Blood Velocity Research Articles

Impaired memory in Sprague-Dawley rats exposed to complex groundwater mixtures of contaminants is associated with reduced cranial blood flow and hippocampal neurotoxicity

Exposure to industrial contaminants has been implicated in neurobehavioral toxicity in humans. To explore this potential risk, we investigated the neurotoxic effects of oral exposure to a complex groundwater mixture containing petroleum hydrocarbons, pesticides, heavy metals, and unknown parent and breakdown products using male and female Sprague Dawley rats. Rats were randomly divided into six groups and orally exposed daily via drinking water to: (i) tap water, (ii) 10 % v/v low impact groundwater, and (iii) 0.01 %, 0.1 %, 1 %, and 10 % high-impact groundwater for 60 days. Medium- and long-term memory (measured using the novel object recognition task) were impaired. However, no gross motor or coordination deficits were observed by the end of the study period (rotarod test). Doppler ultrasound of the middle cerebral and common carotid arteries was performed to examine the hemodynamic changes. The common carotid blood flow decreased in the groundwater-exposed rats compared to that in the control. However, no significant differences in cerebral blood velocity were observed between the exposed and control groups. A significant reduction in hippocampal serotonin levels was observed in groundwater-exposed rats relative to that in the control group. Collectively, these results indicate that impaired recognition memory in rats exposed to groundwater is accompanied by reduced cranial blood flow and hippocampal neurotoxicity, characterized by altered serotonergic signalling. The levels of detected contaminants known to cause neural or vascular damage were of magnitudes lower than the concentrations of contaminants found in the groundwater mixture, meaning the culprit chemical identity remains unknown. This study emphasizes the need to use whole mixture in exposures when dealing with complex contaminated sites rather than the use of individual compounds.

Contrast-enhanced ultrasound features as a potential biomarker for the prediction of breast cancer recurrence.

To investigate the associations between contrast-enhanced ultrasound imaging features and disease recurrence among patients with locally advanced breast cancer treated with neoadjuvant chemotherapy. In the study, pre- and post-neoadjuvant chemotherapy contrast-enhanced ultrasound images of 43 patients with breast cancer were retrospectively analysed. Post-acquisition image processing involved the placement of freehand-drawn regions of interest, followed by the generation of blood flow kinetics representing blood volume and velocity for these regions of interest. Qualitative and quantitative contrast-enhanced ultrasound parameters were compared to predict recurrence, and receiver operating characteristic analysis was used to evaluate predictive ability. Among the 43 patients, 10 (23%) exhibited disease recurrence (median [range]: 27 [4-68] months). Post-neoadjuvant chemotherapy peak enhancement, wash-in area under the curve, wash-out area under the curve, and wash-in and wash-out area under the curve (p=0.003, p=0.004, p=0.026, and p=0.014, respectively) differed between the no-recurrence and recurrence groups. The area under the receiver operating characteristic curve (0.88; 95% confidence interval: 0.75-1.00) for post-neoadjuvant chemotherapy peak enhancement was the highest among the contrast-enhanced ultrasound parameters, with a cut-off of 13.33 arbitrary units. Higher peak enhancement on post-neoadjuvant chemotherapy contrast-enhanced ultrasound images was associated with recurrence in women with locally advanced breast cancer and is a potential biomarker of tumor recurrence.

Quantitative 2-Dimensionsal Digital Subtraction Venography for Venous Interventions: Validation in Phantom and In Vivo Porcine Models

PurposeTo determine the feasibility of using a 2-dimensional quantitative digital subtraction venography (qDSV) technique that employs a temporally modulated contrast medium injection to quantify blood velocity in phantom, normal, and stenotic porcine iliac vein models. Materials and MethodsBlood velocity was calculated using qDSV following temporally modulated pulsed injections of iodinated contrast medium and compared with Doppler ultrasound (US) measurements (phantom, in-line sensor; in vivo, diagnostic linear probe). Phantom evaluation was performed in a compliant polyethylene tube phantom with simulated venous flow. In vivo evaluation of qDSV was performed in normal (n = 7) and stenotic (n = 3) iliac vein models. Stenoses were created using endovenous radiofrequency ablation, and blood velocities were determined at baseline, after stenosis, after venoplasty, and after stent placement. ResultsIn the phantom model, qDSV-calculated blood velocities (12–50 cm/s) had very strong correlations with US-measured velocities (13–51 cm/s) across a range of baseline blood velocities and injection protocols (slope, 1.01–1.13; R2 = 0.96–0.99). qDSV velocities were similar to US velocities regardless of injection method: (a) custom injector, (b) commercial injector, or (c) hand injection. In the normal in vivo model, qDSV-calculated velocities (5–18 cm/s) had strong correlation (slope, 1.22; R2 = 0.90) with US-measured velocities (3–20 cm/s). In the stenosis model, blood velocities at baseline, after stenosis, after venoplasty, and after stent placement were similar on qDSV and US at all time points. ConclusionsVenous blood velocity was accurately quantified in a venous phantom and in vivo porcine models using qDSV. Intraprocedural changes in porcine iliac vein blood velocity were quantified with qDSV after creation of a stenosis and subsequently treating it with venoplasty and stent placement.

The effects of habitual resistance exercise training on cerebrovascular responses to lower body dynamic resistance exercise: A cross-sectional study.

Dynamic resistance exercise (RE) produces sinusoidal fluctuations in blood pressure with simultaneous fluctuations in middle cerebral artery blood velocity (MCAv). Some evidence indicates that RE may alter cerebrovascular function. This study aimed to examine the effects of habitual RE training on the within-RE cerebrovascular responses. RE-trained (n=15, Female=4) and healthy untrained individuals (n=15, Female=12) completed four sets of 10 paced repetitions (15 repetitions per minute) of unilateral leg extension exercise at 60% of predicted 1 repetition maximum. Beat-to-beat blood pressure, MCAv and end-tidal carbon dioxide were measured throughout. Zenith, nadir and zenith-to-nadir difference in mean arterial blood pressure (MAP) and mean MCAv (MCAvmean) for each repetition were averaged across each set. Two-way ANOVA was used to analyse dependent variables (training × sets), Bonferroni corrected t-tests were used for post hoc pairwise comparisons. Group age (26±7 trained vs. 25±6 years untrained, P=0.683) and weight (78±15vs. 71±15kg, P=0.683) were not different. During exercise average MAP was greater for the RE-trained group in sets 2, 3 and 4 (e.g., set 4: 101±11vs. 92±7mmHg for RE trained and untrained, respectively, post hoc tests all P=<0.012). Zenith MAP and zenith-to-nadir MAP difference demonstrated a training effect (P<0.039). Average MCAvmean and MCAvmean zenith-to-nadir difference was not different between groups (interaction effect P=0.166 and P=0.459, respectively). Despite RE-trained individuals demonstrating greater fluctuations in MAP during RE compared to untrained, there were no differences in MCAvmean. Regular RE may lead to vascular adaptations that stabilise MCAv during RE.

The use of neuromuscular electrical stimulation to elicit muscle contractions does not impair the hyperemic response compared to volitional contractions

Abstract Purpose Electrical stimulation-induced muscle contractions in individuals with paralyzed muscles are often associated with early onset fatigue. We examined whether electrical stimulation (ES) of the quadriceps muscle results in vasoconstriction and a reduction in blood flow which may contribute to this early onset fatigue. Methods Seventeen young individuals completed 40 ES isometric contractions (stimulation frequency of 75 Hz, pulse duration of 400 μs, on-off ratio 6.0-20s) and force matched voluntary (VOL) isometric contractions. Isometric force, heart rate, blood pressure, superficial femoral diameter and blood velocity were measured at baseline and during exercise (contractions 1,5,10,15,20,25,30,35, and 40). Net, antegrade, and retrograde blood flow, and conductance were quantified. Two-way, within-subjects ANOVAs were used to evaluate diameter, blood flow and conductance. Results Diameter was not different between ES and VOL (p = 0.57). Net blood flow increased during both conditions with the greatest blood flow occurring during ES compared to VOL (p ≤ 0.01). ES showed a greater increase antegrade and reduced retrograde flow compared to VOL. After the twentieth contraction, ES also elicited greater conductance than VOL (p ≤ 0.049). Conclusion The use of neuromuscular electrical stimulation to elicit muscle contractions does not result in vasoconstriction or a reduced hyperemic response compared to volitional contractions.

Demonstration of angioplasty using a balloon catheter in tetra-hybrid nano-bloodstream within an electrified stenotic arterial cavity under a magnetic field: Artificial neural network analysis

This article focuses on the critical role of advanced computational techniques in enhancing medical diagnostics and treatment planning, especially in procedures like angioplasty. It presents a detailed examination of ballooned catheterization (balloon angioplasty) in a bloodstream carrying tetra-hybrid nanoparticles within a negatively charged stenotic arterial cavity, influenced by a magnetic field. The study models the streaming of blood, considering factors like heat generation, Joule heating, interfacial nanolayers, nanoparticle size, and velocity and thermal slip conditions. The model simplifies complex dynamics through the lubricant and Debye–Hückel linearization approaches and employs the homotopy perturbation method (HPM) for solving dimensionless equations. Mathematica and Matlab are used to illustrate key parameters like velocity, temperature, pressure gradient, wall shear stress (WSS), heat transfer coefficient (HTC), and blood bolus trapping. The study reveals that increasing the balloon catheter’s height boosts blood velocity in the annulus’s central zone, while a thicker interfacial nanolayer diminishes blood temperature and HTC. Larger nanoparticles elevate the blood temperature profile, and increased electro-osmotic parameters enhance the pressure gradient. The tetra-hybrid nano-blood (THNB) shows superior HTC compared to other forms. The study also delves into bolus trapping phenomena, emphasizing the significant changes induced by electro-osmotic forces. Additionally, an artificial neural network (ANN) model, developed using HPM-derived data, accurately predicts WSS and HTC, achieving high accuracy rates of 99.97% in testing and 99.92% in validation for THNB flow. This study paves the way for more targeted, safer, and efficient use of balloon catheters in treating arterial blockages, significantly impacting cardiovascular medicine and patient care.

A hemodynamic study of the relationship between the left and right liver volumes and the blood flow distribution in portal vein branches.

Cirrhosis patients often exhibit clinical symptoms such as right liver atrophy, portal hypertension, spleen enlargement and increased blood supply, which exhibit considerable variation between the left and right liver sections. These differences are hypothesized to stem from disparities in blood flow within the left and right portal vein (PV) branches. However, rigorous quantitative evidence remains scarce. We mainly aim at quantitatively revealing the relationship between the blood flow rates of two PV branches and liver volumes, and providing quantitative evidence and theoretical support for the diagnosis and treatment of cirrhosis from the perspective of hemodynamics. Five cirrhotic patients and two healthy volunteers from Beijing Friendship Hospital are investigated. Their PV blood flow models are established based on computed tomography (CT) images and finite volume simulations. The volume of the left and right liver lobes are measured in 3-matic. The distributions of blood source in the PV branches are tracked by streamline analysis. The blood flow rates are quantitatively counted by integrating the blood source velocities. Linear analysis is performed to build the relationship between liver volumes and PV blood flow distributions. Streamline analysis reveals significant differences in blood distribution between the left and right PV branches. The majority of blood from the superior mesenteric vein (SMV) flowed into the right portal vein (RPV), while most blood from the splenic vein (SV) entered the left portal vein (LPV). The main PV pressure drop linearly increases with the SV blood velocity for all PV structures of patients and healthy volunteers. The flow rate ratio QRPV/QLPV demonstrates an increase in tandem with the volume ratio VR/VL, exhibiting a linear correlation with the Pearson correlation coefficient being 0.93. The differences in the blood distributions are consistent with the clinicians' knowledge and validate our simulations. We demonstrated a linear increase in PV pressure with elevated SV blood velocity. Additionally, the volumes of the left and right hepatic lobes exhibited a positive correlation with blood flow rates in the corresponding PV branches.

Blood viscometer using capillary blood flow under disposable compliance pump

Blood viscosity is considered a promising indicator of cardiovascular disease and helps predict disease risks. However, conventional methods require two highly precise pumps to maintain consistent flow rates in co-flowing streams. In this study, a low-cost and disposable compliance pump was fabricated by inserting three components (a syringe needle, a blood-loaded syringe, and an air compliance unit [ACU]) into a three-way valve. Since the pump induces transient blood flow, accurately obtaining the transient flow rate is necessary. A correction factor was employed to improve the blood velocity obtained by microparticle image velocimetry. Air pressure inside the ACU was estimated using the ideal gas law. A discrete fluid circuit model was constructed to estimate the flow rate and pressure in a microfluidic channel. Four types of fluid physical properties (fluid resistance, fluid viscosity, time constant, and compliance coefficient) were obtained by analysing flow rate and pressure. The proposed method was employed to detect several types of suspended blood (variations in haematocrit, thermal-shocked RBCs, and RBC aggregation-enhanced blood). From the quantitative comparison, the proposed method provides better results than the previous method. Therefore, the proposed method is a promising tool for detecting biophysical variations in suspended blood.

Computational modelling of micropolar blood-based magnetised hybrid nanofluid flow over a porous curved surface in the presence of artificial bacteria.

This work provides a brief comparative analysis of the influence of heat creation on micropolar blood-based unsteady magnetised hybrid nanofluid flow over a curved surface. The Powell-Eyring fluid model was applied for modelling purposes, and this work accounted for the impacts of both viscous dissipation and Joule heating. By investigating the behaviours of Ag and TiO2 nanoparticles dispersed in blood, we aimed to understand the intricate phenomenon of hybridisation. A mathematical framework was created in accordance with the fundamental flow assumptions to build the model. Then, the model was made dimensionless using similarity transformations. The problem of a dimensionless system was then effectively addressed using the homotopy analysis technique. A cylindrical surface was used to calculate the flow quantities, and the outcomes were visualised using graphs and tables. Additionally, a study was conducted to evaluate skin friction and heat transfer in relation to blood flow dynamics; heat transmission was enhanced to raise the Biot number values. According to the findings of this study, increasing the values of the unstable parameters results in increase of the blood velocity profile.

Inclined magnetized infinite shear rate viscosity of non-Newtonian tetra hybrid nanofluid in stenosed artery with non-uniform heat sink/source

Abstract Many scholars performed the analysis by using the non-Newtonian fluids based on the nano and hybrid nano particles in blood arteries to investigate the heat transport for cure in several diseases. These performances are presented to investigate the blood flow behaviour with extended form of the novel tetra hybrid Das and Tiwari nanofluid system attached by the Carreau fluid. The assessment of energy transport has been achieved based on the thermal radiation, heat source/sink, Joule heating, and viscous dissipation. The obtained partial differential equation from physical problem is transformed into ordinary differential equations (ODEs) by using the similarity variables. Furthermore, system of nonlinear ODEs attached with boundary conditions are transported into the system of first-order ODEs with initial conditions. For the numerical solution of obtained ODEs, the numerical solutions have been performed based on the RK method. The numerical results are plotted through figures, tables, and statistical graphs. Magnetic forces and inclined magnetic effects are caused to reduce velocity of blood. Temperature of blood within the arteries is increased by increasing the parameter of thermal radiation.

Numerical simulation of blood flow in coronary bifurcation

A numerical simulation of blood flow in a Y-shaped coronary artery was executed by constructing ideal geometric models. The influences of bifurcation angle, the initial velocity of inlet blood flow, and the diameter ratio of bifurcated vessels on the blood flow velocity field, wall shear stress, wall pressure, etc. were analyzed. The blood velocity at the bifurcation of the blood vessel was slower, while the wall shear stress and wall pressure value were higher. The wall shear stress and wall pressure increased with the increase of blood flow velocity at the entrance. Greater bifurcation angle led to higher wall shear stress. With the increase of the diameter ratio of the two branches, the maximum value of the shear stress became smaller. The probability of thrombosis formation increases as the diameter ratio increases. The numerical results showed that the bifurcation of the blood vessel is the optimal place to form the thrombosis.

Rapid changes in cerebrovascular compliance during vasovagal syncope.

The compensatory mechanisms supporting cerebral perfusion throughout head-up tilt (HUT) in patients with vasovagal syncope (VVS) remain unclear. We tested the hypothesis that increased cerebrovascular compliance (Ci) and decreased cerebrovascular resistance (CVR) support cerebral blood velocity (CBV) during pre-syncope in VVS. Finger arterial blood pressure (ABP) and right middle cerebral artery blood velocity (CBV) were recorded in 15 individuals diagnosed with VVS (n = 11 female, mean age: 40 ± 16years, mean body mass index: 24.9 ± 4.0kg/m2) at supine rest and during HUT (80 degree angle). Individual ABP and CBV waveforms during VVS were input into a modified Windkessel model to calculate Ci and ohmic CVR. Gosling's pulsatility index (Pi; pulse amplitude/mean CBV) was calculated. Diastolic ABP, systolic ABP, mean ABP (72 ± 11 to 51 ± 12mmHg), and CVR decreased progressively during presyncope (all P ≤ 0.04). As expected, systolic CBV was sustained (all P ≥ 0.29) while diastolic and mean CBV (51 ± 13 to 38 ± 13mmHg) fell during presyncope (all P ≤ 0.04). Both Ci and Pi increased during presyncope (128 ± 97 and 60 ± 41%, respectively; all P ≤ 0.049) and were positively correlated (R2 = 0.79, P < 0.01). Increased Ci contributed to changes in mean CBV (P < 0.01) but decreased CVR did not (P = 0.28). These data provide evidence that Ci increases during presyncope in patients with VVS and is likely involved in the maintenance of systolic CBV during a fall in diastolic CBV. However, this regulation is not sufficient to preserve CBV in the presence of such extreme and progressive reductions in ABP.

Determinants of the dynamic cerebral critical closing pressure response to changes in mean arterial pressure

Objective. Cerebral critical closing pressure (CrCP) represents the value of arterial blood pressure (BP) where cerebral blood flow (CBF) becomes zero. Its dynamic response to a step change in mean BP (MAP) has been shown to reflect CBF autoregulation, but robust methods for its estimation are lacking. We aim to improve the quality of estimates of the CrCP dynamic response. Approach. Retrospective analysis of 437 healthy subjects (aged 18–87 years, 218 males) baseline recordings with measurements of cerebral blood velocity in the middle cerebral artery (MCAv, transcranial Doppler), non-invasive arterial BP (Finometer) and end-tidal CO2 (EtCO2, capnography). For each cardiac cycle CrCP was estimated from the instantaneous MCAv-BP relationship. Transfer function analysis of the MAP and MCAv (MAP-MCAv) and CrCP (MAP-CrCP) allowed estimation of the corresponding step responses (SR) to changes in MAP, with the output in MCAv (SRVMCAv) representing the autoregulation index (ARI), ranging from 0 to 9. Four main parameters were considered as potential determinants of the SRVCrCP temporal pattern, including the coherence function, MAP spectral power and the reconstruction error for SRVMAP, from the other three separate SRs. Main results. The reconstruction error for SRVMAP was the main determinant of SRVCrCP signal quality, by removing the largest number of outliers (Grubbs test) compared to the other three parameters. SRVCrCP showed highly significant (p < 0.001) changes with time, but its amplitude or temporal pattern was not influenced by sex or age. The main physiological determinants of SRVCrCP were the ARI and the mean CrCP for the entire 5 min baseline period. The early phase (2–3 s) of SRVCrCP response was influenced by heart rate whereas the late phase (10–14 s) was influenced by diastolic BP. Significance. These results should allow better planning and quality of future research and clinical trials of novel metrics of CBF regulation.

Premature newborns with intraventricular hemorrhage do not have vasospasm pattern by cranial Doppler ultrasound: A pilot study.

Preterm neonates are at risk for neurodevelopmental impairment, especially those with intraventricular hemorrhage (IVH). Cerebral vasospasm (VSP) is a common complication after subarachnoid hemorrhage (SAH) in adult population, but it is unknown if preterm neonates with IVH may develop it. We prospectively enrolled premature newborns < 32weeks with IVH and without IVH. All patients received serial transcranial sonography through the temporal window of the middle cerebral artery, anterior cerebral artery, posterior cerebral artery, and the internal carotid artery with transcranial Doppler sonography days 2, 4, and 10 of life. Cerebral blood velocities (CBFVs) were measured including median velocity flow (MV), peak systolic velocity (PSV), and maximum end-diastolic velocity (EDV). Resistance index and pulsatility index were calculated. VSP was defined as an increase of 50% in the baseline velocity per day and/or a Lindegaard ratio higher than 3. Fifty subjects were enrolled. None of the patients with IVH showed elevation of MV or a Lindegaard ratio > 3. There were no differences between IVH and without IVH groups regarding resistance index and pulsatility index. Conclusion: Preterm infants with IVH do not present a pattern of VSP analyzed by Doppler transcranial ultrasound in this pilot study. What is Known: • In adult population with subarachnoid hemorrhage the most treatable cause of cerebral ischemia is due cerebral vasospasm but is unknown if premature newborn may have vasospasm due the extravasation of blood in the context of intraventricular hemorrhage What is New: •In this pilot study we did not find in premature newborn with intraventricular hemorrhage signs of vasoespam measured by transcranial color doppler ultrasound.

Deciphering Vascular Dynamics Alterations in Sub-Saharan Individuals with Type 2 Diabetes: Overview and Temporal Analysis of Nitric Oxide Administration

Background: Early detection of arterial damage is essential for the primary prevention of complications linked to type 2 diabetes (T2D). The study assessed the cardiovascular risk of sub-Saharan African individuals with T2D, while exploring possible mechanisms involved in the pathogenesis of vascular complications in this population. Methodology: A crossover study of 72 sub-Saharan African adults (36 with T2D and 36 without T2D) was conducted. Outcomes including diameter size (mm) and blood velocity (cm/s) of the brachial artery, were obtained at seven time points: baseline and from 5 seconds to 600 seconds in two conditions: pre- and post Nitric Oxide (NO) administration. HbA1C, fasting glucose, age, BMI, mean arterial pressure (MAP), lipid profile, T2D duration since diagnosis, and binary indicators of insulin and oral diabetes medication were evaluated. Results: NO improved the blood flow compared to the pre-NO after adjustment for clinical factors. The beneficial effect of NO administration on vascular dynamics was influenced by age (&amp;lt;I&amp;gt;B&amp;lt;/I&amp;gt;=1.09; 95%IC: 1.07, 1.11), increased BMI (&amp;lt;I&amp;gt;B&amp;lt;/I&amp;gt;= 1.03; 95%IC: 1.01, 1.04) and insulin use (&amp;lt;I&amp;gt;B&amp;lt;/I&amp;gt; = 1.13; 95%IC 1.10, 1.16). Conclusion: The nuanced impact of these factors on blood flow improvement related to NO necessitates tailored and personalized approaches in managing T2D patients.

#1967 Towards the design optimisation of catheters for paediatric dialysis using a bioengineering approach

Abstract Background and Aims Central venous lines (CVLs) used for haemodialysis (HD) in children are associated with a high complication rate, leading to inadequate dialysis and need for a line replacement in nearly 45% of children on HD. This high complication rate may be due to poor CVL configurations, designed without considering specific anatomical differences between children and adults. Using a bioengineering approach, we aim to provide a fluid dynamics characterization of different CVL models commonly used in children to establish an association between CVL design and clinical complications, and to improve CVL performance by optimising their design. Method Computational fluid dynamics (CFD) using modelling and simulations is a powerful engineering tool that use computers to study complex systems, applying mathematics, physics and computer science. Four models of CVLs of varying designs and sizes (6.5Fr, 8Fr, 10Fr and 14Fr) were scanned by microCT to reconstruct computational models. CFD analyses were set up to simulate blood flow within the CVLs under both ideal and realistic models of superior vena cava. A variety of flow rates, routinely used in clinical practice, were applied to study the whole range of working conditions. Haemodynamic features that cannot be measured in vivo such as high shear stresses and large areas of stagnation, were analysed. CFD findings were compared to clinical outcomes (n = 26 patients with 57 lines) and to the blood clots distribution of CVLs removed from patients (n = 8). Fluid dynamics characteristics of the CVLs studied were used to set up a preliminary design optimisation process of a 6.5F CVL model. Using sampling methods, a variety of CVL designs were created starting from the original model and results were compared. Results In all the simulated CVLs, the arterial lumens showed the highest stagnation and recirculation areas. The role of arterial tip configuration was negligible for the blood flows and the proximal side holes played a major role for blood aspiration being also subject to the highest levels of shear stress, regardless of the design. In all the anatomical models, blood velocity increased after catheter insertion (Fig. 1a) together with wall shear stresses. CFD results were in accordance with the clinical data which showed a higher recurrence rate of thrombosis for the 8Fr and 10Fr CVLs. Also, microCT of the CVLs removed due to complications confirmed presence of thrombosis at the catheter tips. Results suggest that shear stress is the parameter most strongly related to clinical complications. The preliminary design optimisation study was used to find the parameters which have the highest influence on the CVL performance. Preliminarily optimised designs of the 6.5F model showed a better haemodynamic performance, reducing stagnation areas (Fig. 1b). Conclusion Characterisation of the fluid dynamics of commercially available CVLs explains some of the clinical outcomes experienced by patients. Identification of potential design-related complications in CVLs has allowed to set up the optimisation process which will lead to new CVL designs with improved blood flow distribution and minimal damage to blood cells. Funding Kidney Research UK, PhD fellowship and MedTech grants.

Identifiability of spatiotemporal tissue perfusion models

Objective. Standard models for perfusion quantification in DCE-MRI produce a bias by treating voxels as isolated systems. Spatiotemporal models can remove this bias, but it is unknown whether they are fundamentally identifiable. The aim of this study is to investigate this question in silico using one-dimensional toy systems with a one-compartment blood flow model and a two-compartment perfusion model. Approach. For each of the two models, identifiability is explored theoretically and in-silico for three systems. Concentrations over space and time are simulated by forward propagation. Different levels of noise and temporal undersampling are added to investigate sensitivity to measurement error. Model parameters are fitted using a standard gradient descent algorithm, applied iteratively with a stepwise increasing time window. Model fitting is repeated with different initial values to probe uniqueness of the solution. Reconstruction accuracy is quantified for each parameter by comparison to the ground truth. Main results. Theoretical analysis shows that flows and volume fractions are only identifiable up to a constant, and that this degeneracy can be removed by proper choice of parameters. Simulations show that in all cases, the tissue concentrations can be reconstructed accurately. The one-compartment model shows accurate reconstruction of blood velocities and arterial input functions, independent of the initial values and robust to measurement error. The two-compartmental perfusion model was not fully identifiable, showing good reconstruction of arterial velocities and input functions, but multiple valid solutions for the perfusion parameters and venous velocities, and a strong sensitivity to measurement error in these parameters. Significance. These results support the use of one-compartment spatiotemporal flow models, but two-compartment perfusion models were not sufficiently identifiable. Future studies should investigate whether this degeneracy is resolved in more realistic 2D and 3D systems, by adding physically justified constraints, or by optimizing experimental parameters such as injection duration or temporal resolution.

Data-based modeling of cerebral hemodynamics quantifies impairment of cerebral blood flow regulation in type-2 diabetes.

We studied the regulation dynamics of cerebral blood velocity (CBv) at middle cerebral arteries (MCA) in response to spontaneous changes of arterial blood pressure (ABP), termed dynamic cerebral autoregulation (dCA), and end-tidal CO2 as proxy for blood CO2 tension, termed dynamic vasomotor reactivity (DVR), by analyzing time-series data collected at supine rest from 36 patients with Type-2 Diabetes Mellitus (T2DM) and 22 age/sex-matched non-diabetic controls without arterial hypertension. Our analysis employed a robust dynamic modeling methodology that utilizes Principal Dynamic Modes (PDM) to estimate subject-specific dynamic transformations of spontaneous changes in ABP and end-tidal CO2 (viewed as two "inputs") into changes of CBv at MCA measured via Transcranial Doppler ultrasound (viewed as the "output"). The quantitative results of PDM analysis indicate significant alterations in T2DM of both DVR and dCA in terms of two specific PDM contributions that rise to significance (p < 0.05). Our results further suggest that the observed DVR and dCA alterations may be due to reduction of cholinergic activity (based on previously published results from cholinergic blockade data) that may disturb the sympatho-vagal balance in T2DM. Combination of these two model-based "physio-markers" differentiated T2DM patients from controls (p = 0.0007), indicating diabetes-related alteration of cerebrovascular regulation, with possible diagnostic implications.

Cerebral blood flow regulation and cognitive performance in hypertension.

We examined the relation between transcranial Doppler (TCD) markers of cerebral blood flow regulation and cognitive performance in hypertension (HT) patients to evaluate the predictive value of these markers for cognitive decline. We assessed dynamic cerebral autoregulation (dCA), vasoreactivity to carbon dioxide, and neurovascular coupling (NVC) in the middle (MCA) and posterior (PCA) cerebral arteries of 52 patients. Neuropsychological evaluation included the Montreal Cognitive Assessment and tests covering attention, executive function, processing speed, and memory. Notably, reduced rate time in the PCA significantly predicted better processing speed (p = 0.003). Furthermore, reduced overshoot systolic cerebral blood velocity in the PCA and reduced phase in the VLF range in the MCA (p = 0.021 and p = 0.017, respectively) significantly predicted better memory. Intriguingly, enhanced dCA in the MCA predicted poorer memory performance, while reduced NVC in the PCA predicted both superior processing speed and memory performance. These findings suggest that HT-induced changes in cerebral hemodynamics impact cognitive performance. Further research should verify these observations and elucidate whether these changes represent adaptive responses or neurovascular inefficiency. TCD markers might provide insights into HT-related cognitive decline.

Long-term Effects of COVID-19 on Vascular Parameters—A Prospective Longitudinal Ultrasound Clinical Study

Objective: To investigate the longitudinal effects of COVID-19 on major vascular structures and parameters and clinical outcomes. Design: Observational prospective trial. Setting: Post-COVID-19 research clinic established by University of Louisville Division of Infectious Diseases. Participants: The study population consisted of 72 post-COVID-19 individuals and 11 non-COVID-19 infected participants in the control group. The participants were recruited from adult hospitals and from the community. The enrollment started in October 2020 and follow-up periods were at 3, 6, and 12 months from their initial COVID-19 diagnosis. Interventions: The participants were interviewed for medical and COVID-19 infection history. Samples of white blood cell (WBC), C-reactive protein (CRP), and D-dimer were taken at each visit. Certified sonographers performed vascular ultrasound on the study participants. Measurements and Main Results: Median intima-media thickness (IMT) was increased in mild/asymptomatic (0.80 mm) and severe/critical (0.90 mm) groups when compared with controls (0.60 mm; P &lt; .001 for both groups). In the asymptomatic/mild group, 6-month median IMT (0.88 mm) was increased, compared with the 3-month group (0.75 mm), with P = .026. Increased age was associated with decreased mean arterial blood velocities (cm/s): common carotid ( r = −0.236, P = .032), internal carotid ( r = −0.208, P = .048), and subclavian artery mean velocity ( r = −0.357, P = .003). We did not find any instance of deep vein thrombosis. Median D-dimer, CRP, and WBC in the control group differed from asymptomatic/mild COVID-19 group ( P = .026, .011, and .003, respectively). Moreover, WBC in the asymptomatic/mild group and moderate COVID-19 group differed from severe/critical group ( P = .025 and P = .027, respectively); CRP also differed between asymptomatic/mild group and severe/critical group ( P = .014). Conclusions: There were differences in intima-media lumen thickness (IMT), arterial velocities, and inflammatory markers in post-COVID-19 patients. There was no instance of deep vein thrombosis in this post-COVID-19 study cohort. The increased IMT might infer atherosclerosis, which has shown to increase cardiovascular risks. It is not yet known whether the increase in IMT due to COVID should be treated in the same way as non-COVID-19 atherosclerosis—through statins, for example—or whether regular cardiovascular risk reduction would be useful. Clinical trial and mechanistic studies should be performed to further our understanding of COVID-19-related vascular pathologies.