Cerebral blood flow in normal aging adults: cardiovascular determinants, clinical implications, and aerobic fitness

Endothelin B receptor dysfunction mediates elevated myogenic tone in cerebral arteries from aged male Fischer 344 rats

The human brain requires adequate cerebral blood flow to meet the high demand for nutrients and to clear waste products. With age, there is a chronic reduction in cerebral blood flow in small resistance arteries that can eventually limit proper brain function. The endothelin system is a key mediator in the regulation of cerebral blood flow, but the contributions of its constituent receptors in the endothelial and vascular smooth muscle layers of cerebral arteries have not been well defined in the context of aging. We isolated posterior cerebral arteries from young and aged Fischer 344 rats, as well as ET_B receptor knock-out rats and mounted the vessels in plexiglass pressure myograph chambers to measure myogenic tone in response to increasing pressure and targeted pharmacological treatments. We used an ET_A receptor antagonist (BQ-123), an ET_B receptor antagonist (BQ-788), endothelin-1, an endothelin-1 synthesis inhibitor (phosphoramidon), and vessel denudation to dissect the roles of each receptor in aging vasculature. Aged rats exhibited a higher myogenic tone than young rats, and the tone was sensitive to the ET_A antagonist, BQ-123, but insensitive to the ET_B antagonist, BQ-788. By contrast, the tone in the vessels from young rats was raised by BQ-788 but unaffected by BQ-123. When the endothelial layer that is normally enriched with ET_B1 receptors was removed from young vessels, myogenic tone increased. However, denudation of the endothelial layer did not influence vessels from aged animals. This indicated that endothelial ET_B1 receptors were not functional in the vessels from aged rats. There was also an increase in ET_A receptor expression with age, whereas ET_B receptor expression remained constant between young and aged animals. These results demonstrate that in young vessels, ET_B1 receptors maintain a lower myogenic tone, but in aged vessels, a loss of ET_B receptor activity allows ET_A receptors in vascular smooth muscle cells to raise myogenic tone. Our findings have potentially important clinical implications for treatments to improve cerebral perfusion in older adults with diseases characterized by reduced cerebral blood flow.

Separating vascular and neuronal effects of age on fMRI BOLD signals

Accurate identification of brain function is necessary to understand the neurobiology of cognitive ageing, and thereby promote well-being across the lifespan. A common tool used to investigate neurocognitive ageing is functional magnetic resonance imaging (fMRI). However, although fMRI data are often interpreted in terms of neuronal activity, the blood oxygenation level-dependent (BOLD) signal measured by fMRI includes contributions of both vascular and neuronal factors, which change differentially with age. While some studies investigate vascular ageing factors, the results of these studies are not well known within the field of neurocognitive ageing and therefore vascular confounds in neurocognitive fMRI studies are common. Despite over 10 000 BOLD-fMRI papers on ageing, fewer than 20 have applied techniques to correct for vascular effects. However, neurovascular ageing is not only a confound in fMRI, but an important feature in its own right, to be assessed alongside measures of neuronal ageing. We review current approaches to dissociate neuronal and vascular components of BOLD-fMRI of regional activity and functional connectivity. We highlight emerging evidence that vascular mechanisms in the brain do not simply control blood flow to support the metabolic needs of neurons, but form complex neurovascular interactions that influence neuronal function in health and disease. This article is part of the theme issue 'Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity'.

Older age and male sex are associated with higher cerebrovascular impedance

Cerebral blood flow (CBF) becomes pulsatile in response to the pulsatile change in perfusion pressure that is regulated by cerebrovascular impedance. In this study, we aimed to characterize age-related differences in cerebrovascular impedance across the adult lifespan. Carotid artery pressure [(CAP), via applanation tonometry] and CBF velocity (CBFV) in the middle cerebral artery (via transcranial Doppler) were measured in 148 healthy adults (21-79 yr, 62% women). Cerebrovascular impedance was quantified using transfer function analysis. Coherence between changes in CBFV and CAP was >0.90 in the frequency range of 0.78-2.73 Hz, suggesting a linear dynamic relationship between these two variables. Impedance modulus at the first harmonics (0.78-1.56 Hz) of CBFV and CAP oscillations (Z₁), reflecting mainly heart rate frequency, was 20% higher in the old (>64 yr, P = 0.002) and 13% higher in the middle-aged (45-64 yr, P = 0.08) than in young individuals (<45 yr). In addition, Z₁ was 24% higher in men than in women (P < 0.001). Multiple linear regression analysis revealed that Z₁ is negatively associated with systolic (β = -0.470), diastolic (β = -0.418), pulsatile (β = -0.374), and mean CBFV (β = -0.473; P < 0.001 for all) after adjustment for age, sex, and body mass index (BMI). These results suggest that older age and male sex are associated with higher cerebrovascular impedance than young individuals, which may contribute to brain hypoperfusion.NEW & NOTEWORTHY Impedance modulus at the first harmonics of cerebral blood flow velocity (CBFV) and carotid artery pressure oscillations (Z₁) was higher in the old (>64 yr) than in the young individuals (<45 yr), and it was higher in men than in women. Z₁ is negatively associated with CBFV after adjustment for age, sex, and body mass index. Increases in cerebrovascular impedance with age may buffer systemic arterial pressure fluctuations at the cost of increased brain hypoperfusion risk.

Gastrodia elata Blume (Tianma): Hope for Brain Aging and Dementia

Since aging-related diseases, including dementia, represent major public health threats to our society, physician-scientists must develop innovative, interdisciplinary strategies to open new avenues for development of alternative therapies. One such novel approach may lie in traditional Chinese medicine (TCM). Gastrodia elata Blume (G. elata, tianma) is a TCM frequently used for treatment of cerebrocardiovascular diseases (CCVDs). Recent studies of G. elata-based treatment modalities, which have investigated its pharmacologically relevant activity, potential efficacy, and safety, have employed G. elata in well-characterized, aging-related disease models, with a focus on models of aging-related dementia, such as Alzheimer's disease (AD). Here, I examine results from previous studies of G. elata, as well as related herbal preparations and pure natural products, as prophylaxis and remedies for aging-related CCVDs and dementia. Concluding, data suggest that tianma treatment may be used as a promising complementary therapy for AD.

Review of the structural and functional brain changes associated with chronic kidney disease

Chronic kidney disease (CKD) leads to profound metabolic and hemodynamic changes, which damage other organs, such as heart and brain. The brain abnormalities and cognitive deficit progress with the severity of the CKD and are mostly expressed among hemodialysis patients. They have great socio-economic impact. In this review, we present the current knowledge of involved mechanisms.

Renin-Angiotensin System and Alzheimer's Disease Pathophysiology: From the Potential Interactions to Therapeutic Perspectives

New roles of the Renin-Angiotensin System (RAS), apart from fluid homeostasis and Blood Pressure (BP) regulation, are being progressively unveiled, since the discoveries of RAS alternative axes and local RAS in different tissues, including the brain. Brain RAS is reported to interact with pathophysiological mechanisms of many neurological and psychiatric diseases, including Alzheimer's Disease (AD). Even though AD is the most common cause of dementia worldwide, its pathophysiology is far from elucidated. Currently, no treatment can halt the disease course. Successive failures of amyloid-targeting drugs have challenged the amyloid hypothesis and increased the interest in the inflammatory and vascular aspects of AD. RAS compounds, both centrally and peripherally, potentially interact with neuroinflammation and cerebrovascular regulation. This narrative review discusses the AD pathophysiology and its possible interaction with RAS, looking forward to potential therapeutic approaches. RAS molecules affect BP, cerebral blood flow, neuroinflammation, and oxidative stress. Angiotensin (Ang) II, via angiotensin type 1 receptors may promote brain tissue damage, while Ang-(1-7) seems to elicit neuroprotection. Several studies dosed RAS molecules in AD patients' biological material, with heterogeneous results. The link between AD and clinical conditions related to classical RAS axis overactivation (hypertension, heart failure, and chronic kidney disease) supports the hypothesized role of this system in AD. Additionally, RAStargeting drugs as Angiotensin Converting Enzyme inhibitors (ACEis) and Angiotensin Receptor Blockers (ARBs) seem to exert beneficial effects on AD. Results of randomized controlled trials testing ACEi or ARBs in AD are awaited to elucidate whether AD-RAS interaction has implications on AD therapeutics.

Arterial Spin Labeling Applications in Pediatric and Adult Neurologic Disorders

Arterial spin labeling (ASL) is a powerful noncontrast magnetic resonance imaging (MRI) technique that enables quantitative evaluation of brain perfusion. To optimize the clinical and research utilization of ASL, radiologists and physicists must understand the technical considerations and age-related variations in normal and disease states. We discuss advanced applications of ASL across the lifespan, with example cases from children and adults covering a wide variety of pathologies. Through literature review and illustrated clinical cases, we highlight the subtleties as well as pitfalls of ASL interpretation. First, we review basic physical principles, techniques, and artifacts. This is followed by a discussion of normal perfusion variants based on age and physiology. The three major categories of perfusion abnormalities-hypoperfusion, hyperperfusion, and mixed patterns-are covered with an emphasis on clinical interpretation and relationship to the disease process. Major etiologies of hypoperfusion include large artery, small artery, and venous disease; other vascular conditions; global hypoxic-ischemic injury; and neurodegeneration. Hyperperfusion is characteristic of vascular malformations and tumors. Mixed perfusion patterns can be seen with epilepsy, migraine, trauma, infection/inflammation, and toxic-metabolic encephalopathy. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY STAGE: 3.

Role of Regular Physical Activity in Neuroprotection against Acute Ischemia

One of the major obstacles that prevents an effective therapeutic intervention against ischemic stroke is the lack of neuroprotective agents able to reduce neuronal damage; this results in frequent evolution towards a long-term disability with limited alternatives available to aid in recovery. Nevertheless, various treatment options have shown clinical efficacy. Neurotrophins such as brain-derived neurotrophic factor (BDNF), widely produced throughout the brain, but also in distant tissues such as the muscle, have demonstrated regenerative properties with the potential to restore damaged neural tissue. Neurotrophins play a significant role in both protection and recovery of function following neurological diseases such as ischemic stroke or traumatic brain injury. Unfortunately, the efficacy of exogenous administration of these neurotrophins is limited by rapid degradation with subsequent poor half-life and a lack of blood-brain-barrier permeability. Regular exercise seems to be a therapeutic approach able to induce the activation of several pathways related to the neurotrophins release. Exercise, furthermore, reduces the infarct volume in the ischemic brain and ameliorates motor function in animal models increasing astrocyte proliferation, inducing angiogenesis and reducing neuronal apoptosis and oxidative stress. One of the most critical issues is to identify the relationship between neurotrophins and myokines, newly discovered skeletal muscle-derived factors released during and after exercise able to exert several biological functions. Various myokines (e.g., Insulin-Like Growth Factor 1, Irisin) have recently shown their ability to protects against neuronal injury in cerebral ischemia models, suggesting that these substances may influence the degree of neuronal damage in part via inhibiting inflammatory signaling pathways. The aim of this narrative review is to examine the main experimental data available to date on the neuroprotective and anti-ischemic role of regular exercise, analyzing also the possible role played by neurotrophins and myokines.

Cardiorespiratory Fitness Associates with Cerebral Vessel Pulsatility in a Cohort Enriched with Risk for Alzheimer's Disease

BACKGROUND

There is increasing evidence that vascular disease risk factors contribute to evolution of the dementia syndrome of Alzheimer's disease (AD). One important measure of cerebrovascular health is pulsatility index (PI) which is thought to represent distal vascular resistance, and has previously been reported to be elevated in AD clinical syndrome. Physical inactivity has emerged as an independent risk factor for cardiovascular disease.

OBJECTIVE

This study aims to examine the relationship between a measure of habitual physical activity, cardiorespiratory fitness (CRF), and PI in the large cerebral vessels.

METHODS

Ninety-two cognitively-healthy adults (age = 65.34±5.95, 72% female) enrolled in the Wisconsin Registry for Alzheimer's Prevention participated in this study. Participants underwent 4D flow brain MRI to measure PI in the internal carotid artery (ICA), basilar artery, middle cerebral artery (MCA), and superior sagittal sinus. Participants also completed a self-report physical activity questionnaire. CRF was calculated using a previously-validated equation that incorporates sex, age, body-mass index, resting heart rate, and self-reported physical activity. A series of linear regression models adjusted for age, sex, APOE4 status, and 10-year atherosclerotic cardiovascular disease risk were used to analyze the relationship between CRF and PI.

RESULTS

Inverse associations were found between CRF and mean PI in the inferior ICA (p = .001), superior ICA (p = .035), and basilar artery (p = .040). No other cerebral vessels revealed significant associations between CRF and PI (p≥.228).

CONCLUSIONS

Higher CRF was associated with lower PI in several large cerebral vessels. Since increased pulsatility has been associated with poor brain health and reported in persons with AD, this suggests that aerobic fitness might provide protection against cerebrovascular changes related to the progression of AD clinical syndrome.

Aging of the Vascular System and Neural Diseases

Vertebrates have acquired complex high-order functions facilitated by the dispersion of vascular and neural networks to every corner of the body. Blood vessels deliver oxygen and nutrients to all cells and provide essential transport systems for removing waste products. For these functions, tissue vascularization must be spatiotemporally appropriate. Recent studies revealed that blood vessels create a tissue-specific niche, thus attracting attention as biologically active sites for tissue development. Each capillary network is critical for maintaining proper brain function because age-related and disease-related impairment of cognitive function is associated with the loss or diminishment of brain capillaries. This review article highlights how structural and functional alterations in the brain vessels may change with age and neurogenerative diseases. Capillaries are also responsible for filtering toxic byproducts, providing an appropriate vascular environment for neuronal function. Accumulation of amyloid β is a key event in Alzheimer’s disease pathogenesis. Recent studies have focused on associations reported between Alzheimer’s disease and vascular aging. Furthermore, the glymphatic system and meningeal lymphatic systems contribute to a functional unit for clearance of amyloid β from the brain from the central nervous system into the cervical lymph nodes. This review article will also focus on recent advances in stem cell therapies that aim at repopulation or regeneration of a degenerating vascular system for neural diseases.

Influence of Multiple Cardiovascular Risk Factors on Task-Switching in Older Adults: An fMRI Study

Not only are the effects of cardiovascular risk factors such as high blood pressure and low fitness on executive functions and brain activations in older adults scarcely investigated, no fMRI study has investigated the combined effects of multiple risk factors on brain activations in older adults. This fMRI study examined the independent and combined effects of two cardiovascular risk factors, arterial plasticity, and physical fitness, on brain activations during task-switching in older adults. The effects of these two risk factors on age-related differences in activation between older and younger adults were also examined. Independently, low physical fitness and low arterial plasticity were related to reduced suppressions of occipital brain regions. The combined effects of these two risks on occipital regions were greater than the independent effects of either risk factor. Age-related overactivations in frontal cortex were observed in low fitness older adults. Brain-behavior correlation indicates that these frontal overactivations are maladaptive to older adults' task performance. It is possible that the resulting effects of cardiovascular risks on the aging brain, especially the maladaptive overactivations of frontal brain regions by high risk older adults, contribute to often found posterior-anterior shift in aging (PASA) brain activations. Furthermore, observed age-related differences in brain activations during task-switching can be partially attributed to individual differences in cardiovascular risks among older adults.

Cardiorespiratory fitness diminishes the effects of age on white matter hyperintensity volume

White matter hyperintensities (WMHs) are among the most commonly observed marker of cerebrovascular disease. Age is a key risk factor for WMH development. Cardiorespiratory fitness (CRF) is associated with increased vessel compliance, but it remains unknown if high CRF affects WMH volume. This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 (mean age = 65.36 years, SD = 3.92) who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume (beta = .32, p = .015). However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants (beta = -.25, p = .040). Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults.

The Contribution of Plasma and Brain Vitamin C on Age and Gender-Related Cognitive Differences: A Mini-Review of the Literature

There is increasing evidence that sex differences in the brain may contribute to gender-related behavioral differences, including cognitive function. Literature has revealed gender dimorphisms in cognitive function between males and females. Additionally, several risk factors associated with cognitive decline depend on chronological age. It is well recognized that the process of aging is associated with a decline in cognitive ability and brain function. Various explanations may account for these gender-related cognitive differences and age-associated cognitive changes. Recent investigations have highlighted the importance of vitamin C in maintaining brain health and its association with cognitive function in both cognitively intact and impaired cohorts. The present review explores previous literature that has evaluated differences in plasma/brain vitamin C between genders and during aging. It then assesses whether these age and gender-related differences may affect the relationship between plasma/brain vitamin C and cognition. The purpose of this review was to examine the evidence for a link between plasma/brain vitamin C and cognition and the impact of gender and age on this relationship. Epidemiological studies have frequently shown higher vitamin C plasma concentrations in women. Similarly, aging has been systematically associated with reductions in plasma vitamin C levels. A range of animal studies has demonstrated potential gender and age-related differences in vitamin C brain distribution and utilization. The reviewed literature suggests that gender differences in plasma and brain vitamin C may potentially contribute to differences in gender-associated cognitive ability, particularly while females are pre-menopausal. Additionally, we can propose that age-associated differences in plasma and brain vitamin C may be potentially linked to age-associated cognitive differences, with older cohorts appearing more vulnerable to experience declines in plasma vitamin C concentrations alongside compromised vitamin C brain regulation. This review encourages future investigations to take into account both gender and age when assessing the link between plasma vitamin C concentrations and cognitive function. Further large scale investigations are required to assess whether differences in cognitive function between genders and age groups may be causally attributed to plasma vitamin C status and brain distribution and utilization.

Sleep, brain vascular health and ageing

Sleep maintains the function of the entire body through homeostasis. Chronic sleep deprivation (CSD) is a prime health concern in the modern world. Previous reports have shown that CSD has profound negative effects on brain vasculature at both the cellular and molecular levels, and that this is a major cause of cognitive dysfunction and early vascular ageing. However, correlations among sleep deprivation (SD), brain vascular changes and ageing have barely been looked into. This review attempts to correlate the alterations in the levels of major neurotransmitters (acetylcholine, adrenaline, GABA and glutamate) and signalling molecules (Sirt1, PGC1α, FOXO, P66^shc, PARP1) in SD and changes in brain vasculature, cognitive dysfunction and early ageing. It also aims to connect SD-induced loss in the number of dendritic spines and their effects on alterations in synaptic plasticity, cognitive disabilities and early vascular ageing based on data available in scientific literature. To the best of our knowledge, this is the first article providing a pathophysiological basis to link SD to brain vascular ageing.

Fitness, independent of physical activity is associated with cerebral blood flow in adults at risk for Alzheimer's disease

Patterns of decreased resting cerebral blood flow (CBF) within the inferior temporal gyri, angular gyri, and posterior cingulate are a feature of aging and Alzheimer's disease (AD) and have shown to be predictive of cognitive decline among older adults. Fitness and physical activity are both associated with many indices of brain health and may positively influence CBF, however, the majority of research to date has examined these measures in isolation, leaving the potential independent associations unknown. The purpose of this study was to determine the unique contributions of fitness and physical activity when predicting CBF in cognitively healthy adults at risk for AD. One hundred participants (63% female) from the Wisconsin Registry for Alzheimer's Prevention underwent a maximal exercise test, physical activity monitoring, and a 3-D arterial spin labeling magnetic resonance imaging scan. For the entire sample, fitness was significantly associated with CBF while accounting for physical activity, age, gender, APOE ε4, family history of AD, education, and handedness (p = .026). Further, fitness explained significantly more variance than the combined effect of the covariates on CBF (R2 change = .059; p = .047). These results appear to be gender dependent, our data suggest fitness level, independent of physical activity, is associated with greater CBF in regions that are known to decline with age and AD for female (p = .011), but not male participants.

Effects of Physical Exercise on Autophagy and Apoptosis in Aged Brain: Human and Animal Studies

The aging process is characterized by a series of molecular and cellular changes over the years that could culminate in the deterioration of physiological parameters important to keeping an organism alive and healthy. Physical exercise, defined as planned, structured and repetitive physical activity, has been an important force to alter physiology and brain development during the process of human beings' evolution. Among several aspects of aging, the aim of this review is to discuss the balance between two vital cellular processes such as autophagy and apoptosis, based on the fact that physical exercise as a non-pharmacological strategy seems to rescue the imbalance between autophagy and apoptosis during aging. Therefore, the effects of different types or modalities of physical exercise in humans and animals, and the benefits of each of them on aging, will be discussed as a possible preventive strategy against neuronal death.

Intravenous Bone Marrow Mononuclear Cells Transplantation in Aged Mice Increases Transcription of Glucose Transporter 1 and Na+/K+-ATPase at Hippocampus Followed by Restored Neurological Functions

We recently reported that intravenous bone marrow mononuclear cell (BM-MNC) transplantation in stroke improves neurological function through improvement of cerebral metabolism. Cerebral metabolism is known to diminish with aging, and the reduction of metabolism is one of the presumed causes of neurological decline in the elderly. We report herein that transcription of glucose transporters, monocarboxylate transporters, and Na⁺/K⁺-ATPase is downregulated in the hippocampus of aged mice with impaired neurological functions. Intravenous BM-MNC transplantation in aged mice stimulated the transcription of glucose transporter 1 and Na⁺/K⁺-ATPase α1 followed by restoration of neurological function. As glucose transporters and Na⁺/K⁺-ATPases are closely related to cerebral metabolism and neurological function, our data indicate that BM-MNC transplantation in aged mice has the potential to restore neurological function by activating transcription of glucose transporter and Na⁺/K⁺-ATPase. Furthermore, our data indicate that changes in transcription of glucose transporter and Na⁺/K⁺-ATPase could be surrogate biomarkers for age-related neurological impairment as well as quantifying the efficacy of therapies.

The Effect of Stroke on Middle Cerebral Artery Blood Flow Velocity Dynamics During Exercise

BACKGROUND AND PURPOSE

Previous work demonstrates that older adults have a lower response in the middle cerebral artery velocity (MCAv) to an acute bout of moderate-intensity exercise when compared with young adults. However, no information exists regarding MCAv response to exercise after stroke. We tested whether MCAv response to an acute bout of moderate-intensity exercise differed between participants 3 months after stroke and an age- and sex-matched control group of older adults (CON). A secondary objective was to compare MCAv response between the stroke- and non-stroke-affected MCAv.

METHODS

Using transcranial Doppler ultrasound, we recorded MCAv during a 90-second baseline (BL) followed by a 6-minute moderate-intensity exercise bout using a recumbent stepper. Heart rate (HR), end-tidal CO2 (PETCO2), and beat-to-beat mean arterial blood pressure (MAP) were additional variables of interest. The MCAv response measures included BL, peak response amplitude (Amp), time delay (TD), and time constant (τ).

RESULTS

The Amp was significantly lower in the stroke-affected MCAv compared with CON (P < 0.01) and in the nonaffected MCAv compared with CON (P = 0.03). No between-group differences were found between TD and τ. No significant differences were found during exercise for PETCO2 and MAP while HR was lower in participants with stroke (P < 0.01). Within the group of participants with stroke, no differences were found between the stroke-affected and non-stroke-affected sides for any measures.

DISCUSSION AND CONCLUSIONS

Resolution of the dynamic response profile has the potential to increase our understanding of the cerebrovascular control mechanisms and test cerebrovascular response to physical therapy-driven interventions such as exercise.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A284).

A longitudinal, multi-parametric functional MRI study to determine age-related changes in the rodent brain

As the population ages, the incidence of age-related neurological diseases and cognitive decline increases. To further understand disease-related changes in brain function it is advantageous to examine brain activity changes in healthy aging rodent models to permit mechanistic investigation. Here, we examine the suitability, in rodents, of using a novel, minimally invasive anaesthesia protocol in combination with a functional MRI protocol to assess alterations in neuronal activity due to physiological aging. 11 Wistar Han female rats were studied at 7, 9, 12, 15 and 18 months of age. Under an intravenous infusion of propofol, animals underwent functional magnetic resonance imaging (fMRI) and functional magnetic resonance spectroscopy (fMRS) with forepaw stimulation to quantify neurotransmitter activity, and resting cerebral blood flow (CBF) quantification using arterial spin labelling (ASL) to study changes in neurovascular coupling over time. Animals showed a significant decrease in size of the active region with age (P ​< ​0.05). fMRS results showed a significant decrease in glutamate change with stimulation (ΔGlu) with age (P ​< ​0.05), and ΔGlu became negative from 12 months onwards. Global CBF remained constant for the duration of the study. This study shows age related changes in the blood oxygen level dependent (BOLD) response in rodents that correlate with those seen in humans. The results also suggest that a reduction in synaptic glutamate turnover with age may underlie the reduction in the BOLD response, while CBF is preserved.

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Describe a novel anaesthetic protocol to examine age-related alterations in neuronal activity in rodents.

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Size of the BOLD signal in the somatosensory cortex decreased with age.

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Reduction in glutamate turnover with age.

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No change in resting CBF with age.

Hemodynamic Instability in Heart Failure Intensifies Age-Dependent Cognitive Decline

This review attempts to examine two key elements in the evolution of cognitive impairment in the elderly who develop heart failure. First, major left side heart parts can structurally and functionally deteriorate from aging wear and tear to provoke hemodynamic instability where heart failure worsens or is initiated; second, heart failure is a major inducer of cognitive impairment and Alzheimer's disease in the elderly. In heart failure, when the left ventricular myocardium of an elderly person does not properly contract, it cannot pump out adequate blood to the brain, raising the risk of cognitive impairment due to the intensification of chronic brain hypoperfusion. Chronic brain hypoperfusion originates from chronically reduced cardiac output which progresses as heart failure worsens. Other left ventricular heart parts, including atrium, valves, myocardium, and aorta can contribute to the physiological shortfall of cardiac output. It follows that hemodynamic instability and perfusion changes occurring from the aging heart's blood pumping deficiency will, in time, damage vulnerable brain cells linked to specific cognitive regulatory sites, diminishing neuronal energy metabolism to a level where progressive cognitive impairment is the outcome. Could cognitive impairment progress be reversed with a heart transplant? Evidence is presented detailing the errant hemodynamic pathways leading to cognitive impairment during aging as an offshoot of inefficient structural and functional heart parts and their contribution to heart failure.

Pathological Continuum From the Rise in Pulse Pressure to Impaired Neurovascular Coupling and Cognitive Decline

The "biomechanical hypothesis" stipulates that with aging, the cumulative mechanical damages to the cerebral microvasculature, magnified by risk factors for vascular diseases, contribute to a breach in cerebral homeostasis producing neuronal losses. In other words, vascular dysfunction affects brain structure and function, and leads to cognitive failure. This is gathered under the term Vascular Cognitive Impairment and Dementia (VCID). One of the main culprits in the occurrence of cognitive decline could be the inevitable rise in arterial pulse pressure due to the age-dependent stiffening of large conductance arteries like the carotids, which in turn, could accentuate the penetration of the pulse pressure wave deeper into the fragile microvasculature of the brain and damage it. In this review, we will discuss how and why the vascular and brain cells communicate and are interdependent, describe the deleterious impact of a vascular dysfunction on brain function in various neurodegenerative diseases and even of psychiatric disorders, and the potential chronic deleterious effects of the pulsatile blood pressure on the cerebral microcirculation. We will also briefly review data from antihypertensive clinical trial aiming at improving or delaying dementia. Finally, we will debate how the aging process, starting early in life, could determine our sensitivity to risk factors for vascular diseases, including cerebral diseases, and the trajectory to VCID.

Aging reduces cerebral blood flow regulation following an acute hypertensive stimulus

Aging increases arterial stiffness, which has a negative impact on cerebral blood flow (CBF) regulation (decreases CBF and increases CBF pulsatility). The association between arterial stiffness and CBF pulsatility may, in part, explain the relationship between elevated blood pressure (BP) fluctuations and end-organ disease with aging. To understand the mechanisms by which large BP alterations influence cerebral blood flow regulation in both young and old, we examined the effects of age on central and cerebral blood flow regulation following an acute hypertensive stimulus [resistance-exercise (RE)]. Measurements were obtained pre and immediately, 5, and 30 min post-RE in young (n = 35) and older (n = 26) adults. Measurements included cerebral blood velocity (CBv), CBv pulsatility, central pulse-wave velocity (PWV), beta-stiffness index (β), and carotid blood flow pulsatility. Central hemodynamics and BP were continuously recorded. Mean CBv increased immediately post-RE only in the young and decreased below baseline at 5 min post-RE in both groups (interaction, P < 0.05). Older adults had a greater increase in CBv pulsatility immediately post-RE compared with the young (interaction, P < 0.05). Mean BP was higher and carotid pulsatility was lower in the older group and increased immediately post-RE in both groups (P < 0.05). PWV increased immediately post-RE (P < 0.05). There were no changes in β. In conclusion, with aging, greater central arterial stiffness leads to a greater transmission of pulsatile blood velocity from the systemic circulation to the cerebral circulation following an acute hypertensive stress.NEW & NOTEWORTHY Reductions in cerebral blood flow and increases in flow pulsatility with aging are associated to cerebrovascular disease; however, little is known about how an acute hypertensive stimulus effects cerebral blood flow regulation in an aged population. Following the hypertensive stimulus, older adults elicit an attenuated increase in cerebral blood velocity and greater transmission of pulsatile velocity to the brain compared with young adults, demonstrating reduced cerebral blood flow regulation to elevated blood pressure responses with aging.

Multimodal Monitoring of Cardiovascular Responses to Postural Changes

Background

In the poorly understood relationship between orthostatic hypotension and falls, next to blood pressure (BP), baroreflex sensitivity (BRS) and cerebral autoregulation (CAR) may be key measures. The posture- and movement dependency of orthostatic hypotension requires continuous and unobtrusive monitoring. This may be possible using simultaneous photoplethysmography (PPG), electrocardiography (ECG), and near-infrared spectroscopy (NIRS) signal recordings, from which pulse wave velocity (PWV; potentially useful for BP estimation), BRS and CAR can be derived. The PPG, NIRS and PWV signal correlation with BP and BRS/CAR reliability and validity need to be addressed.

Methods

In 34 healthy adults (mean age 25 years, inter quartile range 22–45; 10 female), wrist and finger PPG, ECG, bifrontal NIRS (oxygenated and deoxygenated hemoglobin) and continuous BP were recorded during sit to stand and supine to stand movements. Sixteen participants performed slow and rapid supine to stand movements; eighteen other participants performed a 1-min squat movement. Pulse wave velocity (PWV) was defined as the inverse of the ECG R-peak to PPG pulse delay; PPG, NIRS and PWV signal correlation with BP as their Pearson correlations with mean arterial pressure (MAP) within 30 s after the postural changes; BRS as inter beat interval drop divided by systolic BP (SBP) drop during the postural changes; CAR as oxygenated hemoglobin drop divided by MAP drop. BRS and CAR were separately computed using measured and estimated (linear regression) BP. BRS/CAR reliability was defined by the intra class correlation between repeats of the same postural change; validity as the Pearson correlation between BRS/CAR values based on measured and estimated BP.

Results

The highest correlation with MAP was found for finger PPG and oxygenated hemoglobin, ranging from 0.75–0.79 (sit to stand), 0.66–0.88 (supine to stand), and 0.82–0.94 (1-min squat). BRS and CAR reliability was highest during the different supine to stand movements, ranging from 0.17 – 0.49 (BRS) and 0.42-0.75 (CAR); validity was highest during rapid supine to stand movements, 0.54 and 0.79 respectively.

Conclusion

PPG-ECG-NIRS recordings showed high correlation with BP and enabled computation of reliable and valid BRS and CAR estimates, suggesting their potential for continuous unobtrusive monitoring of orthostatic hypotension key measures.

Cardiovascular risk factors as determinants of cerebral blood flow - a cross-sectional and 6-year follow-up study

Purpose: The parameters of cerebral blood flow are modulated by many factors. The aim of the study was to prospectively assess the relationship between the number of the established cardiovascular risk factors and hemodynamic parameters of cerebral blood flow.Material and methods: The study was cross-sectional baseline and 6-year follow-up data analysis. We analyzed data regarding cardiovascular risk factors, medications use, and ultrasonographically (transcranial Doppler) obtained mean cerebral blood flow velocity (mCBFV), pulsatility (PI), resistance (RI) indexes of middle cerebral artery.Results: After 6.0 ± 0.6 years of follow-up, there was increase in systolic (p = .047), and decrease in diastolic (p = .005) blood pressure, resulting in greater pulse pressure (p < .001). Although intima-media thickness increased during follow-up (p = .019), PI, RI and mCBFV did not differ between baseline and follow-up. In the cohort without follow-up (n = 112), we observed strong association between number of studied cardiovascular risk factors and lower mCBFV, and higher PI and RI (all p < .001), in the cohort with 6 year follow-up (n = 53), we confirmed similar association for mCBFV and PI (p = .002) at baseline, and mCBFV (p = .024) after follow-up. During follow-up, more patients were treated with vasoactive medications (p < .05). Also the median (interquartile range) of total number of taken drugs at follow-up 2 (1-3) was greater than at baseline 1 (0-2), (p < .001). The addition of vasoactive medications during follow-up was associated with increase of the mCBFV (0.012 ± 0.02 m/s, p = .013).Conclusion: The parameters of the cerebral blood flow are adversely influenced by accretion of cardiovascular risk factors, both at baseline and after 6 years of follow-up. The addition of a vasoactive medication during follow-up is associated with an increase of the mCBFV, a possibly beneficial effect.

Current intensity- and polarity-specific online and aftereffects of transcranial direct current stimulation: An fMRI study

Transcranial direct current stimulation (tDCS) induces polarity‐ and dose‐dependent neuroplastic aftereffects on cortical excitability and cortical activity, as demonstrated by transcranial magnetic stimulation (TMS) and functional imaging (fMRI) studies. However, lacking systematic comparative studies between stimulation‐induced changes in cortical excitability obtained from TMS, and cortical neurovascular activity obtained from fMRI, prevent the extrapolation of respective physiological and mechanistic bases. We investigated polarity‐ and intensity‐dependent effects of tDCS on cerebral blood flow (CBF) using resting‐state arterial spin labeling (ASL‐MRI), and compared the respective changes to TMS‐induced cortical excitability (amplitudes of motor evoked potentials, MEP) in separate sessions within the same subjects (n = 29). Fifteen minutes of sham, 0.5, 1.0, 1.5, and 2.0‐mA anodal or cathodal tDCS was applied over the left primary motor cortex (M1) in a randomized repeated‐measure design. Time‐course changes were measured before, during and intermittently up to 120‐min after stimulation. ROI analyses indicated linear intensity‐ and polarity‐dependent tDCS after‐effects: all anodal‐M1 intensities increased CBF under the M1 electrode, with 2.0‐mA increasing CBF the greatest (15.3%) compared to sham, while all cathodal‐M1 intensities decreased left M1 CBF from baseline, with 2.0‐mA decreasing the greatest (−9.3%) from sham after 120‐min. The spatial distribution of perfusion changes correlated with the predicted electric field, as simulated with finite element modeling. Moreover, tDCS‐induced excitability changes correlated more strongly with perfusion changes in the left sensorimotor region compared to the targeted hand‐knob region. Our findings reveal lasting tDCS‐induced alterations in cerebral perfusion, which are dose‐dependent with tDCS parameters, but only partially account for excitability changes.

Rapid Systolic Blood Pressure Changes After Standing Up Associate With Impaired Physical Performance in Geriatric Outpatients

Background

Orthostatic hypotension is a prevalent condition in older adults and is associated with impaired physical performance and falls. The ability of older adults to compensate for rapid changes in systolic blood pressure (SBP; ie, SBP decline rate and SBP variability) may be important for physical performance. This study investigates the association of rapid SBP changes after standing up with physical performance.

Methods and Results

Consecutive patients who visited the Center of Geriatrics Amsterdam in 2014 and 2015 were included. The following SBP parameters were computed in 2 intervals (0–15 and 15–180 seconds) after standing up: steepness of steepest SBP decline; ratio of standing/supine SBP variability; and magnitude of largest SBP decline. Physical performance was assessed using the following measures: chair stand time, timed up and go time, walking speed, handgrip strength, and tandem stance performance. A total of 109 patients (45% men; age, mean, 81.7 years [standard deviation, 7.0 years]) were included. Steepness of steepest SBP decline (0–15 seconds) was associated with slower chair stand time (P<0.001), timed up and go time (P=0.022), and walking speed (P=0.024). Ratio of standing/supine SBP variability (0–15 seconds) was associated with slower chair stand time (P=0.005). Magnitude of largest SBP decline was not associated with physical performance.

Conclusions

SBP parameters reflecting rapid SBP changes were more strongly associated with physical performance compared with SBP decline magnitude in geriatric outpatients. These results support the hypothesis of an inadequate cerebral autoregulation during rapid SBP changes and advocate the use of continuous blood pressure measurements.

Aerobic Exercise Training Improves Cerebral Blood Flow and Executive Function: A Randomized, Controlled Cross-Over Trial in Sedentary Older Men

Background

Physical activity may attenuate age-related cognitive decline by improving cerebrovascular function. The aim of this study was therefore to investigate effects of aerobic exercise training on cerebral blood flow (CBF), which is a sensitive physiological marker of cerebrovascular function, in sedentary older men.

Methods

Seventeen apparently healthy men, aged 60–70 years and with a BMI between 25 and 35 kg/m², were included in a randomized, controlled cross-over trial. Study participants were randomly allocated to a fully-supervised, progressive, aerobic exercise training or no-exercise control period for 8 weeks, separated by a 12-week wash-out period. Measurements at the end of each period included aerobic fitness evaluated using peak oxygen consumption during incremental exercise (VO_2peak), CBF measured with pseudo-continuous arterial spin labeling magnetic resonance imaging, and post-load glucose responses determined using an oral glucose tolerance test (OGTT). Furthermore, cognitive performance was assessed in the domains of executive function, memory, and psychomotor speed.

Results

VO_2peak significantly increased following aerobic exercise training compared to no-exercise control by 262 ± 236 mL (P < 0.001). CBF was increased by 27% bilaterally in the frontal lobe, particularly the subcallosal and anterior cingulate gyrus (cluster volume: 1008 mm³; P < 0.05), while CBF was reduced by 19% in the right medial temporal lobe, mainly temporal fusiform gyrus (cluster volume: 408 mm³; P < 0.05). Mean post-load glucose concentrations determined using an OGTT decreased by 0.33 ± 0.63 mmol/L (P = 0.049). Furthermore, executive function improved as the latency of response was reduced by 5% (P = 0.034), but no changes were observed in memory or psychomotor speed.

Conclusion

Aerobic exercise training improves regional CBF in sedentary older men. These changes in CBF may underlie exercise-induced beneficial effects on executive function, which could be partly mediated by improvements in glucose metabolism. This clinical trial is registered on ClinicalTrials.gov as NCT03272061.

Mapping brain recovery after concussion: From acute injury to 1 year after medical clearance

OBJECTIVE

To test the hypothesis that concussion-related brain alterations seen at symptomatic injury and medical clearance to return to play (RTP) will have dissipated by 1 year after RTP.

METHODS

For this observational study, 24 athletes with concussion were scanned longitudinally within 1 week after injury, at RTP, and 1 year after RTP. A large control cohort of 122 athletes were also scanned before the season. Each imaging session assessed global functional connectivity (Gconn) and cerebral blood flow (CBF), along with white matter fractional anisotropy (FA) and mean diffusivity (MD). The main effects of concussion on MRI parameters were evaluated at each postinjury time point. In addition, covariation was assessed between MRI parameters and clinical measures of acute symptom severity and time to RTP.

RESULTS

Different aspects of brain physiology showed different patterns of recovery over time. Both Gconn and FA displayed no significant effects at 1 year after RTP, whereas CBF and MD exhibited persistent long-term effects. The effects of concussion on MRI parameters were also dependent on acute symptom severity and time to RTP for all postinjury time points.

CONCLUSION

This study provides the first longitudinal evaluation of concussion focused on time of RTP and 1 year after medical clearance, using multiple different MRI measures to assess brain structure and function. These findings significantly enhance our understanding of the natural course of brain recovery after a concussion.

Dose-dependent association of accelerometer-measured physical activity and sedentary time with brain perfusion in aging

INTRODUCTION

Age-related decreases in cerebral blood flow (CBF) may lead to cognitive decline, while physical activity (PA) can maintain CBF and cognition in aging. The intensity of PA needed to affect CBF in aging, and the independent effects of sedentary time on CBF are currently unknown. Moreover, research conducted in free-living environments with objective measures of PA (e.g., accelerometry) is lacking.

METHODS

This cross-sectional study used accelerometry to objectively measure sedentary time, all light PA [AllLightPA], moderate-to-vigorous PA [MVPA], and total activity counts [TAC] in 52 cognitively healthy older adults. Robust linear regressions investigated the association of CBF (using arterial spin labeling magnetic resonance imaging) in frontal and medial temporal regions, with each PA intensity and sedentary time.

RESULTS

Greater sedentary time was significantly associated with lower CBF in lateral and medial frontal regions after adjusting for MVPA, while higher AllLightPA (adjusted for MVPA), MVPA (adjusted for AllLightPA), and TAC were associated with greater CBF in lateral and medial frontal regions.

DISCUSSION

Lighter activities, as well as MVPA, are beneficial to CBF in brain regions typically affected by the aging process and malleable to exercise interventions (i.e., the frontal lobes), whereas sedentary time is an independent risk factor for neurovascular dysregulation in normal aging.

Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions

This work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in structural and functional changes in the eyes of astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight.

Six weeks of high-intensity interval training to exhaustion attenuates dynamic cerebral autoregulation without influencing resting cerebral blood velocity in young fit men

Elevated cardiorespiratory fitness (CRF) is associated with reduced dynamic cerebral autoregulation (dCA), but the impact of exercise training per se on dCA remains equivocal. In addition, resting cerebral blood flow (CBF) and dCA after high-intensity interval training (HIIT) in individuals with already high CRF remains unknown. We examined to what extent 6 weeks of HIIT affect resting CBF and dCA in cardiorespiratory fit men and explored if potential changes are intensity-dependent. Endurance-trained men were assigned to group HIIT85 (85% of maximal aerobic power, 1-7 min effort bouts, n = 8) and HIIT115 (115% of maximal aerobic power, 30 sec to 1 min effort bouts, n = 9). Training sessions were completed until exhaustion 3 times/week over 6 weeks. Mean arterial pressure (MAP) and middle cerebral artery mean blood velocity (MCAvmean ) were measured continuously at rest and during repeated squat-stands (0.05 and 0.10 Hz). Transfer function analysis (TFA) was used to characterize dCA on driven blood pressure oscillations during repeated squat-stands. Neither training nor intensity had an effect on resting MAP and MCAvmean (both P > 0.05). TFA phase during 0.10 Hz squat-stands decreased after HIIT irrespective of intensity (HIIT85 : 0.77 ± 0.22 vs. 0.67 ± 0.18 radians; HIIT115 : pre: 0.62 ± 0.19 vs. post: 0.59 ± 0.13 radians, time effect P = 0.048). These results suggest that HIIT over 6 weeks have no apparent benefits on resting CBF, but a subtle attenuation in dCA is seen posttraining irrespective of intensity training in endurance-trained men.

Cerebral Blood Flow in Community-Based Older Twins Is Moderately Heritable: An Arterial Spin Labeling Perfusion Imaging Study

Adequate cerebral blood flow (CBF) is necessary to maintain brain metabolism and function. Arterial spin labeling (ASL) is an emerging MRI technique offering a non-invasive and reliable quantification of CBF. The genetic basis of CBF has not been well documented, and one approach to investigate this is to examine its heritability. The current study aimed to examine the heritability of CBF using ASL data from a cohort of community-dwelling older twins (41 monozygotic (MZ) and 25 dizygotic (DZ) twin pairs; age range, 65–93 years; 56.4% female). The results showed that the cortex had higher CBF than subcortical gray matter (GM) regions, and CBF in the GM regions of the anterior cerebral artery (ACA) territory was lower than that of the middle (MCA) and posterior (PCA) cerebral arteries. After accounting for the effects of age, sex and scanner, moderate heritability was identified for global CBF (h² = 0.611; 95% CI = 0.380–0.761), as well as for cortical and subcortical GM and the GM in the major arterial territories (h² = 0.500–0.612). Strong genetic correlations (GCs) were found between CBF in subcortical and cortical GM regions, as well as among the three arterial territories (ACA, MCA, PCA), suggesting a largely convergent genetic control for the CBF in brain GM. The moderate heritability of CBF warrants future investigations to uncover the genetic variants and genes that regulate CBF.

Neurovascular Ageing and Age-Related Diseases

Proper functioning of the brain is dependent on integrity of the cerebral vasculature. During ageing, a number of factors including aortic or arterial stiffness, autonomic dysregulation, neurovascular uncoupling and blood-brain barrier (BBB) damage will define the dynamics of brain blood flow and local perfusion. The nature and extent of ageing-related cerebrovascular changes, the degree of involvement of the heart and extracranial vessels and the consequent location of tissue pathology may vary considerably. Atheromatous disease retarding flow is a common vascular insult, which increases exponentially with increasing age. Arteriolosclerosis characterized as a prominent feature of small vessel disease is one of the first changes to occur during the natural history of cerebrovascular pathology. At the capillary level, the cerebral endothelium, which forms the BBB undergoes changes including reduced cytoplasm, fewer mitochondria, loss of tight junctions and thickened basement membranes with collagenosis. Astrocyte end-feet protecting the BBB retract as part of the clasmatodendrotic response whereas pericyte coverage is altered. The consequences of these microvascular changes are lacunar infarcts, cortical and subcortical microinfarcts, microbleeds and diffuse white matter disease, which involves myelin loss and axonal abnormalities. The deeper structures are particularly vulnerable because of the relatively reduced density of the microvascular network formed by perforating and penetrating end arteries. Ultimately, the integrity of both the neurovascular and gliovascular units is compromised such that there is an overall synergistic effect reflecting on ageing associated cerebral perfusion and permeability. More than one protagonist appears to be involved in ageing-related cognitive dysfunction characteristically associated with the neurocognitive disorders.

A Systematic Review on the Cognitive Benefits and Neurophysiological Correlates of Exergaming in Healthy Older Adults

Human aging is associated with structural and functional brain deteriorations and a corresponding cognitive decline. Exergaming (i.e., physically active video-gaming) has been supposed to attenuate age-related brain deteriorations and may even improve cognitive functions in healthy older adults. Effects of exergaming, however, vary largely across studies. Moreover, the underlying neurophysiological mechanisms by which exergaming may affect cognitive and brain function are still poorly understood. Therefore, we systematically reviewed the effects of exergame interventions on cognitive outcomes and neurophysiological correlates in healthy older adults (>60 years). After screening 2709 studies (Cochrane Library, PsycINFO, Pubmed, Scopus), we found 15 eligible studies, four of which comprised neurophysiological measures. Most studies reported within group improvements in exergamers and favorable interaction effects compared to passive controls. Fewer studies found superior effects of exergaming over physically active control groups and, if so, solely for executive functions. Regarding individual cognitive domains, results showed no consistence. Positive effects on neurophysiological outcomes were present in all respective studies. In summary, exergaming seems to be equally or slightly more effective than other physical interventions on cognitive functions in healthy older adults. Tailored interventions using well-considered exergames and intervention designs, however, may result in more distinct effects on cognitive functions.

Interspecific scaling of blood flow rates and arterial sizes in mammals

This meta-study investigated the relationships between blood flow rate (Q̇; cm³ s^-1), wall shear stress (τ_w; dyn cm^-2) and lumen radius (r _i; cm) in 20 named systemic arteries of nine species of mammals, ranging in mass from 23 g mice to 652 kg cows, at rest. In the dataset, derived from 50 studies, lumen radius varied between 3.7 µm in a cremaster artery of a rat and 11.2 mm in the aorta of a human. The 92 logged data points of [Formula: see text] and r _i are described by a single second-order polynomial curve with the equation: [Formula: see text] The slope of the curve increased from approximately 2 in the largest arteries to approximately 3 in the smallest ones. Thus, da Vinci's rule ([Formula: see text]) applies to the main arteries and Murray's law ([Formula: see text]) applies to the microcirculation. A subset of the data, comprising only cephalic arteries in which [Formula: see text] is fairly constant, yielded the allometric power equation: [Formula: see text] These empirical equations allow calculation of resting perfusion rates from arterial lumen size alone, without reliance on theoretical models or assumptions on the scaling of wall shear stress in relation to body mass. As expected, [Formula: see text] of individual named arteries is strongly affected by body mass; however, [Formula: see text] of the common carotid artery from six species (mouse to horse) is also sensitive to differences in whole-body basal metabolic rate, independent of the effect of body mass.

Sensitivity and reliability of cerebral oxygenation responses to postural changes measured with near-infrared spectroscopy

Purpose

Cerebral oxygenation as measured by near-infrared spectroscopy (NIRS) might be useful to discriminate between physiological and pathological responses after standing up in individuals with orthostatic hypotension. This study addressed the physiological sensitivity of the cerebral oxygenation responses as measured by NIRS to different types and speeds of postural changes in healthy adults and assessed the reliability of these responses.

Methods

Cerebral oxygenated hemoglobin (O₂Hb), deoxygenated hemoglobin (HHb) and tissue saturation index (TSI) were measured bilaterally on the forehead of 15 healthy individuals (12 male, age range 18–27) using NIRS. Participants performed three repeats of sit to stand, and slow and rapid supine to stand movements. Responses were defined as the difference between mean, minimum and maximum O₂Hb, HHb and TSI values after standing up and baseline. Test–retest, interobserver and intersensor reliabilities were addressed using intraclass correlation coefficients (ICCs).

Results

The minimum O₂Hb response was most sensitive to postural changes and showed significant differences (− 4.09 µmol/L, p < 0.001) between standing up from sitting and supine position, but not between standing up at different speeds (− 0.31 µmol/L, p = 0.70). The minimum O₂Hb response was the most reliable parameter (ICC > 0.6).

Conclusions

In healthy individuals, NIRS-based cerebral oxygenation parameters are sensitive to postural change and discriminate between standing up from supine and sitting position with minimum O₂Hb response as the most sensitive and reliable parameter. The results underpin the potential value for future clinical use of NIRS in individuals with orthostatic hypotension.

Electronic supplementary material

The online version of this article (10.1007/s00421-019-04101-0) contains supplementary material, which is available to authorized users.

Association between physical activity and dementia's risk factors in patients with Parkinson's disease

Evidence suggests that physical activity (PA) exerts beneficial effects on neurodegenerative processes, either as symptomatic relief or disease-modifying strategy. Actually, it may represent a viable neuroprotective intervention in Parkinson's disease dementia (PDD), a severe, frequent, and untreatable complication of Parkinson's disease (PD). According to such hypothesis, this cross-sectional study tested, in PD patients, the association between levels of PA and well-known risk factors for PDD, such as mood disorders and amyloid-β42 CSF content. Amount of PA was measured by the International Physical Activity Questionnaires-Short Form (IPAQ-SF) in 128 cognitively intact PD patients and correlated with the Hamilton-Depression (HAM-D) and the Hamilton-Anxiety (HAM-A) scores; in a homogenous subgroup of 40 patients, it was further correlated with a panel of CSF biomarkers, including amyloid-β42, total α-synuclein, total, and phosphorylated tau. The statistical model was corrected for the main potential confounding factors (motor impairment, dopaminergic treatment, disease duration, age, and sex). Both the HAM-A and HAM-D scores, as well as the Aβ42 CSF content, improved in parallel with the increase of the total week amount of PA. Although with several limitations, we preliminarily demonstrated that a high level of PA is associated with a more favourable profile of PDD risk factors, in terms of both mood disturbances and CSF markers of neurodegeneration. However, confirmative studies are necessary to validate the efficacy of PA as protective intervention for PDD.

Sleep disordered breathing in children disrupts the maturation of autonomic control of heart rate and its association with cerebral oxygenation

KEY POINTS

Sleep disordered breathing (SDB) affects 4-11% of children and is associated with adverse neurocognitive, behavioural and cardiovascular outcomes, including reduced autonomic control. The relationship between heart rate variability (HRV; a measure of autonomic control) and age found in non-snoring control children was absent during sleep in children with SDB. Age significantly predicted increasing cerebral oxygenation during wake in non-snoring control children, whereas during sleep, HRV significantly predicted decreasing cerebral oxygenation. Cerebral oxygenation was not associated with either age or HRV in children with SDB during both wake and sleep. SDB significantly disrupts the normal maturation of autonomic control and the positive association between autonomic control and cerebral oxygenation found in non-snoring children, and we speculate that the dampened autonomic control exhibited by children with SDB may have an attenuating effect on cerebral autoregulation via the moderating influence of HRV on cerebral blood flow.

ABSTRACT

The repetitive episodes of hypoxia that are features of sleep disordered breathing (SDB) in children are associated with alterations in autonomic control of heart rate in an age-dependent manner. We aimed to relate heart rate variability (HRV) parameters to age and measures of cerebral oxygenation in children (3-12 years old) with SDB and non-snoring controls. Children (SDB, n = 117; controls, n = 42; 3-12 years) underwent overnight polysomnography. Total (TP), low- (LF) and high-frequency (HF) power, tissue oxygenation index (TOI) and fractional tissue oxygen extraction (FTOE) were analysed during wake and sleep. Pearson's correlations determined the association between age and HRV parameters, and multiple linear regressions between HRV, age and cerebral oxygenation parameters. During wake, age had a positive association with LF power, reflecting increased parasympathetic and sympathetic activity with increasing age for both control and SDB groups. This association was also evident during sleep in controls, but was absent in children with SDB. In controls, during wake TOI had a positive, and FTOE a negative association with age. During sleep, TP, LF and HF power were significant, negative determinants of TOI and positive determinants of FTOE. These associations were not seen in children with SDB during wake or sleep. SDB disrupts the normal maturation of the autonomic control of heart rate and the association between HRV and cerebral oxygenation exhibited by non-snoring control children of primary school age. These results highlight the impact SDB has on cardiovascular control and the potential impact on adverse cardiovascular outcomes.

Vascular pathomechanism in acute encephalopathy with biphasic seizures and late reduced diffusion

Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a childhood-onset encephalopathy, but the precise pathophysiology remains unclear. We encountered a child with Moyamoya syndrome and AESD. He exhibited left-predominant stenosis of the middle cerebral artery (MCA), and later developed broad lesions in the left hemisphere, raising the possibility that insufficient blood supply relates to formation of the lesions. To test the hypothesis, we investigated the relationship between MCA volume and lesion extent in seven AESD children without preexisting diseases. The MCA volume and lesion extent were quantified with time of flight images for construction of magnetic resonance angiography and apparent diffusion coefficient maps, respectively. Lateralization indices ([right - left]/[right + left]) of the MCA volume and lesion extent were calculated. We found that the lateralization indices were negatively correlated (r = -0.786, p = .036), that is, when the MCA volume was smaller in one side than the other side, the lesions were likely to develop more extensively in the ipsilateral side than the contralateral side. This indicates the association of insufficient blood supply with the lesions. The present study provides the first observation to suggest the involvement of vascular mechanism in AESD and has potential implications for novel therapeutic approach.

Neurobiology of substance use in adolescents and potential therapeutic effects of exercise for prevention and treatment of substance use disorders

Substance use (e.g., alcohol, marijuana, opioids, cocaine., etc,) use often initiates during adolescence, a critical period of physiological and social development marked by an increase in risk-taking due, in part, to heightened motivation to obtain arousal from rewards. Substance use during adolescence has been associated with a greater risk of substance use disorders (SUD) in adulthood. Although use rates for most substances have remained relatively stable, the frequency of marijuana use and the perception that regular marijuana use is not harmful has increased in adolescents. Furthermore, the nonmedical use of opioids has increased, particularly in the South, Midwest, and rural low-income communities. Substance use in adolescence has been associated with adverse structural and functional brain changes and, may exacerbate the natural "imbalance" between frontal/regulatory and cortical-subcortical circuits, leading to further heightened impulsive and reward-driven behaviors. Exercise increases growth and brain-derived neurotrophic factors that stimulate endogenous dopaminergic systems that, in turn, enhance general plasticity, learning, and memory. Exercise may help to reinforce the "naïve" or underdeveloped connections between neurological reward and regulatory processes in adolescence from the "bottom up" and "offset" reward seeking from substances, while concomitantly improving cardiovascular health, as well as academic and social achievement. In this review, we provide an overview of the current state of substance use in adolescents and rationale for the utilization of exercise, particularly "assisted" exercise, which we have shown increases neural activity in cortical-subcortical regions and may modulate brain dopamine levels during adolescence, a unique window of heightened reward sensitivity and neural plasticity, for the prevention and adjunctive treatment of SUD.

Age-Dependent Impairment of Neurovascular and Neurometabolic Coupling in the Hippocampus

Neurovascular and neurometabolic coupling are critical and complex processes underlying brain function. Perturbations in the regulation of these processes are, likely, early dysfunctional alterations in pathological brain aging and age-related neurodegeneration. Evidences support the role of nitric oxide (•NO) as a key messenger both in neurovascular coupling, by signaling from neurons to blood vessels, and in neurometabolic coupling, by modulating O₂ utilization by mitochondria. In the present study, we investigated the functionality of neurovascular and neurometabolic coupling in connection to •NO signaling and in association to cognitive performance during aging. For this, we performed in vivo simultaneous measurements of •NO, O₂ and cerebral blood flow (CBF) in the hippocampus of F344 rats along chronological age in response to glutamatergic activation and in correlation with cognitive performance. Firstly, it is evidenced the temporal sequence of events upon glutamate stimulation of hippocampal dentate gyrus, encompassing the local and transitory increase of •NO followed by transitory local changes of CBF and pO₂. Specifically, the transient increase of •NO is followed by an increase of CBF and biphasic changes of the local pO₂. We observed that, although the glutamate-induced •NO dynamics were not significantly affected by aging, the correspondent hemodynamic was progressively diminished accompanying a decline in learning and memory. Noteworthy, in spite of a compromised blood supply, in aged rats we observed an increased ΔpO₂ associated to the hemodynamic response, suggestive of a decrease in the global metabolic rate of O₂. Furthermore, the impairment in the neurovascular coupling observed along aging in F344 rats was mimicked in young rats by promoting an unbalance in redox status toward oxidation via intracellular generation of superoxide radical. This observation strengthens the idea that oxidative stress may have a critical role in the neurovascular uncoupling underlying brain aging and dysfunction. Overall, data supports an impairment of neurovascular response in connection with cognition decline due to oxidative environment-dependent compromised •NO signaling from neurons to vessels during aging.

Effect of healthy aging and sex on middle cerebral artery blood velocity dynamics during moderate-intensity exercise

Blood velocity measured in the middle cerebral artery (MCA_V) increases with finite kinetics during moderate-intensity exercise, and the amplitude and dynamics of the response provide invaluable insights into the controlling mechanisms. The MCA_V response after exercise onset is well fit to an exponential model in young individuals but remains to be characterized in their older counterparts. The responsiveness of vasomotor control degrades with advancing age, especially in skeletal muscle. We tested the hypothesis that older subjects would evince a slower and reduced MCA_V response to exercise. Twenty-nine healthy young (25 ± 1 yr old) and older (69 ± 1 yr old) adults each performed a rapid transition from rest to moderate-intensity exercise on a recumbent stepper. Resting MCA_V was lower in older than young subjects (47 ± 2 vs. 64 ± 3 cm/s, P < 0.001), and amplitude from rest to steady-state exercise was lower in older than young subjects (12 ± 2 vs. 18 ± 3 cm/s, P = 0.04), even after subjects were matched for work rate. As hypothesized, the time constant was significantly longer (slower) in the older than young subjects (51 ± 10 vs. 31 ± 4 s, P = 0.03), driven primarily by older women. Neither age-related differences in fitness, end-tidal CO₂, nor blood pressure could account for this effect. Thus, MCA_V kinetic analyses revealed a marked impairment in the cerebrovascular response to exercise in older individuals. Kinetic analysis offers a novel approach to evaluate the efficacy of therapeutic interventions for improving cerebrovascular function in elderly and patient populations. NEW & NOTEWORTHY Understanding the dynamic cerebrovascular response to exercise has provided insights into sex-related cerebrovascular control mechanisms throughout the aging process. We report novel differences in the kinetics response of cerebrovascular blood velocity after the onset of moderate-intensity exercise. The exponential increase in brain blood flow from rest to exercise revealed that 1) the kinetics profile of the older group was blunted compared with their young counterparts and 2) the older women demonstrated a slowed response.

Human cerebrovascular function in health and disease: insights from integrative approaches

Background

The marked increase in the size of the brain, and consequently, in neural processing capability, throughout human evolution is the basis of the higher cognitive function in humans. However, greater neural, and thus information processing capability, comes at a significant metabolic cost; despite its relatively small size, the modern human brain consumes almost a quarter of the glucose and oxygen supply in the human body.

Fortunately, several vascular mechanisms ensure sufficient delivery of glucose and oxygen to the active neural tissue (neurovascular coupling), prompt removal of neural metabolic by-products (cerebral vasoreactivity), and constant global blood supply despite daily variations in perfusion pressure (cerebral autoregulation). The aim of this review is to provide an integrated overview of the available data on these vascular mechanisms and their underlying physiology. We also briefly review modern experimental approaches to assess these mechanisms in humans, and further highlight the importance of these mechanisms for humans’ evolutionary success by providing examples of their healthy adaptations as well as pathophysiological alterations.

Conclusions

Data reviewed in this paper demonstrate the importance of the cerebrovascular function to support humans’ unique ability to form new and different interactions with each other and their surroundings. This highlights that there is much insight into the neural and cognitive functions that could be gleaned from interrogating the cerebrovascular function.

The many faces of vascular cognitive impairment

This Preface introduces the articles of the special issue on "Vascular Dementia" in which several recognized experts provide an overview of this research field. The brain is a highly vascularized organ and consequently, vascular dysfunction and related pathways affect cognitive performance and memory. Vascular dementia or vascular cognitive impairment is the second most common type of dementia after Alzheimer's disease, and both disorders often occur in parallel. With this special issue, we hope to provide insight and a stimulating discussion for the future development of this research field. This article is part of the Special Issue "Vascular Dementia".