Age-related cerebral white matter changes and pulse-wave encephalopathy: observations with three-dimensional MRI

Brain atrophy, reduced cerebral perfusion, arterial stiffening, and wall thickening with aging coincide with stimulus-specific changes in fMRI-BOLD responses

The aim of this study was to investigate how aging affects blood flow and structure of the brain. It was hypothesized older individuals would have lower gray matter volume (GMV), resting cerebral blood flow (CBF0), and depressed responses to isometabolic and neurometabolic stimuli. In addition, increased carotid-femoral pulse-wave velocity (PWV), carotid intima-media thickness (IMT), and decreased brachial flow-mediated dilation (FMD) would be associated with lower CBF0, cerebrovascular reactivity (CVR), and GMV. Brain scans (magnetic resonance imaging) and cardiovascular examinations were conducted in young (age = 24 ± 3 yr, range = 22-28 yr; n = 13) and old (age = 71 ± 4 yr; range = 67-82 yr, n = 14) participants, and CBF0, CVR [isometabolic % blood oxygen level-dependent (BOLD) in response to a breath hold (BH)], brain activation patterns during a working memory task (neurometabolic %BOLD response to N-back trial), GMV, PWV, IMT, and FMD were measured. CBF0 and to a lesser extent CVRBH were lower in the old group (P ≤ 0.050); however, the increase in the %BOLD response to the memory task was not blunted (P ≥ 0.2867). Age-related differential activation patterns during the working memory task were characterized by disinhibition of the default mode network in the old group (P < 0.0001). Linear regression analyses revealed PWV, and IMT were negatively correlated with CBF0, CVRBH, and GMV across age groups, but within the old group alone only the relationships between PWV-CVRBH and IMT-GMV remained significant (P ≤ 0.0183). These findings suggest the impacts of age on cerebral %BOLD responses are stimulus specific, brain aging involves alterations in cerebrovascular and possibly neurocognitive control, and arterial stiffening and wall thickening may serve a role in cerebrovascular aging.NEW & NOTEWORTHY Cerebral perfusion was lower in old versus young adults. %Blood oxygen level-dependent (BOLD) responses to an isometabolic stimulus and gray matter volume were decreased in old versus young adults and associated with arterial stiffening and wall thickening. The increased %BOLD response to a neurometabolic stimulus appeared unaffected by age; however, the old group displayed disinhibition of the default mode network during the stimulus. Thus, age-related alterations in cerebral %BOLD responses were stimulus specific and related to arterial remodeling.

Pulsatility analysis of the circle of Willis

Purpose

To evaluate the phenomenological significance of cerebral blood pulsatility imaging in aging research.

Methods

N = 38 subjects from 20 to 72 years of age (24 females) were imaged with ultrafast MRI with a sampling rate of 100 ms and simultaneous acquisition of pulse oximetry data. Of these, 28 subjects had acceptable MRI and pulse data, with 16 subjects between 20 and 28 years of age, and 12 subjects between 61 and 72 years of age. Pulse amplitude in the circle of Willis was assessed with the recently developed method of analytic phase projection to extract blood volume waveforms.

Results

Arteries in the circle of Willis showed pulsatility in the MRI for both the young and old age groups. Pulse amplitude in the circle of Willis significantly increased with age (p = 0.01) but was independent of gender, heart rate, and head motion during MRI.

Discussion and conclusion

Increased pulse wave amplitude in the circle of Willis in the elderly suggests a phenomenological significance of cerebral blood pulsatility imaging in aging research. The physiologic origin of increased pulse amplitude (increased pulse pressure vs. change in arterial morphology vs. re-shaping of pulse waveforms caused by the heart, and possible interaction with cerebrospinal fluid pulsatility) requires further investigation.

An Investigation of the Relationship Between Carotid Artery Stenosis and White Matter Hyperintensities

Introduction White matter hyperintensities (WMHs) are frequently detected on magnetic resonance imaging (MRI) with age. Although the etiology of WMH has not been fully explained, it was reported to be associated with internal carotid artery (ICA) stenosis as well as small vessel diseases. The number and volume of these lesions might increase in cases of internal carotid artery (ICA) stenosis. The present study aimed to calculate the localization and volumes of white matter lesions in the VolBrain Program and investigate the relationship between age and sex in patients with symptomatic and asymptomatic internal carotid artery stenosis. Methods MRI scans of patients with carotid stenosis with T1-weighted and fluid-attenuated inversion recovery (FLAIR) sequences were performed retrospectively for the present study, which had a retrospective design. The patients were divided into two groups (<70% and ≥70%) because endovascular intervention was considered in patients with asymptomatic stenosis over 70%. Digital subtraction angiography was used to detect carotid artery stenosis. They were also divided into four groups. According to laterality and degree of stenosis, ICA stenosis was separated as those with <70% stenosis on both sides (group 1), right side ICA <70%, left side ≥70% stenosis (group 2), right side ICA ≥70%, left side <70% stenosis (group 3), and ≥70% stenosis on both sides (group 4). A total of 102 patient images were selected that met the inclusion criteria. The measurements of white matter lesion volumes were made using the LesionBrain application in the VolBrain Program. Results The MRI of 82 patients (mean age: 65.55 ± 9.28 years), 28 females and 54 males, were used in the present study. According to LesionBrain Analysis, the total WMH volume was seen in the first and third groups at most. When analyzed in regional terms, stenosis was mostly detected in the first and third groups in the periventricular region. WMH volume was less in all areas in group 4. When examined according to the number of lesions, the most lesions were detected in the third group in the juxtacortical region. When the difference between the groups was examined, a significant difference was detected only in the volume change in the deep white region (p=0.011). No significant differences were found between WMH volumes and age and gender (p>0.05). Conclusion Stenosis of the external internal carotid artery might cause hypoperfusion and silent embolization in the brain. As a result, as well as pathological conditions in cortical areas, ischemic areas in the white matter might also cause cognitive disorders.

Brain deficit patterns of metabolic illnesses overlap with those for major depressive disorder: A new metric of brain metabolic disease

Metabolic illnesses (MET) are detrimental to brain integrity and are common comorbidities in patients with mental illnesses, including major depressive disorder (MDD). We quantified effects of MET on standard regional brain morphometric measures from 3D brain MRI as well as diffusion MRI in a large sample of UK BioBank participants. The pattern of regional effect sizes of MET in non-psychiatric UKBB subjects was significantly correlated with the spatial profile of regional effects reported by the largest meta-analyses in MDD but not in bipolar disorder, schizophrenia or Alzheimer's disease. We used a regional vulnerability index (RVI) for MET (RVI-MET) to measure individual's brain similarity to the expected patterns in MET in the UK Biobank sample. Subjects with MET showed a higher effect size for RVI-MET than for any of the individual brain measures. We replicated elevation of RVI-MET in a sample of MDD participants with MET versus non-MET. RVI-MET scores were significantly correlated with the volume of white matter hyperintensities, a neurological consequence of MET and age, in both groups. Higher RVI-MET in both samples was associated with obesity, tobacco smoking and frequent alcohol use but was unrelated to antidepressant use. In summary, MET effects on the brain were regionally specific and individual similarity to the pattern was more strongly associated with MET than any regional brain structural metric. Effects of MET overlapped with the reported brain differences in MDD, likely due to higher incidence of MET, smoking and alcohol use in subjects with MDD.

Cardiac-Related Pulsatility in the Insula Is Directly Associated With Middle Cerebral Artery Pulsatility Index

BACKGROUND

Arterial stiffness in large arteries is a risk factor for cerebral small vessel disease and neurodegeneration. The challenge of accessing intracranial pulsatility noninvasively is one reason few studies provide empirical insight on the relationship between large artery and tissue pulsatility in the human brain.

PURPOSE

To investigate the association between the functional magnetic resonance imaging (fMRI)-derived cardiac-related pulsatility in the insular cortex and the ultrasound-derived pulsatility index in the middle cerebral artery (MCA-PI).

STUDY TYPE

Cross-sectional.

POPULATION

Younger adults (11; 25 ± 4 years) and older adults with and without cardiovascular risk factors (44; 70 ± 6 years).

FIELD STRENGTH/SEQUENCE

T₁ -weighted, fluid attenuated inversion recovery, and T₂ *-weighted blood oxygenation level-dependent (BOLD) sequences at 3T.

ASSESSMENT

MCA-PI and cardiac-related pulsatility were assessed at rest by transcranial Doppler ultrasound and BOLD fMRI, respectively.

STATISTICAL TESTS

Multivariate analyses of covariance between MCA-PI and cardiac-related pulsatility. Analysis of variance was used to assess regional differences.

RESULTS

MCA-PI was associated with cardiac-related insular pulsatility (P = 0.037), but not whole-brain pulsatility (P = 0.81). Left insular pulsatility was higher than right insular pulsatility (P < 0.01) and was associated with diastolic blood pressure (P = 0.028).

DATA CONCLUSION

We show a correlation between ultrasound and fMRI measures of cerebrovascular pulsatility. This association provides insight into the transmission of pulsatile energy from large basal arteries at the Circle of Willis to downstream cerebrovascular beds and has implications for the utility of cardiac-related pulsatility as a potential marker for cerebral small vessel disease.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;51:1454-1462.

Carotid Flow Augmentation, Arterial Aging, and Cerebral White Matter Hyperintensities

Objective—

Aortic stiffness and pressure wave reflection are associated with age-related cerebral microvascular disease, but the underlying mechanism remains obscure. We hypothesized that cerebral (carotid) flow alterations potentially mediate these associations.

Approach and Results—

Doppler waveforms were recorded in 286 patients with hypertension to measure the carotid flow augmentation index (FAIx) as the late/early-systolic velocity amplitude ratio. Tonometric waveforms were recorded to estimate the aortic pressure AIx (PAIx), aortic compliance, and carotid-femoral and carotid-radial pulse wave velocities. Additionally, white matter hyperintensities on brain magnetic resonance imaging were evaluated using the Fazekas scale. With increasing age, the carotid late systolic velocity increased, whereas the early systolic velocity decreased, although the aortic augmented pressure increased in parallel with the incident wave height ( P <0.001). Both FAIx and PAIx increased with age, but the age-dependent curves were upwardly concave and convex, respectively. FAIx increased exponentially with increasing PAIx ( r =0.71). Compared with PAIx, FAIx was more closely ( P ≤0.001) correlated with the aortic pulse wave velocity, aortic compliance, and elastic/muscular pulse wave velocity ratio. FAIx was associated with white matter hyperintensities scores independently of confounders including age, sex, diabetes mellitus, hypercholesterolemia, and aortic pulse wave velocity ( P =0.01), and was more predictive of white matter hyperintensities presence than PAIx.

Conclusions—

Carotid FAIx had closer associations with age, aortic stiffness, and cerebral white matter hyperintensities than aortic PAIx. These results indicate that carotid flow augmentation (enhanced by aortic stiffening and pressure wave reflection from the lower body) causes microcerebrovascular injury potentially through increasing cerebral flow pulsations, but this detrimental effect is greater than that estimated from PAIx.

Cerebral Haemodynamics: Effects of Systemic Arterial Pulsatile Function and Hypertension

PURPOSE OF REVIEW

Concepts of pulsatile arterial haemodynamics, including relationships between oscillatory blood pressure and flow in systemic arteries, arterial stiffness and wave propagation phenomena have provided basic understanding of underlying haemodynamic mechanisms associated with elevated arterial blood pressure as a major factor of cardiovascular risk, particularly the deleterious effects of isolated systolic hypertension in the elderly. This topical review assesses the effects of pulsatility of blood pressure and flow in the systemic arteries on the brain. The review builds on the emerging notion of the "pulsating brain", taking into account the high throughput of blood flow in the cerebral circulation in the presence of mechanisms involved in ensuring efficient and regulated cerebral perfusion.

RECENT FINDINGS

Recent studies have provided evidence of the relevance of pulsatility and hypertension in the following areas: (i) pressure and flow pulsatility and regulation of cerebral blood flow, (ii) cerebral and systemic haemodynamics, hypertension and brain pathologies (cognitive impairment, dementia, Alzheimer's disease), (iii) stroke and cerebral small vessel disease, (iv) cerebral haemodynamics and noninvasive estimation of cerebral vascular impedance, (v) cerebral and systemic pulsatile haemodynamics and intracranial pressure, (iv) response of brain endothelial cells to cyclic mechanical stretch and increase in amyloid burden. Studies to date, producing increasing epidemiological, clinical and experimental evidence, suggest a potentially significant role of systemic haemodynamic pulsatility on structure and function of the brain.

Impact of pulse pressure on cerebrovascular events leading to age-related cognitive decline

Aging is a modern concept: human life expectancy has more than doubled in less than 150 yr in Western countries. Longer life span, however, reveals age-related diseases, including cerebrovascular diseases. The vascular system is a prime target of aging: the "wear and tear" of large elastic arteries exposed to a lifelong pulsatile pressure causes arterial stiffening by fragmentation of elastin fibers and replacement by stiffer collagen. This arterial stiffening increases in return the amplitude of the pulse pressure (PP), its wave penetrating deeper into the microcirculation of low-resistance, high-flow organs such as the brain. Several studies have associated peripheral arterial stiffness responsible for the sustained increase in PP, with brain microvascular diseases such as cerebral small vessel disease, cortical gray matter thinning, white matter atrophy, and cognitive dysfunction in older individuals and prematurely in hypertensive and diabetic patients. The rarefaction of white matter is also associated with middle cerebral artery pulsatility that is strongly dependent on PP and artery stiffness. PP and brain damage are likely associated, but the sequence of mechanistic events has not been established. Elevated PP promotes endothelial dysfunction that may slowly develop in parallel with the accumulation of proinflammatory senescent cells and oxidative stress, generating cerebrovascular damage and remodeling, as well as brain structural changes. Here, we review data suggesting that age-related increased peripheral artery stiffness may promote the penetration of a high PP to cerebral microvessels, likely causing functional, structural, metabolic, and hemodynamic alterations that could ultimately promote neuronal dysfunction and cognitive decline.

Prevalence of white matter hyperintensities increases with age

White matter hyperintensities (WMHs) that arise with age and/or atherosclerosis constitute a heterogeneous disorder in the white matter of the brain. However, the relationship between age-related risk factors and the prevalence of WMHs is still obscure. More clinical data is needed to confirm the relationship between age and the prevalence of WMHs. We collected 836 patients, who were treated in the Renmin Hospital, Hubei University of Medicine, China from January 2015 to February 2016, for a case-controlled retrospective analysis. According to T2-weighted magnetic resonance imaging results, all patients were divided into a WMHs group (n = 333) and a non-WMHs group (n = 503). The WMHs group contained 159 males and 174 females. The prevalence of WMHs increased with age and was associated with age-related risk factors, such as cardiovascular diseases, smoking, drinking, diabetes, hypertension and history of cerebral infarction. There was no significant difference in sex, education level, hyperlipidemia and hyperhomocysteinemia among the different age ranges. These findings confirm that age is an independent risk factor for the prevalence and severity of WMHs. The age-related risk factors enhance the occurrence of WMHs.

Endothelial Function Is Associated with White Matter Microstructure and Executive Function in Older Adults

Age-related declines in endothelial function can lead to cognitive decline. However, little is known about the relationships between endothelial function and specific neurocognitive functions. This study explored the relationship between measures of endothelial function (reactive hyperemia index; RHI), white matter (WM) health (fractional anisotropy, FA, and WM hyperintensity volume, WMH), and executive function (Trail Making Test (TMT); Trail B - Trail A). Participants were 36 older adults between the ages of 59 and 69 (mean age = 63.89 years, SD = 2.94). WMH volume showed no relationship with RHI or executive function. However, there was a positive relationship between RHI and FA in the genu and body of the corpus callosum. In addition, higher RHI and FA were each associated with better executive task performance. Tractography was used to localize the WM tracts associated with RHI to specific portions of cortex. Results indicated that the RHI-FA relationship observed in the corpus callosum primarily involved tracts interconnecting frontal regions, including the superior frontal gyrus (SFG) and frontopolar cortex, linked with executive function. These findings suggest that superior endothelial function may help to attenuate age-related declines in WM microstructure in portions of the corpus callosum that interconnect prefrontal brain regions involved in executive function.

Arterial Stiffening in Perspective: Advances in Physical and Physiological Science Over Centuries

Arterial stiffening is not a new issue in medicine or research but was the prime concern of Richard Bright in the early 19th century and of the prominent London physicians and pathologists who tried to unscramble the relationship between kidney, heart, and cerebrovascular disease and hardness of the pulse in the late 19th century. It was of major concern to medical educators including Osler and Mackenzie who were still active in practice 100 years ago. It is all too easy (when dependent on the Internet) to consider arterial stiffness to be a new issue. The terms arterial stiffness, aortic stiffness, or wave reflection do not appear as categories for articles such as this in respectable journals, nor in categories for meetings of specialized physicians. Yet as described in this article, the subject was of interest to clinicians, to investigators such as Harvey in the 17th century, and to physicists who developed laws and principles of elasticity from the study of biological materials including ligaments and arteries. This paper provides a perspective on arterial stiffness from the time of William Harvey and Isaac Newton to the present, with a glance into the future.

Arterial aging: pathophysiological principles

In the nineteenth century, prior to the introduction of the cuff sphygmomanometer, arteriosclerosis (stiffening of arteries) was recognized by clinicians and by life insurance companies as an indicator of vascular aging and cardiovascular risk, even in asymptomatic individuals. Through the twentieth century, views on aging came to focus on values of systolic and diastolic pressure and on obstructive atherosclerotic disease. Such focus deflected attention from the primary aging change which occurs in all societies, and is represented by stiffening and dilation of the proximal aorta. This review emphasizes the cushioning function of elastic arteries — principally the aorta — and how in youth this results in optimal interaction with the heart, and optimal steady flow through peripheral resistance vessels. Aortic stiffening with age is principally due to fatigue and fracture of elastin lamellae, with transfer of stress to stiffer collagenous components. Stiffening increases left ventricular load and myocardial blood requirement, but limits the capacity for blood supply during diastole. Consequences are cardiac failure and predisposition to ischaemia. The second, under-appreciated effect of aortic stiffening is transmission of flow pulsations downstream into vasodilated organs, principally brain and kidney, where pulsatile energy is dissipated and fragile microvessels are damaged. This accounts for micro infarcts and microhaemorrhages, with specialized cell damage, cognitive decline and renal failure. The aging process can be best monitored by change in the arterial pressure wave rather than by reliance on the cuff sphygmomanometer. This reintroduces the approaches by clinicians and life insurance examiners of the nineteenth century, endorses modern treatments for established disease, and holds the promise of detecting premature arterial degeneration, and better applying lifestyle measures and vasoactive medications to modify the aging process.

The Role of the Craniocervical Junction in Craniospinal Hydrodynamics and Neurodegenerative Conditions

The craniocervical junction (CCJ) is a potential choke point for craniospinal hydrodynamics and may play a causative or contributory role in the pathogenesis and progression of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, MS, and ALS, as well as many other neurological conditions including hydrocephalus, idiopathic intracranial hypertension, migraines, seizures, silent-strokes, affective disorders, schizophrenia, and psychosis. The purpose of this paper is to provide an overview of the critical role of the CCJ in craniospinal hydrodynamics and to stimulate further research that may lead to new approaches for the prevention and treatment of the above neurodegenerative and neurological conditions.

Vasculopathy of Aging and the Revised Cardiovascular Continuum

There have been attempts to explain the process of developments in overt cardiovascular disease, resulting in the presentation of the classic cardiovascular disease continuum and the aging cardiovascular continuum. Although the starting points of these two continua are different, they meet in the midstream of the cycle and reach a consensus at the end of the process. The announcement of the aging cardiovascular continuum made both continua complete, explaining the cardiovascular events in patients without atherosclerotic cardiovascular disease with aging. Impairment of the vascular structure by pulse wave and reflected wave is considered the cause of aortic damage, which influences the development of ischemic heart disease and the development of overt renal disease or cerebrovascular disease. The pathophysiology of vascular aging through pulse wave and its effect on other organs was discussed with Prof. Michael F. O'Rourke who devised the aging cardiovascular continuum.

Arterial stiffness, the brain and cognition: a systematic review

BACKGROUND

Arterial stiffness is a known predictor of cardiovascular disease, and has also been associated with markers of cerebral small vessel disease as well as poor cognitive function and cognitive decline. The consistency of these associations and their relationship to each other are unclear.

METHOD

We conducted a systematic review of the evidence associating arterial stiffness with cognitive function and cognitive decline, and with makers of cerebral small vessel disease, specifically lacunar infarcts and white matter hyperintensities.

RESULTS

Thirteen cross-sectional studies examining arterial stiffness and white matter hyperintensities or lacunar infarctions reported a positive association between increased arterial stiffness and radiological findings of cerebral small vessel disease. Two longitudinal studies examining the relationship between arterial stiffness and white matter hyperintensities found increased pulse wave velocity to be an independent predictor of white matter hyperintensity volume. Fifteen cross-sectional and seven longitudinal studies examining arterial stiffness and cognition were identified. Fourteen of the fifteen cross-sectional studies associated increased arterial stiffness with lower cognitive function, and six of the seven longitudinal studies found arterial stiffness to be predictive of cognitive decline.

CONCLUSION

Arterial stiffness is associated with cerebral small vessel disease and decreased cognitive function. However methodological limitations such as differing covariates between studies and an over-reliance on the MMSE to measure cognition are a concern across much of the literature.

Early detection of microstructural white matter changes associated with arterial pulsatility

Increased cerebral blood flow pulsatility is common in vascular dementia and is associated with macrostructural damage to cerebral white matter or leukoaraiosis (LA). In this study, we examine whether cerebral blood flow pulsatility is associated with macrostructural and microstructural changes in cerebral white matter in older adults with no or mild LA and no evidence of dementia. Diffusion Tensor Imaging was used to measure fractional anisotropy (FA), an index of the microstructural integrity of white matter, and radial diffusivity (RaD), a measure sensitive to the integrity of myelin. When controlling for age, increased arterial pulsation was associated with deterioration in both measures of white matter microstructure but not LA severity. A stepwise multiple linear regression model revealed that arterial pulsatility index was the strongest predictor of FA (R = 0.483, adjusted R (2) = 0.220), followed by LA severity, but not age. These findings suggest that arterial pulsatility may provide insight into age-related reduction in white matter FA. Specifically, increased arterial pulsatility may increase perivascular shear stress and lead to accumulation of damage to perivascular oligodendrocytes, resulting in microstructural changes in white matter and contributing to proliferation of LA over time. Changes in cerebral blood flow pulsatility may therefore provide a sensitive index of white matter health that could facilitate the early detection of risk for perivascular white matter damage and the assessment of the effectiveness of preventative treatment targeted at reducing pulsatility.

White matter hyperintensities on MRI in high-altitude U-2 pilots

OBJECTIVE

To demonstrate that U-2 pilot occupational exposure to hypobaria leads to increased incidence of white matter hyperintensities (WMH) with a more uniform distribution throughout the brain irrespective of clinical neurologic decompression sickness history.

METHODS

We evaluated imaging findings in 102 U-2 pilots and 91 controls matched for age, health, and education levels. Three-dimensional, T2-weighted, high-resolution (1-mm isotropic) imaging data were collected using fluid-attenuated inversion recovery sequence on a 3-tesla MRI scanner. Whole-brain and regional WMH volume and number were compared between groups using a 2-tailed Wilcoxon rank sum test.

RESULTS

U-2 pilots demonstrated an increase in volume (394%; p = 0.004) and number (295%; p < 0.001) of WMH. Analysis of regional distribution demonstrated WMH more uniformly distributed throughout the brain in U-2 pilots compared with mainly frontal distribution in controls.

CONCLUSION

Pilots with occupational exposure to hypobaria showed a significant increase in WMH lesion volume and number. Unlike the healthy controls with predominantly WMH in the frontal white matter, WMH in pilots were more uniformly distributed throughout the brain. This is consistent with our hypothesized pattern of damage produced by interaction between microemboli and cerebral tissue, leading to thrombosis, coagulation, inflammation, and/or activation of innate immune response, although further studies will be necessary to clarify the pathologic mechanisms responsible.

Hyperintense white matter lesions in 50 high-altitude pilots with neurologic decompression sickness

INTRODUCTION

Neurologic decompression sickness (NDCS) can affect high-altitude pilots, causing variable central nervous system symptoms. Five recent severe episodes prompted further investigation.

METHODS

We report the hyperintense white matter (HWM) lesion imaging findings in 50 U-2 pilot volunteers, and compare 12 U-2 pilots who experienced clinical NDCS to 38 U-2 pilots who did not. The imaging data were collected using a 3T magnetic resonance imaging scanner and high-resolution (1-mm isotropic) three-dimensional fluid-attenuated inversion recovery sequence. Whole-brain and regional lesion volume and number were compared between groups.

RESULTS

The NDCS group had significantly increased whole brain and insular volumes of HWM lesions. The intergroup difference in lesion numbers was not significant.

CONCLUSION

A clinical episode of NDCS was associated with a significant increase in HWM lesion volume, especially in the insula. We postulate this to be due to hypobaric exposure rather than hypoxia since all pilots were maintained on 100% oxygen throughout the flight. Further studies will be necessary to better understand the pathophysiology underlying these lesions.

P-selectin Expression Tracks Cerebral Atrophy in Mexican-Americans

Background and Purpose: We hypothesized that the P-selectin (SELP) gene, localized to a region on chromosome 1q24, pleiotropically contributes to increased blood pressure and cerebral atrophy. We tested this hypothesis by performing genetic correlation analyses for 13 mRNA gene expression measures from P-selectin and 11 other genes located in 1q24 region and three magnetic resonance imaging derived indices of cerebral integrity. Methods: The subject pool consisted of 369 (219F; aged 28–85, average = 47.1 ± 12.7 years) normally aging, community-dwelling members of large extended Mexican-American families. Genetic correlation analysis decomposed phenotypic correlation coefficients into genetic and environmental components among 13 leukocyte-based mRNA gene expressions and three whole-brain and regional measurements of cerebral integrity: cortical gray matter thickness, fractional anisotropy of cerebral white matter, and the volume of hyperintensive WM lesions. Results: From the 13 gene expressions, significant phenotypic correlations were only found for the P- and L-selectin expression levels. Increases in P-selectin expression levels tracked with decline in cerebral integrity while the opposite trend was observed for L-selectin expression. The correlations for the P-selectin expression were driven by shared genetic factors, while the correlations with L-selectin expression were due to shared environmental effects. Conclusion: This study demonstrated that P-selectin expression shared a significant variance with measurements of cerebral integrity and posits elevated P-selectin expression levels as a potential risk factor of hypertension-related cerebral atrophy.

Blood pressure and cerebral white matter share common genetic factors in Mexican Americans

Elevated arterial pulse pressure and blood pressure (BP) can lead to atrophy of cerebral white matter (WM), potentially attributable to shared genetic factors. We calculated the magnitude of shared genetic variance between BP and fractional anisotropy of water diffusion, a sensitive measurement of WM integrity in a well-characterized population of Mexican Americans. The patterns of whole-brain and regional genetic overlap between BP and fractional anisotropy were interpreted in the context the pulse-wave encephalopathy theory. We also tested whether regional pattern in genetic pleiotropy is modulated by the phylogeny of WM development. BP and high-resolution (1.7 × 1.7 × 3 mm; 55 directions) diffusion tensor imaging data were analyzed for 332 (202 females; mean age 47.9 ± 13.3 years) members of the San Antonio Family Heart Study. Bivariate genetic correlation analysis was used to calculate the genetic overlap between several BP measurements (pulse pressure, systolic BP, and diastolic BP) and fractional anisotropy (whole-brain and regional values). Intersubject variance in pulse pressure and systolic BP exhibited a significant genetic overlap with variance in whole-brain fractional anisotropy values, sharing 36% and 22% of genetic variance, respectively. Regionally, shared genetic variance was significantly influenced by rates of WM development (r=-0.75; P=0.01). The pattern of genetic overlap between BP and WM integrity was generally in agreement with the pulse-wave encephalopathy theory. Our study provides evidence that a set of pleiotropically acting genetic factors jointly influence phenotypic variation in BP and WM integrity. The magnitude of this overlap appears to be influenced by phylogeny of WM development, suggesting a possible role for genotype-by-age interactions.

The Cardiovascular Continuum extended: Aging effects on the aorta and microvasculature

The ‘Cardiovascular Continuum’ was described by Dzau and colleagues in 2006 to explain the development over many years of coronary disease with its complications, then end-stage heart failure. The Continuum identified different points along the way where the process could be interrupted by drug therapies or interventions, then described the trials that have been undertaken over the last three decades to establish their value. The approach summarized the major steps in cardiology through modern times, but it had an emphasis on coronary atherosclerosis in prosperous nations, and did not account fully for the problems of aging, which occur in all societies. Aging of the aorta and elastic arteries causes arterial stiffening and leads to development of cardiac failure and microvascular disease in highly perfused organs such as the brain and kidneys. The ‘Vascular Aging Continuum’ which we introduce, dovetails with the late phases of the Cardiovascular Continuum and provides a more comprehensive explanation, especially for vascular diseases in nations with little atherosclerosis. It will become more common in the Western World where attention to risk factors and widespread use of statins are responsible for a decrease in atherosclerotic disease, prolongation of life, and dominance of macrovascular and microvascular arterial disease, as well as of cardiac failure.

Risk of "silent stroke" in patients older than 60 years: risk assessment and clinical perspectives

With the increasing size of the elderly population and evolving imaging technology, silent brain infarction (SBI) has garnered attention from both the public and the physicians. Over 20% of the elderly exhibit SBI, and the prevalence of SBI increases steadily with age, ie, 30%–40% in those older than 70 years. Well-known cardiovascular risk factors such as hypertension has been identified as a risk factor of SBI (odds ratio [OR] = 3.47) Besides this, blood pressure (BP) reactivity to mental stress, morning BP surges, and orthostatic BP changes have been demonstrated to contribute to the presence of SBI. Further, a metabolic syndrome not only as a whole syndrome (OR =2.18) but also as individual components could have an influence on SBI. Increased C-reactive protein and interleukin-6, coronary artery disease, body mass index, and alcohol consumption have also been associated with SBI. The ORs and possible mechanisms have been discussed in this article. Overt stroke, dementia, depression, and aspiration pneumonia were all associated with SBI. (overt stroke: hazard ratio [HR] =1.9, 95% confidence interval [CI]: 1.2–2.8; dementia: HR =2.26, 95% CI: 1.09–4.70). We also looked into their close relationship with SBI in this review.

Whole brain and regional hyperintense white matter volume and blood pressure: overlap of genetic loci produced by bivariate, whole-genome linkage analyses

BACKGROUND AND PURPOSE

The volume of T2-hyperintense white matter (HWM) is an important neuroimaging marker of cerebral integrity with a demonstrated high heritability. Pathophysiology studies have shown that the regional, ependymal, and subcortical HWM lesions are associated with elevated arterial pulse pressure and arterial blood pressure (BP), respectively. We performed bivariate, whole-genome linkage analyses for HWM volumes and BP measurements to identify chromosomal regions that contribute jointly to both traits in a population of healthy Mexican Americans. Our aims were to localize novel quantitative trait loci acting pleiotropically on these phenotypes and to replicate previous genetic findings on whole brain HWM volume and BP measurements.

METHODS

BP measurements and volumes of whole-brain (WB), subcortical, and ependymal HWM lesions, measured from high-resolution (1 mm(3)) 3-dimensional fluid-attenuated inversion recovery images, served as focal quantitative phenotypes. Data were collected from 357 (218 females; mean age=47.9±13.2 years) members of large extended families who participated in the San Antonio Family Heart Study.

RESULTS

Bivariate genomewide linkage analyses localized a significant quantitative trait locus influencing WB and regional (ependymal) HWM volumes and pulse pressure and systolic BP to chromosomal location 1q24 between markers D1S196 and D1S1619. Several other chromosomal regions (1q42, 10q24-q26, and 15q26) exhibited suggestive linkages. The results of the post hoc analyses that excluded 55 subjects taking antihypertensive medication showed no substantive differences from the results obtained in the full cohort.

CONCLUSIONS

This study confirms several previously observed quantitative trait loci influencing BP and cerebral integrity and identifies a novel significant quantitative trait locus at chromosome 1q24. The genetic results strongly support a role for pleiotropically acting genes jointly influencing BP and cerebral white matter integrity.

Association of central systolic blood pressure with intracerebral small vessel disease in Japanese

BACKGROUND

Recent studies have reported the association between advanced arterial stiffness and brain small vessel diseases (SVDs). Two possible hemodynamic mechanisms, increases in central blood pressure (BP) and pulsatile flow load to the brain, have been speculated to link arterial stiffness and SVD. The carotid flow augmentation index (AI) has been proposed as an index of pulsatile flow to the brain. We compared its association with brain SVD with that of central BP in a general population.

METHODS

Subjects were 500 individuals free from symptomatic cardiovascular diseases with a mean age of 66.9 +/- 8.4 years. Brachial-ankle pulse wave velocity (baPWV) was measured as an index of arterial stiffness. Carotid flow AI was obtained by Doppler ultrasonography. The presence of silent cerebral lacunar infarcts (SCI) was determined as a manifestation of SVD by 3-tesla magnetic resonance imaging (MRI). Second peak radial systolic BP (SBP2) and pulse pressure (PP2) were used as estimates of central BP.

RESULTS

baPWV was significantly associated with radial BP2 (r = 0.55, P < 0.0001) but not with carotid flow AI (r = 0.03, P = 0.51). Radial BPs and baPWV, but not flow AI, were significantly higher in subjects with SCI. Radial SBP2 had higher odds ratio for the presence of SCI than brachial SBP, PP, and radial PP2. Logistic regression analysis showed that radial SBP2, but not flow AI, was independently related to the presence of SCI.

CONCLUSION

These findings indicate that the SBP2, an estimate of central SBP, is significantly associated with the presence of SVD in an apparently healthy general population.

Assessment of craniospinal pressure-volume indices

BACKGROUND AND PURPOSE

The PVI(CC) of the craniospinal compartment defines the shape of the pressure-volume curve and determines the damping of cyclic arterial pulsations. Despite no reports of direct measurements of the PVI(CC) among healthy elderly, it is believed that a change away from adequate accommodation of cardiac-related pulsations may be a pathophysiologic mechanism seen in neurodegenerative disorders such as Alzheimer disease and idiopathic normal pressure hydrocephalus. In this study, blood and CSF flow measurements are combined with lumbar CSF infusion measurements to assess the craniospinal PVI(CC) and its distribution of cranial and spinal compartments in healthy elderly.

MATERIALS AND METHODS

Thirty-seven healthy elderly were included (60-82 years of age). The cyclic arterial volume change and the resulting shift of CSF to the spinal compartment were quantified by PC-MR imaging. In addition, each subject underwent a lumbar CSF infusion test in which the magnitude of cardiac-related pulsations in intracranial pressure was quantified. Finally, the PVI was calculated by using a mathematic model.

RESULTS

After excluding 2 extreme values, the craniospinal PVI(CC) was calculated to a mean of 9.8 ± 2.7 mL and the estimated average 95% confidence interval of individual measurements was ± 9%. The average intracranial and spinal contributions to the overall compliance were 65% and 35% respectively (n = 35).

CONCLUSIONS

Combining lumbar CSF infusion and PC-MR imaging proved feasible and robust for assessment of the craniospinal PVI(CC). This study produced normative values and showed that the major compensatory contribution was located intracranially.

Limitations of the usual blood-pressure hypothesis and importance of variability, instability, and episodic hypertension

Although hypertension is the most prevalent treatable vascular risk factor, how it causes end-organ damage and vascular events is poorly understood. Yet, a widespread belief exists that underlying usual blood pressure can alone account for all blood-pressure-related risk of vascular events and for the benefits of antihypertensive drugs, and this notion has come to underpin all major clinical guidelines on diagnosis and treatment of hypertension. Other potentially informative measures, such as variability in clinic blood pressure or maximum blood pressure reached, have been neglected, and effects of antihypertensive drugs on such measures are largely unknown. Clinical guidelines recommend that episodic hypertension is not treated, and the potential risks of residual variability in blood pressure in treated hypertensive patients have been ignored. This Review discusses shortcomings of the usual blood-pressure hypothesis, provides background to accompanying reports on the importance of blood-pressure variability in prediction of risk of vascular events and in accounting for benefits of antihypertensive drugs, and draws attention to clinical implications and directions for future research.

Analysis of genetic variability and whole genome linkage of whole-brain, subcortical, and ependymal hyperintense white matter volume

BACKGROUND AND PURPOSE

The cerebral volume of T2-hyperintense white matter (HWM) is an important neuroimaging marker of cerebral integrity. Pathophysiology studies identified that subcortical and ependymal HWM are produced by 2 different mechanisms but shared a common risk factor: high arterial pulse pressure. Recent studies have demonstrated high heritability of the whole-brain HMW volume and reported significant and suggestive evidence of genetic linkage. We performed heritability and whole-genome linkage analysis to replicate previous reported findings and to study shared genetic variance, and possible overlap for specific loci, between subcortical and ependymal HWM volumes in a population of healthy Mexican Americans.

METHODS

The volumes of subcortical and ependymal HWM regions were measured from high-resolution (1 mm(3)), 3-dimensional fluid-attenuated inversion recovery images acquired for 459 (283 females, 176 males) active participants in the San Antonio Family Heart Study. Subjects ranged in age from 19 to 85 years of age (47.9+/-13.5 years) and were part of 49 families (9.4+/-8.5 individuals per family).

RESULTS

The volumes of whole-brain, subcortical, and ependymal HWM were highly heritable (h(2)=0.72, 0.66, and 0.73, respectively). The subcortical and ependymal HWM volumes shared 21% of genetic variability indicating significant pleiotropy. Genomewide linkage analysis showed only a suggestive bivariate linkage for subcortical and ependymal HWM volumes (log of odds=2.12) on chromosome 1 at 288 cM.

CONCLUSIONS

We replicated previous findings of high heritability for the whole-brain HWM volume. We also showed that subcortical and ependymal volume shared a significant portion of genetic variability and the bivarate linkage analysis produced a suggestive linkage near the locus previously identified in a study of whole-brain HWM volume and arterial pulse pressure.

Assessing cerebrovascular contribution to late dementia of the Alzheimer's type: the role of combined hemodynamic and structural MR analysis

The critical question as to the respective role of Alzheimer's disease (AD) and cerebrovascular disease in dementia of the Alzheimer's type (DAT), the most common form of dementia, is still debated. But there has been considerable progress in understanding cerebral hemodynamics and the relationship between structural brain damage and cognitive decline, in routine neuro imaging techniques. These advances now allow the proposition of a novel MR classification of DAT including indicators of both cerebrovascular function and regional brain atrophy. MR indicators of windkessel function include the arterial pulsatility index, the intracranial blood stroke volume, the cerebral relative venous outflow rates and a relative index of craniospinal compliance. MR indicators of vascular conduct function include total arterial and superficial venous flow rates that are closely related to brain metabolism. Structural MR sequences allow the detection of structural markers of windkessel dysfunction and, beyond the non specific hippocampal atrophy, a more extensive AD-like MR pattern of atrophy. The first illustration of this MR classification in elderly patients that later progressed to dementia converges with recent neuropathological observations to suggest that the major enemy to combat in late-life dementia is not AD but cerebrovascular dysfunction.

Leukoaraiosis and pulse-wave encephalopathy: observations with phase-contrast MRI in mild cognitive impairment

PURPOSE

To test the pathogenic hypothesis of a breakdown in the vital buffering of the arterial pulsations behind leukoaraiosis (LA) in mild cognitive impairment (MCI).

METHODS

Seventy-one elderly patients with MCI underwent a combined structural and dynamic MR examination (3D T1-weighted and fast-FLAIR T2-weighted sequences, phase contrast sequences). Arterial indices of pulsatility (IP) and composite indicators of the amplitude transfer function between cerebrospinal fluid and cerebral venous flow (Icsf/veins) were used to assess the large artery stiffness and the intracranial compliance respectively. Cerebral total arterial blood flow (tCBF), superficial and deep venous flow rates were also measured. Intracranial dynamic parameters and potential confounders including age, gender and vascular risk factors were compared between two groups respectively with and without significant LA.

RESULTS

The only dynamic changes on multivariate analyse were an IP increase, a lowering of deep venous outflow and Icsf/veins in patients with LA. There was a significant interaction between IP and Icsf/veins in the logistic regression: as compared with patients with low IP (suggestive of high large artery compliance) and high Icsf/veins (suggestive of high intracranial compliance), the adjusted odds ratios for the presence of LA were 9 (95% CI 1-64, P=0.02) in cases of both high IP and Icsf/veins, 10 (95% CI 1-64, P=0.02) in cases of both high IP and low Icsf/veins and 19 (95% CI 3-127, P=0.002) in cases of both low IP and Icsf/veins.

CONCLUSION

LA may reflect an arteriosclerotic and/or resistive pulse wave encephalopathy in MCI.

Classifying late-onset dementia with MRI: is arteriosclerotic brain degeneration the most common cause of Alzheimer's syndrome?

Our aim was to use early magnetic resonance imaging (MRI) to investigate the causes of cognitive decline in elderly people with mild cognitive impairment (MCI). Baseline structural and flow quantification MR sequences, and clinical and neuropsychological follow-up for at least two years, were performed on 62 elderly subjects with MCI. Of these subjects, 17 progressed to dementia, and 15 of these progressed to dementia of the Alzheimer type (DAT). Conversion to clinically diagnosed DAT was related to six distinct MR profiles, including one profile suggesting severe AD (20% of these converters) and five profiles suggesting severe cerebrovascular dysfunction. Two profiles suggested arteriosclerotic brain degeneration, one profile suggested severe venous windkessel dysfunction, and two suggested marked cerebral hypoperfusion associated with very low craniospinal compliance or marked brain atrophy. As compared with vascular MR type converters, AD MR type converters showed high executive and mobility predementia performances. Severe whole anteromesial temporal atrophy and predominantly left brain atrophy on visual MR analysis was only observed in AD MR type converters. In conclusion, these observations enhance the pathogenic complexity of the Alzheimer syndrome, and suggest that the role of arteriosclerotic brain degeneration in late life dementia is underestimated.

Improvement after cerebrospinal fluid drainage is related to levels of N-acetyl-aspartate in idiopathic normal pressure hydrocephalus

OBJECTIVE

This study uses proton magnetic resonance spectroscopy to investigate whether or not idiopathic normal pressure hydrocephalus is associated with neuronal dysfunction or ischemia in the brain. We evaluate whether or not proton magnetic resonance spectroscopy is useful for predicting improvement after long-term external lumbar drainage (ELD) of cerebrospinal fluid.

METHODS

Eighteen patients (mean age, 73 yr; six women) and 10 matching controls participated. Participants were characterized by clinical features, cognitive and motor function tests, and cerebrospinal fluid hydrodynamics (patients only). Signals from N-acetyl-aspartate (NAA), choline, lactate, and creatine (Cr) (reference) were sampled once in controls and twice in patients (before and after a 3-day ELD of approximately 135 mL/24 h) by proton magnetic resonance spectroscopy (1.5 T) from a 7.2-mL volume in the frontal white matter. Improvement was defined by video recordings of the patients' gait.

RESULTS

Sixteen patients finished the ELD (one patient had meningitis, and one patient had catheter insertion failure) with a mean drain volume of 395 mL. NAA/Cr ratios were lower in patients than in controls (1.60 versus 1.84, P = 0.02), but no difference was found for choline/Cr ratios. No lactate signals were detected. Fifty percent of patients improved after ELD. They had higher NAA/Cr ratios than nonimproved patients (1.70 versus 1.51, P = 0.01), but no differences were found in choline/Cr ratios or drain volume.

CONCLUSION

NAA/Cr ratios were decreased in patients with idiopathic normal pressure hydrocephalus, which is consistent with neuronal dysfunction in the frontal white matter. Improved patients had NAA/Cr ratios close to normal, indicating that enough functional neurons are a prerequisite for the cerebrospinal fluid drainage to have an effect.

Alzheimer’s disease in late-life dementia: A minor toxic consequence of devastating cerebrovascular dysfunction

Alzheimer's disease (AD) is thought to be the most common cause of late-life dementia. But pure AD is infrequent whereas AD pathology is often insufficient to explain dementia in the elderly. Conversely, cerebrovascular disease is omnipresent and the crucial role of microvascular alterations increasingly recognized in late dementia or "Alzheimer syndrome". Pathomechanisms of vascular cognitive impairment are still debated but recent data indicate that the initial concept of chronic low grade cerebral hypoxia should not have been abandoned. Thus, it is proposed that windkessel dysfunction is the missing link between vascular and craniospinal senescence on the one hand, and chronic low grade cerebral hypoxia, "senile brain degeneration" and "Alzheimer syndrome" on the other hand. An age-related decrease in the buffering capacity of both the vessels and the craniospinal cavity favours cerebral hypoxia; due to increased capillary pulsatility with disturbances in capillary exchanges or due to a marked reduction in craniospinal compliance with a mechanical reduction in cerebral arterial inflow. "Invisible" windkessel dysfunction, most often related to "hardening of the arteries" may be the most frequent pathomechanism of late-onset dementia whereas associated mild or moderate AD may be merely a toxic manifestation of a primarily hypoxic disease. Structural patterns of arteriosclerotic dementia fit well with an underlying arterial windkessel dysfunction: with secondary mechanical damage to the cerebral small vessels and the brain and predominantly deep hypoxia. The clinical significance of leukoaraïosis, small foci of necrosis, ventricular dilatation, hippocampal and cortical atrophy is in good agreement with their value as indirect markers of windkessel dysfunction. An age-related "invisible" reduction in craniospinal compliance may also contribute to the associations between heart failure, arterial hypotension and cognitive impairment in the elderly and to the high percentage of dementia of unknown origin in the very old. Both neuropathological and clinical overlap between AD and windkessel dysfunction can explain that cerebrovascular dysfunction remains misdiagnosed for AD in the elderly. Evidence of the key role of cerebrovascular dysfunction should markedly facilitate and widen therapeutic research in late-life dementia. Routine MRI including direct assessment of intracranial dynamics should be increasingly used to define etiological subtypes of the "Alzheimer syndrome" and develop a well-targeted therapeutic strategy.

MRI of the 'Alzheimer syndrome'

Interest in the identification of cognitive decline in its earliest manifestations and the heterogeneity of clinically diagnosed Alzheimer's disease (AD) explain the growing number of neuroimaging studies of AD. Alzheimer-type lesions are associated with loss of neurons, and magnetic resonance imaging (MRI) can detect predominantly left atrophic changes in the entorhinal cortex, amygdala and anterior hippocampus several years before the onset of clinical symptoms. Cerebrovascular disease can mimic AD in the elderly whereas MR markers of subcortical vascular disease-leukoaraiosis, lacunar infarcts, microbleeds, ventricular enlargement, cortical and hippocampal atrophy-appear to be structural changes associated with vascular-related cognitive impairment. Furthermore, analysis of prodromal forms of late-onset dementia of Alzheimer's type (DAT) differentiates amnesic single-domain mild cognitive impairment, which shows MR patterns similar to those observed in early-onset DAT, from other predementia patterns without atrophy at the earliest sites of AD pathology. Mesiotemporal atrophy on MRI predicts late-onset DAT, but the current rating scales or measurements of mesiotemporal atrophy do not differentiate anteromesial temporal atrophy that is highly suggestive of AD from predominantly hippocampal atrophy, suggestive of non-AD damage and, usually, vascular disease. The other, most common MRI predictors of late-onset DAT may be considered indirect markers of arterial senescence whereas brain atrophy is diffusely milder and MR markers of small-vessel disease more frequent in late-onset, compared with early-onset, DAT. Thus, MRI suggests an overestimation of AD pathology while underestimating 'arteriosclerotic brain degeneration' in the clinical picture of 'Alzheimer syndrome'.

Mechanical factors in arterial aging: a clinical perspective

The human arterial system in youth is beautifully designed for its role of receiving spurts of blood from the left ventricle and distributing this as steady flow through peripheral capillaries. Central to such design is "tuning" of the heart to arterial tree; this minimizes aortic pressure fluctuations and confines flow pulsations to the larger arteries. With aging, repetitive pulsations (some 30 million/year) cause fatigue and fracture of elastin lamellae of central arteries, causing them to stiffen (and dilate), so that reflections return earlier to the heart; in consequence, aortic systolic pressure rises, diastolic pressure falls, and pulsations of flow extend further into smaller vessels of vasodilated organs (notably the brain and kidney). Stiffening leads to increased left ventricular (LV) load with hypertrophy, decreased capacity for myocardial perfusion, and increased stresses on small arterial vessels, particularly of brain and kidney. Clinical manifestations are a result of diastolic LV dysfunction with dyspnea, predisposition to angina, and heart failure, and small vessel degeneration in brain and kidney with intellectual deterioration and renal failure. While aortic stiffening is the principal cause of cardiovascular disease with age in persons who escape atherosclerotic complications, it is not a specific target for therapy. The principal target is the smooth muscle in distributing arteries, whose relaxation has little effect on peripheral resistance but causes substantial reduction in the magnitude of wave reflection. Such relaxation is achieved through regular exercise and with the vasodilating drugs that are used in modern treatment of hypertension and cardiac failure.

Age-Related Changes in Carotid Artery Flow and Pressure Pulses

BACKGROUND AND PURPOSE

We sought to establish the relation between the pulsatile components of pressure and flow waveforms in the carotid artery and their change with age.

METHODS

Distention (pressure) and axial flow velocity waveforms were recorded noninvasively and simultaneously from the common carotid artery of 56 healthy subjects aged 20 to 72 years.

RESULTS

There was a close relation between the time intervals of pressure and flow waves: from foot to first shoulder or peak, to second shoulder or peak, and to incisura (r=0.97, P<0.0001 for each), which approximated the line of identity. The peak and nadir of flow velocity decreased with age, but late systolic flow augmentation increased substantially (1.6 times in the older group); this can be attributed to earlier wave reflection from the lower body. Pressure augmentation index (PAI) and flow augmentation index (FAI) increased similarly with age (PAI (%) = 0.84 x age - 26.6; FAI (%) = 0.75 x age + 11.9; both P<0.0001).

CONCLUSIONS

Arterial stiffening with aging increases carotid flow augmentation and can explain the increasing flow fluctuations in cerebral blood vessels. Measurement of carotid FAI may provide a gauge for risk of cerebral microvascular damage, just as PAI provides a gauge for risk of left ventricular hypertrophy and failure.