular health in hypertensive older males using multimodal magnetic resonance imaging.

METHODS

A total of 189 hypertensive male subjects without previous cardiovascular or cerebrovascular disease were included. Daily urinary sodium and potassium excretion were estimated from a fasting spot urine sample using a formula approach. A dedicated cerebrovascular health imaging protocol including vessel wall imaging, angiography, arterial spin labeling imaging and T2-weighted fluid-attenuated inversion recovery imaging was performed to study intracranial atherosclerosis, vascular rarefaction (defined as fewer discernible vessels on angiography), brain perfusion and small vessel disease, respectively.

RESULTS

The mean age was 64.9 (± 7.2) years. The average daily urinary and potassium excretion was 4.7 (± 1.4) g/L and 2.1 (± 0.5) g/L, respectively. Increased urinary sodium excretion was associated with decreased cerebral blood flow and elevated urinary potassium excretion was associated with reduced prevalence of intracranial plaque. The associations remained significant after adjusting for covariates, even including blood pressure control. Quadratic regression analysis indicated a marginally significant U-shaped association between urinary sodium intake and white matter hyperintensity, which lost significance in fully adjusted models. No significant association of urinary sodium and potassium excretion with other cerebrovascular health measures was noted.

CONCLUSION

We concluded that in hypertensive older males without overt cardiovascular disease, increased sodium intake and reduced potassium intake are associated with impaired subclinical cerebrovascular health.

Association of Cardiovascular Risk Factors with Cerebral Perfusion in Whites and African Americans

BACKGROUND

Midlife cardiovascular risk factors increase risk for Alzheimer's disease (AD). Despite disproportionately high cardiovascular disease and dementia rates, African Americans are under-represented in studies of AD risk and research-based guidance on targeting vascular risk factors is lacking.

OBJECTIVE

This study investigated relationships between specific cardiovascular risk factors and cerebral perfusion in White and African American adults enriched for AD risk.

METHODS

Participants included 397 cognitively unimpaired White (n = 330) and African American (n = 67) adults enrolled in the Wisconsin Alzheimer's Disease Research Center who underwent pseudo-continuous arterial spin labeling MRI. Multiple linear regression models examined independent relationships between cardiovascular risk factors and mean cerebral perfusion. Subsequent interaction and stratified models assessed the role for APOE genotype and race.

RESULTS

When risk factor p-values were FDR-adjusted, diastolic blood pressure was significantly associated with mean perfusion. Tobacco use, triglycerides, waist-to-hip ratio, and a composite risk score were not associated with perfusion. Without FDR adjustment, a relationship was also observed between perfusion and obesity, cholesterol, and fasting glucose. Neither APOE genotype nor race moderated relationships between risk factors and perfusion.

CONCLUSION

Higher diastolic blood pressure predicted lower perfusion more strongly than other cardiovascular risk factors. This relationship did not vary by racial group or genetic risk for AD, although the African American sample had greater vascular risk burden and lower perfusion rates. Our findings highlight the need to prioritize inclusion of underrepresented groups in neuroimaging studies and to continue exploring the link between modifiable risk factors, cerebrovascular health, and AD risk in underrepresented populations.

Effect of anesthesia induction on cerebral tissue oxygen saturation in hypertensive patients: an observational study

OBJECTIVE

In hypertensive patients, the autoregulation curve shifts rightward, making these patients more sensitive than normotensive individuals to hypotension. Hypotension following the induction of anesthesia has been studied in normotensive patients to determine its effects on brain tissue oxygenation, but not enough studies have examined the effect of hypotension on brain oxygenation in hypertensive patients. The current study aimed to use near-infrared spectroscopy to evaluate brain tissue oxygen saturation after the induction of anesthesia in hypertensive patients, who may have impaired brain tissue oxygen saturation.

METHODS

The study included a total of 200 patients aged > 18 years old with ASA I-III. Measurements were taken while the patient was breathing room air, after the induction of anesthesia, when the lash reflex had disappeared following the induction of anesthesia, after intubation, and in the 5th, 10th, and 15th minutes of surgery. The patients were divided into nonhypertensive and hypertensive groups.

RESULTS

There was a significant difference in age between the groups (p = 0.000). No correlation was found between cerebral tissue oxygen saturation and age (r = 0.015, p = 0.596). Anesthesia induction was observed to decrease mean arterial blood pressure in both groups (p = 0.000). Given these changes, there was no significant difference in brain tissue oxygen saturation between the nonhypertensive and hypertensive groups (p > 0.05).

CONCLUSION

There was no difference between hypertensive and normotensive groups in terms of the change rates in cSO₂ values. However, there was a difference between the groups in terms of cSO₂ values.

Age-related normative changes in cerebral perfusion: Data from The Irish Longitudinal Study on Ageing (TILDA)

OBJECTIVE

To establish normative reference values for total grey matter cerebral blood flow (CBF_GM) measured using pseudo-continuous arterial spin labelling (pCASL) MRI in a large cohort of community-dwelling adults aged 54 years and older.

BACKGROUND

Quantitative assessment of CBF_GM may provide an imaging biomarker for the early detection of those at risk of neurodegenerative diseases, such as Alzheimer's and dementia. However, the use of this method to differentiate normal age-related decline in CBF_GM from pathological reduction has been hampered by the lack of reference values for cerebral perfusion.

METHODS

The study cohort comprised a subset of wave 3 (2014-2015) participants from The Irish Longitudinal Study on Ageing (TILDA), a large-scale prospective cohort study of individuals aged 50 and over. Of 4309 participants attending for health centre assessment, 578 individuals returned for 3T multi-parametric MRI brain examinations. In total, CBF_GM data acquired from 468 subjects using pCASL-MRI were included in this analysis. Normative values were estimated using Generalised Additive Models for Location Shape and Scale (GAMLSS) and are presented as percentiles, means and standard deviations.

RESULTS

The mean age of the cohort was 68.2 ± 6.9 years and 51.7% were female. Mean CBF_GM for the cohort was 36.5 ± 8.2 ml/100 g/min. CBF_GM decreased by 0.2 ml/100 g/min for each year increase in age (95% CI = -0.3, -0.1; p ≤ 0.001) and was 3.1 ml/100 g/min higher in females (95% CI = 1.6, 4.5; p ≤ 0.001).

CONCLUSIONS

This study is by far the largest single-site study focused on an elderly community-dwelling cohort to present normative reference values for CBF_GM measured at 3T using pCASL-MRI. Significant age- and sex-related differences exist in CBF_GM.

Uncontrolled hypertension associates with subclinical cerebrovascular health globally: a multimodal imaging study

OBJECTIVES

The study aimed to analyze the association between hypertension control and subclinical cerebrovascular health using a comprehensive multimodal imaging approach.

METHODS

The study included 200 hypertensive older males without previous cardiovascular diseases. Clinic blood pressure (BP) was measured using a standard approach. Cerebrovascular health was evaluated using magnetic resonance imaging in the following four aspects: Intracranial atherosclerosis as determined by vessel wall imaging; Vascular rarefaction (defined as less discernible vessels on angiography) was evaluated using a custom-developed technique. Cerebral blood flow (CBF) and white matter hyperintensity (WMH) were assessed using arterial spin-labeling imaging and fluid-attenuated inversion recovery imaging, respectively.

RESULTS

A total of 189 subjects had MRI scans. The mean age was 64.9 (± 7.2) years. For intracranial atherosclerosis, there was a significant association between uncontrolled hypertension and presence of intracranial plaque. When systolic and diastolic BP were analyzed separately, the association remained significant for both. For vascular rarefaction, uncontrolled hypertension was associated with less discernible vessel branches or shorter vessel length on angiography. Further analysis revealed that this is due to uncontrolled diastolic BP, but not uncontrolled systolic BP. There was an association between uncontrolled hypertension and reduced CBF, which was also mainly driven by uncontrolled diastolic BP. We also found that uncontrolled diastolic BP, but not uncontrolled systolic BP, was associated with increased WMH volume.

CONCLUSIONS

Uncontrolled hypertension was associated with subclinical cerebrovascular injury globally, with both small and medium-to-large arteries being affected.

KEY POINTS

• In this study, we leveraged the advantage of a series of cutting-edge MR imaging and analysis techniques and found uncontrolled hypertension is associated with subclinical globally compromised cerebrovascular health. • The detrimental consequences of uncontrolled BP affect not only the small vessels but also the medium-to-large arteries, and uncontrolled systolic and diastolic BP are both independently associated with certain types of cerebrovascular injury. • Our data suggest that cerebrovascular health is impaired globally in uncontrolled hypertension before the onset of stroke.

Cerebrovascular function in hypertension: Does high blood pressure make you old?

The majority of individuals over an age of 60 have hypertension. Elevated blood pressure and older age are associated with very similar changes in brain structure and function. We review the parallel brain changes associated with increasing age and blood pressure. This review focuses on joint associations of aging and elevated blood pressure with neuropsychological function, regional cerebral blood flow responses to cognitive and metabolic challenges, white matter disruptions, grey matter volume, cortical thinning, and neurovascular coupling. Treatment of hypertension ameliorates many of these changes but fails to reverse them. Treatment of hypertension itself appears more successful with better initial brain function. We show evidence that sympathetic and renal influences known to increase blood pressure also impact brain integrity. Possible central mechanisms contributing to the course of hypertension and aging are then suggested. An emphasis is placed on psychologically relevant factors: stress, cardiovascular reactions to stress, and diet/obesity. The contribution of some of these factors to biological aging remains unclear and may provide a starting point for defining the independent and interacting effects of aging and increasing blood pressure on the brain.

The role of exercise in the reversal of IGF-1 deficiencies in microvascular rarefaction and hypertension

Hypertension has been linked with peripheral and central reductions in vascular density, and with devastating effects on brain function. However, the underlying mechanisms in the relationship between blood pressure and cognitive impairment have yet to be fully elucidated. Here, we review compelling evidence from two lines of inquiry: one that links microvascular rarefaction with insulin-like growth factor 1 (IGF-1) deficiencies, and another which posits that vascular dysfunction precedes hypertension. Based on the findings from experimental and clinical studies, we propose that these lines of evidence converge, and suggest that age-related declines in IGF-1 concentrations precede microvascular rarefaction, initiate an increase in vascular resistance, and therefore are causally linked to onset of hypertension. Physical exercise provides a relevant model for supporting our premise, given the well-established effects of exercise in attenuating vascular dysfunction, hypertension, IGF-1 deficiency, and cognitive decline. We highlight here the role of exercise-induced increases in blood flow in improving vascular integrity and enhancing angiogenesis via the actions of IGF-1, resulting in reversal of rarefaction and hypertension, and enhancement of cerebral blood flow and cognition.

Contralateral Hemispheric Cerebral Blood Flow Measured With Arterial Spin Labeling Can Predict Outcome in Acute Stroke

Background and Purpose- Imaging is frequently used to select acute stroke patients for intra-arterial therapy. Quantitative cerebral blood flow can be measured noninvasively with arterial spin labeling magnetic resonance imaging. Cerebral blood flow levels in the contralateral (unaffected) hemisphere may affect capacity for collateral flow and patient outcome. The goal of this study was to determine whether higher contralateral cerebral blood flow (cCBF) in acute stroke identifies patients with better 90-day functional outcome. Methods- Patients were part of the prospective, multicenter iCAS study (Imaging Collaterals in Acute Stroke) between 2013 and 2017. Consecutive patients were enrolled after being diagnosed with anterior circulation acute ischemic stroke. Inclusion criteria were ischemic anterior circulation stroke, baseline National Institutes of Health Stroke Scale score ≥1, prestroke modified Rankin Scale score ≤2, onset-to-imaging time <24 hours, with imaging including diffusion-weighted imaging and arterial spin labeling. Patients were dichotomized into high and low cCBF groups based on median cCBF. Outcomes were assessed by day-1 and day-5 National Institutes of Health Stroke Scale; and day-30 and day-90 modified Rankin Scale. Multivariable logistic regression was used to test whether cCBF predicted good neurological outcome (modified Rankin Scale score, 0-2) at 90 days. Results- Seventy-seven patients (41 women) met the inclusion criteria with median (interquartile range) age of 66 (55-76) yrs, onset-to-imaging time of 4.8 (3.6-7.7) hours, and baseline National Institutes of Health Stroke Scale score of 13 (9-20). Median cCBF was 38.9 (31.2-44.5) mL per 100 g/min. Higher cCBF predicted good outcome at day 90 (odds ratio, 4.6 [95% CI, 1.4-14.7]; P=0.01), after controlling for baseline National Institutes of Health Stroke Scale, diffusion-weighted imaging lesion volume, and intra-arterial therapy. Conclusions- Higher quantitative cCBF at baseline is a significant predictor of good neurological outcome at day 90. cCBF levels may inform decisions regarding stroke triage, treatment of acute stroke, and general outcome prognosis. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT02225730.

Pathogenetic pathways of cognitive dysfunction and dementia in metabolic syndrome

The prevalence of dementia worldwide is growing at an alarming rate. A number of studies and meta-analyses have provided evidence for increased risk of dementia in patients with metabolic syndrome (MS) as compared to persons without MS. However, there are some reports demonstrating a lack of association between MS and increased dementia risk. In this review, taking into account the potential role of individual MS components in the pathogenesis of MS-related cognitive dysfunction, we considered the underlying mechanisms in arterial hypertension, diabetes mellitus, dyslipidemia, and obesity. The pathogenesis of dementia in MS is multifactorial, involving both vascular injury and non-ischemic neuronal death due to neurodegeneration. Neurodegenerative and ischemic lesions do not simply coexist in the brain due to independent evolution, but rather exacerbate each other, leading to more severe consequences for cognition than would either pathology alone. In addition to universal mechanisms of cognitive dysfunction shared by all MS components, other pathogenetic pathways leading to cognitive deficits and dementia, which are specific for each component, also play a role. Examples of such component-specific pathogenetic pathways include central insulin resistance and hypoglycemia in diabetes, neuroinflammation and adipokine imbalance in obesity, as well as arteriolosclerosis and lipohyalinosis in arterial hypertension. A more detailed understanding of cognitive disorders based on the recognition of underlying molecular mechanisms will aid in the development of new methods for prevention and treatment of devastating cognitive problems in MS.

Blood Pressure after Endovascular Therapy for Ischemic Stroke (BEST): A Multicenter Prospective Cohort Study

Background and Purpose- To identify the specific post-endovascular stroke therapy (EVT) peak systolic blood pressure (SBP) threshold that best discriminates good from bad functional outcomes (a priori hypothesized to be 160 mm Hg), we conducted a prospective, multicenter, cohort study with a prespecified analysis plan. Methods- Consecutive adult patients treated with EVT for an anterior ischemic stroke were enrolled from November 2017 to July 2018 at 12 comprehensive stroke centers accross the United States. All SBP values within 24 hours post-EVT were recorded. Using Youden index, the threshold of peak SBP that best discriminated primary outcome of dichotomized 90-day modified Rankin Scale score (0-2 versus 3-6) was identified. Association of this SBP threshold with the outcomes was quantified using multiple logistic regression. Results- Among 485 enrolled patients (median age, 69 [interquartile range, 57-79] years; 51% females), a peak SBP of 158 mm Hg was associated with the largest difference in the dichotomous modified Rankin Scale score (absolute risk reduction of 19%). Having a peak SBP >158 mm Hg resulted in an increased likelihood of modified Rankin Scale score 3 to 6 (odds ratio, 2.24 [1.52-3.29], P<0.01; adjusted odds ratio, 1.29 [0.81-2.06], P=0.28, after adjustment for prespecified variables). Conclusions- A peak post-EVT SBP of 158 mm Hg was prospectively identified to best discriminate good from bad functional outcome. Those with a peak SBP >158 had an increased likelihood of having a bad outcome in unadjusted, but not in adjusted analysis. The observed effect size was similar to prior studies. This finding should undergo further testing in a future randomized trial of goal-targeted post-EVT antihypertensive treatment.

Metabolic Syndrome and Amyloid Accumulation in the Aging Brain

BACKGROUND

Recent studies show links between metabolic syndrome and Alzheimer's disease (AD) neuropathology. Understanding the link between vascular-related health conditions and dementia will help target at risk populations and inform clinical strategies for early detection and prevention of AD.

OBJECTIVE

To determine whether metabolic syndrome is associated with global cerebral amyloid-β (Aβ) positivity and longitudinal Aβ accumulation.

METHODS

Prospective study of 165 participants who underwent (11)C-Pittsburgh compound B (PiB) PET neuroimaging to measure Aβ, from June 2005 to May 2016. Metabolic syndrome was defined using the revised Third Adults Treatment Panel of the National Cholesterol Education Program criteria. Participants were classified as PiB+/-. Linear mixed effects models assessed the relationships between baseline metabolic syndrome and PiB status and regional Aβ change over time.

RESULTS

A total of 165 cognitively normal participants of the Baltimore Longitudinal Study of Aging (BLSA) Neuroimaging substudy, aged 55-92 years (mean baseline age = 76.4 years, 85 participants were male), received an average of 2.5 PET-PiB scans over an average interval of 2.6 (3.08 SD) years between first and last visits. Metabolic syndrome was not associated with baseline PiB positivity or concurrent regional Aβ. Metabolic syndrome was associated with increased rates of Aβ accumulation in superior parietal and precuneus regions over time in the PiB+ group. Elevated fasting glucose and blood pressure showed individual associations with accelerated Aβ accumulation.

CONCLUSION

Metabolic syndrome was associated with accelerated Aβ accumulation in PiB+ individuals and may be an important factor in the progression of AD pathology.

Executive function in systemic arterial hypertension: A systematic review

Systemic arterial hypertension (SAH) may be associated with worse cognitive performance, especially in tasks that evaluate the executive functions (EF).

OBJECTIVE

we aimed to review the evidence regarding which components of executive functions are most affected in adults with SAH.

METHODS

this systematic review used the PRISMA statement for searching Pubmed, Scielo and Lilacs databases with the keywords "executive function OR executive functioning AND hypertension".

RESULTS

EF tasks were divided into shifting, inhibitory control and updating. A total of 9 cross-sectional and 3 longitudinal studies were selected. Only 3 studies did not report worse performance among SAH patients on EF tasks when compared to normotensive controls. The measures of shifting and inhibitory control were the most frequently investigated and reported as altered among SAH individuals, assessed mainly by the Stroop Test and Trail-Making Test part B, respectively.

CONCLUSION

inhibitory control and shifting are the EF components most influenced by SAH. The results of this review may contribute to the devising of hypotheses about mechanisms underlying these cognitive impairments.

Association of Midlife Cardiovascular Risk Profiles With Cerebral Perfusion at Older Ages

Importance

Poor cardiovascular health is an established risk factor for dementia, but little is known about its association with brain physiology in older adults.

Objective

To examine the association of cardiovascular risk factors, measured repeatedly during a 20-year period, with cerebral perfusion at older ages.

Design, Setting, and Participants

In this longitudinal cohort study, individuals were selected from the Whitehall II Imaging Substudy. Participants were included if they had no clinical diagnosis of dementia, had no gross brain structural abnormalities on magnetic resonance imaging scans, and had received pseudocontinuous arterial spin labeling magnetic resonance imaging. Cardiovascular risk was measured at 5-year intervals across 5 phases from September 1991 to October 2013. Arterial spin labeling scans were acquired between April 2014 and December 2014. Data analysis was performed from June 2016 to September 2018.

Exposures

Framingham Risk Score (FRS) for cardiovascular disease, comprising age, sex, high-density lipoprotein cholesterol level, total cholesterol level, systolic blood pressure, use of antihypertensive medications, cigarette smoking, and diabetes, was assessed at 5 visits.

Main Outcomes and Measures

Cerebral blood flow (CBF; in milliliters per 100 g of tissue per minute) was quantified with pseudocontinuous arterial spin labeling magnetic resonance imaging.

Results

Of 116 adult participants, 99 (85.3%) were men. At the first examination, mean (SD) age was 47.1 (5.0) years; at the last examination, mean (SD) age was 67.4 (4.9) years. Mean (SD) age at MRI scan was 69.3 (5.0) years. Log-FRS increased with time (B = 0.058; 95% CI, 0.044 to 0.072; P < .001). Higher cumulative FRS over the 20-year period (measured as the integral of the rate of change of log-FRS) was associated with lower gray matter CBF (B = -0.513; 95% CI -0.802 to -0.224; P < .001) after adjustment for age, sex, education, socioeconomic status, cognitive status, arterial transit time, use of statins, and weekly alcohol consumption. Voxelwise analyses revealed that this association was significant in 39.6% of gray matter regions, including the posterior cingulate, precuneus, lateral parietal cortex, occipital cortex, hippocampi, and parahippocampal gyrus. The strength of the association of higher log-FRS with lower CBF decreased progressively from the first examination (R2 = 0.253; B = -10.816; 99% CI -18.375 to -3.257; P < .001) to the last (R2 = 0.188; B = -7.139; 99% CI -14.861 to 0.582; P = .02), such that the most recent FRS measurement at mean (SD) age 67.4 (4.9) years was not significantly associated with CBF with a Bonferroni-corrected P < .01 .

Conclusions and Relevance

Cardiovascular risk in midlife was significantly associated with lower gray matter perfusion at older ages, but this association was not significant for cardiovascular risk in later life. This finding could inform the timing of cardiovascular interventions so as to be optimally effective.

The Blood Pressure Pendulum following Spinal Cord Injury: Implications for Vascular Cognitive Impairment

Cognitive impairment following spinal cord injury (SCI) has received considerable attention in recent years. Among the various systemic effects of SCI that contribute towards cognitive decline in this population, cardiovascular dysfunction is arguably one of the most significant. The majority of individuals with a cervical or upper-thoracic SCI commonly experience conditions called orthostatic hypotension and autonomic dysreflexia, which are characterized by dangerous fluctuations in systemic blood pressure (BP). Herein, we review the potential impact of extreme BP lability on vascular cognitive impairment (VCI) in individuals with SCI. Albeit preliminary in the SCI population, there is convincing evidence that chronic hypotension and hypertension in able-bodied individuals results in devastating impairments in cerebrovascular health, leading to VCI. We discuss the pertinent literature, and while drawing mechanistic comparisons between able-bodied cohorts and individuals with SCI, we emphasize the need for additional research to elucidate the mechanisms of cognitive impairment specific to the SCI population. Lastly, we highlight the current and potential future therapies to manage and treat BP instability, thereby possibly mitigating VCI in the SCI population.

Neurovascular and Cognitive Dysfunction in Hypertension

Hypertension has emerged as a leading cause of age-related cognitive impairment. Long known to be associated with dementia caused by vascular factors, hypertension has more recently been linked also to Alzheimer disease-the major cause of dementia in older people. Thus, although midlife hypertension is a risk factor for late-life dementia, hypertension may also promote the neurodegenerative pathology underlying Alzheimer disease. The mechanistic bases of these harmful effects remain to be established. Hypertension is well known to alter in the structure and function of cerebral blood vessels, but how these cerebrovascular effects lead to cognitive impairment and promote Alzheimer disease pathology is not well understood. Furthermore, critical questions also concern whether treatment of hypertension prevents cognitive impairment, the blood pressure threshold for treatment, and the antihypertensive agents to be used. Recent advances in neurovascular biology, epidemiology, brain imaging, and biomarker development have started to provide new insights into these critical issues. In this review, we will examine the progress made to date, and, after a critical evaluation of the evidence, we will highlight questions still outstanding and seek to provide a path forward for future studies.

Neuroimaging of Small Vessel Disease in Late-Life Depression

Cerebral small vessel disease is associated with late-life depression, cognitive impairment, executive dysfunction, distress, and loss of life for older adults. Late-life depression is becoming a substantial public health burden, and a considerable number of older adults presenting to primary care have significant clinical depression. Even though white matter hyperintensities are linked with small vessel disease, white matter hyperintensities are nonspecific to small vessel disease and can co-occur with other brain diseases. Advanced neuroimaging techniques at the ultrahigh field magnetic resonance imaging are enabling improved characterization, identification of cerebral small vessel disease and are elucidating some of the mechanisms that associate small vessel disease with late-life depression.

Different Relationship Between Systolic Blood Pressure and Cerebral Perfusion in Subjects With and Without Hypertension

Although there is an increasing agreement that hypertension is associated with cerebrovascular compromise, relationships between blood pressure (BP) and cerebral blood flow are not fully understood. It is not known what BP level, and consequently what therapeutic goal, is optimal for brain perfusion. Moreover, there is limited data on how BP affects hippocampal perfusion, a structure critically involved in memory. We conducted a cross-sectional (n=445) and longitudinal (n=185) study of adults and elderly without dementia or clinically apparent stroke, who underwent clinical examination and brain perfusion assessment (age 69.2±7.5 years, 62% women, 45% hypertensive). Linear models were used to test baseline BP-blood flow relationship and to examine how changes in BP influence changes in perfusion. In the entire group, systolic BP (SBP) was negatively related to cortical (β=-0.13, P=0.005) and hippocampal blood flow (β=-0.12, P=0.01). Notably, this negative relationship was apparent already in subjects without hypertension. Hypertensive subjects showed a quadratic relationship between SBP and hippocampal blood flow (β=-1.55, P=0.03): Perfusion was the highest in subjects with mid-range SBP around 125 mm Hg. Longitudinally, in hypertensive subjects perfusion increased with increased SBP at low baseline SBP but increased with decreased SBP at high baseline SBP. Cortical and hippocampal perfusion decrease with increasing SBP across the entire BP spectrum. However, in hypertension, there seems to be a window of mid-range SBP which maximizes perfusion.

The effect of age-related risk factors and comorbidities on white matter injury and repair after ischemic stroke

White matter injury is a crucial component of human stroke, but it has often been neglected in preclinical studies. Most human stroke is associated with one or more comorbidities, including aging, hypertension, diabetes and metabolic syndrome including hyperlipidemia. The purpose of this review is to examine how age and hypertension impact stroke-induced white matter injury as well as white matter repair in both human stroke and preclinical models. It is essential that comorbidities be examined in preclinical trials as they may impact translatability to the clinic. In addition, understanding how comorbidities impact white matter injury and repair may provide new therapeutic opportunities for patients with those conditions.

Protective Role of Recent and Past Long-Term Physical Activity on Age-Related Cognitive Decline: The Moderating Effect of Sex

This study aimed to investigate if the impact of both recent and long-term physical activity on age-related cognitive decline would be modified by sex. One-hundred thirty-five men (N = 67) and women (N = 68) aged 18 to 80 years completed the Modifiable Activity Questionnaire and the Historical Leisure Activity Questionnaire. A composite score of cognitive functions was computed from five experimental tasks. Hierarchical regression analyses performed to test the moderating effect of recent physical activity on age-cognition relationship had not revealed significant result regardless of sex. Conversely, past long-term physical activity was found to slow down the age-related cognitive decline among women (β = 0.22,p = .03), but not men. The findings support a lifecourse approach in identifying determinants of cognitive aging and the importance of taking into account the moderating role of sex. This article presented potential explanations for these moderators and future avenues to explore.