Blood Pressure Is Not Associated With Cerebral Blood Flow in Older Persons

Phasic perfusion dynamics among migraine subtypes: a multimodel arterial spin labeling investigation

BACKGROUND

Migraine-related perfusion changes are documented but inconsistent across studies due to limited sample size and insufficient phenotyping. The phasic and spatial dynamics across migraine subtypes remains poorly characterized. This study aimed to determine spatiotemporal dynamics of gray matter (GM) perfusion in migraine.

METHODS

We prospectively recruited episodic (EM) and chronic migraine (CM) patients, diagnosed with the International Headache Society criteria and healthy controls (HCs) between 2021 and 2023 from the headache center in a tertiary medical center, and adjacent communities. Magnetic resonance (3-tesla) arterial spin labeling (ASL) was conducted for whole brain cerebral blood flow (CBF) in all participants. The voxel-wise and whole brain gray matter (GM) CBF were compared between subgroups. Spatial pattern analysis of CBF and its correlations with headache frequency were investigated regarding different migraine phases and subtypes. Sex- and age-adjusted voxel-wise and whole brain GM comparisons were performed between HCs and different EM and CM phases. Spatial pattern analysis was conducted by CBF clusters with phasic differences and spin permutation test. Correlations between headache frequency and CBF were investigated regarding different EM and CM phases.

RESULTS

Totally 344 subjects (172 EM, 120 CM, and 52 HCs) were enrolled. Higher CBF in different anatomical locations was identified in ictal EM and CM. The combined panels of the specific locations with altered CBF in ictal EM on receiver operating characteristic curve analysis demonstrated areas under curve of 0.780 (vs. HCs) and 0.811 (vs. preictal EM). The spatial distribution of ictal-interictal CBF alteration of EM and CM were not correlated with each other (p = 0.665; r = - 0.018). Positive correlations between headache frequency and CBF were noted in ictal EM and CM regarding whole GM and specific anatomical locations.

CONCLUSIONS

Patients with migraine exhibited unique spatiotemporal CBF dynamics across different phases and distinct between subtypes. The findings provide neurobiological insights into how selected anatomical structures engage in a migraine attack and adapt to plastic change of repeated attacks along with chronicity.

Low Versus High Blood Pressure Targets in Critically Ill and Surgical Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

OBJECTIVES

Hypotension is associated with adverse outcomes in critically ill and perioperative patients. However, these assumptions are supported by observational studies. This meta-analysis of randomized controlled trials aims to compare the impact of lower versus higher blood pressure targets on mortality.

DATA SOURCES

We searched PubMed, Cochrane, and Scholar from inception to February 10, 2024.

STUDY SELECTION

Randomized trials comparing lower versus higher blood pressure targets in the management of critically ill and perioperative settings.

DATA EXTRACTION

The primary outcome was all-cause mortality at the longest follow-up available. This review was registered in the Prospective International Register of Systematic Reviews, CRD42023452928.

DATA SYNTHESIS

Of 2940 studies identified by the search string, 28 (12 in critically ill and 16 in perioperative settings) were included totaling 15,672 patients. Patients in the low blood pressure target group had lower mortality (23 studies included: 1019/7679 [13.3%] vs. 1103/7649 [14.4%]; relative risk 0.93; 95% CI, 0.87-0.99; p = 0.03; I2 = 0%). This corresponded to a 97.4% probability of any increase in mortality with a Bayesian approach. These findings were mainly driven by studies performed in the ICU setting and with treatment lasting more than 24 hours; however, the magnitude and direction of the results were similar in the majority of sensitivity analyses including the analysis restricted to low risk of bias studies. We also observed a lower rate of atrial fibrillation and fewer patients requiring transfusion in low-pressure target groups. No differences were found in the other secondary outcomes.

CONCLUSIONS

Based on pooled randomized trial evidence, a lower compared with a higher blood pressure target results in a reduction of mortality, atrial fibrillation, and transfusion requirements. Lower blood pressure targets may be beneficial but there is ongoing uncertainty. However, the present meta-analysis does not confirm previous findings and recommendations. These results might inform future guidelines and promote the study of the concept of protective hemodynamics.

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.

Mean Arterial Pressure and Cerebral Hemodynamics Across The Lifespan: A Cross-Sectional Study From Human Connectome Project-Aging

BACKGROUND

Cerebral perfusion is directly affected by systemic blood pressure, which has been shown to be negatively correlated with cerebral blood flow (CBF). The impact of aging on these effects is not fully understood.

PURPOSE

To determine whether the relationship between mean arterial pressure (MAP) and cerebral hemodynamics persists throughout the lifespan.

STUDY TYPE

Retrospective, cross-sectional study.

POPULATION

Six hundred and sixty-nine participants from the Human Connectome Project-Aging ranging between 36 and 100+ years and without a major neurological disorder.

FIELD STRENGTH/SEQUENCE

Imaging data was acquired at 3.0 Tesla using a 32-channel head coil. CBF and arterial transit time (ATT) were measured by multi-delay pseudo-continuous arterial spin labeling.

ASSESSMENT

The relationships between cerebral hemodynamic parameters and MAP were evaluated globally in gray and white matter and regionally using surface-based analysis in the whole group, separately within different age groups (young: <60 years; younger-old: 60-79 years; oldest-old: ≥80 years).

STATISTICAL TESTS

Chi-squared, Kruskal-Wallis, ANOVA, Spearman rank correlation and linear regression models. The general linear model setup in FreeSurfer was used for surface-based analyses. P < 0.05 was considered significant.

RESULTS

Globally, there was a significant negative correlation between MAP and CBF in both gray (ρ = -0.275) and white matter (ρ = -0.117). This association was most prominent in the younger-old [gray matter CBF (β = -0.271); white matter CBF (β = -0.241)]. In surface-based analyses, CBF exhibited a widespread significant negative association with MAP throughout the brain, whereas a limited number of regions showed significant prolongation in ATT with higher MAP. The associations between regional CBF and MAP in the younger-old showed a different topographic pattern in comparison to young subjects.

DATA CONCLUSION

These observations further emphasize the importance of cardiovascular health in mid-to-late adulthood for healthy brain aging. The differences in the topographic pattern with aging indicate a spatially heterogeneous relationship between high blood pressure and CBF.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 3.

Test-retest reliability of 3D velocity-selective arterial spin labeling for detecting normal variations of cerebral blood flow

Velocity-selective inversion (VSI) based velocity-selective arterial spin labeling (VSASL) has been developed to measure cerebral blood flow (CBF) with low susceptibility to the prolonged arterial transit time and high sensitivity to brain perfusion signal. The purpose of this magnetic resonance imaging study is to evaluate the test-retest reliability of a VSI-prepared 3D VSASL protocol with whole-brain coverage to detect baseline CBF variations among cognitively normal participants in different brain regions. Coefficients of variation (CoV) of both absolute and relative CBF across scans or sessions, subjects, and gray matter regions were calculated, and corresponding intraclass correlation coefficients (ICC) were computed. The higher between-subject CoV of absolute CBF (13.4 ± 2.0%) over within-subject CoV (within-session: 3.8 ± 1.1%; between-session: 4.9 ± 0.9%) yielded moderate to excellent ICC (within-session: 0.88±0.08; between-session: 0.77±0.14) to detect normal variations of individual CBF. The higher between-region CoV of relative CBF (11.4 ± 3.0%) over within-region CoV (within-session: 2.3 ± 0.9%; between-session: 3.3 ± 1.0%) yielded excellent ICC (within-session: 0.92±0.06; between-session: 0.85±0.12) to detect normal variations of regional CBF. Age, blood pressure, end-tidal CO2, and hematocrit partially explained the variability of CBF across subjects. Together these results show excellent test-retest reliability of VSASL to detect both between-subject and between-region variations supporting its clinical utility.

Association of Intensive vs Standard Blood Pressure Control With Regional Changes in Cerebral Small Vessel Disease Biomarkers: Post Hoc Secondary Analysis of the SPRINT MIND Randomized Clinical Trial

IMPORTANCE

Little is known about the associations of strict blood pressure (BP) control with microstructural changes in small vessel disease markers.

OBJECTIVE

To investigate the regional associations of intensive vs standard BP control with small vessel disease biomarkers, such as white matter lesions (WMLs), fractional anisotropy (FA), mean diffusivity (MD), and cerebral blood flow (CBF).

DESIGN, SETTING, AND PARTICIPANTS

The Systolic Blood Pressure Intervention Trial (SPRINT) is a multicenter randomized clinical trial that compared intensive systolic BP (SBP) control (SBP target <120 mm Hg) vs standard control (SBP target <140 mm Hg) among participants aged 50 years or older with hypertension and without diabetes or a history of stroke. The study began randomization on November 8, 2010, and stopped July 1, 2016, with a follow-up duration of approximately 4 years. A total of 670 and 458 participants completed brain magnetic resonance imaging at baseline and follow-up, respectively, and comprise the cohort for this post hoc analysis. Statistical analyses for this post hoc analysis were performed between August 2020 and October 2022.

INTERVENTIONS

At baseline, 355 participants received intensive SBP treatment and 315 participants received standard SBP treatment.

MAIN OUTCOMES AND MEASURES

The main outcomes were regional changes in WMLs, FA, MD (in white matter regions of interest), and CBF (in gray matter regions of interest).

RESULTS

At baseline, 355 participants (mean [SD] age, 67.7 [8.0] years; 200 men [56.3%]) received intensive BP treatment and 315 participants (mean [SD] age, 67.0 [8.4] years; 199 men [63.2%]) received standard BP treatment. Intensive treatment was associated with smaller mean increases in WML volume compared with standard treatment (644.5 mm3 vs 1258.1 mm3). The smaller mean increases were observed specifically in the deep white matter regions of the left anterior corona radiata (intensive treatment, 30.3 mm3 [95% CI, 16.0-44.5 mm3]; standard treatment, 80.5 mm3 [95% CI, 53.8-107.2 mm3]), left tapetum (intensive treatment, 11.8 mm3 [95% CI, 4.4-19.2 mm3]; standard treatment, 27.2 mm3 [95% CI, 19.4-35.0 mm3]), left superior fronto-occipital fasciculus (intensive treatment, 3.2 mm3 [95% CI, 0.7-5.8 mm3]; standard treatment, 9.4 mm3 [95% CI, 5.5-13.4 mm3]), left posterior corona radiata (intensive treatment, 26.0 mm3 [95% CI, 12.9-39.1 mm3]; standard treatment, 52.3 mm3 [95% CI, 34.8-69.8 mm3]), left splenium of the corpus callosum (intensive treatment, 45.4 mm3 [95% CI, 25.1-65.7 mm3]; standard treatment, 83.0 mm3 [95% CI, 58.7-107.2 mm3]), left posterior thalamic radiation (intensive treatment, 53.0 mm3 [95% CI, 29.8-76.2 mm3]; standard treatment, 106.9 mm3 [95% CI, 73.4-140.3 mm3]), and right posterior thalamic radiation (intensive treatment, 49.5 mm3 [95% CI, 24.3-74.7 mm3]; standard treatment, 102.6 mm3 [95% CI, 71.0-134.2 mm3]).

CONCLUSIONS AND RELEVANCE

This study suggests that intensive BP treatment, compared with standard treatment, was associated with a slower increase of WMLs, improved diffusion tensor imaging, and FA and CBF changes in several brain regions that represent vulnerable areas that may benefit from more strict BP control.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01206062.

Cerebral blood flow predicts multiple demand network activity and fluid intelligence across the adult lifespan

The preservation of cognitive function in old age is a public health priority. Cerebral hypoperfusion is a hallmark of dementia but its impact on maintaining cognitive ability across the lifespan is less clear. We investigated the relationship between baseline cerebral blood flow (CBF) and blood oxygenation level-dependent (BOLD) response during a fluid reasoning task in a population-based adult lifespan cohort. As age differences in CBF could lead to non-neuronal contributions to the BOLD signal, we introduced commonality analysis to neuroimaging to dissociate performance-related CBF effects from the physiological confounding effects of CBF on the BOLD response. Accounting for CBF, we confirmed that performance- and age-related differences in BOLD responses in the multiple-demand network were implicated in fluid reasoning. Age differences in CBF explained not only performance-related BOLD responses but also performance-independent BOLD responses. Our results suggest that CBF is important for maintaining cognitive function, while its non-neuronal contributions to BOLD signals reflect an age-related confound. Maintaining perfusion into old age may serve to support brain function and preserve cognitive performance.

Contrast-agent-free state-of-the-art MRI on cerebral small vessel disease-part 1. ASL, IVIM, and CVR

Cerebral small vessel disease (cSVD), a common cause of stroke and dementia, is traditionally considered the small vessel equivalent of large artery occlusion or rupture that leads to cortical and subcortical brain damage. Microvessel endothelial dysfunction can also contribute to it. Brain imaging, including MRI, is useful to show the presence of lesions of several types, although the association between conventional MRI measures and clinical features of cSVD is not always concordant. We assessed the additional contribution of contrast-agent-free, state-of-the-art MRI techniques such as arterial spin labeling (ASL), diffusion tensor imaging, functional MRI, and intravoxel incoherent motion (IVIM) applied to cSVD in the existing literature. We performed a review following the PICO Worksheet and Search Strategy, including original papers in English, published between 2000 and 2022. For each MRI method, we extracted information about their contributions, in addition to those established with traditional MRI methods and related information about the origins, pathology, markers, and clinical outcomes in cSVD. This paper presents the first part of the review, which includes 37 studies focusing on ASL, IVIM, and cerebrovascular reactivity (CVR) measures. In general, they have shown that, in addition to white matter hyperintensities, alterations in other neuroimaging parameters such as blood flow and CVR also indicate the presence of cSVD. Such quantitative parameters were also related to cSVD risk factors. Therefore, they are promising, noninvasive tools to explore questions that have not yet been clarified about this clinical condition. However, protocol standardization is essential to increase their clinical use.

Effects of Cilostazol and Isosorbide Mononitrate on Cerebral Hemodynamics in the LACI-1 Randomized Controlled Trial

Supplemental Digital Content is available in the text.

Cerebral small vessel disease—a major cause of stroke and dementia—is associated with cerebrovascular dysfunction. We investigated whether short-term isosorbide mononitrate (ISMN) and cilostazol, alone or in combination, improved magnetic resonance imaging–measured cerebrovascular function in patients with lacunar ischemic stroke.

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

MRI of healthy brain aging: A review

We present a review of the characterization of healthy brain aging using MRI with an emphasis on morphology, lesions, and quantitative MR parameters. A scope review found 6612 articles encompassing the keywords "Brain Aging" and "Magnetic Resonance"; papers involving functional MRI or not involving imaging of healthy human brain aging were discarded, leaving 2246 articles. We first consider some of the biogerontological mechanisms of aging, and the consequences of aging in terms of cognition and onset of disease. Morphological changes with aging are reviewed for the whole brain, cerebral cortex, white matter, subcortical gray matter, and other individual structures. In general, volume and cortical thickness decline with age, beginning in mid-life. Prevalent silent lesions such as white matter hyperintensities, microbleeds, and lacunar infarcts are also observed with increasing frequency. The literature regarding quantitative MR parameter changes includes T₁ , T₂ , T₂ *, magnetic susceptibility, spectroscopy, magnetization transfer, diffusion, and blood flow. We summarize the findings on how each of these parameters varies with aging. Finally, we examine how the aforementioned techniques have been used for age prediction. While relatively large in scope, we present a comprehensive review that should provide the reader with sound understanding of what MRI has been able to tell us about how the healthy brain ages.

Longitudinal relation between blood pressure, antihypertensive use and cerebral blood flow, using arterial spin labelling MRI

Consistent cerebral blood flow (CBF) is fundamental to brain function. Cerebral autoregulation ensures CBF stability. Chronic hypertension can lead to disrupted cerebral autoregulation in older people, potentially leading to blood pressure levels interfering with CBF. This study tested whether low BP and AHD use are associated with contemporaneous low CBF, and whether longitudinal change in BP is associated with change in CBF, using arterial spin labelling (ASL) MRI, in a prospective longitudinal cohort of 186 community-dwelling older individuals with hypertension (77 ± 3 years, 53% female), 125 (67%) of whom with 3-year follow-up. Diastolic blood pressure, systolic blood pressure, mean arterial pressure, and pulse pressure were assessed as blood pressure parameters. As additional cerebrovascular marker, we evaluated the ASL signal spatial coefficient of variation (ASL SCoV), a measure of ASL signal heterogeneity that may reflect cerebrovascular health. We found no associations between any of the blood pressure measures and concurrent CBF nor between changes in blood pressure measures and CBF over three-year follow-up. Antihypertensive use was associated with lower grey matter CBF (-5.49 ml/100 g/min, 95%CI = -10.7|-0.27, p = 0.04) and higher ASL SCoV (0.32 SD, 95%CI = 0.12|0.52, p = 0.002). These results warrant future research on the potential relations between antihypertensive use and cerebral perfusion.

Effect of Perindopril/Indapamide on Cerebral Blood Flow in Middle-Aged, Treatment-Naïve Patients with Hypertension

INTRODUCTION

The relationship between blood pressure (BP) and cerebral blood flow (CBF) is not fully understood. This study evaluated the impact of a perindopril arginine/indapamide (Pa/I) single-pill combination (SPC) on CBF in middle-aged patients.

METHODS

A total of 22 treatment-naïve patients with essential hypertension and at least one hypertension-mediated organ damage and 41 healthy controls were enrolled. At baseline, all participants underwent brain magnetic resonance imaging (MRI); patients with hypertension underwent an additional MRI at end of follow-up. Arterial spin labeling (ASL) was used to calculate CBF in the frontal lobe cortical plate. Patients with hypertension received once-daily Pa/I 5 mg/1.25 mg SPC, which could be increased to Pa/I 10 mg/2.5 mg at 2 weeks if necessary. Patients with hypertension underwent 24-h ambulatory BP monitoring (ABPM) at baseline and end of follow-up.

RESULTS

Mean baseline BP values were 146.2/93.1 and 119.1/76.1 mmHg in the hypertension and control groups, respectively. Patients with hypertension had significantly (p < 0.001) lower CBF in the cortical plate of both left (36.2 ± 8.3 vs. 45.3 ± 3.5 ml/100 g/min) and right (37.9 ± 7.9 vs. 45.8 ± 3.2 ml/100 g/min) frontal lobes compared to normotensive controls. At the end of follow-up, there was a statistically significant (p < 0.001) increase in CBF in the cortical plate of both left (from 36.2 ± 8.3 to 47.5 ± 9.8 ml/100 g/min) and right frontal lobes (from 37.9 ± 7.9 to 47.4 ± 10.1 ml/100 g/min) compared to baseline. No significant difference was found between end of follow-up CBF levels in frontal lobes of patients with hypertension and those of healthy controls at baseline. Office BP decreased by 24.2/15.5 mmHg and 24-h ABPM from 145.5/95.3 to 120.8/79.3 mmHg.

CONCLUSION

In middle-aged, treatment-naïve patients with hypertension, Pa/I SPC was associated with increased CBF in the cortical plate of the frontal lobes, which achieved levels of normotensive controls. The increase in CBF had no clear association with observed BP changes.

REGISTRATION NUMBER

ISRCTN67799751.

Prevention and Treatment of Alzheimer's Disease: Biological Mechanisms of Exercise

Alzheimer's disease (AD) is the most common form of dementia. With an aging population and no disease modifying treatments available, AD is quickly becoming a global pandemic. A substantial body of research indicates that lifestyle behaviors contribute to the development of AD, and that it may be worthwhile to approach AD like other chronic diseases such as cardiovascular disease, in which prevention is paramount. Exercise is an important lifestyle behavior that may influence the course and pathology of AD, but the biological mechanisms underpinning these effects remain unclear. This review focuses on how exercise can modify four possible mechanisms which are involved with the pathology of AD: oxidative stress, inflammation, peripheral organ and metabolic health, and direct interaction with AD pathology. Exercise is just one of many lifestyle behaviors that may assist in preventing AD, but understanding the systemic and neurobiological mechanisms by which exercise affects AD could help guide the development of novel pharmaceutical agents and non-pharmacological personalized lifestyle interventions for at-risk populations.

Cerebral macro- and microcirculatory blood flow dynamics in successfully treated chronic hypertensive patients with and without white mater lesions

The mechanisms of high blood pressure (HBP) -related brain pathology progression remain relatively unclear. We investigated whether lowering BP in chronic HBP patients normalizes cerebral perfusion dynamics at resistance vessel and capillary levels. Sixty-seven patients with HBP and 49 age- and sex-matched healthy controls underwent simultaneous recordings of middle cerebral artery blood flow velocity (CBFV), BP, and end-tidal CO₂ concentration. Thirty-four controls and 28 patients underwent additional near-infrared spectroscopy recordings (oxygenated [O₂Hb] and deoxygenated [HHb] hemoglobin). Degree of microcirculatory white matter lesions was graded by Fazekas scale. Dynamic cerebral autoregulation (dCA) was assessed by transfer function analysis. BP was successfully lowered (patients = 89 ± 15 mm Hg, controls = 87 ± 17), but cerebrovascular resistance was higher in BP patients (p < 0.05). BP-CBFV phase was lower in very low frequency (VLF) (left/right: 48 ± 20°/44 ± 17; controls: 61 ± 20/60 ± 21; p < 0.001) and low frequency (LF) (34 ± 14/35 ± 14; controls: 48 ± 20/44 ± 17; p < 0.05) ranges. Gain was higher in VLF range (in %/ mm Hg 0.56 ± 0.44/0.59 ± 0.49; controls: 0.32 ± 0.29/0.34 ± 0.32; p ≤ 0.005). BP-CBFV phase and gain did not differ across Fazekas groups. Across all patients, the capillary phases and gains (CBFV-[O2Hb], CBFV-[HHb]) were comparable to controls. Successfully treated chronic HBP results in normal brain capillary hemodynamics while the resistance vessel state is disturbed (phase decrease, gain increase).

Metabolic and vascular risk factors are associated with reduced cerebral blood flow and poorer midlife memory performance

Midlife metabolic and vascular risk factors (MVRFs) predict cognitive decline and dementia; however, these risk factors tend to overlap, and the mechanisms underlying their effects on cognitive performance are not well understood. This cross-sectional study investigates the contributions of MVRFs to regional cerebral blood flow (CBF) and verbal learning & memory among middle-aged adults. We used partial least squares (PLS) analysis to create latent risk factor profiles and examine their associations to CBF in 93 regions of interest among 451 participants (age 50.3 ± 3.5 years) of the Coronary Artery Risk Development in Young Adults. This multivariate analysis revealed regional CBF was lower in relation to obesity (higher body mass index and waist circumference), dysregulated glucose homeostasis (higher fasting glucose, oral glucose tolerance, and higher fasting insulin), and adverse fasting lipid profile (lower high-density lipoprotein cholesterol and higher triglycerides). In a sensitivity analysis, we found that significant associations between MVRFs and CBF were prominent in the hypertension-medicated subgroup. In a mediation model, the PLS-based MVRFs profile was associated with memory performance (rey auditory verbal learning test); however, CBF was not a significant mediator of this association. The results describe an adverse midlife metabolic profile that might set the stage for incipient dementia and contribute to widespread changes in CBF.

Orthostatic hypotension in older persons is not associated with cognitive functioning, features of cerebral damage or cerebral blood flow

OBJECTIVE

Particularly in old age, orthostatic hypotension has been related to worse cognitive functioning, possibly caused by reduced cerebral blood flow (CBF). This study investigates whether orthostatic hypotension in older people is associated with cognitive dysfunction and, if so, whether this association is mediated by cerebral vascular damage and/or decreased CBF.

METHODS

Four hundred and twenty participants of the Discontinuation of ANtihypertensive Treatment in Elderly People (DANTE) Study Leiden (mean age 81 years, all using antihypertensive medication and with mild cognitive deficits), and MRI data from 214 participants of the nested DANTE MRI sub-study. Orthostatic hypotension was defined as either a SBP decrease at least 20 mmHg and/or a DBP decrease of at least 10 mmHg within 3 min of standing up. Cognitive functioning was assessed using a battery of six cognitive tests covering global cognition, memory function, executive function and psychomotor speed. Cerebral vascular damage and CBF were assessed using MRI.

RESULTS

The prevalence of orthostatic hypotension was 47% (n = 199). Compared with the group without orthostatic hypotension, participants with orthostatic hypotension showed no differences in any of the cognitive functions, features of cerebral small vessel disease, microstructural integrity or CBF.

CONCLUSION

In this population of older persons, the presence of orthostatic hypotension was not associated with decreased cognition. In addition, no differences were found in the supposedly underlying cerebral vascular mechanisms.

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.

Dynamic Regulation of Cerebral Blood Flow in Patients With Alzheimer Disease

Cerebral autoregulation and baroreflex sensitivity are key mechanisms that maintain cerebral blood flow. This study assessed whether these control mechanisms are affected in patients with dementia and mild cognitive impairment due to Alzheimer disease, as this would increase the risks of antihypertensive treatment. We studied 53 patients with dementia (73.1 years [95% confidence interval (CI), 71.4–74.8]), 37 patients with mild cognitive impairment (69.2 years [95% CI, 66.4–72.0]), and 47 controls (69.4 years [95% CI, 68.3–70.5]). Beat-to-beat blood pressure (photoplethysmography), heart rate, and cerebral blood flow velocity (transcranial Doppler) were measured during 5-minute rest (sitting) and 5 minutes of orthostatic challenges, using repeated sit-to-stand maneuvers. Cerebral autoregulation was assessed using transfer function analysis and the autoregulatory index. Baroreflex sensitivity was estimated with transfer function analysis and by calculating the heart rate response to blood pressure changes during the orthostatic challenges. Dementia patients had the lowest cerebral blood flow velocity ( P =0.004). During rest, neither transfer function analysis nor the autoregulatory index indicated impairments in cerebral autoregulation. During the orthostatic challenges, higher autoregulatory index ( P =0.011) and lower transfer function gain ( P =0.017), indicating better cerebral autoregulation, were found in dementia (4.56 arb. unit [95% CI, 4.14–4.97]; 0.59 cm/s per mm Hg [95% CI, 0.51–0.66]) and mild cognitive impairment (4.59 arb. unit [95% CI, 4.04–5.13]; 0.51 cm/s per mm Hg [95% CI, 0.44–0.59]) compared with controls (3.71 arb. unit [95% CI, 3.35–4.07]; 0.67 cm/s per mm Hg [95% CI, 0.59–0.74]). Baroreflex sensitivity measures did not differ between groups. In conclusion, the key mechanisms to control blood pressure and cerebral blood flow are not reduced in 2 stages of Alzheimer disease compared with controls, both in rest and during orthostatic changes that reflect daily life challenges.

Advanced Neuroimaging of Cerebral Small Vessel Disease

Cerebral small vessel disease (SVD) is characterised by damage to deep grey and white matter structures of the brain and is responsible for a diverse range of clinical problems that include stroke and dementia. In this review, we describe advances in neuroimaging published since January 2015, mainly with magnetic resonance imaging (MRI), that, in general, are improving quantification, observation and investigation of SVD focussing on three areas: quantifying the total SVD burden, imaging brain microstructural integrity and imaging vascular malfunction. Methods to capture ‘whole brain SVD burden’ across the spectrum of SVD imaging changes will be useful for patient stratification in clinical trials, an approach that we are already testing. More sophisticated imaging measures of SVD microstructural damage are allowing the disease to be studied at earlier stages, will help identify specific factors that are important in development of overt SVD imaging features and in understanding why specific clinical consequences may occur. Imaging vascular function will help establish the precise blood vessel and blood flow alterations at early disease stages and, together with microstructural integrity measures, may provide important surrogate endpoints in clinical trials testing new interventions. Better knowledge of SVD pathophysiology will help identify new treatment targets, improve patient stratification and may in future increase efficiency of clinical trials through smaller sample sizes or shorter follow-up periods. However, most of these methods are not yet sufficiently mature to use with confidence in clinical trials, although rapid advances in the field suggest that reliable quantification of SVD lesion burden, tissue microstructural integrity and vascular dysfunction are imminent.

Influence of sleep duration on cortical oxygenation in elderly individuals

AIM

Short sleep duration is a risk factor for cardiovascular diseases. Cerebral blood flow and its regulation are affected by pathological conditions commonly observed in the elderly population, such as dementia, atherosclerosis, diabetes mellitus (DM), stroke, and hypertension. The purpose of this study was to examine the influence of sleep duration on cortical oxygenated hemoglobin (OxyHb) using near-infrared spectroscopy (NIRS).

METHODS

Seventy-three individuals (age, 70.1 ± 3.9 years, 51 men and 22 women) participated in this study. Cortical OxyHb levels were measured with NIRS. We evaluated age, body mass index (BMI), smoking status, alcohol intake, sleep duration, hypertension, DM, and hyperlipidemia using a questionnaire. Blood pressure was measured using plethysmography.

RESULTS

Peak OxyHb and area under the NIRS curve significantly decreased in participants with sleep duration <7 h compared with those with sleep duration ≥7 h (0.136 ± 0.212 mM·mm vs 0.378 ± 0.342 mM·mm, P = 0.001; 112.0 ± 243.6 vs 331.7 ± 428.7, P  = 0.012, respectively). Sleep duration was significantly correlated with peak OxyHb level and area under the NIRS curve (r = 0.378, P  = 0.001; r = 0.285, P  = 0.015, respectively). Multiple regression analysis, including age, BMI, sex, smoking status, alcohol intake, sleep duration, hypertension, DM, and hyperlipidemia revealed that sleep duration was the only significant independent factor associated with peak OxyHb and area under the NIRS curve (β = 0.343, P  = 0.004; β = 0.244, P  = 0.049, respectively), and smoking status was independently correlated with time to the peak OxyHb (β = -0.319, P  = 0.009).

CONCLUSION

Sleep duration may be an important factor that influences cortical oxygenation in the elderly population.

Structural Covariance Networks and Their Association with Age, Features of Cerebral Small-Vessel Disease, and Cognitive Functioning in Older Persons

Recently, cerebral structural covariance networks (SCNs) have been shown to partially overlap with functional networks. However, although for some of these SCNs a strong association with age is reported, less is known about the association of individual SCNs with separate cognition domains and the potential mediation effect in this of cerebral small vessel disease (SVD). In 219 participants (aged 75-96 years) with mild cognitive deficits, 8 SCNs were defined based on structural covariance of gray matter intensity with independent component analysis on 3DT1-weighted magnetic resonance imaging (MRI). Features of SVD included volume of white matter hyperintensities (WMH), lacunar infarcts, and microbleeds. Associations with SCNs were examined with multiple linear regression analyses, adjusted for age and/or gender. In addition to higher age, which was associated with decreased expression of subcortical, premotor, temporal, and occipital-precuneus networks, the presence of SVD and especially higher WMH volume was associated with a decreased expression in the occipital, cerebellar, subcortical, and anterior cingulate network. The temporal network was associated with memory (p = 0.005), whereas the cerebellar-occipital and occipital-precuneus networks were associated with psychomotor speed (p = 0.002 and p < 0.001). Our data show that a decreased expression of specific networks, including the temporal and occipital lobe and cerebellum, was related to decreased cognitive functioning, independently of age and SVD. This indicates the potential of SCNs in substantiating cognitive functioning in older persons.

Cognitive Impairment Among the Aging Population in a Community in Southwest Nigeria

Background. Vascular risk models can be quite informative in assisting the clinician to make a prediction of an individual’s risk of cognitive impairment. Thus, a simple marker is a priority for low-capacity settings. This study examines the association of selected simple to deploy vascular markers with cognitive impairment in an elderly population. Method. This cross-sectional study assessed the cognitive functions of older persons 65 years and older in southwest Nigeria. Vascular parameters and risk factors were also measured. Analysis was done using SPSS, and logistic regression was used to explore the association between cognitive impairment and certain vascular risk factors such as elevated blood pressure, diabetes, and pulse pressure. Results. The study population comprised 623 participants (29.1% men) with mean age 73 ± 8.9 years. Having mean arterial pressure (MAP) and pulse pressure in the fourth quartiles (27% and 29.9%, respectively) was significantly associated with cognitive impairment ( p = .001, p < .001). Predicted cardiovascular risks of 10% or more was significantly associated with cognitive impairment ( p < .001). After adjusting for age, gender, educational level, and years of smoking, those with MAP in the fourth quartile were up to 3 times more likely to have cognitive impairment compared to those within the first quartile. Conclusion. Our study demonstrated that among elderly Nigerians, MAPs of 114 mmHg and more was an independent predictor of cognitive impairment. This is a simple measure that is available in low-capacity areas.

Hypertension in the frail elderly

Extant data indicate that treating to lower systolic pressure confers significant advantage to younger people in general good health and to relatively healthy octogenarians. Few data exist to guide practitioners on the treatment of frail elderly hypertensives. Chronological age alone does not suffice to make useful judgments regarding therapy. The definition of frailty remains controversial. One method, use of a simple questionnaire or a test of walking speed is practical but not universally accepted. Frail subjects, while at higher risk for cardiovascular complications, seem to benefit less or not at all from antihypertensive drug treatment. Clinicians should treat robust older patients as they would younger patients because the benefits far outweigh the low risk of adverse effects. Successful antihypertensive therapy in those younger than 80 years should not be discontinued simply because that age milestone has been crossed. Treatment of frail older patients must be individualized. Some frail survivors age 80 years or older may actually fare better with elevated systolic pressures. Pending the cognitive function substudy of Systolic Blood Pressure Intervention Trial, there is little evidence that antihypertensive treatment benefits established cognitive dysfunction. Because hypertension in middle age is a good predictor of later cognitive dysfunction, the clinical approach should be one of early prevention.

Aging is associated with changes to the biomechanical properties of the posterior cerebral artery and parenchymal arterioles

Artery remodeling, described as a change in artery structure, may be responsible for the increased risk of cardiovascular disease with aging. Although the risk for stroke is known to increase with age, relatively young animals have been used in most stroke studies. Therefore, more information is needed on how aging alters the biomechanical properties of cerebral arteries. Posterior cerebral arteries (PCAs) and parenchymal arterioles (PAs) are important in controlling brain perfusion. We hypothesized that aged (22-24 mo old) C57bl/6 mice would have stiffer PCAs and PAs than young (3-5 mo old) mice. The biomechanical properties of the PCAs and PAs were assessed by pressure myography. Data are presented as means ± SE of young vs. old. In the PCA, older mice had increased outer (155.6 ± 3.2 vs. 169.9 ± 3.2 μm) and lumen (116.4 ± 3.6 vs. 137.1 ± 4.7 μm) diameters. Wall stress (375.6 ± 35.4 vs. 504.7 ± 60.0 dyn/cm(2)) and artery stiffness (β-coefficient: 5.2 ± 0.3 vs. 7.6 ± 0.9) were also increased. However, wall strain (0.8 ± 0.1 vs. 0.6 ± 0.1) was reduced with age. In the PAs from old mice, wall thickness (3.9 ± 0.3 vs. 5.1 ± 0.2 μm) and area (591.1 ± 95.4 vs. 852.8 ± 100 μm(2)) were increased while stress (758.1 ± 100.0 vs. 587.2 ± 35.1 dyn/cm(2)) was reduced. Aging also increased mean arterial and pulse pressures. We conclude that age-associated remodeling occurs in large cerebral arteries and arterioles and may increase the risk of cerebrovascular disease.