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

Kidney function and cognitive impairment: a systematic review and meta-analysis

BACKGROUND

A worldwide evaluation exploring the link between a broad-spectrum kidney function and cognitive impairment (CI) prevalence, and related risk factors has yet to be conducted.

METHODS

Studies published before November 2024 were retrieved from PubMed and Web of Science. R software (R Foundation for Statistical Computing, Vienna, Austria) and Review Manager (Cochrane Collaboration, London, UK) were used to analyze the relationship of CI with various estimated glomerular filtration rate (eGFR) level and the associated risk factors. A random model effect was adopted for a heterogeneity (I2) of more than 50%.

RESULTS

Seventeen (involving 32,141 participants) out of 5892 studies were included. The MMSE and MoCA were the most commonly used tests to assess cognitive function. The prevalence of CI raised significantly with declining kidney function: 10% for eGFR ≥60 mL/min/1.73 m2, 47.3% for 60-30 mL/min/1.73 m2, and 60.6% for <30 mL/min/1.73 m2, totaling 16.7% overall. Thirteen potential risk factors were ascertained and analyzed. In the forest-plot analysis, T2DM, cardiovascular diseases, cerebrovascular diseases, and lower education emerged as strong predictors of risk, with odds ratios of 1.55, 1.63, 1.95, and 2.59, respectively. A mean meta-analysis of the continuous variable indicators revealed that advanced age and elevated parathyroid hormone (PTH) levels were statistically significant in the occurrence of CI.

CONCLUSIONS

The poorer the renal function, the higher the prevalence rate of CI. Patients with chronic kidney disease (CKD) have multiple risk factors that lead to CI.

Scientific status analysis of exercise benefits for vascular cognitive impairment: Evidence of neuroinflammation

Vascular cognitive impairment (VCI) is a syndrome characterized by cognitive decline resulting from insufficient perfusion to the entire brain or specific brain regions. The lack of a clear understanding of the mechanisms linking cerebrovascular disease to cognitive impairment has impeded the development of targeted treatments for VCI. Increasing evidence indicates that exercise may offer significant benefits for patients with VCI. This study explores how neuroinflammatory mechanisms mediate the effects of exercise on VCI, focusing on the broader biological processes involved. Exercise plays a crucial role in mitigating vascular risk factors, reducing oxidative stress, and promoting neurogenesis. Furthermore, exercise influences neuroinflammatory mediators and central immune cells via various signaling pathways. Different types and intensities of exercise, including resistance and endurance training, have been shown to differentially modulate neuroinflammation during the progression of VCI. This paper summarizes the current mechanisms of action and proposes exercise interventions targeting neuroinflammatory pathways, along with biomarker studies, to enhance our understanding of VCI pathogenesis and inform clinical practice. A more in-depth understanding of the inflammatory mechanisms underlying VCI may facilitate the development of targeted therapeutic interventions.

18F-FDG Brain PET/MRI in Postischemic Hyperperfusion

A 58-year-old man with a past medical history of myocardial infarction and ventricular thrombus presented with successive stroke codes, initially for left arm weakness, then for dysarthria and right-sided weakness. Structural imaging showed an acute/subacute ischemic stroke in the right frontal and right parietal lobes. During the hospitalization, the patient suffered from impaired memory not attributable to the areas of ischemia, prompting a dementia workup. 18F-FDG brain PET/MRI showed no evidence of neurodegenerative disease, but instead demonstrated focal hypermetabolism in the areas of acute/subacute infarcts, which was favored to represent luxury perfusion (postischemic hyperperfusion).

Intracranial response to positive end-expiratory pressure is influenced by lung recruitability and gas distribution during mechanical ventilation in acute brain injury patients: a proof-of-concept physiological study

BACKGROUND

The effect of positive end-expiratory pressure (PEEP) on intracranial pressure (ICP) dynamics in patients with acute brain injury (ABI) remains controversial. PEEP can benefit oxygenation by promoting alveolar recruitment, but its influence on ICP is complex. The primary aims of this study were to investigate 1) how lung recruitability influences oxygenation and 2) how lung recruitability and regional gas distribution, measured via recruitment-to-inflation (RI) ratio and electrical impedance tomography (EIT), affect ICP in response to PEEP changes in critically ill patients in their early phase of ABI.

METHODS

Ten mechanically ventilated ABI patients were included. Pressure reactivity index (PRx) was estimated. Using RI manoeuvre and EIT, lung recruitability and gas distribution were assessed in response to a standardised PEEP change (from high to low levels, with a delta of 10 cmH2O). Changes in ICP (ΔICP) were calculated between high and low PEEP. Lung inhomogeneity indices (global inhomogeneity index [GI] and local inhomogeneity index [LI]) were derived from EIT. Correlations between ventilatory variables and ICP were analysed.

RESULTS

Blood oxygenation significantly decreased, going from high (14 [IQR: 12-15] cmH₂O) to low (4 [IQR: 2-5] cmH₂O) PEEP. Reducing PEEP significantly increased ICP (from 9 [IQR: 5-13] to 12 [IQR: 8-16] mmHg, p < 0.01), while cerebral perfusion pressure (CPP) improved (from 71 [IQR:67-83] to 75 [IQR: 70-84] mmHg, p = 0.03) and mean arterial pressure (MAP) increased (from 79 [IQR: 69-95] to 84 [IQR: 76-99] mmHg, p < 0.01). The RI ratio correlated significantly with ΔICP (rho = 0.87, p < 0.01), as did Vrec% (proportion of recruited volume, rho = 0.65) and GI (rho = 0.5). LI did not correlate with ΔICP. PRx was 0.30 [IQR: 0.12-0.42], indicating a deranged cerebral autoregulation.

CONCLUSIONS

Patients with a higher potential for lung recruitability had a more beneficial effect of PEEP on oxygenation. These effects should be interpreted cautiously, given that lung recruitability and global inhomogeneity of gas distribution significantly influenced the intracranial response to PEEP in ABI patients. As indicated by MAP and CPP, PEEP may impact systemic haemodynamics and cerebral perfusion when cerebral autoregulation is deranged. These findings underscore the importance of multimodal (i.e. respiratory, cerebral and haemodynamics) monitoring for optimising ventilation strategies in ABI patients and provide a framework for future research. Trial registration Registration number: NCT05363085, Date of registration: May 2022.

Pathophysiology and Management of Cerebral Venous Thrombosis

Cerebral venous thrombosis (CVT) is a less common type of stroke that can occur across all age groups but predominantly affects children and young adults. Diagnosis is often challenging due to the nonspecific and variable clinical presentation. The disease course is heterogeneous, with CVT-related parenchymal lesions developing in approximately 50 to 60% of cases. Despite some advancements, significant gaps persist in understanding the pathophysiology of CVT, including the mechanisms underlying brain injury. Anticoagulation is the cornerstone of CVT treatment, but strategies targeting secondary mechanisms of parenchymal damage are still lacking. Here, the current state of the field is briefly reviewed, with the aim to introduce a wide audience (neuroscientists and clinicians alike) to the disease and inform clinical practice and future research.

Perfusion-mechanics coupling of the hippocampus

The hippocampus is a highly scrutinized brain structure due to its entanglement in multiple neuropathologies and vulnerability to metabolic insults. This study aims to non-invasively assess the perfusion-mechanics relationship of the hippocampus in the healthy brain across magnetic resonance imaging sequences and magnetic field strengths. In total, 17 subjects (aged 22-35, 7 males/10 females) were scanned with magnetic resonance elastography and arterial spin labelling acquisitions at 3T and 7T in a baseline physiological state. No significant differences in perfusion or stiffness were observed across magnetic field strengths or acquisitions. The hippocampus had the highest vascularity within the deep grey matter, followed closely by the caudate nucleus and putamen. We discovered a positive perfusion-mechanics correlation in the hippocampus across both 3T and 7T groups, with a highly significant correlation overall (R = 0.71, p = 0.0019), which was not observed in the caudate nucleus, a similarly vascular region. Furthermore, we supported our hypothesis that increased perfusion in the hippocampus would lead to greater pulsatile displacement in a small cohort (n = 10). Given that the hippocampus is an exceptionally vulnerable structure, with perfusion deficits often seen in diseases related to learning and memory, our results suggest a unique mechanistic link between metabolic health and stiffness biomarkers in this key region for the first time.

Catecholamines in sepsis: pharmacological insights and clinical applications-a narrative review

Catecholamines, essential neurotransmitters and hormones, play a critical role in the body's physiological response to stress and are pivotal in the management of various clinical conditions, particularly in critical care settings. This narrative review delves into the pharmacological properties of catecholamines, including their mechanisms of action, pharmacokinetics, and pharmacodynamics. Key clinical applications of catecholamines, especially in the cardiovascular and immune systems, are highlighted, emphasizing their roles in modulating heart rate, vascular tone, and immune responses during critical conditions such as sepsis and septic shock. Additionally, the review explores catecholamines' immunomodulatory effects and their interactions with other therapeutic agents, such as corticosteroids, in the management of septic shock. Further research is suggested to optimize catecholamine usage and improve patient outcomes in critical care settings.

Age and gender-related patterns of arterial transit time and cerebral blood flow in healthy adults

Normal aging has been associated with increased arterial transit time (ATT) and reduced cerebral blood flow (CBF). However, age-related patterns of ATT and CBF and their relationship remain unclear. This is partly due to the lengthy scan times required for ATT measurements, which caused previous age-related CBF studies to not fully account for transit time. In this work, we aimed to elucidate age-related ATT and ATT-corrected CBF patterns. We examined 131 healthy subjects aged 19 to 82 years old using two pseudo-continuous arterial spin labeling (PCASL) MRI scans: one to measure fast low-resolution ATT maps with five post-labeling delays and the other to measure high-resolution perfusion-weighted maps with a single post-labeling delay. Both ATT and perfusion-weighed maps were applied with vessel suppression. We found that ATT increases with age in the frontal, temporoparietal, and occipital regions, with a more pronounced elongation in males compared to females in the middle temporal gyrus. ATT-corrected CBF decreases with age in several brain regions, including the anterior cingulate, insula, posterior cingulate, angular, precuneus, supramarginal, frontal, parietal, superior and middle temporal, occipital, and cerebellar regions, while remaining stable in the inferior temporal and subcortical regions. In contrast, without ATT correction, we detected artifactual decreases in the inferior temporal and precentral regions. These findings suggest that ATT provides valuable and independent insights into microvascular deficits and should be incorporated into CBF measurements for studies involving aging populations.

Directional sensitivity analysis of the cerebral pressure-flow relationship during normothermia and moderate hyperthermia

Dynamic cerebral autoregulation (dCA) reacts differently when mean arterial pressure (MAP) increases versus decreases (i.e., directional sensitivity). Although heat stress alters dCA, its influence on directional sensitivity remains unclear. This analysis investigated the impact of moderate hyperthermia on the directional sensitivity in the cerebral pressure-flow relationship. Ten healthy participants (7 males; age: 37 ± 12 yr; body mass: 75 ± 9 kg) underwent 6 min of oscillatory lower body negative pressure (OLBNP) to induce large MAP fluctuations at 0.03 and 0.10 Hz under normothermic and moderately hyperthermic conditions (+1.0°C increase in core temperature) induced via a water-perfused suit. We calculated changes in middle cerebral artery mean blood velocity (MCAv) per alterations to MAP to compute absolute and relative ratios adjusted for time intervals during each OLBNP-induced MAP increase (ΔMCAvT/[Formula: see text]; %MCAvT/[Formula: see text]) and decrease (ΔMCAvT/[Formula: see text]; %MCAvT/[Formula: see text]). Thereafter, we compared average absolute and relative ratios. There was no main effect of MAP direction on ΔMCAvT/ΔMAPT or %MCAvT/%MAPT during either 0.03 Hz (P = 0.291, P = 0.281) or 0.10 Hz (P = 0.295, P = 0.178) OLBNP. Regardless of MAP direction, ΔMCAvT/[Formula: see text] (0.65 ± 0.17 vs. 0.84 ± 0.22 cm·s-1·mmHg-1), ΔMCAvT/[Formula: see text] (0.70 ± 0.15 vs. 0.85 ± 0.18 cm·s-1·mmHg-1) (thermal state: P = 0.009), %MCAvT/[Formula: see text] (0.92 ± 0.22 vs. 1.33 ± 0.60), and %MCAvT/[Formula: see text] (1.01 ± 0.27 vs. 1.30 ± 0.51) (thermal state: P = 0.001) were lower in hyperthermia at 0.03-Hz OLBNP. Regardless of thermal states, these findings suggest an absence of dCA directional sensitivity. Reduced directional sensitivity metrics during hyperthermia may indicate more efficient dCA at very low frequency.NEW & NOTEWORTHY Recent evidence highlights the importance of considering directional sensitivity in dynamic cerebral autoregulation. The current analysis found no directional sensitivity in the cerebral pressure-flow relationship during 0.03- and 0.10-Hz oscillatory lower body negative pressure in normothermia or moderate hyperthermia in healthy participants. However, reduced directional sensitivity metrics during moderate hyperthermia suggest that dynamic cerebral autoregulation may become more efficient under moderate heat stress.

Ramp protocol for non-linear cerebrovascular reactivity with transcranial doppler ultrasound

BACKGROUND

Cerebrovascular reactivity (CVR) reflects the ability of cerebral blood vessels to adjust their diameter in response to vasoactive stimuli, which is crucial for maintaining brain health. Traditional CVR assessments commonly use a two-point measurement, assuming a linear relationship between cerebral blood flow (CBF) and arterial CO2. However, this approach fails to capture non-linear characteristics, particularly the plateaus at extreme CO2 levels.

NEW METHOD

This study introduces a cost-effective, ramp-based end-tidal CO2 (PETCO2) protocol to assess non-linear aspects of CVR. Using transcranial Doppler ultrasound, we monitored blood velocity responses to progressive increases in arterial CO2 levels in eleven healthy adults, covering a spectrum from hypocapnia to hypercapnia.

RESULTS

All eleven participants successfully completed the protocol, with an average PETCO2 range of 26 ± 4 mmHg and blood velocity changes from -29 % to + 50 % relative to baseline. Non-linear CVR characteristics were observed in all subjects. Sigmoid models provided significantly better fits to the CVR data than linear models, while Bayesian approaches followed expected physiological ranges more accurately than least squares regression methods.

COMPARISON WITH EXISTING METHODS

Unlike traditional CVR methods, this ramp protocol captures the full, non-linear CVR profile. The sigmoid modeling approach offers a more accurate representation of cerebrovascular dynamics, particularly at CO2 extremes.

CONCLUSIONS

The PETCO2 ramp protocol with non-linear CVR modeling shows promise as an accessible and reliable tool for assessing CBF dynamics. With high completion rates, straightforward implementation, and low equipment cost, this approach holds significant potential for clinical applications in cerebrovascular health evaluation.

Effects of Argon in the Acute Phase of Subarachnoid Hemorrhage in an Endovascular Perforation Model in Rats

BACKGROUND

Subarachnoid hemorrhage (SAH) is a devastating disease with high morbidity and mortality. Neuroprotective effects of the noble gas argon have been shown in animal models of ischemia. The aim of this study was to investigate the effects of argon in the immediate early phase of SAH in a rat model.

METHODS

A total of 19 male Wistar rats were randomly assigned to three treatment groups. SAH was induced using a endovascular filament perforation model. Cerebral blood flow, mean arterial blood pressure (MAP), and body temperature were measured continuously. Group A received 2 h of ventilation by 50% argon/50% O2 (n = 7) immediately following SAH. Group B underwent a sham operation and was also ventilated by 50% argon/50% O2 (n = 6). Group C underwent SAH and 50% O2/50% N2 ventilation (n = 6). Preoperative and postoperative neurological and behavioral testing were performed. Histology and immunohistochemistry were used to evaluate the extent of brain injury and vasospasm.

RESULTS

The cerebral blood flow dropped in both treatment groups after SAH induction (SAH, 63.0 ± 11.6% of baseline; SAH + argon, 80.2 ± 8.2% of baseline). During SAH, MAP increased (135.2 ± 10.5%) compared with baseline values (85.8 ± 26.0 mm Hg) and normalized thereafter. MAP in both groups showed no significant differences (p = 0.3123). Immunohistochemical staining for neuronal nuclear antigen demonstrated a decrease of hippocampal immunoreactivity after SAH in the cornu ammonis region (CA) 1-3 compared with baseline hippocampal immunoreactivity (p = 0.0127). Animals in the argon-ventilated group showed less neuronal loss compared with untreated SAH animals (p < 0.0001). Ionized calcium-binding adaptor molecule 1 staining showed a decreased accumulation after SAH + argon (CA1, 2.57 ± 2.35%; CA2, 1.89 ± 1.89%; CA3, 2.19 ± 1.99%; DG, 2.6 ± 2.24%) compared with untreated SAH animals (CA1, 5.48 ± 2.39%; CA2, 4.85 ± 4.06%; CA3, 4.22 ± 3.01%; dentate gyrus (DG), 3.82 ± 3.23%; p = 0.0007). The neuroscore assessment revealed no treatment benefit after SAH compared with baseline (p = 0.385).

CONCLUSION

In the present study, neuroprotective effects of argon occurred early after SAH. Because neurological deterioration was similar in the preadministration and absence of argon, it remains uncertain if neuroprotective effects translate in improved outcome over time.

Neuromechanical Simulation of Human Postural Sway in the Sagittal Plane Based on a Hybrid Triple Inverted Pendulum Model and State-Dependent Intermittent Neural Control

OBJECTIVE

This study introduces a novel neuromechanical model that employs a hybrid triple inverted pendulum (HTIP) framework combined with state-dependent intermittent control to simulate human quiet stance in the sagittal plane.

METHODS

The proposed neuromechanical model integrates the biomechanics of the ankle, knee, and hip joints, focusing on the stabilization of the body's center of mass (CoM) rather than controlling each joint individually. Unlike computational models that require precise joint control, the central nervous system maintains posture by simplifying neural control mechanisms. Specifically, the state-dependent control strategy activates neural feedback only as the CoM approaches the stability boundaries.

RESULTS

Experimental validation against real-world data demonstrated that the model can accurately replicate natural postural sway patterns in the sagittal plane.

CONCLUSION

The model provides a computationally efficient mechanism and a realistic simulation of human posture control, addressing a long-standing challenge in neuromechanical modeling of human quiet stance.

SIGNIFICANCE

This study enhances understanding and simulation capability offers significant new insights for developing targeted interventions for individuals with impairments in postural control.

Macrovascular blood flow and microvascular cerebrovascular reactivity are regionally coupled in adolescence

Cerebrovascular imaging assessments are particularly challenging in adolescent cohorts, where not all modalities are appropriate, and rapid brain maturation alters hemodynamics at both macro- and microvascular scales. In a preliminary sample of healthy adolescents (n = 12, 8-25 years), we investigated relationships between 4D flow MRI-derived blood velocity and blood flow in bilateral anterior, middle, and posterior cerebral arteries and BOLD cerebrovascular reactivity (CVR) in associated vascular territories. As hypothesized, higher velocities in large arteries are associated with an earlier response to a vasodilatory stimulus (cerebrovascular reactivity delay) in the downstream territory. Higher blood flow through these arteries is associated with a larger BOLD response to a vasodilatory stimulus (cerebrovascular reactivity amplitude) in the associated territory. These trends are consistent in a case study of adult moyamoya disease. In our small adolescent cohort, macrovascular-microvascular relationships for velocity/delay and flow/CVR change with age, though underlying mechanisms are unclear. Our work emphasizes the need to better characterize this key stage of human brain development, when cerebrovascular hemodynamics are changing, and standard imaging methods offer limited insight into these processes. We provide important normative data for future comparisons in pathology, where combining macro- and microvascular assessments may better help us prevent, stratify, and treat cerebrovascular disease.

Impact of successive sets of high-intensity leg press on cerebral hemodynamics across menstrual cycle phases

This study examined how successive sets of high-intensity leg press (LP) resistance exercise impact the cerebral pressure-flow relationship in untrained males and eumenorrheic females not taking oral contraceptives and assessed how the menstrual cycle (MC) phase influences the cerebral pressure-flow relationship and cerebral hemodynamics (middle cerebral artery blood velocity, MCAv; via transcranial Doppler ultrasound) during and after LP exercise in females. Young adults (11M;11F) performed three sets of leg-press exercises at 90% of their one-repetition maximum. Data from males and females in the early follicular phase were pooled together. Directional sensitivity of the cerebral pressure-flow relationship was calculated as the ratio of the rate of changes in MCAv and mean arterial pressure (MAP) (ΔMCAvT/ΔMAPT) per transition between eccentric and concentric muscular contractions during each repetition of LP exercise. ΔMCAvT/ΔMAPT was higher during concentric than eccentric phases (P < 0.001) in males and early follicular (EF) phase in females. There were no effects of successive leg press sets on any systemic or cerebral hemodynamic measures. The MC phase affected directional sensitivity and cerebral hemodynamics, with greater responses in the mid-luteal (ML) phase than the EF phase. We observed a MAP direction by MC phase interaction on relative directional sensitivity, with greater sensitivity during concentric contractions in the ML phase (P = 0.02). Our results suggest that successive sets of LP exercises do not impact the cerebral pressure-flow relationship or cerebral hemodynamics during and immediately following LP exercise. The MC phase appears to influence the cerebral pressure-flow relationship and cerebral hemodynamics both during and following LP exercise, mediated by vasoprotective effects of increased estrogen concentration in the ML phase compared with the EF phase.NEW & NOTEWORTHY Successive sets of high-intensity bilateral leg press exercises do not appear to affect cerebral or systemic hemodynamic measures, given adequate recovery time. The menstrual cycle phase impacts the directional sensitivity of the cerebral pressure-flow relationship during high-intensity bilateral leg press exercises. During high-intensity bilateral leg press exercises, the cerebrovasculature appears to be more pressure passive in the mid-luteal phase of the menstrual cycle.

Associations of life-course cardiovascular risk factors with late-life cerebral hemodynamics

While the associations of mid-life cardiovascular risk factors with late-life white matter lesions (WMH) and cognitive decline have been established, the role of cerebral haemodynamics is unclear. We investigated the relation of late-life (69-71 years) arterial spin labelling (ASL) MRI-derived cerebral blood flow (CBF) with life-course cardiovascular risk factors (36-71 years) and late-life white matter hyperintensity (WMH) load in 282 cognitively healthy participants (52.8% female). Late-life (69-71 years) high systolic (B = -0.15) and diastolic (B = -0.25) blood pressure, and mean arterial pressure (B = -0.25) were associated with low grey matter (GM) CBF (p < 0.03), and white matter CBF (B = -0.25; B = -0.15; B = -0.13, p < 0.03, respectively). The association between systolic blood pressure and GM CBF differed between sexes (male/female B = -0.15/0.02, p = 0.04). No associations were found with early- or mid-life cardiovascular risk factors. Furthermore, WMHs were associated with cerebral haemodynamics but not cardiovascular risk factors. These findings suggest that cerebral blood flow autoregulation is able to maintain stable global cerebral haemodynamics until later in life. Future studies are encouraged to investigate why cardiovascular risk factors have differential effects on haemodynamics and WMH, and their implications for cognitive decline.

Unlocking the potential of high-resolution multimodality neuromonitoring for traumatic brain injury management: lessons and insights from cases, events, and patterns

Multimodality neuromonitoring represents a crucial cornerstone for patient management after acute brain injury. Despite the potential of multimodality neuromonitoring (particularly high-resolution neuromonitoring data) to transform care, its full benefits are not yet universally realized. There remains a critical need to integrate the interpretation of complex patterns and indices into the real-time clinical decision-making processes. This requires a multidisciplinary approach, to evaluate and discuss the implications of observed patterns in a timely manner, ideally in close temporal proximity to their occurrence. Such a collaborative effort could enable clinicians to harness the full potential of multimodal data. In this educational case-based scoping review, we aim to provide clinicians, researchers, and healthcare professionals with detailed, compelling examples of potential applications of multimodality neuromonitoring, focused on high-resolution modalities within the field of traumatic brain injury. This case series showcases how neuromonitoring modalities such as intracranial pressure, brain tissue oxygenation, near-infrared spectroscopy, and transcranial Doppler can be integrated with cerebral microdialysis, neuroimaging and systemic physiology monitoring. The aim is to demonstrate the value of a multimodal approach based on high-resolution data and derived indices integrated in one monitoring tool, allowing for the improvement of diagnosis, monitoring, and treatment of patients with traumatic brain injury. For this purpose, key concepts are covered, and various cases have been described to illustrate how to make the most of this advanced monitoring technology.

Regulation of blood-brain barrier integrity by brain microvascular endothelial cells in ischemic stroke: A therapeutic opportunity

Stroke is the second leading cause of death from cardiovascular diseases. Brain microvascular endothelial cells (BMECs) are crucial in the treatment of cerebral ischemic stroke, as their functional status directly affects the integrity of the blood-brain barrier (BBB). This review systematically discusses the central role of BMECs in ischemia. The mitochondrial dysfunction and activation of apoptosis/necrosis pathways in BMECs directly disrupt the integrity of the BBB and the degradation of junctional complexes (such as TJs and AJs) further exacerbates its permeability. In the neurovascular unit (NVU), astrocytes, microglia, and pericytes regulate the function of BMECs by secreting cytokines (such as TGF-β and VEGF), showing dual effects of promoting repair and damage. The dynamic changes of transporters, including those from the ATP-binding cassette and solute carrier families, as well as ion channels and exchangers, such as potassium and calcium channels, offer novel insights for the development of targeted drug delivery systems.

Continuous monitoring of intracranial pressure and end tidal carbon dioxide variations in traumatic brain injury: introducing the carbon dioxide reactivity index (CO2Rx)

PURPOSE

The continuous monitoring of cerebral metabolic autoregulation in patients with severe traumatic brain injury (TBI) is poorly documented in the literature and largely absent from clinical practice. This study aimed to assess whether variations in intracranial pressure (ICP) and end-tidal carbon dioxide (ETCO2) can form the basis of an index for cerebrovascular autoregulation reactivity, and whether this index can improve the prediction of clinical outcomes in both adult and pediatric TBI patients.

METHODS

Data from adult and pediatric patients with severe TBI were retrospectively analyzed. The Carbon Dioxide Reactivity Index (CO2Rx) was introduced as a novel tool to assess cerebrovascular reactivity in response to variations in CO2 and ICP. CO2Rx was calculated by analyzing the relationship between ICP and ETCO2, sampled at approximately 5-minute intervals, using linear correlation within moving time windows ranging from 40 to 180 min in 10-minute increments. The discriminatory power of CO2Rx in predicting clinical outcomes was evaluated through Receiver Operating Characteristic (ROC) curve analysis. The primary outcome measures included in-hospital mortality and the 12-month Glasgow Outcome Scale-Extended (GOSE) score.

RESULTS

The study included 218 TBI patients (40 pediatric and 178 adult). CO2Rx values showed a significant correlation with outcomes, with a CO2Rx threshold of 0.28 effectively distinguishing between favorable and unfavorable outcomes. For the fatal/non-fatal outcome, the CO2Rx crude model alone had an Area Under the Curve (AUC) of 0.737. When combined with other predictors (Impact Core + ICP + CO2Rx), this model achieved the highest AUC of 0.929.

CONCLUSION

CO2Rx demonstrated significant predictive value for mortality and unfavorable outcomes in TBI patients, serving as a continuous index of cerebrovascular reactivity to CO2. It holds potential to improve severe TBI management by optimizing the interaction between ventilation and metabolic autoregulation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT NCT05043545.

Multi-Layer Autocatalytic Feedback Enables Integral Control Amidst Resource Competition and Across Scales

Integral feedback control strategies have proven effective in regulating protein expression in unpredictable cellular environments. These strategies, grounded in model-based designs and control theory, have advanced synthetic biology applications. Autocatalytic integral feedback controllers, utilizing positive autoregulation for integral action, are one class of simplest architectures to design integrators. This class of controllers offers unique features, such as robustness against dilution effects and cellular growth, as well as the potential for synthetic realizations across different biological scales, owing to their similarity to self-regenerative behaviors widely observed in nature. Despite this, their potential has not yet been fully exploited. One key reason, we discuss, is that their effectiveness is often hindered by resource competition and context-dependent couplings. This study addresses these challenges using a multilayer feedback strategy. Our designs enabled population-level integral feedback and multicellular integrators, where the control function emerges as a property of coordinated interactions distributed across different cell populations coexisting in a multicellular consortium. We provide a generalized mathematical framework for modeling resource competition in complex genetic networks, supporting the design of intracellular control circuits. The use of our proposed multilayer autocatalytic controllers is examined in two typical control tasks that pose significant relevance to synthetic biology applications: concentration regulation and ratiometric control. We define a ratiometric control task and solve it using a variant of our controller. The effectiveness of our controller motifs is demonstrated through a range of application examples, from precise regulation of gene expression and gene ratios in embedded designs to population growth and coculture composition control in multicellular designs within engineered microbial ecosystems. These findings offer a versatile approach to achieving robust adaptation and homeostasis from subcellular to multicellular scales.

Characterising the protective vasodilatory effects of hypobaric hypoxia on the neurovascular coupling response

Neurovascular coupling (NVC) is the link between local neuronal activity and regional cerebral blood flow. High altitude (HA) ascent induces acute hypoxic vasodilation of the cerebral vasculature, with associated changes in CO2 and acid-base status. We aimed to characterise the effects of (a) acute removal of the HA-induced vasodilation and (b) rapid ascent to and residency at HA on NVC responses. In twelve healthy participants (7 M/5F), arterial blood gases and NVC were measured at baseline (1130 m) and on days two (<24 h at HA) and nine (post-acclimatisation) at 3800 m. Acute gas challenges were performed using end-tidal forcing, with (a) normoxia and isocapnic hypoxia at 1130 m and (b) poikilocapnic hypoxia and isocapnic hyperoxia on days two and nine at 3800 m. Posterior cerebral artery velocity (PCAv) was measured using transcranial Doppler ultrasound in each condition and time-point. NVC was assessed via a standardized 30 s intermittent strobe light visual stimulus (VS), and quantified as the peak and mean change from baseline in PCAv. No significant differences were observed for any NVC metric across all conditions and time points. Our results reveal remarkable stability of the NVC response following (a) acute removal of HA-induced hypoxic vasodilation and (b) rapid ascent to and residency at 3800 m.

Impaired Cerebral Autoregulation in Children

Managing acute brain injury involves protecting the brain from secondary injury by addressing the mismatch between metabolic demand and cerebral perfusion. Observational studies have associated impaired cerebral autoregulation, a physiological process governing the regulation of cerebral blood flow, with unfavorable neurological outcomes in both pediatric and adult populations. We review the pathophysiology of cerebral autoregulation and discuss methods for assessing and monitoring it in children after acquired brain injury. We also examine the current research investigating the relationship between impaired cerebral autoregulation and outcomes following traumatic brain injury, cardiac arrest, cardiopulmonary bypass, and extracorporeal membrane oxygenation. Furthermore, we outline potential areas for future research in cerebral autoregulation and its clinical implications for pediatric patients with brain injuries.

Collateral blood vessels in stroke and ischemic disease: Formation, physiology, rarefaction, remodeling

Collateral blood vessels are unique, naturally occurring endogenous bypass vessels that provide alternative pathways for oxygen delivery in obstructive arterial conditions and diseases. Surprisingly however, the capacity of the collateral circulation to provide protection varies greatly among individuals, resulting in a significant fraction having poor collateral circulation in their tissues. We recently reviewed evidence that the presence of naturally-occurring polymorphisms in genes that determine the number and diameter of collaterals that form during development (ie, genetic background), is a major contributor to this variation. The purpose of this review is to summarize current understanding of the other determinants of collateral blood flow, drawing on both animal and human studies. These include the level of smooth muscle tone in collaterals, hemodynamic forces, how collaterals form during development (collaterogenesis), de novo formation of additional new collaterals during adulthood, loss of collaterals with aging and cardiovascular risk factor presence (rarefaction), and collateral remodeling (structural lumen enlargement). We also review emerging evidence that collaterals not only provide protection in ischemic conditions but may also serve a physiological function in healthy individuals. Primary focus is on studies conducted in brain, however relevant findings in other tissues are also reviewed, as are questions for future investigation.

Acute Effect of Moderate-Intensity Interval Intradialytic Exercise on Cerebral Oxygenation in Hemodialysis Patients: A Randomized Crossover Trial

Background

Cognitive dysfunction in hemodialysis (HD) patients is associated with decreased regional cerebral oxygenation (rSO2). Intradialytic exercise improves cognitive function; nonetheless, the acute effect of intradialytic exercise on cerebral circulation remains unknown. This study aimed to evaluate the acute effect of intradialytic exercise on rSO2 during HD.

Methods

This single-center, open-label, randomized crossover trial included 20 HD patients. Patients received the control condition as usual care and the intradialytic exercise condition in random order. The intradialytic exercise condition involved the performance of anaerobic threshold-intensity interval exercise for 35 min. Cerebral oxygenation (rSO2, oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin) in the prefrontal cortex was measured using near-infrared spectroscopy during HD. Cardiovascular responses, including the heart rate, cardiac index, mean arterial pressure, and blood gas, were also assessed. The two conditions were compared using two-way repeated-measures analysis of variance.

Results

The analysis included 16 patients, four of whom were excluded because of artifacts in the cerebral oxygenation data. The rSO2 (P<0.001), oxygenated hemoglobin (P<0.001), and total hemoglobin (P=0.004) showed significant interactions and were significantly increased at end of exercise (rSO2 1.3%, 95%CI [0.5, 2.1]; oxygenated hemoglobin 0.01 mM, 95%CI [0.00, 0.02]; total hemoglobin 0.01 mM, 95%CI [0.00, 0.03]) and 15-min after exercise (rSO2 1.1%, 95%CI [0.2, 2.0]; oxygenated hemoglobin 0.01 mM, 95%CI [0.00, 0.03]; total hemoglobin 0.02 mM, 95%CI [0.00, 0.03]) in the intradialytic exercise condition compared with the control condition. The rSO2 at the end of HD in the control condition was significantly decreased compared with that during pre-HD (-1.5%, 95%CI [-2.7, -0.3]), but not in the intradialytic exercise condition (-1.2%, 95%CI [-2.8, 0.5]).

Conclusions

Intradialytic exercise significantly increased rSO2 during and after exercise and improved rSO2 to the same extent as pre-dialysis.

Metabolic pathway and genetically causal links of 1,400 circulating metabolites on the risk of intracranial aneurysms and aneurysmal subarachnoid hemorrhage

BACKGROUND

The rupture of intracranial aneurysms (IAs) leads to aneurysmal subarachnoid hemorrhage (aSAH), which is associated with significant disability and mortality rates. This study aims to identify metabolic markers causally linked to the occurrence of IAs and aSAH through Mendelian randomization (MR), thereby offering novel predictive and therapeutic targets.

METHODS

We conducted a genome-wide association study (GWAS) on IAs and aSAH, analyzing 1,400 metabolomic indices from the Canadian Longitudinal Study on Aging (CLSA) cohort (n = 8,299). Subsequently, we employed two-sample Mendelian randomization to ascertain potential causal relationships between each metabolite and the conditions IAs and aSAH by various MR methodologies, including MR Egger, Weighted median, Inverse variance weighted (IVW), MR-PRESSO, Simple mode, and Weighted mode. The heterogeneity of instrumental variables was assessed using Cochran's Q statistics, and metabolic pathway analyses were performed via the Metaconflict 5.0 platform.

RESULTS

Our analysis found that 87 metabolites/metabolic ratios were associated with IAs, and 85 metabolites/metabolic ratios were associated with aSAH. After false discovery rate (FDR) correction and sensitivity analyses, nine metabolites/metabolic ratios were significantly causally associated with aSAH. Conversely, while 87 metabolites and their ratios initially showed potential causal links with IA, none demonstrated significant causal associations post-FDR correction. The study also pinpointed eight significant metabolic pathways implicated in both IAs and aSAH.

CONCLUSION

This study found that nine circulating metabolites and their ratios with significant causal associations to aSAH, while no metabolites and their ratios were causally linked to IAs. These results suggest possible mechanisms and predictive molecular targets for IAs and aSAH.

The brain-heart axis: integrative cooperation of neural, mechanical and biochemical pathways

The neural and cardiovascular systems are pivotal in regulating human physiological, cognitive and emotional states, constantly interacting through anatomical and functional connections referred to as the brain-heart axis. When this axis is dysfunctional, neurological conditions can lead to cardiovascular disorders and, conversely, cardiovascular dysfunction can substantially affect brain health. However, the mechanisms and fundamental physiological components of the brain-heart axis remain largely unknown. In this Review, we elucidate these components and identify three primary pathways: neural, mechanical and biochemical. The neural pathway involves the interaction between the autonomic nervous system and the central autonomic network in the brain. The mechanical pathway involves mechanoreceptors, particularly those expressing mechanosensitive Piezo protein channels, which relay crucial information about blood pressure through peripheral and cerebrovascular connections. The biochemical pathway comprises many endogenous compounds that are important mediators of neural and cardiovascular function. This multisystem perspective calls for the development of integrative approaches, leading to new clinical specialties in neurocardiology.

Brain Ischemia in Alzheimer's Disease May Partly Counteract the Disruption of the Blood-Brain Barrier

BACKGROUND

In normal pressure hydrocephalus (NPH) there is blood-brain barrier (BBB) disruption, which should increase the CSF formation rate (CSFfr) and, therefore, also increase the intracranial pressure (ICP). However, the ICP is normal in NPH. A lumped parameter study was performed to look at the interrelation between the ICP, cerebral blood flow (CBF), and the degree of BBB disruption in NPH. The model suggested that the CSFfr could be reduced in this condition if the BBB disruption was moderated by a reduction in the capillary transmural pressure (TMP) secondary to arteriolar constriction and a reduced CBF. In early Alzheimer's disease (AD), there is BBB disruption, reduced ICP, and global ischemia. This raises the possibility that the same physiology may occur in AD as occurs in NPH.

METHODS

A lumped parameter model previously used to describe the hydrodynamics of NPH was modified to investigate the effects of changes in CSF pressure and blood flow in patients with mild cognitive impairment (MCI) and AD.

RESULTS

The model indicates that the average capillary TMP is normal in MCI, but decreases as AD progresses. Removing CSF in AD patients during a tap test initially increases the capillary TMP. The brain in AD responds to a tap test by increasing its level of ischemia, and this reduces the capillary TMP.

CONCLUSIONS

A hypothesis is put forward that the BBB disruption in AD is partially mitigated by the brain making itself ischemic. Modelling gives support to this hypothesis. The model can suggest a cause for the development of ischemic neuronal loss and amyloid accumulation secondary to glymphatic flow disruption as AD progresses.

Impact of intravenous antihypertensive therapy on cerebral blood flow and neurocognition: a systematic review and meta-analysis

BACKGROUND

Intravenous antihypertensivedrugs are commonly used in acute care settings, yet their impact on cerebral blood flow (CBF) remains uncertain.

METHODS

A systematic review and meta-analysis of 50 studies evaluated the effects of commonly used i.v. antihypertensive agents on CBF in normotensive, hypertensive, and intracranial pathology populations. Meta-analyses used standardised mean differences (SMD), stratified by population type, consciousness state, antihypertensive agent, and CBF measurement method.

RESULTS

Intravenous antihypertensivedrug therapy significantly reduced CBF in normotensive individuals without intracranial pathology (SMD -0.31, 95% confidence interval -0.51 to -0.11), primarily driven by nitroprusside and nitroglycerin in awake subjects (SMD -0.80, 95% confidence interval -1.15 to -0.46), with a median CBF decrease of 14% (interquartile range 13-16%) and a median mean arterial pressure reduction of 17% (interquartile range 9-22%). Other antihypertensives showed no significant effects on CBF in normotensive individuals, nor were changes observed in hypertensive patients or those with intracranial pathology when the median mean arterial pressure reduction was ∼20%. No correlation was found between mean arterial pressure reduction and CBF change, supporting intact cerebral autoregulation. Historical data revealed neurocognitive changes when CBF fell to ∼30 ml 100 g-1 min-1, associated with a 58% mean arterial pressure reduction and a 38% CBF reduction.

CONCLUSIONS

Most i.v. antihypertensive agents do not significantly affect CBF in clinical dose ranges; however, nitroprusside and nitroglycerin can reduce CBF under specific clinical conditions. The certainty of evidence remains low. Neurocognitive changes appear to depend on the magnitude of blood pressure and CBF reductions.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO (CRD42024511954).

Cerebral blood flow alterations and host genetic association in individuals with long COVID: A transcriptomic-neuroimaging study

Neuroimaging studies have indicated that altered cerebral blood flow (CBF) was associated with the long-term symptoms of postacute sequelae of SARS-CoV-2 infection (PASC), also known as "long COVID". COVID-19 and long COVID were found to be strongly associated with host gene expression. Nevertheless, the relationships between altered CBF, clinical symptoms, and gene expression in the central nervous system (CNS) remain unclear in individuals with long COVID. This study aimed to explore the genetic mechanisms of CBF abnormalities in individuals with long COVID by transcriptomic-neuroimaging spatial association. Lower CBF in the left frontal-temporal gyrus was associated with higher fatigue and worse cognition in individuals with long COVID. This CBF pattern was spatially associated with the expression of 2,178 genes, which were enriched in the molecular functions and biological pathways of COVID-19. Our study suggested that lower CBF is associated with persistent clinical symptoms in long COVID individuals, possibly as a consequence of the complex interactions among multiple COVID-19-related genes, which contributes to our understanding of the impact of adverse CNS outcomes and the trajectory of development to long COVID.

Ultrasound-cavitation-enhanced drug delivery via microbubble clustering induced by acoustic vortex tweezers

The application of acoustic vortex tweezers (AVT) in conjunction with ultrasound (US) cavitation pulses presents a promising noninvasive approach for the delivery of high concentrations of therapeutic agents. This methodology facilitates the aggregation of drug-loaded microbubbles (MBs) into clusters, which are subsequently destroyed to release their contents. Nevertheless, prior investigations have not thoroughly examined the resonance frequency and cavitation activity of MB clusters, critical factors that could enhance the efficiency of payload release. Theoretically, the resonance frequency of an MB cluster is expected to approximate that of a single large bubble of comparable size, thus being significantly lower than that of the individual MBs constituting the cluster. Accordingly, this study aims to optimize the release of payloads from AVT-trapped MB clusters, which measure 15 to 40 μm (mean radius: 24.7 μm) in size, by employing US at their resonance frequency of 100 kHz, henceforth referred to as "on-resonance US." In this investigation, MBs were loaded with the model drug DiI, resulting in the formation of DiI-MBs, which were then clustered utilizing AVT. On-resonance US excitation was subsequently applied to enhance the release of the drug payload. The dimensional characteristics of the DiI-MB clusters formed via 3-MHz AVT were measured to determine the range of resonance frequencies. Concurrent optical and acoustic analyses were conducted to evaluate the size, oscillation dynamics, and cavitation activity of the DiI-MB clusters in response to on-resonance US excitation. Additionally, the payload release from these clusters was quantitatively assessed. Our results indicate that significant oscillations of individual DiI-MB clusters commenced at a pressure of 44 kPa during 100 kHz US excitation. Further quantitative experiments demonstrated that the synergistic combination of AVT and 100-kHz US at 65 kPa significantly enhanced the payload release efficiency to 93 %. This efficiency surpassed that achieved with either method independently, with increases of 1.8-fold relative to AVT alone and 2.3-fold compared to 100-kHz US alone. The acoustic analyses revealed the onset of inertial cavitation at 44 kPa, which strongly correlated with payload release efficiency (R2 = 0.78). These findings underscore the potential of our proposed methodology in monitoring and enhancing the efficiency of drug release.

Competing influences of arterial pressure and carbon dioxide on the dynamic cerebrovascular response to step transitions in exercise intensity

Recent investigations of middle cerebral artery blood velocity (MCAv) kinetics at the onset of exercise have not accounted for potential dynamic changes in arterial partial pressure of carbon dioxide ([Formula: see text]) during the transient phase of exercise transitions when modeling MCAv kinetics, despite [Formula: see text] having known effects on cerebrovascular tone. The purpose of our study was to determine the independent effects of mean arterial pressure (MAP) and estimated [Formula: see text] ([Formula: see text]) on mean MCAv during repeated moderate-intensity exercise transitions. We hypothesized that cerebral autoregulation would minimize the effect of sustained exercise-induced changes in MAP on mean MCAv and that dynamic changes in [Formula: see text] would contribute to changes in mean MCAv. Eighteen young healthy adults (7 women, age: 28 ± 5 yr) performed three exercise transitions from 25 W to 90% of the ventilatory threshold in sequence with 5-min stages. Mean MCAv increased (P < 0.001) from 25 W (60.5 ± 14.0 cm·s-1) to 90% of the ventilatory threshold (68.8 ± 15.1 cm·s-1). MAP at the level of the middle cerebral artery (MAPMCA) (Δ = 14 ± 8 mmHg, P < 0.001) and [Formula: see text] (Δ = 2.7 ± 1.8 mmHg, P < 0.001) also increased with exercise intensity. Autoregressive moving average (ARMA) analysis isolated the independent effects of dynamic changes in MAPMCA and [Formula: see text] on MCAv, with low prediction error (mean absolute error = 1.12 ± 0.25 cm·s-1). Calculated steady states of the ARMA step responses were 0.13 ± 0.15 cm·s-1·mmHg-1 for Δmean MCAv/ΔMAPMCA and 1.95 ± 0.83 cm·s-1·mmHg-1 for Δmean MCAv/Δ[Formula: see text]. These data demonstrate that the combination of dynamic changes in MAP and [Formula: see text] largely explains the MCAv response during transitions in exercise intensity.NEW & NOTEWORTHY Time-series analysis of moderate-intensity exercise transitions suggested that cerebral autoregulation buffered the effect of sustained changes in mean arterial pressure on middle cerebral artery blood velocity (MCAv) and that changes in estimated arterial partial pressure of carbon dioxide ([Formula: see text]) contributed to the dynamic changes in MCAv during exercise transitions. Therefore, changes in [Formula: see text] at the onset of exercise are central to modeling dynamic MCAv responses and understanding the benefits of exercise on cerebral blood flow.

Cold pressor-induced sympathetic activation blunts the femoral but not carotid artery vascular responsiveness

Vascular responsiveness due to passive leg movement (PLM) on the brain remains unknown. This study aimed to evaluate the effects of cold-induced sympathetic activation (CPT) on femoral and ipsilateral and contralateral carotid arteries' vascular responsiveness evoked by PLM. Thirteen participants (seven males and six females; age: 27.0 ± 2.3 years) undertook a randomized session in which PLM was performed on the right leg at rest and during CPT. Right femoral (fBF) and right (ipsilateral) and left (contralateral) carotid (cBF) blood flows were measured by ultrasounds, and heart hemodynamics were assessed via photoplethysmography and impedance cardiograph. Systolic arterial pressure (SAP) time series were used to infer sympathetic modulation to the vessels. Femoral (fVC) and carotid (cVC) vascular conductance (BF/MAP) were calculated. CPT evoked changes in PLM on cBF, fBF, and fVC (interaction and time effect). cBF peak and cBF and cVC area under the curve were higher in the contralateral carotid in the two interventions. Low-frequency power of SAP was higher in PLM-CPT than in PLM; all p < 0.05. These results suggest that the CPT-induced increases in sympathetic modulation attenuate the vascular responsiveness in the femoral, but not the carotid, arteries. Also, the contralateral carotid increased blood flow during PLM, regardless of the CPT.

Cerebral blood flow and cognitive functioning in patients undergoing transcatheter aortic valve implantation

Background

Approximately one-third of patients with symptomatic severe aortic valve stenosis scheduled for transcatheter aortic valve implantation (TAVI) have some degree of cognitive impairment. The effect of TAVI on cardiac output, cerebral blood flow (CBF), and cognitive functioning has not been systematically studied.

Methods

CAPITA (NCT05481008) is a prospective longitudinal study assessing cerebral and cognitive outcomes in patients that underwent TAVI between August 2020 and October 2022. At baseline (<24 h before TAVI) and three-month follow-up, patients underwent echocardiography, brain magnetic resonance imaging (MRI), and multidomain neuropsychological assessment. Primary outcome measures were change in CBF (Δml/100 g/min on arterial spin labelling MRI) and change in global cognitive functioning (Δz-scores). Secondary outcomes included cardiac output (L/min), and white matter hyperintensities (mL, number). Differences were tested with paired t-test and associations were tested with linear mixed models.

Findings

A total of 148 patients (80.5 ± 5.7 years, 43% female) underwent TAVI. Three months after TAVI, cardiac output increased from 5.9 ± 1.4 L/min to 6.3 ± 1.4 L/min (mean difference 0.37, 95% CI 0.12-0.62, p = 0.004). CBF increased from 52.2 ± 14.5 mL/100 g/min to 55.9 ± 17.7 mL/100 g/min (mean difference 3.8, 95% CI 1.15-6.36, p = 0.005). Global cognitive functioning also increased from 0.02 ± 0.52 to 0.15 ± 0.49 (mean difference 0.13, 95% CI 0.06-0.20, p < 0.001) with most prominent increase in patients with worst baseline cognitive functioning. Patients with cognitive decline (22%), had a higher volume of new in white matter hyperintensities than patients with stable or improved cognition (78%): 1.26 ± 2.96, vs 0.29 ± 0.45, vs 0.31 ± 0.91 mL (p = 0.06).

Interpretation

In patients with severe symptomatic aortic valve stenosis undergoing TAVI, cardiac output, CBF, and cognitive functioning improved after three months.

Funding

The Heart-Brain Connection crossroad consortium of the Dutch Cardiovascular Alliance. The Netherlands CardioVascular Research Initiative: Dutch Heart Foundation (CVON 2018-28 & 2012-06 Heart Brain Connection).

A higher vertebrobasilar pulsatility index is associated with lower parietal perfusion in Alzheimer's disease

BACKGROUND

While cerebrovascular hemodynamics exhibits critical interplay with the pathogenesis of dementia, limited articles have examined the impact of vertebrobasilar (VB) hemodynamics on cerebral blood flow (CBF), and to what extent it varies by dementia subtypes.

OBJECTIVE

To explore the associations between VB hemodynamics and CBF by dementia subtypes.

METHODS

This research recruited a total of 120 dementia patients [43 subcortical ischemic vascular dementia (SIVD); 59 Alzheimer's disease (AD); 18 mixed dementia] and 40 older adults with normal cognition and compared their transcranial doppler (TCD) flow parameters and arterial spin labeling-measured CBF. Using the partial correlation analysis, the associations between TCD parameters and CBF values were explored among the defined subgroups.

RESULTS

A higher VB pulsatility index (PI) was related to lower parietal CBF and lower VB end-diastolic velocity (EDV). Moreover, the significance of flow parameters in the basilar artery (BA) to parietal CBF was identified: peak-systolic velocity (PSV) unanimously showed positive correlations among all subgroups except SIVD, and both PSV and EDV showed positive correlations in AD. Of note, there were more noticeable "BA flow-frontoparietal CBF" associations among the high than low VB PI group, and AD than SIVD group.

CONCLUSIONS

The findings indicate that VB-resistance-related parietal vulnerability and topological CBF associations vary by dementia subtypes. Given VB hemodynamics-CBF relationships, the current research extends our understanding of the vasocognopathic effects among dementia patients.

Neurovascular Decoupling Is Associated With Lobar Intracerebral Hemorrhages and White Matter Hyperintensities

BACKGROUND

Neurovascular coupling is a fundamental aspect of brain function by regulating cerebral blood flow in response to regional neuronal activity. Increasing evidence suggest neurovascular decoupling occurs early in the progression of Alzheimer disease (AD), potentially reflecting early vascular damage. Therefore, understanding the relationship between neurovascular coupling and established vascular risk factors for AD is essential to gain deeper insights into the vascular mechanisms underlying AD.

METHODS

This cross-sectional observational study investigated the association between neurovascular coupling and vascular risk factors for AD, specifically small vessel disease magnetic resonance imaging markers, cardiovascular risk factors, and the apolipoprotein E genotype. The cohort included 119 participants diagnosed with subjective cognitive impairment, mild cognitive impairment, and AD-related dementia, as well as individuals without cognitive complaints. Neurovascular coupling was measured by blood-oxygen-level-dependent functional magnetic resonance imaging amplitude in response to visual stimulation.

RESULTS

Our findings revealed that decreased neurovascular coupling is linked to structural brain changes typically seen in small vessel disease; specifically we found an association between neurovascular coupling and white matter hyperintensities load (β=-0.199, P=0.030) and presence of lobar intracerebral hemorrhage (β=-0.228, P=0.011).

CONCLUSIONS

This raises the suggestion that a decreased neurovascular coupling in the disease process of AD is related to comorbid small vessel disease.

PINNing cerebral blood flow: analysis of perfusion MRI in infants using physics-informed neural networks

Arterial spin labelling (ASL) magnetic resonance imaging (MRI) enables cerebral perfusion measurement, which is crucial in detecting and managing neurological issues in infants born prematurely or after perinatal complications. However, cerebral blood flow (CBF) estimation in infants using ASL remains challenging due to the complex interplay of network physiology, involving dynamic interactions between cardiac output and cerebral perfusion, as well as issues with parameter uncertainty and data noise. We propose a new spatial uncertainty-based physics-informed neural network (PINN), SUPINN, to estimate CBF and other parameters from infant ASL data. SUPINN employs a multi-branch architecture to concurrently estimate regional and global model parameters across multiple voxels. It computes regional spatial uncertainties to weigh the signal. SUPINN can reliably estimate CBF (relative error - 0.3 ± 71.7 ), bolus arrival time (AT) ( 30.5 ± 257.8 ) , and blood longitudinal relaxation time ( T 1 b ) (-4.4 ± 28.9), surpassing parameter estimates performed using least squares or standard PINNs. Furthermore, SUPINN produces physiologically plausible spatially smooth CBF and AT maps. Our study demonstrates the successful modification of PINNs for accurate multi-parameter perfusion estimation from noisy and limited ASL data in infants. Frameworks like SUPINN have the potential to advance our understanding of the complex cardio-brain network physiology, aiding in the detection and management of diseases. Source code is provided at: https://github.com/cgalaz01/supinn.

Orthostatic hypotension is involved in cognitive impairment in patients with multiple system atrophy: a multi-center cohort study in China

BACKGROUND

Orthostatic hypotension (OH) is a common symptom of multiple system atrophy (MSA), however, its role in cognitive impairment and the mechanism in these patients remains unclear. This study aims to assess the role of OH on cognitive impairment in MSA patients, as well as to explore the potential association of cerebral autoregulation (CA) and white matter hyperintensities (WMHs) on cognitive impairment.

METHODS

This observational study was conducted in three general hospitals in China from January 2018 to October 2023, with patients at one center followed up for 6 months after enrollment. The primary outcomes included cognitive function assessed using the Mini-Mental State Examination (MMSE) and Montreal cognitive assessment (MoCA). Secondary outcomes included the results of the Head-up tilt test, scores for CA and the extent of WMHs.

RESULTS

The 132 MSA patients included 72 men (54.54%) with a mean age of 61.16 (7.80) years. Among them, 80 patients (60.61%) had orthostatic hypotension, and 48 patients (36.36%) had cognitive impairment. OH plays an important role in cognitive impairment in MSA patients (OR = 0.328,95% CI 0.135-0.797, P = 0.014). Cognitive impairment was associated with impaired CA (OR = 0.088,95% CI 0.012-0.657, P = 0.018) and severe WMHs (OR = 0.030,95% CI 0.002-0.423, P = 0.009), particularly in the presence of OH.

CONCLUSION

OH is associated with cognitive impairment in MSA patients, and cognitive decline is linked to impaired CA and increased WMHs. Future studies are needed to explore the mechanisms underlying cognitive impairment in MSA patients.

Cerebral autoregulation in patients with acute lacunar infarction: a reliable predictor of outcome

OBJECTIVE

To further investigate the association between dynamic cerebral autoregulation (dCA) and the outcomes in patients with acute lacunar infarction.

METHODS

Patients were prospectively and consecutively enrolled at The First Hospital of Jilin University between 2016 and 2023. dCA was monitored at 1-3 and 7-10 days after the stroke. The outcomes were evaluated using a 3-month modified Rankin Scale score. Binary and ordered logistic regression were employed to analyze the relationship between dCA parameters and outcomes. dCA-based nomogram models were also developed to assess the predictive value of dCA for these patients.

RESULTS

Overall, 332 patients were included in analysis. dCA showed no significant differences between bilateral cerebral hemispheres, as well as two measurement time points (all P > 0.05). Regression analyses showed that dCA at 1-3 and 7-10 days were independently associated with the outcomes of patients with acute lacunar infarction after adjusting for confounders (all P < 0.05). Incorporating dCA parameters into conventional risk factors enhanced the risk-predictive ability of a 3-month unfavorable outcome, significantly improving the area under the receiver operating characteristic curve from 0.798(95% confidence interval [CI], 0.748-0.848) to 0.829(95% CI, 0.783-0.875) (P = 0.046).

INTERPRETATION

dCA remained consistent in bilateral cerebral hemispheres within acute and subacute periods among patients with lacunar infarction. It was independently associated with 3-month outcomes and could be regarded as a reliable predictor for discriminating outcome.

Genetic determinants of insufficiency of the collateral circulation

It has been estimated that approximately two million neurons, sixteen billion synapses and twelve kilometers of axons are lost each minute following anterior large-vessel stroke. The level of collateral blood flow has become recognized as a primary determinant of the pace of this loss and an important factor in clinical decision-making. Many of the topics in this review cover recent developments that have not been reviewed elsewhere. These include that: the number and diameter of collaterals and collateral blood flow vary greatly in the brain and other tissues of healthy individuals; a large percentage of individuals are deficient in collaterals; the underlying mechanism arises primarily from naturally occurring polymorphisms in genes/genetic loci within the pathway that drives collateral formation during development; evidence indicates collateral abundance does not exhibit sexual dimorphism; and that collaterals-besides their function as endogenous bypass vessels-may have a physiological role in optimizing oxygen delivery. Animal and human studies in brain and other tissues, where available, are reviewed. Details of many of the studies are provided so that the strength of the findings and conclusions can be assessed without consulting the original literature. Key questions that remain unanswered and strategies to address them are also discussed.

Inhibition of soluble epoxide hydrolase ameliorates cerebral blood flow autoregulation and cognition in alzheimer's disease and diabetes-related dementia rat models

Alzheimer's Disease and Alzheimer's Disease-related dementias (AD/ADRD) pose major global healthcare challenges, with diabetes mellitus (DM) being a key risk factor. Both AD and DM-related ADRD are characterized by reduced cerebral blood flow, although the exact mechanisms remain unclear. We previously identified compromised cerebral hemodynamics as early signs in TgF344-AD and type 2 DM-ADRD (T2DN) rat models. Genome-wide studies have linked AD/ADRD to SNPs in soluble epoxide hydrolase (sEH). This study explored the effects of sEH inhibition with TPPU on cerebral vascular function and cognition in AD and DM-ADRD models. Chronic TPPU treatment improved cognition in both AD and DM-ADRD rats without affecting body weight. In DM-ADRD rats, TPPU reduced plasma glucose and HbA1c levels. Transcriptomic analysis of primary cerebral vascular smooth muscle cells from AD rats treated with TPPU revealed enhanced pathways related to cell contraction, alongside decreased oxidative stress and inflammation. Both AD and DM-ADRD rats exhibited impaired myogenic responses and autoregulation in the cerebral circulation, which were normalized with chronic sEH inhibition. Additionally, TPPU improved acetylcholine-induced vasodilation in the middle cerebral arteries (MCA) of DM-ADRD rats. Acute TPPU administration unexpectedly caused vasoconstriction in the MCA of DM-ADRD rats at lower doses. In contrast, higher doses or longer durations were required to induce effective vasodilation at physiological perfusion pressure in both control and ADRD rats. Additionally, TPPU decreased reactive oxygen species production in cerebral vessels of AD and DM-ADRD rats. These findings provide novel evidence that chronic sEH inhibition can reverse cerebrovascular dysfunction and cognitive impairments in AD/ADRD, offering a promising avenue for therapeutic development.

Cerebral Blood Flow in Orthostatic Intolerance

Cerebral blood flow (CBF) is vital for delivering oxygen and nutrients to the brain. Many forms of orthostatic intolerance (OI) involve impaired regulation of CBF in the upright posture, which results in disabling symptoms that decrease quality of life. Because CBF is not easy to measure, rises in heart rate or drops in blood pressure are used as proxies for abnormal CBF. These result in diagnoses such as postural orthostatic tachycardia syndrome and orthostatic hypotension. However, in many other OI syndromes such as myalgic encephalomyelitis/chronic fatigue syndrome and long COVID, heart rate and blood pressure are frequently normal despite significant drops in CBF. This often leads to the incorrect conclusion that there is nothing hemodynamically abnormal in these patients and thus no explanation or treatment is needed. There is a need to measure CBF, as orthostatic hypoperfusion is the shared pathophysiology for all forms of OI. In this review, we examine the literature studying CBF dysfunction in various syndromes with OI and evaluate methods of measuring CBF including transcranial Doppler ultrasound, extracranial cerebral blood flow ultrasound, near infrared spectroscopy, and wearable devices.

Sub-symptom threshold aerobic exercise improves executive function during the early stage of sport-related concussion recovery

We examined whether persons with a sport-related concussion (SRC) derive a postexercise executive function (EF) benefit, and whether a putative benefit is related to an exercise-mediated increase in cerebral blood flow (CBF). Participants with an SRC completed the Buffalo Concussion Bike Test to determine the heart rate threshold (HRt) associated with symptom exacerbation and/or voluntary exhaustion. On a separate day, SRC participants - and healthy controls (HC group) - completed 20-min of aerobic exercise at 80% HRt while middle cerebral artery velocity (MCAv) was measured to estimate CBF. The antisaccade task (i.e. saccade mirror-symmetrical to target) was completed pre- and postexercise to evaluate EF. SRC and HC groups showed a comparable exercise-mediated increase in CBF (ps < .001), and both groups elicited a postexercise EF benefit (ps < .001); however, the benefit was unrelated to the magnitude of the MCAv change. Moreover, SRC symptomology was not increased when assessed immediately postexercise and showed a 24 h follow-up benefit. Accordingly, persons with an SRC demonstrated an EF benefit following a single bout of sub-symptom threshold aerobic exercise. Moreover, the exercise intervention did not result in symptom exacerbation and thus demonstrates that a tailored aerobic exercise program may support cognitive and symptom recovery following an SRC.

Baroreflex Sensitivity and Long-Term Dementia Risk in Older Adults

BACKGROUND

Increased blood pressure (BP) variability is linked to dementia risk, but the relationship between baroreflex sensitivity (BRS), a fundamental mechanism for maintaining stable BP, and dementia risk is undetermined.

METHODS

We tested the hypothesis that impaired BRS is associated with increased dementia risk in 1819 older adults (63% women; age, 71.0±6.3 years) from the community-based Rotterdam Study. Cardiac BRS was determined from a 5-minute beat-to-beat BP recording at supine rest between 1997 and 1999. Cardiac BRS measures the correlation between changes in consecutive beat-to-beat systolic BP and subsequent responses in heartbeat intervals, with a higher value indicating better BRS. The primary outcome was incident dementia ascertained from baseline through January 1, 2020; the secondary outcome was all-cause mortality.

RESULTS

During a median follow-up of 14.8 years, 421 participants developed dementia. The association of cardiac BRS with dementia risk differed by antihypertensive medication use (Pinteraction=0.03) and was only observed in participants not taking antihypertensives. Specifically, in those not taking antihypertensive medication, reduced BRS was associated with a higher risk of dementia (adjusted hazard ratio comparing bottom versus top quintiles, 1.60 [95% CI, 1.07-2.40]; Ptrend=0.02). Reduced BRS was also associated with an increased risk of death (corresponding hazard ratio, 1.76 [95% CI, 1.32-2.35]). The association remained after adjusting for average BP and BP variability.

CONCLUSIONS

Impaired BRS partly explains hypertension-related brain damage and excessive dementia risk beyond conventional BP measures, making it a potential novel biomarker for the early detection and prevention of dementia.

Role of pterygopalatine ganglion in regulating isoflurane-induced cerebral hyper-perfusion

Cerebral perfusion is functionally regulated by neural mechanisms in addition to the systemic hemodynamic variation, vascular reactivity and cerebral metabolism. Although anesthesia is generally esteemed to suppress the overall brain neural activity and metabolism, a few inhalation anesthetics, such as isoflurane, can increase cerebral perfusion, thus heightening the risks of higher intracranial pressure, bleeding, and brain edema during surgery. With the aid of laser speckle contrast imaging, we observed a transient yet limited effect of cerebral perfusion enhancement in mice from awake to anesthetized conditions with different concentration of isoflurane. Retrograde and antegrade tracing revealed a higher proportion of parasympathetic control more than sympathetic innervation for the blood vessels. Surprisingly, isoflurane directly activated pterygopalatine ganglion (PPG) explants and induced FOS expression in the cholinergic neurons. Chemogenetic activation of cholinergic PPG neurons reduced isoflurane-related cerebral perfusion. On the contrary, ablation of the cholinergic PPG neurons resulted in further enhancement of cerebral perfusion induced by isoflurane. While blocking muscarinic cholinergic receptors resulted in the overall reduction upon isoflurane stimulation, the blockage of nicotinic cholinergic receptors enhanced the isoflurane-induced cerebral perfusion only when PPG neurons exist. Collectively, these results suggest that PPG play important roles in regulating cerebral perfusion under isoflurane inhalation.

Dobutamine-induced alterations in internal carotid artery blood flow and cerebral blood flow in healthy adults

PURPOSE

Dobutamine, a sympathomimetic agent, is widely used clinically, influencing cardiac output, heart rate (HR), and blood pressure (BP), which may impact cerebral blood flow (CBF), critical for brain metabolism. However, the effects of dobutamine on CBF and internal carotid artery (ICA) blood flow remain unclear, with contradictory reported in both clinical and animal studies. It is necessary to investigate the effects of dobutamine on cervical and cerebral hemodynamics. This study aimed to evaluate the effects of dobutamine infusion on ICA blood flow and CBF, explore their relationship, and identify factors influencing CBF to facilitate timely monitoring in clinical practice.

METHODS

Forty-eight healthy volunteers underwent physiological assessment, ICA ultrasound, and brain magnetic resonance imaging (MRI) data before and after the administration of dobutamine. Paired t and Wilcoxon signed-rank tests were used to analyze changes, while logistic regression explored associations between hemodynamic factors and CBF.

RESULTS

Dobutamine infusion significantly increased HR, respiration rate, systolic BP (SBP), diastolic BP (DBP), and mean arterial pressure, while blood oxygen remained stable. Compared with those in the resting state, the peak systolic velocity (Vs), resistance index, pulsatility index, and systolic/diastolic ratio (S/D) increased, whereas end-diastolic velocity (Vd) decreased. ICA diameter and mean velocity showed no significant changes. CBF significantly decreased in the anterior and middle cerebral arteries. Logistic regression identified SBP, DBP, and S/D difference as key factors associated with CBF reduction.

CONCLUSIONS

Dobutamine altered ICA hemodynamics and reduced CBF in anterior and middle cerebral arteries. Real-time ICA ultrasound monitoring provides valuable guidance during clinical use.

New evidence for baroreflex and respiratory chemoreflex-mediated cerebral sympathetic activation in humans

The brain is highly innervated by sympathetic nerve fibers; however, their physiological purpose is poorly understood. We hypothesized that unilateral cerebral norepinephrine (NE) spillover, an index of cerebral sympathetic nerve activity (SNA), would be elevated when engaging the baroreflex [via lower-body negative pressure (LBNP; -20 and -40 Torr)] and respiratory chemoreflexes [via carbon dioxide (CO2) administration (+8 Torr)], independently and in combination. Twelve young and healthy participants (five females) underwent simultaneous blood sampling from the right radial artery and internal jugular vein. Tritiated NE was infused through the participants' right forearm vein. Right internal jugular vein and internal carotid artery blood flow were measured using duplex ultrasound. Unilateral cerebral NE spillover remained unchanged when only LBNP was applied (P = 0.29) but increased with hypercapnia (P = 0.035) and -40 Torr LBNP + CO2 (P < 0.01). There were no changes in total NE spillover during the LBNP and LBNP + CO2 trials (both P = 0.66), nor during CO2 alone (P = 0.13). No correlations were present between the increase in unilateral cerebral NE spillover during -40 Torr LBNP + CO2 and reductions in internal carotid artery blood flow (P = 0.56). These results indicate that baroreflex and respiratory chemoreflex stressors elevate cerebral SNA; however, the observed cerebral sympathetic activation has no impact on blood flow regulation in the internal carotid artery.NEW & NOTEWORTHY The results of the current study suggest that baroreflex and respiratory chemoreflex stressors elevate cerebral sympathetic nervous activity, quantified using the brain norepinephrine spillover method. However, the observed cerebral sympathetic activation has no impact on blood flow regulation in the internal carotid artery.

Cerebral oximetry index indicates delirium or stroke after carotid endarterectomy: An observational study

BACKGROUNDS

The cerebral oximetry index (COx) uses near-infrared spectroscopy to estimate cerebral autoregulation during cardiac surgery. However, the relationship between intraoperative loss of cerebral autoregulation and postoperative delirium or stroke remains unclear in patients recovering from carotid endarterectomy (CEA).

METHODS

Our prospective observational cohort study enrolled patients scheduled for CEA. COx was estimated as the coefficient of a continuous, moving Spearman correlation between mean arterial pressure and cerebral oxygen saturation. A receiver operating characteristics curve with Youden's index identified the optimal COx threshold for predicting a composite of postoperative delirium or new-onset overt stroke.

RESULTS

One hundred and forty patients scheduled for CEA were enrolled. The incidence of delirium was 10.7 % (15/140) and the incidence of stroke was 3.6 % (5/140), including 1 patient who had both. The cumulative anesthesia time when COx exceeded 0.3 was longer in patients with complications than those without. When COx > 0.6, the corresponding predictive ability was AUC = 0.69, Youden index = 0.61, P = 0.0003, with a positive predictive value of 100 %. In the post hoc subgroup analyses, before clamping, the greatest increase in the risk was observed when COx > 0.7 for 20 min (Odds ratio = 3.10, 95 % CI 2.20, 3.78). In contrast, COx was not predictive during clamping. After clamping, the optimal COx threshold was 0.4 (AUC = 0.85, Youden index = 0.82, P < 0.0001), with the positive predictive value being 100 %.

CONCLUSIONS

COx is a promising metric for predicting postoperative delirium or new-onset overt stroke in patients having CEA. The optimal COx threshold was 0.7 in the pre-clamping phase and 0.4 in the post-clamping phase.

Respiratory influence on cerebral blood flow and blood volume - A 4D flow MRI study

Variations in cerebral blood flow and blood volume interact with intracranial pressure and cerebrospinal fluid dynamics, all of which play a crucial role in brain homeostasis. A key physiological modulator is respiration, but its impact on cerebral blood flow and volume has not been thoroughly investigated. Here we used 4D flow MRI in a population-based sample of 65 participants (mean age = 75 ± 1) to quantify these effects. Two gating approaches were considered, one using respiratory-phase and the other using respiratory-time (i.e. raw time in the cycle). For both gating methods, the arterial inflow was significantly larger during exhalation compared to inhalation, whereas the venous outflow was significantly larger during inhalation compared to exhalation. The cerebral blood volume variation per respiratory cycle was 0.83 [0.62, 1.13] ml for respiratory-phase gating and 0.78 [0.59, 1.02] ml for respiratory-time gating. For comparison, the volume variation of the cardiac cycle was 1.01 [0.80, 1.30] ml. Taken together, our results clearly demonstrate respiratory influences on cerebral blood flow. The corresponding vascular volume variations appear to be of the same order of magnitude as those of the cardiac cycle, highlighting respiration as an important modulator of cerebral blood flow and blood volume.

A novel method for detecting intracranial pressure changes by monitoring cerebral perfusion via electrical impedance tomography

BACKGROUND

Acute and critical neurological diseases are often accompanied with elevated intracranial pressure (ICP), leading to insufficient cerebral perfusion, which may cause severe secondary lesion. Existing ICP monitoring techniques often fail to effectively meet the demand for real-time noninvasive ICP monitoring and warning. This study aimed to explore the use of electrical impedance tomography (EIT) to provide real-time early warning of elevated ICP by observing cerebral perfusion.

METHODS

An intracranial hypertension model was prepared by injecting autologous un-anticoagulated blood into the brain parenchyma of twelve Landrace swine. Invasive ICP monitoring was used as a control method, and a high-precision EIT system was used to acquire and analyze the changing patterns of cerebral perfusion EIT image parameters with respect to ICP. Four EIT parameters related to cerebral perfusion were extracted from the images, and their potential application in detecting ICP elevation was analyzed.

RESULTS

When ICP increased, all EIT perfusion parameters decreased significantly (P < 0.05). When the subjects were in a state of intracranial hypertension (ICP > 22 mmHg), the correlation between EIT perfusion parameters and ICP was more significant (P < 0.01), with correlation coefficients ranging from -0.72 to -0.83. We tested the objects when they were in baseline ICP and in ICP of 15-40 mmHg. Under both circumstances, ROC curve analysis showed that the comprehensive model of perfusion parameters based on the random forest algorithm had a sensitivity and specificity of more than 90% and an area under the curve (AUC) of more than 0.9 for detecting ICP increments of both 5 and 10 mmHg.

CONCLUSION

This study demonstrates the feasibility of using perfusion EIT to detect ICP increases in real time, which may provide a new method for real-time non-invasive monitoring of patients with increased ICP.