Wave Reflection at the Origin of a First-Generation Branch Artery and Target Organ Protection: The AGES-Reykjavik Study

Effects of aerobic exercise training on cerebral pulsatile hemodynamics in middle-aged adults with elevated blood pressure/stage 1 hypertension

Mechanisms behind the protective effects of aerobic exercise on brain health remain elusive but may be vascular in origin and relate to cerebral pulsatility. This pilot study investigated the effects of 12-wk aerobic exercise training on cerebral pulsatility and its vascular contributors (large artery stiffness, characteristic impedance) in at-risk middle-aged adults. Twenty-eight inactive middle-aged adults with elevated blood pressure or stage 1 hypertension were assigned to either moderate/vigorous aerobic exercise training (AET) for 3 days/wk or no-exercise control (CON) group. Middle cerebral artery (MCA) pulsatility index (PI), large artery (i.e., aorta, carotid) stiffness, and characteristic impedance were assessed via Doppler and tonometry at baseline, 6, and 12 wk, whereas cardiorespiratory fitness (V̇o2peak) was assessed via incremental exercise test and cognitive function via computerized battery at baseline and 12 wk. V̇o2peak increased 6% in AET and decreased 4% in CON (P < 0.05). Proximal aortic compliance increased (P = 0.04, partial η2 = 0.14) and aortic characteristic impedance decreased (P = 0.02, partial η2 = 0.17) with AET but not CON. Cerebral pulsatility showed a medium-to-large effect size increase with AET, although not statistically significant (P = 0.07, partial η2 = 0.11) compared with CON. Working memory reaction time improved with AET but not CON (P = 0.02, partial η2 = 0.20). Our data suggest 12-wk AET elicited improvements in central vascular hemodynamics (e.g., proximal aortic compliance and characteristic impedance) along with apparent, paradoxical increases in cerebral pulsatile hemodynamics.NEW & NOTEWORTHY We identify differential central versus cerebrovascular responses to 12 wk of aerobic exercise training in middle-aged adults. Although proximal aortic compliance and characteristic impedance improved after 12 wk of exercise, cerebral pulsatility tended to unexpectedly increase. These data suggest short-term aerobic exercise training may lead to more immediate benefits in the central vasculature, whereas longer duration exercise training may be required for beneficial changes in pulsatility within the cerebrovasculature.

Left ventricular hypertrophy as a risk factor for accelerated brain aging: Results from the Study of Health in Pomerania

Previous studies provided evidence for the importance of cardiac structure abnormalities, in particular greater left ventricular (LV) mass, for brain aging, but longitudinal studies are lacking to date. We included 926 individuals (median age 48 years; 53% women) from the TREND cohort of the Study of Health in Pomerania (SHIP) without reduced ejection fraction or a history of myocardial infarction. LV mass index (LVMI) was determined by echocardiography at baseline. Brain morphometric measurements were derived from magnetic resonance images at baseline and 7-year follow-up. Direct effects of baseline LVMI on brain morphometry at follow-up were estimated using linear regression models with adjustment for baseline brain morphometry. At baseline, median LVMI was 40 g/m2.7 and 241 individuals (26%) met the criterion of LV hypertrophy. After correction for multiple testing, baseline LVMI was directly associated with reduced global cortical thickness and increased cortical brain age at follow-up independent from hypertension and blood pressure. Exposure-outcome relations were nonlinear and significantly stronger in the upper half of the exposure distribution. Specifically, an increase in baseline LVMI from the 50% quantile to the 95% quantile was associated additional 2.7 years (95% confidence interval = [1.5 years, 3.8 years]) of cortical brain age at follow-up. Additional regional analyses yielded bilateral effects on multiple frontal cortical regions. Our findings highlight the role of cardiac structure in brain aging. LVMI constitutes an easily measurable marker that might help to identify persons at risk for cognitive impairment and dementia.

Associations of Cerebrovascular Regulation and Arterial Stiffness With Cerebral Small Vessel Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Cerebral small vessel disease (cSVD) is a major contributing factor to ischemic stroke and dementia. However, the vascular pathologies of cSVD remain inconclusive. The aim of this systematic review and meta-analysis was to characterize the associations between cSVD and cerebrovascular reactivity (CVR), cerebral autoregulation, and arterial stiffness (AS).

METHODS AND RESULTS

MEDLINE, Web of Science, and Embase were searched from inception to September 2023 for studies reporting CVR, cerebral autoregulation, or AS in relation to radiological markers of cSVD. Data were extracted in predefined tables, reviewed, and meta-analyses performed using inverse-variance random effects models to determine pooled odds ratios (ORs). A total of 1611 studies were identified; 142 were included in the systematic review, of which 60 had data available for meta-analyses. Systematic review revealed that CVR, cerebral autoregulation, and AS were consistently associated with cSVD (80.4%, 78.6%, and 85.4% of studies, respectively). Meta-analysis in 7 studies (536 participants, 32.9% women) revealed a borderline association between impaired CVR and cSVD (OR, 2.26 [95% CI, 0.99-5.14]; P=0.05). In 37 studies (27 952 participants, 53.0% women) increased AS, per SD, was associated with cSVD (OR, 1.24 [95% CI, 1.15-1.33]; P<0.01). Meta-regression adjusted for comorbidities accounted for one-third of the AS model variance (R2=29.4%, Pmoderators=0.02). Subgroup analysis of AS studies demonstrated an association with white matter hyperintensities (OR, 1.42 [95% CI, 1.18-1.70]; P<0.01).

CONCLUSIONS

The collective findings of the present systematic review and meta-analyses suggest an association between cSVD and impaired CVR and elevated AS. However, longitudinal investigations into vascular stiffness and regulatory function as possible risk factors for cSVD remain warranted.

Longitudinal Hemodynamic Correlates of and Sex Differences in the Evolution of Blood Pressure Across the Adult Lifespan: The Framingham Heart Study

Background Systolic blood pressure increases with age after midlife, particularly in women, and contributes to development of wide pulse pressure hypertension in middle-aged and older adults. Relative contributions of aortic stiffness and premature wave reflection to increases in pulse pressure remain controversial. Methods and Results We evaluated visit-specific values and change in key correlates of pulse pressure, aortic characteristic impedance, forward and backward wave amplitude, and global reflection coefficient, at 3 sequential examinations of the Framingham Generation 3 (N=4082), Omni-2 (N=410), and New Offspring Spouse (N=103) cohorts (53% women). Data were analyzed using repeated-measures linear mixed models adjusted for age, sex, and risk factor exposures. Pulse pressure increased markedly with age after midlife (age and age-squared terms, P<0.0001), particularly in women (age slope 3.1±0.2 mm Hg/decade higher in women, P<0.0001). In sex-specific models, change in pulse pressure was closely related (all P<0.0001) to baseline (6.7±0.2 and 7.3±0.2 mm Hg/SD in men and women, respectively) and change (11.8±0.1 and 11.7±0.1 mm Hg/SD) in forward wave amplitude, whereas relations with baseline (2.1±0.15 and 2.0±0.14 mm Hg/SD) and change (4.0±0.13 and 3.4±0.11 mm Hg/SD) in global reflection coefficient were weaker. Global reflection coefficient fell as aortic characteristic impedance increased (P<0.0001), consistent with the hypothesis that impedance matching reduces relative wave reflection in the arterial system. Conclusions Proximal aortic stiffening, as assessed by higher aortic characteristic impedance and larger forward wave amplitude, is strongly associated with longitudinal increase in pulse pressure, especially in women, whereas wave reflection has more modest relations.

Association of blood pressure variability during acute care hospitalization and incident dementia

Background and objectives

Recognized as a potential risk factor for Alzheimer's disease and related dementias (ADRD), blood pressure variability (BPV) could be leveraged to facilitate identification of at-risk individuals at a population level. Granular BPV data are available during acute care hospitalization periods for potentially high-risk patients, but the incident ADRD risk association with BPV measured in this setting is unknown. Our objective was to evaluate the relation of BPV, measured during acute care hospitalization, and incidence of ADRD.

Methods

We retrospectively studied adults, without a prior ADRD diagnosis, who were admitted to a large quaternary care medical center in Southern California between January 1, 2013 and December 31, 2019. For all patients, determined BPV, calculated as variability independent of the mean (VIM), using blood pressure readings obtained as part of routine clinical care. We used multivariable Cox proportional hazards regression to examine the association between BP VIM during hospitalization and the development of incident dementia, determined by new ICD-9/10 coding or the new prescription of dementia medication, occurring at least 2 years after the index hospitalization.

Results

Of 81,892 adults hospitalized without a prior ADRD diagnosis, 2,442 (2.98%) went on to develop ADRD (2.6 to 5.2 years after hospitalization). In multivariable-adjusted Cox models, both systolic (HR 1.05, 95% CI 1.00-1.09) and diastolic (1.06, 1.02-1.10) VIM were associated with incident ADRD. In pre-specified stratified analyses, the VIM associations with incident ADRD were most pronounced in individuals over age 60 years and among those with renal disease or hypertension. Results were similar when repeated to include incident ADRD diagnoses made at least 1 or 3 years after index hospitalization.

Discussion

We found that measurements of BPV from acute care hospitalizations can be used to identify individuals at risk for developing a diagnosis of ADRD within approximately 5 years. Use of the readily accessible BPV measure may allow healthcare systems to risk stratify patients during periods of intense patient-provider interaction and, in turn, facilitate engagement in ADRD screening programs.

Effects of Carotid Artery Stiffness on Cerebral Small-Vessel Disease and Cognition

Background Carotid artery stiffness is associated with cognitive impairment and dementia, but the underlying mechanisms remain unknown. We examined the associations of carotid artery stiffness with cerebral small-vessel disease markers, cognition, and dementia subtypes in a memory clinic cohort. Methods and Results A total of 272 participants underwent carotid ultrasonography, 3 Tesla brain magnetic resonance imaging, and neuropsychological assessment. Carotid ultrasonography was used to assess β-index, pressure-strain elastic modulus, and pulse-wave velocity-β. Brain magnetic resonance images were graded for cerebral small-vessel disease markers, including white matter hyperintensities, lacunes, and cerebral microbleeds. Participants were classified as having no cognitive impairment, cognitive impairment and no dementia, or dementia subtyped as Alzheimer disease and vascular dementia. Cognition was assessed using National Institute of Neurological Disorders and Stroke-Canadian Stroke Network harmonization battery. After adjusting for age, sex, cardiovascular risk factors, and diseases, multivariable models showed that β-index (β=0.69; P=0.002), elastic modulus (β=0.78; P<0.001), and pulse-wave velocity-β (β=0.80; P<0.001) were associated with white matter hyperintensities, and elastic modulus (odds ratio [OR], 1.39 [95% CI, 1.04-1.85]) and pulse-wave velocity-β (OR, 1.47 [95% CI, 1.10-1.98]) were independently associated with lacunes. Similarly, β-index (OR, 2.04 [95% CI, 1.14-4.13]), elastic modulus (OR, 2.22 [95% CI, 1.25-4.42]), and pulse-wave velocity-β (OR, 2.50 [95% CI, 1.36-5.18]) were independently associated with vascular dementia. Carotid stiffness measures were independently associated with worse performance in global cognition, visuomotor speed, visuospatial function, and executive function. These associations became largely nonsignificant after further adjusting for cerebral small-vessel disease markers. Conclusions In memory clinic patients, carotid artery stiffness was associated with white matter hyperintensities and lacunes, impairment in global and domain-specific cognition, and causative subtypes of dementia, particularly vascular. The effects of carotid stiffness on cognition were not independent of, and were partially mediated by, cerebral small-vessel disease.

The Relationship of Vascular Aging to Reduced Cognitive Function: Pulsatile and Steady State Arterial Hemodynamics

Aortic stiffness increases with age and is a robust predictor of cerebrovascular events and cognitive decline including Alzheimer's disease and other forms of dementia. Recent clinical studies have investigated the association between proximal aortic stiffness and pulsatile energy transmission that has deleterious effects on the cerebrovascular network in order to identify potential therapeutic targets. Aging causes disproportionate stiffening of the aorta compared with the carotid arteries, reducing protective impedance mismatches at their interface, increasing the transmission of destructive pulsatile pressure and energy to the cerebral circulation, and leading to cerebral small vessel disease. Thus, aortic stiffening and high-flow pulsatility are associated with alterations in the microvasculature of the brain, vascular endothelial dysfunction, and white matter damage, which contribute to impaired memory function with advancing age. Previous studies have also shown that silent lacunar infarcts and white matter hyperintensities are strongly associated with arterial stiffness. More and more evidence suggests that vascular etiologies, including aortic stiffness, impedance match, and microvascular damage, are associated with cognitive impairment and the pathogenesis of dementia. The measurement of arterial flow and pressure can help understand pulsatile hemodynamics and its impact on vital organs. Interventions that reduce aortic stiffness, such as improvement of the living environment, management of risk factors, and innovation and development of novel drugs, may reduce the risk for dementia.

Arterial Stiffness and Long-Term Risk of Health Outcomes: The Framingham Heart Study

BACKGROUND

Arterial stiffness increases with age and is associated with an increased risk of adverse outcomes on short-term follow-up (typically <10 years). Data regarding associations of arterial stiffness with health outcomes on longer-term follow-up are lacking.

METHODS

We evaluated 7283 Framingham Study participants (mean age 50 years, 53% women) who underwent assessment of carotid-femoral pulse wave velocity (a marker of arterial stiffness) via applanation tonometry at one or more routine examinations. We used time-dependent Cox proportional hazards regression models to relate carotid-femoral pulse wave velocity to the incidence of health outcomes (updating carotid-femoral pulse wave velocity and all covariates at serial examinations).

RESULTS

On long-term follow-up (median 15 years; minimum-maximum, 0-20), participants developed cardiometabolic disease (hypertension [1255 events]; diabetes [381 events]), chronic kidney disease (529 events), dementia (235 events), cardiovascular disease (684 events) and its components (coronary heart disease [314 events], heart failure [191 events], transient ischemic attacks or stroke [250 events]), and death (1086 events). In multivariable-adjusted models, each SD increment in carotid-femoral pulse wave velocity was associated with increased risk of hypertension (hazard ratio [HR], 1.32 [95% CI, 1.21-1.44]), diabetes (HR, 1.32 [95% CI, 1.11-1.58]), chronic kidney disease (1.19 [95% CI, 1.05-1.34]), dementia (HR 1.27 [95% CI, 1.06-1.53]), cardiovascular disease (HR, 1.20 [95% CI, 1.06-1.36]) and its components (coronary heart disease, HR 1.37 [95% CI, 1.13-1.65]; transient ischemic attack/stroke, HR, 1.24 [95% CI, 1.00-1.53]), and death (HR, 1.29 [95% CI, 1.17-1.43]). The association with heart failure was borderline nonsignificant (HR, 1.21 [95% CI, 0.98-1.51], P=0.08).

CONCLUSIONS

Our prospective observations of a large community-based sample establish the long-term prognostic importance of arterial stiffness for multiple health outcomes.

Is It Good to Have a Stiff Aorta with Aging? Causes and Consequences

Aortic stiffness increases with advancing age, more than doubling during the human life span, and is a robust predictor of cardiovascular disease (CVD) clinical events independent of traditional risk factors. The aorta increases in diameter and length to accommodate growing body size and cardiac output in youth, but in middle and older age the aorta continues to remodel to a larger diameter, thinning the pool of permanent elastin fibers, increasing intramural wall stress and resulting in the transfer of load bearing onto stiffer collagen fibers. Whereas aortic stiffening in early middle age may be a compensatory mechanism to normalize intramural wall stress and therefore theoretically "good" early in the life span, the negative clinical consequences of accelerated aortic stiffening beyond middle age far outweigh any earlier physiological benefit. Indeed, aortic stiffness and the loss of the "windkessel effect" with advancing age result in elevated pulsatile pressure and flow in downstream microvasculature that is associated with subclinical damage to high-flow, low-resistance organs such as brain, kidney, retina, and heart. The mechanisms of aortic stiffness include alterations in extracellular matrix proteins (collagen deposition, elastin fragmentation), increased arterial tone (oxidative stress and inflammation-related reduced vasodilators and augmented vasoconstrictors; enhanced sympathetic activity), arterial calcification, vascular smooth muscle cell stiffness, and extracellular matrix glycosaminoglycans. Given the rapidly aging population of the United States, aortic stiffening will likely contribute to substantial CVD burden over the next 2-3 decades unless new therapeutic targets and interventions are identified to prevent the potential avalanche of clinical sequelae related to age-related aortic stiffness.