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The Windkessel (WK) model is a simplified mathematical model used to represent the systemic arterial circulation. While the WK model is useful for studying blood flow dynamics, it suffers from inaccuracies or uncertainties that should be considered when using it to make physiological predictions. This paper aims to develop an efficient and easy‐to‐implement uncertainty quantification method based on a local gradient‐based formulation to quantify the uncertainty of the pressure waveform resulting from aleatory uncertainties of the WK parameters and flow waveform. The proposed methodology, tested against Monte Carlo simulations, demonstrates good agreement in estimating blood pressure uncertainties due to uncertain Windkessel parameters, but less agreement considering uncertain blood‐flow waveforms. To illustrate our methodology's applicability, we assessed the aortic pressure uncertainty generated by Windkessel parameters‐sets from an available in silico database representing healthy adults. The results from the proposed formulation align qualitatively with those in the database and in vivo data. Furthermore, we investigated how changes in the uncertainty of the Windkessel parameters affect the uncertainty of systolic, diastolic, and pulse pressures. We found that peripheral resistance uncertainty produces the most significant change in the systolic and diastolic blood pressure uncertainties. On the other hand, compliance uncertainty considerably modifies the pulse pressure standard deviation. The presented expansion‐based method is a tool for efficiently propagating the Windkessel parameters' uncertainty to the pressure waveform. The Windkessel model's clinical use depends on the reliability of the pressure in the presence of input uncertainties, which can be efficiently investigated with the proposed methodology. For instance, in wearable technology that uses sensor data and the Windkessel model to estimate systolic and diastolic blood pressures, it is important to check the confidence level in these calculations to ensure that the pressures accurately reflect the patient's cardiovascular condition. [ABSTRACT FROM AUTHOR]

Seminars in Thrombosis and Hemostasis (STH) celebrates 50 years of publishing in 2024. To celebrate this landmark event, STH is republishing some archival material. This article represents the most highly cited paper ever published in STH. The original abstract follows. Blood is a two-phase suspension of formed elements (i.e., red blood cells [RBCs], white blood cells [WBCs], platelets) suspended in an aqueous solution of organic molecules, proteins, and salts called plasma. The apparent viscosity of blood depends on the existing shear forces (i.e., blood behaves as a non-Newtonian fluid) and is determined by hematocrit, plasma viscosity, RBC aggregation, and the mechanical properties of RBCs. RBCs are highly deformable, and this physical property significantly contributes to aiding blood flow both under bulk flow conditions and in the microcirculation. The tendency of RBCs to undergo reversible aggregation is an important determinant of apparent viscosity because the size of RBC aggregates is inversely proportional to the magnitude of shear forces; the aggregates are dispersed with increasing shear forces, then reform under low-flow or static conditions. RBC aggregation also affects the in vivo fluidity of blood, especially in the low-shear regions of the circulatory system. Blood rheology has been reported to be altered in various physiopathological processes: (1) Alterations of hematocrit significantly contribute to hemorheological variations in diseases and in certain extreme physiological conditions; (2) RBC deformability is sensitive to local and general homeostasis, with RBC deformability affected by alterations of the properties and associations of membrane skeletal proteins, the ratio of RBC membrane surface area to cell volume, cell morphology, and cytoplasmic viscosity. Such alterations may result from genetic disorders or may be induced by such factors as abnormal local tissue metabolism, oxidant stress, and activated leukocytes; and (3) RBC aggregation is mainly determined by plasma protein composition and surface properties of RBCs, with increased plasma concentrations of acute phase reactants in inflammatory disorders a common cause of increased RBC aggregation. In addition, RBC aggregation tendency can be modified by alterations of RBC surface properties because of RBC in vivo aging, oxygen-free radicals, or proteolytic enzymes. Impairment of blood fluidity may significantly affect tissue perfusion and result in functional deteriorations, especially if disease processes also disturb vascular properties. [ABSTRACT FROM AUTHOR]

Nonthrombotic iliac vein lesions (NIVLs) are significant causes of chronic venous insufficiency (CVI) in the left lower limb and symptom recurrence following left lower limb varicose vein treatment. The goal of this study was to explore the haemodynamic and morphological characteristics of iliac veins in patients with NIVLs. Pressure at the caudal end of the stenotic left common iliac vein (LCIV) segment, local blood flow velocity, and time-averaged wall shear stress in the stenotic segment exhibited positive correlations with the clinical CVI classification (R = 0.92, p < 0.001; R = 0.94, p < 0.001; R = 0.87, p < 0.001), while the relative retention time showed a negative correlation (R = -0.94, p < 0.001). The pressure difference (∆P) between the two ends of the stenotic segment and the velocity difference (∆V) between the stenotic segment and the caudal end were positively correlated with the clinical classification (R = 0.92, p < 0.001; R = 0.9, p < 0.001). The cross-sectional area stenosis rate and length of the stenotic LCIV segment were positively correlated with the clinical classification (R = 0.93, p < 0.001; R = 0.63, p < 0.001). The results suggest that haemodynamic assessment of the iliac vein could effectively portray blood flow disturbances in stenotic segments of the LCIV, potentially reflecting the degree of iliac vein stenosis. Haemodynamic indicators are correlated with the severity of clinical CVI symptoms. [ABSTRACT FROM AUTHOR]

Intracranial aneurysms (IAs) pose severe health risks influenced by hemodynamics. This study focuses on the intricate characterization of hemodynamic conditions within the IA walls and their influence on bleb development, aiming to enhance understanding of aneurysm stability and the risk of rupture. The methods emphasized utilizing a comprehensive dataset of 359 IAs and 213 IA blebs from 268 patients to reconstruct patient‐specific vascular models, analyzing blood flow using finite element methods to solve the unsteady Navier–Stokes equations, the segmentation of aneurysm wall subregions and the hemodynamic metrics wall shear stress (WSS), its metrics, and the critical points in WSS fields were computed and analyzed across different aneurysm subregions defined by saccular, streamwise, and topographical divisions. The results revealed significant variations in these metrics, correlating distinct hemodynamic environments with wall features on the aneurysm walls, such as bleb formation. Critical findings indicated that regions with low WSS and high OSI, particularly in the body and central regions of aneurysms, are prone to conditions that promote bleb formation. Conversely, areas exposed to high WSS and positive divergence, like the aneurysm neck, inflow, and outflow regions, exhibited a different but substantial risk profile for bleb development, influenced by flow impingements and convergences. These insights highlight the complexity of aneurysm behavior, suggesting that both high and low‐shear environments can contribute to aneurysm pathology through distinct mechanisms. [ABSTRACT FROM AUTHOR]

The primary objective of this study was to determine whether or not hemodynamic parameters and laboratory values at the time of admission to the pediatric cardiac intensive care unit after the Norwood operation were associated with a composite outcome of either need for extracorporeal membrane oxygenation or inpatient mortality. This was a single-center retrospective study of infants with functionally univentricular hearts admitted to intensive care after the Norwood procedure from January 2011 to January 2020. Data were obtained at a single point (after a Norwood procedure) and then compared between two subsets of patients based on the presence or not of the composite outcome of interest. In univariate and multiple regression analyses, a series of receiver operator curves were generated to assess the relationship between the variables of interest and the composite outcome. Eight (7.6%) experienced the composite outcome out of a total of 104 patients. Those who experienced the composite endpoint had significantly higher oxygen extraction ratio (0.43 vs. 0.31, p = 0.01), lower systemic blood flow (2.5 L/min versus 3.1 L/min, p = 0.01), and higher systemic vascular resistance (20.2 indexed woods units versus 14.8 indexed woods units, p = 0.01). Those with systemic blood flow of less than 2.5 L/min/m2 had a 17% risk of experiencing the composite endpoint AUC = 0.79. Those with systemic vascular resistance of greater than 19 indexed woods units had a 22% risk of experiencing the composite endpoint AUC 0.80. Systemic blood flow and systemic vascular resistance are independently associated with this composite outcome. [ABSTRACT FROM AUTHOR]

A data-driven reduced order model (ROM) based on a proper orthogonal decomposition-radial basis function (POD-RBF) approach is adopted in this paper for the analysis of blood flow dynamics in a patient-specific case of atrial fibrillation (AF). The full order model (FOM) is represented by incompressible Navier–Stokes equations, discretized with a finite volume (FV) approach. Both the Newtonian and the Casson's constitutive laws are employed. The aim is to build a computational tool able to efficiently and accurately reconstruct the patterns of relevant hemodynamics indices related to the stasis of the blood in a physical parametrization framework including the cardiac output in the Newtonian case and also the plasma viscosity and the hematocrit in the non-Newtonian one. Many FOM-ROM comparisons are shown to analyze the performance of our approach as regards errors and computational speed-up. [ABSTRACT FROM AUTHOR]

Autologous arteriovenous fistula (AVF) is a commonly used vascular access (VA) for hemodialysis, and hemodynamic changes are one of the main factors for its failure. To explore the effect of geometry on the hemodynamics in the AVF, a modified model is built with a gradual and smooth turn at the anastomosis and is compared with the traditional model, which has an abrupt sharp turn at the anastomisis. Transient computational fluid dynamics (CFD) simulations were performed for the comparison and analysis of the hemodynamic fields of the two models at different stages of the pulse cycle. The results showed that the low shear stress region and high oscillatory shear stress region in the modified AVF model coincided with regions of intimal hyperplasia that have been identified by previous studies. A comparison with the blood flow velocities measured in vivo was performed, and the error between the simulation results and the medical data was reduced by 22% in the modified model, which verifies the rationality and utility of the modified model. [ABSTRACT FROM AUTHOR]

Objective Methods Results Conclusion The aim of the present study was to compare the fetal umbilical artery blood flow parameters in the third trimester and perinatal outcomes between pregnant women with and without thalassemia minor in South China.This was a retrospective cohort study. Doppler ultrasound was used to detect fetal umbilical artery hemodynamics in pregnant women with or without thalassemia minor during the third trimester. The main parameters assessed were umbilical artery peak systolic flow velocity/end‐diastolic flow velocity (S/D), resistance index (RI), pulsation index (PI), and relevant perinatal outcomes.This study included 540 pregnant women, 180 with thalassemia minor and 360 being healthy controls. In the third trimester, the thalassemia minor group had higher umbilical artery S/D (P = 0.002), RI (P = 0.002), and PI (P = 0.012) than healthy pregnant women, as well as lower levels of hemoglobin (Hb) (P < 0.001) and higher ferritin levels (P < 0.001). Compared to the non‐thalassemia group, neonatal body weight in the thalassemia minor group was significantly lower (P = 0.001). Additionally, the incidence of maternal anemia (odds ratio [OR] 3.92; 95% confidence interval [CI]: 2.57–5.99, P < 0.001), low birth weight (OR 15.35; 95% CI: 1.71–137.93, P = 0.015), fetal distress (OR 2.18; 95% CI: 1.12–4.26, P = 0.023), neonatal asphyxia (OR 12.81; 95% CI: 1.40–117.33, P = 0.024), oligohydramnios (OR 18.25; 95% CI: 2.21–150.36, P = 0.007) and Apgar score <7 at 1 min after birth (OR 7.97; 95% CI: 1.53–41.54, P = 0.014) was significantly higher in the thalassemia minor group.Pregnant women with thalassemia minor have higher umbilical artery S/D, RI and PI during the third trimester and a higher risk of adverse perinatal outcomes. [ABSTRACT FROM AUTHOR]

Modeling an aortic dissection represents a particular challenge from a numerical perspective, especially when it comes to the interaction between solid (aortic wall) and liquid (blood flow). The complexity of patient‐specific simulations requires a variety of parameters, modeling assumptions and simplifications that currently hinder their routine use in clinical settings. We present a numerical framework that captures, among other things, the layer‐specific anisotropic properties of the aortic wall, the non‐Newtonian behavior of blood, patient‐specific geometry, and patient‐specific flow conditions. We compare hemodynamic indicators and stress measurements in simulations with increasingly complex material models for the vessel tissue ranging from rigid walls to anisotropic hyperelastic materials. We find that for the present geometry and boundary conditions, rigid wall simulations produce different results than fluid–structure interaction simulations. Considering anisotropic fiber contributions in the tissue model, stress measurements in the aortic wall differ, but shear stress‐based biomarkers are less affected. In summary, the increasing complexity of the tissue model enables capturing more details. However, an extensive parameter set is also required. Since the simulation results depend on these modeling choices, variations can lead to different recommendations in clinical applications. [ABSTRACT FROM AUTHOR]

ABSTRACT Objective Methods Results Conclusions Abnormal tumor vascular network contributes to aberrant blood perfusion and reduced oxygenation in tumors, which lead to poor efficacy of chemotherapy and radiotherapy. We aimed to explore the effects of the tumor‐derived exosomes (TDEs) and C188‐9 (a small molecule inhibitor of signal transducer and activator of transcription 3, STAT3) on tumor microvascular hemodynamics and determine which blood flow oscillations for various frequency intervals are responsible for these changes.Microvascular hemodynamics parameters were recorded using a PeriFlux 6000 EPOS system in tumor surface in a nude mouse subcutaneous xenograft model. Oscillations of laser Doppler flowmetry (LDF) signal were investigated by wavelet transform analysis.TDEs facilitated tumor growth at least partially was associated with increasing blood flow in smaller vessels with lower speed and decreasing the blood flow at larger vessels with higher speed. Lower oxyhemoglobin saturation (SO2) on tumor surface was aggravated by TDEs, and C188‐9 treatment significantly alleviated this decrease. Wavelet transform spectral analysis revealed that TDEs increased the amplitude of oscillations in four frequency intervals related to endothelial (NO‐dependent and ‐independent), myogenic and neurogenic activities, and C188‐9 had no effect on this increase.TDEs facilitated tumor growth partially was associated with increasing blood flow in distributing vessels, reducing blood perfusion in larger vessels, and lowering SO2 on tumor surface. Enhanced vascular smooth muscle, endothelial and neurogenic activities occurred in tumor superficial zone. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the systemic hemodynamic and vascular changes in women during and after two commonly used clinical blood flow restriction (BFR) pressures at rest. There are minimal data regarding the independent effects of BFR on hemodynamic and systemic vascular changes due to pressor response, particularly among women. Therefore, this study investigated BFR‐induced alterations in pressor response and systemic flow redistribution at rest during two commonly used pressures (50% and 80% limb occlusion pressure [LOP]). Fifteen women (22.1 ± 4.2 years) completed two randomised sessions involving 8‐min of bilateral, lower limb restriction at 50% or 80% LOP followed by 8‐min of recovery post‐deflation. Changes in vascular (arterial diameter [DIA], time‐averaged mean velocity [TAMV], volume flow [VF], and area) and hemodynamic (heart rate [HR] and blood pressure) measures over time (pre‐, during, post‐occlusion) and by session (50% vs. 80% LOP) were tested using repeated measures analysis of variance. Repeated measures correlations (rrm) quantified common intraindividual associations between BFR‐induced hemodynamic and vascular responses. HR increased from baseline during 50% LOP and remained elevated during recovery (p < 0.05). HR increased from baseline during 80% LOP, while tibial VF and TAMV decreased (p < 0.03 for all). HR and TAMV values returned to baseline during recovery, while brachial artery VF decreased (p < 0.05). Changes in HR, brachial VF, and brachial TAMV were similar between 50% and 80% LOP (rrm = 0.32–0.70, p < 0.05 for all). At 80% LOP, changes in HR were positively correlated with brachial VF (rrm = 0.38) and TAMV (rrm = 0.43) and negatively correlated with tibial VF (rrm = −0.36) and TAMV (rrm = −0.30) (p < 0.05 for all). Results suggest that BFR at 80% LOP elicits an acute systemic pressor reflex without concomitant increases in brachial arterial flow, while 50% LOP elicits a subdued response. [ABSTRACT FROM AUTHOR]

In this paper, we present a re-established functional fractal circuit model of arterial blood flow that incorporates the shunt effect of the branch vessels. Under the background of hemodynamics, we abstracted a family of fractal operators and investigate the kernel function and properties thereof. Based on fractal operators, the intrinsic relation between Bessel function and Struve function was revealed, and some new special functions were found. The results provide mathematical tools for biomechanics and automatic control. [ABSTRACT FROM AUTHOR]

This study provides comprehensive information about the impact of the parent vessel's shape on the risk of cerebral aneurysm rupture. It focuses on internal carotid artery (ICA) aneurysms with varying parent vessel sizes, analyzing different aspects of blood flow dynamics. By comparing various hemodynamic factors such as wall shear stress (WSS), oscillatory shear index (OSI) and pressure distribution, the researchers aim to establish a meaningful relationship between the parent vessel's mean diameter and these significant hemodynamic parameters. [ABSTRACT FROM AUTHOR]

Purpose: Abnormalities in cerebral veins are a common finding in many neurological diseases, yet there is a scarcity of MRI techniques to assess venous hemodynamic function. The present study aims to develop a noncontrast technique to measure a novel blood flow circulatory measure, venous transit time (VTT), which denotes the time it takes for water to travel from capillary to major veins. Methods: The proposed sequence, venous transit time imaging by changes in T1 relaxation (VICTR), is based on the notion that as water molecules transition from the tissue into the veins, they undergo a change in T1 relaxation time. The validity of the measured VTT was tested by studying the VTT along the anatomically known flow trajectory of venous vessels as well as using a physiological vasoconstrictive challenge of caffeine ingestion. Finally, we compared the VTT measured with VICTR MRI to a bolus‐tracking method using gadolinium‐based contrast agent. Results: VTT was measured to be 3116.3 ± 326.0 ms in the posterior superior sagittal sinus (SSS), which was significantly longer than 2865.0 ± 390.8 ms at the anterior superior sagittal sinus (p = 0.004). The test–retest assessment showed an interclass correlation coefficient of 0.964. VTT was significantly increased by 513.8 ± 239.3 ms after caffeine ingestion (p < 0.001). VTT measured with VICTR MRI revealed a strong correlation (R = 0.84, p = 0.002) with that measured with the contrast‐based approach. VTT was found inversely correlated to cerebral blood flow and venous oxygenation across individuals. Conclusion: A noncontrast MRI technique, VICTR MRI, was developed to measure the VTT of the brain. [ABSTRACT FROM AUTHOR]

SIGNIFICANCE: Speckle contrast analysis is the basis of laser speckle imaging (LSI), a simple, inexpensive, noninvasive technique used in various fields of medicine and engineering. A common application of LSI is the measurement of tissue blood flow. Accurate measurement of speckle contrast is essential to correctly measure blood flow. Variables, such as speckle grain size and camera pixel size, affect the speckle pattern and thus the speckle contrast. AIM: We studied the effects of spatial correlation among adjacent camera pixels on the resulting speckle contrast values. APPROACH: We derived a model that accounts for the potential correlation of intensity values in the common experimental situation where the speckle grain size is larger than the camera pixel size. In vitro phantom experiments were performed to test the model. RESULTS: Our spatial correlation model predicts that speckle contrast first increases, then decreases as the speckle grain size increases relative to the pixel size. This decreasing trend opposes what is observed with a standard speckle contrast model that does not consider spatial correlation. Experimental data are in good agreement with the predictions of our spatial correlation model. CONCLUSIONS: We present a spatial correlation model that provides a more accurate measurement of speckle contrast, which should lead to improved accuracy in tissue blood flow measurements. The associated correlation factors only need to be calculated once, and open-source software is provided to assist with the calculation.

SignificanceMeasuring hemodynamic function is crucial for health assessment. Optical signals provide relative hemoglobin concentration changes, but absolute measurements require costly, bulky technology. Speckleplethysmography (SPG) uses coherent light to detect speckle fluctuations. Combining SPG with multispectral measurements may provide important physiological information on blood flow and absolute hemoglobin concentration.AimTo develop an affordable optical technology to measure tissue absorption, scattering, hemoglobin concentrations, tissue oxygen saturation (StO2), and blood flow.ApproachWe integrated reflectance spectroscopy and laser speckle imaging to create coherent spatial imaging (CSI). CSI was validated against spatial frequency domain imaging (SFDI) using phantom-based measurements. In vivo arterial and venous occlusion experiments compared CSI with diffuse optical spectroscopy/diffuse correlation spectroscopy (DOS/DCS) measurements.ResultsCSI and SFDI agreed on tissue absorption and scattering in phantom tests. CSI and DOS/DCS showed similar trends and agreement in arterial occlusion results. During venous occlusion, both uncorrected and corrected blood flow decreased with increasing pressure, with an ∼200% difference in overall blood flow decrease between the methods. CSI and DOS/DCS data showed expected hemoglobin concentrations, StO2, and blood flow trends.ConclusionsCSI provides affordable and comprehensive hemodynamic information. It can potentially detect dysfunction and improve measurements, such as blood pressure, SpO2, and metabolism.

This research concerns examining the non-Newtonian blood flow behavior through an artery of elliptic cross-section, affected by several stenoses. The Rabinowitsch fluid model is used to investigate the non-Newtonian behavior of the blood for uniform and nonuniform shapes of stenosis. The mathematical equations have been converted into a dimensionless form, and their nonlinearity is reduced by applying the assumptions of mild stenosis. The resulting differential equations are solved by using analytical techniques. A new polynomial of degree eight is introduced to complete the solutions of mathematical equations. The entropy generation is studied mathematically to analyze the irreversibility effects. The detailed graphical examination delineates the physical aspects of mathematical results. The flow velocity is higher for uniform shape than for nonuniform stenosis. The rising percentage of stenosis significantly enhances the flow velocity of the stenotic region. The entropy is enormous near the stenotic wall and has small values near the centerline, which assures the smooth flow in this region. Further, the streamlines are plotted to find the position of stenosis and assess the flow nature for the growing height of stenosis and rising flow rate. [ABSTRACT FROM AUTHOR]

Cervical spinal cord injury usually results in cardiorespiratory dysfunctions due to interruptions of the bulbospinal pathways innervating the cervical phrenic motoneurons and thoracic sympathetic preganglionic neurons. The present study aimed to evaluate the therapeutic effects of adrenergic agents on systemic and spinal hemodynamics during acute cervical spinal cord injury. In vivo animal study. The cardiorespiratory function and spinal cord blood flow and oxygenation level were monitored in response to cervical spinal cord contusion and intravenous infusion of three types of adrenergic agents (phenylephrine, dobutamine, and norepinephrine). Cervical spinal cord contusion resulted in immediate reduction of respiratory airflow, arterial blood pressure, and spinal cord blood flow. The arterial blood pressure and spinal cord blood flow remained lower than the preinjury value in contused animals infused with saline at 60 min postinjury. Infusion of phenylephrine (500, 1000, and 2000 μg/kg) and norepinephrine (125, 250, and 500 μg/kg) significantly increased the arterial blood pressure, while only norepinephrine augmented the spinal cord blood flow. Conversely, dobutamine (1000 and 2000 μg/kg) reduced both arterial blood pressure and spinal cord blood flow. Notably, administration of adrenergic agents tended to increase spinal cord hemorrhage in contused animals. Infusion of norepinephrine can effectively maintain the blood pressure and improve spinal cord blood flow during acute spinal cord injury. Norepinephrine may be a superior medicine for hemodynamic management; however, the potential hemorrhage should be considered when utilizing the vasopressor to regulate systemic and spinal hemodynamics at the acute injured stage. [ABSTRACT FROM AUTHOR]

The human forearm model is commonly employed in physiological investigations exploring local vascular function and oxygen delivery; however, the effect of arm dominance on exercising forearm hemodynamics and skeletal muscle oxygen saturation (SmO2) in untrained individuals is poorly understood. Therefore, the purpose of this study was to explore the effect of self-identified arm dominance on forearm hemodynamics and SmO2 in untrained individuals during submaximal, non-ischemic forearm exercise. Twenty healthy individuals (23±4 years, 50% female; 80% right-handed) completed three-minute bouts of supine rhythmic (1 second contraction: 2 second relaxation duty cycle) forearm handgrip exercise at both absolute (10kg; 98N) and relative (30% of maximal voluntary contraction) intensities in each forearm. Beat-by-beat measures of forearm blood flow (FBF; ml/min), mean arterial blood pressure (MAP; mmHg) and flexor digitorum superficialis SmO2 (%) were obtained throughout and averaged during the final 30 seconds of rest, exercise, and recovery while forearm vascular conductance was calculated (FVC; ml/min/100mmHg). Data are Δ from rest (mean±SD). Absolute force production did not differ between non-dominant and dominant arms (97±11 vs. 98±13 N, p = 0.606) whereas relative force production in females did (69±24 vs. 82±25 N, p = 0.001). At both exercise intensities, FBFRELAX, FVCRELAX, MAPRELAX, and the time constant tau for FBF and SmO2 were unaffected by arm dominance (all p>0.05). While arm dominance did not influence SmO2 during absolute intensity exercise (p = 0.506), the non-dominant arm in females experienced an attenuated reduction in SmO2 during relative intensity exercise (-14±10 vs. -19±8%, p = 0.026)–though exercise intensity was also reduced (p = 0.001). The present investigation has demonstrated that arm dominance in untrained individuals does not impact forearm hemodynamics or SmO2 during handgrip exercise. [ABSTRACT FROM AUTHOR]

Atherosclerosis is an inflammatory reaction that develops at specific regions within the artery wall and at specific sites of the arterial tree over a varying time frame in response to a variety of risk factors. The mechanisms that account for the interaction of systemic factors and atherosclerosis-susceptible regions of the arterial tree to mediate this site-specific development of atherosclerosis are not clear. The dynamics of blood flow has a major influence on where in the arterial tree atherosclerosis develops, priming the site for interactions with atherosclerotic risk factors and inducing cellular and molecular participants in atherogenesis. But how this accounts for lesion development at various locations along the vascular tree across differing time frames still requires additional study. Currently, murine models are favored for the experimental study of atherogenesis and provide the most insight into the mechanisms that may contribute to the development of atherosclerosis. Based largely on these studies, in this review, we discuss the role of hemodynamic shear stress, SR-B1, and other factors that may contribute to the site-specific development of atherosclerosis. [ABSTRACT FROM AUTHOR]

Background/Aims: The growing prevalence of sedentary behaviour across the life course is linked to an increased risk of chronic venous disease and related mortality, warranting the need for non-invasive interventions to improve blood flow and lower extremity function. The aim of this study was to investigate the change in venous blood flow, heart rate and blood pressure after 8 minutes of using the Leeper device, Circulation Booster and light intensity walking. Methods: A quasi-experimental crossover study involving 11 participants (eight women, three men, mean age 23.91 years, standard deviation 1.04 years) was conducted using Leeper and Circulation Booster devices and light intensity walking. During each intervention, participants exercised for 8 minutes, and blood flow was recorded at 0, 4 and 8 minutes. Heart rate and blood pressure were recorded at 0 and 8 minutes. Blood flow was the primary outcome measure, and heart rate and blood pressure were secondary outcomes. Participants rested for 10 minutes between exercise. A two-way repeated measures analysis of variance was used to analyse the effect of intervention and time on blood flow, blood pressure and heart rate. Results: There was no significant interaction between intervention and time on blood flow (P=0.180) indicating that blood flow did not change over time depending on intervention. There was no significant main effect of time on blood flow (P=0.206), indicating that no intervention caused a significant increase or decrease in blood flow after 8 minutes of exercise. Conclusions: The interventions involving the Leeper and Circulation Booster devices and light intensity walking did not appear to significantly increase blood flow in young adults. Further studies involving participants from older age groups and those with pathological interventions are warranted to examine the potential effectiveness of these interventions. Implications for practice: The findings may assist with the advice that allied health professionals provide regarding the use of seated exercise trainers and EMS devices and their ability to influence changes in blood flow. [ABSTRACT FROM AUTHOR]

Hemodynamics in intracranial aneurysm strongly depends on the non-Newtonian blood behavior due to the large number of suspended cells and the ability of red blood cells to deform and aggregate. However, most numerical investigations on intracranial hemodynamics adopt the Newtonian hypothesis to model blood flow and predict aneurysm occlusion. The aim of this study was to analyze the effect of the blood rheological model on the hemodynamics of intracranial aneurysms in the presence or absence of endovascular treatment. A numerical investigation was performed under pulsatile flow conditions in a patient-specific aneurysm with and without the insertion of an appropriately reconstructed flow diverter stent (FDS). The numerical simulations were performed using Newtonian and non-Newtonian assumptions for blood rheology. In all cases, FDS placement reduced the intra-aneurysmal velocity and increased the relative residence time (RRT) on the aneurysmal wall, indicating progressive thrombus formation and aneurysm occlusion. However, the Newtonian model largely overestimated RRT values and consequent aneurysm healing with respect to the non-Newtonian models. Due to the non-Newtonian blood properties and the large discrepancy between Newtonian and non-Newtonian simulations, the Newtonian hypothesis should not be used in the study of the hemodynamics of intracranial aneurysm, especially in the presence of endovascular treatment. [ABSTRACT FROM AUTHOR]

Abdominal aortic aneurysm (AAA) is a cardiovascular disease caused by the enlargement of the aorta in the abdomen over time. Unless treated, the growth of AAA continues, resulting in 80% death in the case of rupture. Today, the width of the aneurysm diameter is taken into account in clinical practice to examine the status of AAA. Although there are aneurysms that do not rupture despite reaching a diameter of 9 cm, it is reported that aneurysms with a diameter of 3 cm are ruptured in several cases. Therefore, analyzing only the AAA diameter is not a reliable method, and a deeper investigation is necessary for the rupture risk assessment. In this study, a patient's situation is analyzed using computational fluid dynamics (CFD) simulations, which allows to elucidate the flow dependent parameters such as velocity, vorticity, pressure, and wall shear stress (WSS). First, the patient-specific geometry was obtained and boundary conditions were defined at the inlet and the outlet of the flow domain. The effects of intraluminal thrombus (ILT) formation and patient’s effort conditions were also included in the analysis. According to the results, WSS and vorticity increase with the increasing blood flow velocity. In terms of the rupture risk, it has been found that the effect of patient’s effort level is more critical than the amount of ILT in the AAA. [ABSTRACT FROM AUTHOR]

Blood flow to the brain is a critical physiological function and is useful to monitor in critical care settings. Despite that, a surrogate is most likely measured instead of actual blood flow. Such surrogates include velocity measurements in the carotid artery and systemic blood pressure, even though true blood flow can actually be obtained using MRI and other modalities. Ultrasound is regularly used to measure blood flow and is, under certain conditions, able to provide quantitative volumetric blood flow in milliliters per minute. Unfortunately, most times the resulting flow data is not valid due to unmet assumptions (such as flow profile and angle correction). Color flow, acquired in three dimensions, has been shown to yield quantitative blood flow without any assumptions (3DVF). Here we are testing whether color flow can perform during physiological conditions common to severe injury. Specifically, we are simulating severe traumatic brain injury (epidural hematoma) as well as hemorrhagic shock with 50% blood loss. Blood flow was measured in the carotid artery of a cohort of 7 Yorkshire mix pigs (40–60 kg) using 3DVF (4D16L, LOGIQ 9, GE HealthCare, Milwaukee, WI, USA) and compared to an invasive flow meter (TS420, Transonic Systems Inc., Ithaca, NY, USA). Six distinct physiological conditions were achieved: baseline, hematoma, baseline 2, hemorrhagic shock, hemorrhagic shock plus hematoma, and post-hemorrhage resuscitation. Mean cerebral oxygen extraction ratio varied from 40.6% ± 13.0% of baseline to a peak of 68.4% ± 15.6% during hemorrhagic shock. On average 3DVF estimated blood flow with a bias of -9.6% (-14.3% root mean squared error) relative to the invasive flow meter. No significant flow estimation error was detected during phases of flow reversal, that was seen in the carotid artery during traumatic conditions. The invasive flow meter showed a median error of -11.5% to 39.7%. Results suggest that absolute volumetric carotid blood flow to the brain can be obtained and potentially become a more specific biomarker related to cerebral hemodynamics than current surrogate markers. [ABSTRACT FROM AUTHOR]

Atherosclerosis is one of the most common diseases of the arterial tree, especially in the coronary arteries. Stenoses exceeding 50% area reduction are shown to alternate the downstream coronary flow, and hemodynamics will lead to further atherogenesis. Clinical evidence also confirms that vascular stenoses are not stagnant since they are usually associated with downstream lesions. In this study, it is hypothesized that the formation of secondary plaques, or aneurysms downstream of a primary stenosis, compensates for the abnormal ranges of hemodynamic forces caused by the primary stenosis. An experimental setup captured the hemodynamics of non-Newtonian blood flow in three-dimensional (3D) printed phantoms of coronary arteries with various sequences of lesions. Then, based on the collected data, in silico models of these lesions were simulated using computational fluid dynamics. For the proposed cases, time-averaged wall shear stress, velocity profile, oscillatory shear index, and relative residence time were extracted at the plaque side and the plaque front walls and compared to the reference model with only the primary plaque. The secondary plaque postulated the abnormal hemodynamic conditions to its downstream, which implies endothelial activation and onset of further pathologic events. However, the secondary aneurysm restored flow conditions to normal after its distal shoulder, preventing more damage to the endothelium. Examined angiograms of patients with developed atherosclerotic lesions unveiled that a sequence of plaques is formed over time, and most interestingly, the series stopped after the formation of an aneurysm. [ABSTRACT FROM AUTHOR]

Objective measurement tool for assessing the effects of SGB on arterial elasticity and blood flow velocity, especially for patients needing evaluation of its impact on the upper limbs. [ABSTRACT FROM AUTHOR]

Hemodynamic parameters have been correlated with stroke, hypertension, and arterial stenosis. While only a few small studies have examined the link between hemodynamics and diabetes mellitus (DM). This case-control study enrolled 417 DM patients and 3475 non-DM controls from a community-based cohort. Peak systolic velocity (PSV), end-diastolic velocity (EDV), blood flow velocity (MFV), pulsatility index (PI), and the resistance index (RI) of the common carotid arteries were measured by color Doppler ultrasonography. Generalized linear regression analyses showed that as compared to the non-DM controls, the age-sex-adjusted means of PSV, EDV, and MFV were − 3.28 cm/sec, − 1.94 cm/sec, and − 2.38 cm/sec, respectively, lower and the age-sex-adjusted means of RI and PI were 0.013 and 0.0061, respectively, higher for the DM cases (all p-values < 0.0005). As compared to the lowest quartiles, the multivariable-adjusted ORs of DM for the highest quartiles of PSV, EDV, MFV, RI, and PI were 0.59 (95% confidence interval [CI] 0.41–0.83), 0.45 (95% CI 0.31–0.66), 0.53 (95% CI 0.37–0.77), 1.61 (95% CI 1.15–2.25), and 1.58 (95% CI 1.12–2.23), respectively. More importantly, the additions of EDV significantly improved the predictabilities of the regression models on DM. As compared to the model contained conventional CVD risk factors alone, the area under the receiver operating curve (AUROC) increased by 1.00% (95% CI 0.29–1.73%; p = 0.0059) and 0.80% (95% CI 0.15–1.46%; p = 0.017) for models that added EDV in continuous and quartile scales, respectively. Additionally, the additions of PSV and MFV also significantly improved the predictabilities of the regression models (all 0.01 < p-value < 0.05). This study reveals a significant correlation between DM and altered hemodynamic parameters. Understanding this relationship could help identify individuals at higher risk of DM and facilitate targeted preventive strategies to reduce cardiovascular complications in DM patients. [ABSTRACT FROM AUTHOR]

Background: To evaluate the hemodynamic characteristics of normal upper extremity arteries from the brachial artery to the fingertip arterioles. Methods: We analyzed the characteristics and changes in the regularities of ultrasonic parameters in the upper extremity arteries of 104 healthy volunteers using color Doppler flow imaging and Angio Planewave UltraSensitive™ imaging. The measured ultrasonic parameters included the vessel diameter, blood-flow spectrum waveform, peak systolic velocity, end-diastolic velocity, resistance index, pulsatility index, ratio of PSV to EDV, blood-flow volume, along with systolic acceleration of each BA, radial artery, superficial palmar arch artery, palmar proper digital artery, and third-grade artery arch of the fingernail bed. Results: From BA to FN3AA, the diameter, PSV, RI, S/D, VFlow, and slope of the artery significantly decreased (P < 0.001), and size of the parameters significantly correlated with the anatomic position of the arteries. The blood-flow spectrum gradually changed from various waveforms to fixed monophasic waves. There was a linear relationship between the distribution of monophasic waveforms and arterial groups (R = -0.453; P < 0.001). When the blood-flow spectrum of BA and RA showed a monophasic waveform, their branch arteries showed the same. The waveforms of PPDA and FN3AA were also monophasic. Conclusion: Regular changes in the blood-flow spectrum waveform and hemodynamic parameters are related to the anatomic position of the upper limb arteries. CDFI combined with Angio PLUS accurately and systematically evaluates the hemodynamic characteristics of the upper extremity arteries. [ABSTRACT FROM AUTHOR]

Objective: We examined sex‐specific microvascular reactivity and hemodynamic responses under conditions of augmented resting blood flow induced by passive heating compared to normal blood flow. Methods: Thirty‐eight adults (19 females) completed a vascular occlusion test (VOT) on two occasions preceded by rest with or without passive heating in a randomized, counterbalanced order. Skeletal muscle tissue oxygenation (StO2, %) was assessed with near‐infrared spectroscopy (NIRS), and the rate of desaturation and resaturation as well as maximal StO2 (StO2max) and prolonged hypersaturation (area under the curve, StO2AUC) were quantified. Before the VOT, brachial artery blood flow (BABF), vascular conductance, and relative BABF (BABF normalized to forearm lean mass) were determined. Sex × condition ANOVAs were used. A p‐value ≤.05 was considered statistically significant. Results: Twenty minutes of heating increased BABF compared to the control (102.9 ± 28.3 vs. 36.0 ± 20.9 mL min−1; p <.01). Males demonstrated greater BABF than females (91.9 ± 34.0 vs. 47.0 ± 19.1 mL min−1; p <.01). There was no sex difference in normalized BABF. There were no significant interactions for NIRS‐VOT outcomes, but heat did increase the rate of desaturation (−0.140 ± 0.02 vs. −0.119 ± 0.03% s−1; p <.01), whereas regardless of condition, males exhibited greater rates of resaturation and StO2max than females. Conclusions: These results suggest that blood flow is not the primary factor causing sex differences in NIRS‐VOT outcomes. [ABSTRACT FROM AUTHOR]

Vascular remodeling is a physiological and pathological process in which abnormal changes in vascular cells and non-cellular components lead to the remodeling of inward and outward blood vessel wall or changes in lumen diameter. As the channels for blood flow, blood vessels are continuously affected by hemodynamic forces. When sensing the abnormal blood flow forces, the mechanically sensitive cell membrane structures such as G protein-coupled receptors, ion channels, cell surface glycocalyx, and integrins, as well as the extracellular matrix will induce the process of vascular endothelial dysfunction, endothelial-mesenchymal transition, smooth muscle cell phenotypic switching, pericyte morphological changes and extracellular matrix remodeling to participate in vascular remodeling. As shown by research, abnormal hemodynamics caused abnormal changes in vascular structure and function, which was the basic process for the occurrence and development of pan-vascular diseases such as atherosclerosis, hypertension, diabetes, non-alcoholic fatty liver disease, pulmonary hypertension and COVID-19. This paper reviewed the interaction and molecular mechanism between abnormal hemodynamics and vascular remodeling, and analyzed its influence on the pathogenesis of pan-vascular diseases, which could provide reference for formulating prevention and treatment strategies for pan-vascular diseases. [ABSTRACT FROM AUTHOR]

Purpose: Self-myofascial release (SMR) is a form of self-massage aiming to release tension, improve blood flow, and alleviate muscle soreness. This study aimed to determine whether a single session of SMR could impact cardiovascular parameters at rest and during a cold pressor test (CPT). Methods: Twenty male participants (aged 26 ± 2 years) underwent a 20-min SMR and a 20-min seated control condition (CON) on two separate test days in a randomized order. Peripheral and central blood pressure (BP), total peripheral resistance (TPR), pulse wave velocity (PWV), heart rate (HR), root mean square of successive RR interval differences (RMSSD), and the quotient of low-frequency power and high-frequency power (LF/HF) were measured both at rest and during a CPT before (t0), 2 min (t1), and 20 min (t2) after the SMR and CON. Results: Time × condition interactions could be detected for peripheral and central diastolic BP, TPR, HR, and RMSSD. Following the SMR, peripheral diastolic BP, central diastolic BP, TPR, and RMSSD were reduced, while HR was increased compared to the CON. Regarding the CPT time × condition interactions could be detected for peripheral, and central diastolic BP, with lower values after SMR. Conclusion: The results of the present study suggest that a single bout of SMR confers favorable cardiovascular benefits in healthy normotensive individuals. Furthermore, SMR can attenuate the hemodynamic reactivity to a stress test. Future research should address whether regular SMR leads to chronic adaptations similar to regular, moderate aerobic exercise, massage therapy, and static stretching. [ABSTRACT FROM AUTHOR]

Resistance breathing may restore cardiac output (CO) and cerebral blood flow (CBF) during hypovolemia. We assessed CBF and cerebral autoregulation (CA) during tilt, resistance breathing, and paced breathing in 10 healthy subjects. Blood velocities in the internal carotid artery (ICA), middle cerebral arteries (MCA, four subjects), and aorta were measured by Doppler ultrasound in 30° and 60° semi‐recumbent positions. ICA blood flow and CO were calculated. Arterial blood pressure (ABP, Finometer), and end‐tidal CO2 (ETCO2) were recorded. ICA blood flow response was assessed by mixed‐models regression analysis. The synchronization index (SI) for the variable pairs ABP–ICA blood velocity, ABP–MCA velocities in 0.005–0.08 Hz frequency interval was calculated as a measure of CA. Passive tilting from 30° to 60° resulted in 12% decrease in CO (p = 0.001); ICA blood flow tended to fall (p = 0.04); Resistance breathing restored CO and ICA blood flow despite a 10% ETCO2 drop. ETCO2 and CO contributed to ICA blood flow variance (adjusted R2: 0.9, p < 0.0001). The median SI was low (<0.2) indicating intact CA, confirmed by surrogate date testing. The peak SI was transiently elevated during resistance breathing in the 60° position. Resistance breathing may transiently reduce CA efficiency. Paced breathing did not restore CO or ICA blood flow. [ABSTRACT FROM AUTHOR]

Dynamic cerebral autoregulation (dCA) is the mechanism that describes how the brain maintains cerebral blood flow approximately constant in response to short‐term changes in arterial blood pressure. This is known to be impaired in many different pathological conditions, including ischaemic and haemorrhagic stroke, dementia and traumatic brain injury. Many different approaches have thus been used both to analyse and to quantify this mechanism in a range of healthy and diseased subjects, including data‐driven models (in both the time and the frequency domain) and biophysical models. However, despite the substantial body of work on both biophysical models and data‐driven models of dCA, there remains little work that links the two together. One of the reasons for this is proposed to be the discrepancies between the time constants that govern dCA in models and in experimental data. In this study, the processes that govern dCA are examined and it is proposed that the application of biophysical models remains limited due to a lack of understanding about the physical processes that are being modelled, partly due to the specific model formulation that has been most widely used (the equivalent electrical circuit). Based on the analysis presented here, it is proposed that the two most important time constants are arterial transit time and feedback time constant. It is therefore time to revisit equivalent electrical circuit models of dCA and to develop a more physiologically realistic alternative, one that can more easily be related to experimental data. Key points: Dynamic cerebral autoregulation is governed by two time constants.The first time constant is the arterial transit time, rather than the traditional 'RC' time constant widely used in previous models.This arterial transit time is approximately 1 s in the brain.The second time constant is the feedback time constant, which is less accurately known, although it is somewhat larger than the arterial transit time.The equivalent electrical circuit model of dynamic cerebral autoregulation should be replaced with a more physiologically representative model. [ABSTRACT FROM AUTHOR]

In this research, a computational approach is applied to model the blood flow inside the MCA aneurysm when the coiling technique is used for the treatment of the patients. To this end, porous condition with different permeability factors is applied and their impacts on the hemodynamic factors of wall shear stress, pressure and oscillatory shear index. The main attention is to find how endovascular technique could efficiently decrease the risk of bleeding in MCA aneurysms. Blood hemodynamic is simulated via solving transient Navier–Stokes equations with Casson model for the non-Newtonian condition for the blood stream. Besides, the impacts of the blood hematocrit are also examined on the hemodynamic characteristics. Attained results show that the effects of coiling permeability are significant on the reduction of the blood stress on the aneurysm. [ABSTRACT FROM AUTHOR]

PURPOSE: To compare the hemodynamic performance of three (Bottom Up non-ballet, Top-Down non-ballet, Top Down ballet) idealized stent graft configurations used during endovascular repair of abdominal aortic aneurysms, under the influence of various rheological models. METHODS: Ten rheological models are assumed and a commercial finite volume solver is employed for the simulation of blood flow under realistic boundary conditions. An appropriate mesh convergence study is performed and five hemodynamic variables are computed: the time average wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), endothelial cell activation potential (ECAP) and displacement force (DF) for all three configurations. RESULTS: The choice of blood flow model may affect results, but does not constitute a significant determinant on the overall performance of the assumed stent grafts. On the contrary, stent graft geometry has a major effect. Specifically, the Bottom Up non-ballet type is characterized by the least favorable performance presenting the lowest TAWSS and the highest OSI, RRT and ECAP values. On the other hand, the Top Down ballet type presents hemodynamic advantages yielding the highest TAWSS and lowest OSI, RRT and ECAP average values. Furthermore, the ballet type is characterized by the lowest DF, although differences observed are small and their clinical relevance uncertain. CONCLUSIONS: The effect of the assumed rheological model on the overall performance of the grafts is not significant. It is thus relatively safe to claim that it is the type of stent graft that determines its overall performance rather than the adopted blood flow model. [ABSTRACT FROM AUTHOR]

The influence of the aneurysm evolution on the hemodynamic characteristic of the blood flow inside the sac region is comprehensively investigated. By using the computational method, the blood flow through the vessel and aneurysm of the sac region is examined to find the role of aneurysm evolution on the wall shear stress, pressure, and risk of aneurysm rupture. Three different models of ICA aneurysms are chosen for the investigation of the aneurysm evolution at risk of rupture. Obtained data shows that the evolution of the aneurysm decreases the wall shear stress and pressure on the sac surface while an oscillatory index of blood increases on the aneurysm wall. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to investigate the effects of two different positions on lower extremity hemodynamics during robot-assisted laparoscopic radical prostatectomy (RARP) for prostate cancer. Methods: A total of 196 patients who underwent RARP in our hospital from February 2020 to March 2022 were included in this study. Among them, 98 patients who underwent surgery with the Trendelenburg position and split-leg position with calf reverse arch from March 2021 to March 2022 were assigned to the observation group, while 98 patients who underwent surgery with the Trendelenburg position and low lithotomy position from February 2020 to February 2021 were assigned to the control group. Using an ultrasound diagnostic instrument to detect the internal diameter, mean blood flow velocity, and mean blood flow volume of the left deep femoral vein at different times, such as the supine position (T0), after 5 minutes of placing the patient in the leg spilt or low lithotomy position (T1), after 5 minutes of pneumoperitoneum (T2), after 5 minutes of head-down tilt or head-down tilt and calf reverse arch (T3), 1.5 hours after the start of surgery (T4), before the removal of CO2 gas (T5), and before the patient left the operating room (T6). As well as the patency of deep venous blood flow in both lower extremities before leaving the operating room, Results: After establishment of pneumoperitoneum, the internal diameter of the deep femoral vein increased significantly, while the mean blood flow velocity and mean blood flow volume decreased significantly in both groups(T0) (P<0.001). With the prolongation of surgical time, the impact on lower extremity hemodynamics in the observation group was smaller than that in the control group. From T2 to T6, the internal diameter of the femoral vein in the observation group was smaller than that in the control group, while the mean blood flow velocity and mean blood flow volume were increased compared to the control group (P<0.05). Before leaving the operating room, the patency of deep venous blood flow in the observation group was better than that in the control group (P=0.003). Conclusion: Placing patients in the Trendelenburg position and split-leg position with calf reverse arch during RARP for prostate cancer has a smaller impact on lower extremity hemodynamics than the low lithotomy position, and can relatively reduce the risk of postoperative deep vein thrombosis. [ABSTRACT FROM AUTHOR]

It is well‐recognized that blood flow at branches and bends of arteries generates disturbed shear stress, which plays a crucial in driving atherosclerosis. Flow‐generated fluid shear stress (FSS), as one of the key hemodynamic factors, is appreciated for its critical involvement in regulating angiogenesis to facilitate wound healing and tissue repair. Endothelial cells can directly sense FSS but the mechanobiological mechanism by which they decode different patterns of FSS to trigger angiogenesis remains unclear. In the current study, laminar shear stress (LSS, 15 dyn/cm2) was employed to mimic physiological blood flow, while disturbed shear stress (DSS, ranging from 0.5 ± 4 dyn/cm2) was applied to simulate pathological conditions. The aim was to investigate how these distinct types of blood flow regulated endothelial angiogenesis. Initially, we observed that DSS impaired angiogenesis and downregulated endogenous vascular endothelial growth factor B (VEGFB) expression compared to LSS. We further found that the changes in membrane protein, migration and invasion enhancer 1 (MIEN1) play a role in regulating ERK/MAPK signaling, thereby contributing to endothelial angiogenesis in response to FSS. We also showed the involvement of MIEN1‐directed cytoskeleton organization. These findings suggest the significance of shear stress in endothelial angiogenesis, thereby enhancing our understanding of the alterations in angiogenesis that occur during the transition from physiological to pathological blood flow. [ABSTRACT FROM AUTHOR]

Heart valves serve a vital hemodynamic function to ensure unidirectional blood flow. Additionally, native heart valves serve biological functions such as growth and self‐repair. Heart valve implants mimic the hemodynamic function of native heart valves, but are unable to fulfill their biological functions. We developed partial heart transplantation to deliver heart valve implants that fulfill all functions of native heart valves. This is particularly advantageous for children, who require growing heart valve implants. This invited review outlines the past, present and future of partial heart transplantation. [ABSTRACT FROM AUTHOR]

Rhabdomyoma is the most common fetal cardiac tumor accounting for 60-65% of all fetal tumors and up to 90% of cardiac tumors in pediatric population. Rhabdomyomas are benign lesions and the symptoms depend on the size and location of the rhabdomyomas. A single or multiple lesions are usually located within the left ventricle and projecting into the ventricular cavity or moving freely as a pedunculated mass. Intracavitary growth may cause ventricular outflow tract obstruction, valvular compromise, and disruption of intracardiac blood flows, leading to congestive heart failure. Rhabdomyomas >30 mm in diameter, regardless of number and location, are associated with postnatal arrhythmia. Cardiac rhabdomyoma is associated with tuberous sclerosis in about 50-90% of cases. Rhabdomyomas can be detected as early as the second trimester by echocardiography which is the primary diagnostic tool for the evaluation of cardiac tumors. They usually grow until 32 weeks gestation due to the transmission of maternal estrogens to the fetus, and then gradually regress. When cardiac rhabdomyoma is suspected on fetal echocardiography, it is important to check the kidneys and brain for tuberous sclerosis complex (TSC)-specific lesions. The prognosis depends on the number, size, and location of the tumors, as well as the presence or absence of associated anomalies. Rhabdomyomas, single or multiple, in the majority of cases, are not hemodynamically relevant and regress in infancy. Expectant management is the recommended approach, and neonatal management is always preferred when lung maturity is assured. Prenatal therapy is recommended only in case of severe fetal hemodynamic deterioration, hydrops, or uncontrollable arrhythmias. [ABSTRACT FROM AUTHOR]

Purpose: Autonomic control of orofacial areas is an integral part of the stress response, controlling functions such as pupil dilatation, salivation, and skin blood flow. However, the specific control of blood flow in head muscles during stress is unknown. This study aims to investigate the hemodynamic response of temporalis and masseter muscles in response to five different stressors. Methods: Sixteen healthy individuals were subjected to a randomized series of stressors, including cold pressor test, mental arithmetic test, apnea, isometric handgrip, and post-handgrip muscle ischemia, while in the sitting posture. Finger-pulse photoplethysmography was used to measure arterial blood pressure, heart rate, and cardiac output. Near-infrared spectroscopy was used to measure changes in tissue oxygenation and hemoglobin indices from the temporalis and masseter muscles. Results: All stressors effectively and significantly increased arterial blood pressure. Tissue oxygenation index significantly increased in both investigated head muscles during mental arithmetic test (temporalis: 4.22 ± 3.52%; masseter: 3.43 ± 3.63%) and isometric handgrip (temporalis: 3.45 ± 3.09%; masseter: 3.26 ± 3.07%), suggesting increased muscle blood flow. Neither the masseter nor the temporalis muscles evidenced a vasoconstrictive response to any of the stressors tested. Conclusion: In the different conditions, temporalis and masseter muscles exhibited similar hemodynamic patterns of response, which do not include the marked vasoconstriction generally observed in limb muscles. The peculiar sympathetic control of head muscles is possibly related to the involvement of these muscles in aggressive/defensive reactions and/or to their unfavorable position with regard to hydrostatic blood levels. [ABSTRACT FROM AUTHOR]

Climbing performance is greatly dependent on the endurance of the finger flexors which, in turn, depends on the ability to deliver and use oxygen within the muscle. Near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) have provided new possibilities to explore these phenomena in the microvascular environment. The aim of the present study was to explore climbing-related microvascular adaptations through the comparison of the oxygen concentration and hemodynamics of the forearm between climbers and non-climber active individuals during a vascular occlusion test (VOT). Seventeen climbers and fifteen non-climbers joined the study. Through NIRS and DCS, the oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) concentrations, tissue saturation index (TSI), and blood flow index (BFI) were obtained from the flexor digitorum profundus during the VOT. During the reactive hyperemia, climbers presented greater blood flow slopes (p = 0.043, d = 0.573), as well as greater O2Hb maximum values (p = 0.001, d = 1.263) and HHb minimum values (p = 0.009, d = 0.998), than non-climbers. The superior hemodynamics presented by climbers could indicate potential training-induced structural and functional adaptations that could enhance oxygen transportation to the muscle, and thus enhance muscle endurance and climbing performance. [ABSTRACT FROM AUTHOR]

Recent advancements in computational performance and medical simulation technology have made significant strides, particularly in predictive diagnosis. This study focuses on the blood flow simulation reduced-order models, which provide swift and cost-effective solutions for complex vascular systems, positioning them as practical alternatives to 3D simulations in resource-limited medical settings. The paper introduces a visualization platform for patient-specific and image-based 1D–0D simulations. This platform covers the entire workflow, from modeling to dynamic 3D visualization of simulation results. Two case studies on, respectively, carotid stenosis and arterial remodeling demonstrate its utility in blood flow simulation applications. [ABSTRACT FROM AUTHOR]

The emerging high-frame-rate vector flow imaging provides a new way of hemodynamic evaluation for complex blood flow. This study was aimed at exploring quantitatively the characteristics of complex flow with turbulence (Tur) index and analyzing flow patterns in atherosclerotic internal carotid artery stenosis (ICAS) using high-frame-rate vector flow imaging. This study prospectively included 60 patients with ICAS. Tur values in different segments of stenosis and cardiac phases were compared. Spearman correlation analysis was performed between clinical plaque characteristics with turbulence grading by ln(Tur). Three complex flow patterns were qualitatively drawn on vector flow mode, and the rates of detection of flow patterns in different stenosis groups and ulceration groups were compared. Highly disordered blood flow was observed in the stenotic (Tur [M, QR] = 12.5%, 21.5%) and distal segment (15.4%, 27.2%), particularly during systole (21.0%, 30.7%, 33.3%, 38.7%, p < 0.05). Spearman correlation analysis revealed that stenosis rate was correlated with turbulence grading in the stenotic (ρ = 0.65, p < 0.05) and distal segment (ρ = 0.79, p < 0.05), and ulcer formation was correlated with turbulence grading in the stenotic segment (ρ = 0.58, p < 0.05). The overall rate of detection of three flow patterns was higher in the severe stenosis group (22/22) versus the mild to moderate stenosis group (21/38) (p < 0.001) and in the ulcer group (21/23) versus the non-ulcer group (23/37) (p < 0.001). High-frame-rate vector flow imaging was helpful in assessing the severity and characteristics of flow turbulence. Lumen geometric factors could affect flow turbulence and blood flow patterns around the plaque. This would provide important hemodynamic information for the detection of high-risk plaque. [ABSTRACT FROM AUTHOR]

Objectives: To assess the predictive value of hemodynamic features for stroke relapse in patients with intracranial vertebrobasilar atherosclerotic stenosis treated with percutaneous transluminal angioplasty and stenting (PTAS) using quantitative digital subtraction angiography (q-DSA). Methods: In this retrospective longitudinal study, patients with intracranial vertebrobasilar atherosclerotic stenosis and who underwent PTAS treatment between January 2012 and May 2020 were enrolled. The q-DSA assessment was performed before and after PTAS. ROIs 1–4 were placed along the vertebral artery, proximal and distal basilar artery, and posterior cerebral artery; ROIs 5–8 were in 5 mm and 10 mm proximal and distal to the lesion, respectively. Relative time to peak (rTTP) was defined as the difference in TTP between ROIs. Cox regression analyses were performed to determine risk factors for recurrent stroke. Results: A total of 137 patients (mean age, 62 years ± 10 [standard deviation], 83.2% males) were included, and 26 (19.0%) patients had stroke relapse during follow-up (median time of 42.6 months [interquartile range, 19.7–60.7]). Preprocedural rTTP4-1 (adjusted hazard ratio (HR) = 2.270; 95% CI 1.371–3.758; p = 0.001) and preprocedural rTTP8-5 (adjusted HR = 0.240; 95% CI 0.088–0.658; p = 0.006) were independently associated with the recurrent stroke. These hemodynamic parameters provided an incremental prognostic value for stroke relapse (AUC, 0.817 [0.704–0.931]; the net reclassification index, 0.431 [0.057–0.625]; and the integrated discrimination index, 0.140 [0.035–0.292]). Conclusions: In patients with intracranial vertebrobasilar atherosclerosis treated with PTAS, preprocedural prolonged TTP of the target vessel and shortened trans-stenotic TTP difference were associated with stroke relapse. Q-DSA-defined hemodynamic parameters provided incremental predictive value over conventional parameters for stroke recurrence. Clinical relevance statement: Quantitative DSA analysis enables intuitive observation and semi-quantitative evaluation of peri-therapeutic cerebral blood flow. More importantly, quantitative DSA–defined hemodynamic parameters have the potential for risk stratification of patients with intracranial atherosclerotic stenosis. Key Points: Semi-quantitative angiography-based parameters can reflect pre- and postprocedural subtle changes in blood flow in patients with intracranial atherosclerotic stenosis. Although angioplasty procedures can significantly improve blood flow status, patients with more restricted baseline blood flow still show a higher risk of stroke recurrence. Angiography-based hemodynamic features possess prognostic value and can serve as clinical markers to assess stroke risk of patients with intracranial atherosclerotic stenosis. [ABSTRACT FROM AUTHOR]

There is a lack of data regarding the baseline hemodynamic blood flow parameters of the wrist and digits. Therefore, we aimed to quantify the digital and radial artery blood flow parameters using ultrasound and assess the influence of patient characteristics on hemodynamics. We analyzed ultrasonographic data from 25 patients (50 hands) between October 2019 and December 2021. Variables of interest included dimensions of the radial artery and index finger (IF) ulnar and radial digital arteries at the palmodigital crease and their corresponding flow parameters. We compared variables among men and women and patients with and without diabetes using Wilcoxon Rank Sum test. Our cohort consisted of 18 women (36 hands) and three participants with diabetes (six hands). The mean diameter of the IF radial digital artery was 7 mm, and that of the ulnar digital artery was 10 mm. The average peak systolic velocity for the radial digital artery was 21.31 cm/sec, and for the ulnar digital artery, it was 30.03 cm/sec. Comparing men and women, the only significant difference found was in the time-averaged mean velocity for the ulnar digital artery (men:5.66 cm/sec vs. women:9.68 cm/sec, P = 0.02) and volume of flow for the ulnar digital artery (men:10.87cc/min vs. women:18.58cc/min, P = 0.03). We found no differences in blood flow parameters comparing participants with and without diabetes. These data provide a baseline measurement of digital flow hemodynamics that can be used in future studies to model vascular flow after replantation. [ABSTRACT FROM AUTHOR]

Characterization of the physiological hemodynamic environment in normal pulmonary arteries is a key factor in understanding pathological conditions. This study aimed to analyze the morphology and hemodynamics in the healthy adult pulmonary bifurcation in comparison to age-matched repaired Tetralogy of Fallot (rTOF) geometries. The pulmonary trunk of five healthy volunteers was reconstructed from 4D Flow-MRI data and was compared to rTOF results. Subject-specific boundary conditions were assigned in both the inlet and outlets of the models, and flow characteristics were analyzed computationally. The morphological and flow features were consistent among the healthy geometries, highlighting the ability of an averaged geometry derived from this small cohort to capture the main flow characteristics. A slightly higher mean time-averaged wall shear stress (TAWSS) was found in the right pulmonary artery, which was also the branch with a higher mean curvature and local Reynolds number. Compared to rTOF results, the averaged healthy geometry demonstrated more than an 8-fold lower value in TAWSS, with the individual patient-specific healthy volunteers showing further reduced TAWSS than the rTOF patients. These observations could be useful in clinical assessment and decision making based on hemodynamic indices. [ABSTRACT FROM AUTHOR]

We present a technique called photoacoustic vector-flow (PAVF) to quantify the speed and direction of flowing optical absorbers at each pixel from acoustic-resolution PA images. By varying the receiving angle at each pixel in post-processing, we obtain multiple estimates of the phase difference between consecutive frames. These are used to solve the overdetermined photoacoustic Doppler equation with a least-squares approach to estimate a velocity vector at each pixel. This technique is tested in bench-top experiments and compared to simultaneous pulse-echo ultrasound vector-flow (USVF) on whole rat blood at speeds on the order of 1 mm/s. Unlike USVF, PAVF can detect flow without stationary clutter filtering in this experiment, although the velocity estimates are highly underestimated. When applying spatio-temporal singular value decomposition clutter filtering, the flow speed can be accurately estimated with an error of 16.8% for USVF and −8.9% for PAVF for an average flow speed of 2.5 mm/s.

The endovascular neural interface provides an appealing minimally invasive alternative to invasive brain electrodes for recording and stimulation. However, stents placed in blood vessels have long been known to affect blood flow (haemodynamics) and lead to neointimal growth within the blood vessel. Both the stent elements (struts and electrodes) and blood vessel wall geometries can affect the mechanical environment on the blood vessel wall, which could lead to unfavourable vascular remodelling after stent placement. With increasing applications of stents and stent-like neural interfaces in venous blood vessels in the brain, it is necessary to understand how stents affect blood flow and tissue growth in veins. We explored the haemodynamics of a stent-mounted neural interface in a blood vessel model. Results indicated that blood vessel deformation and tapering caused a substantial change to the lumen geometry and the haemodynamics. The neointimal proliferation was evaluated in sheep implanted with an endovascular neural interface. Analysis showed a negative correlation with the mean Wall Shear Stress pattern. The results presented here indicate that the optimal stent oversizing ratio must be considered to minimise the haemodynamic impact of stenting. [ABSTRACT FROM AUTHOR]