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The brachiopods are sessile invertebrates with an unusual blood system, which consists of a long‐branched dorsal vessel. It is still unknown how blood circulates in this system. In the present study, for the first time we propose the circulation of blood in brachiopod Hemithiris psittacea based on morphological and experimental data. The main heart is located on the dorsal side of the stomach and divides the dorsal vessel into anterior and posterior parts. The anterior part enters the lophophore, where it gives off blind branches to each tentacle. The posterior part passes by the funnels of the nephridia and forms a blindly closed network in the gonads. We suggest that the circulation of blood includes three successive stages. During the first phase of systole of the main heart, blood flows through the anterior dorsal vessel. During the second phase of systole, blood flows through the posterior dorsal vessel. During diastole, blood flows from the anterior and posterior vessels and fills the main heart. The origin of a peculiar blood system in brachiopods can be explained by reduction of the ventral vessel, which is probably correlates with the reduction of the ventral side of the brachiopod ancestor's body. Another peculiarity of brachiopod blood system is the presence of an ampullar heart, which functions as a blood depot and allows blood to move in the vessels in two directions in an oscillatory mode. The brachiopod blood system contains vessels lacking true endothelium and can be classified as an "incompletely closed" type. Research Highlights: The blood system of brachiopods contains a dorsal vessel divided into anterior and posterior parts. Circulation includes three stages: during the first phase of systole, blood flows in the anterior vessel, during the second phase of systole, blood flows in the posterior vessel, and during diastole, blood flows from the anterior and posterior vessels and fills the main heart. [ABSTRACT FROM AUTHOR]

Distinguishing arteries from veins in the cerebral cortex is critical for studying hemodynamics under pathophysiological conditions, which plays an important role in the diagnosis and treatment of various vessel‐related diseases. However, due to the complexity of the cerebral vascular network, it is challenging to identify arteries and veins in vivo. Here, we demonstrate an artery–vein separation method that employs a combination of multiple scanning modes of two‐photon microscopy and a custom‐designed stereoscopic fixation device for mice. In this process, we propose a novel method for determining the line scanning direction, which allows us to determine the blood flow directions. The vasculature branches have been identified using an optimized z‐stack scanning mode, followed by the separation of blood vessel types according to the directions of blood flow and branching patterns. Using this strategy, the penetrating arterioles and penetrating venules in awake mice could be accurately identified and the type of cerebral thrombus has been also successfully isolated without any empirical knowledge or algorithms. Our research presents a new, more accurate, and efficient method for cortical artery–vein separation in awake mice, providing a useful strategy for the application of two‐photon microscopy in the study of cerebrovascular pathophysiology. [ABSTRACT FROM AUTHOR]

The dialysis catheter indwelling in human bodies has a high risk of inducing thrombus and stenosis. Biomechanical research showed that such physiological complications are triggered by the wall shear stress of the vascular vessel. This study aimed to assess the impact of CVC implantation on central venous haemodynamics and the potential alterations in the haemodynamic environment related to thrombus development. The SVC structure was built from the images from computed tomography. The blood flow was calculated using the Carreau model, and the fluid domain was determined by CFD. The vascular wall and the CVC were computed using FEA. The elastic interaction between the vessel wall and the flow field was considered using FSI simulation. With consideration of the effect of coupling, it was shown that the catheter vibrated in the vascular systems due to the periodic variation of blood pressure, with an amplitude of up to 10% of the vessel width. Spiral flow was observed along the catheter after CVC indwelling, and recirculation flow appeared near the catheter tip. High OSI and WSS regions occurred at the catheter tip and the vascular junction. The arterial lumen tip had a larger effect on the WSS and OSI values on the vascular wall. Considering FSI simulation, the movement of the catheter inside the blood flow was simulated in the deformable vessel. After CVC indwelling, spiral flow and recirculation flow were observed near the regions with high WSS and OSI values. [ABSTRACT FROM AUTHOR]

The deformability of blood vessels in one‐dimensional blood flow models is typically described through a pressure‐area relation, known as the tube law. The most used tube laws take into account the elastic and viscous components of the tension of the vessel wall. Accurately parametrizing the tube laws is vital for replicating pressure and flow wave propagation phenomena. Here, we present a novel mathematical‐property‐preserving approach for the estimation of the parameters of the elastic and viscoelastic tube laws. Our goal was to estimate the parameters by using ovine and human in vitro data, while constraining them to meet prescribed mathematical properties. Results show that both elastic and viscoelastic tube laws accurately describe experimental pressure‐area data concerning both quantitative and qualitative aspects. Additionally, the viscoelastic tube law can provide a qualitative explanation for the observed hysteresis cycles. The two models were evaluated using two approaches: (i) allowing all parameters to freely vary within their respective ranges and (ii) fixing some of the parameters. The former approach was found to be the most suitable for reproducing pressure‐area curves. [ABSTRACT FROM AUTHOR]

Objectives: Intrapulpal calcifications can occur in the dental pulp of patients with diabetes. We focused on the association between ectopic calcifications in the dental pulp and advanced glycation end products (AGEs) in Spontaneously Diabetic Torii (SDT)‐fatty rats, an obese type 2 diabetic rat model, to determine the mechanism of calcification with pulp stone in the dental pulp. Materials and Methods: Pathologic calcification in the dental pulp of SDT‐fatty rats was observed using electron microscopy and immunohistochemical analysis. Moreover, mechanical analysis of periapical region of molar tooth against occlusal force was performed. Results: In SDT‐fatty rats, pathogenic pulpal calcifications occurred during blood glucose elevation after 6 weeks, and granular calcification was observed in the dental pulp after 11 weeks. Pentosidine, a major AGE, and the receptor for AGEs were strongly expressed in the dental pulp of SDT‐fatty rats. S100A8, TNF‐α, and IL‐6 also showed positive response in the dental pulp of the SDT‐fatty rat, which indicated pulpal inflammation. Blood flow disorder and hypoxic dental pulp cells were also observed. In silico simulation, strain from occlusal force concentrates on the root apex. Conclusions: Glycation makes blood vessels fragile, and occlusal forces damage the vessels mechanically. These are factors for intrapulpal calcification of diabetes. [ABSTRACT FROM AUTHOR]

The reconstruction of blood velocity in a vessel from contrast enhanced x‐ray computed tomography projections is a complex inverse problem. It can be formulated as reconstruction problem with a partial differential equation constraint. A solution can be estimated with the a variational adjoint method and proper orthogonal decomposition (POD) basis. In this work, we investigate new inversion approaches based on PODs coupled with deep learning methods. The effectiveness of the reconstruction methods is shown with simulated realistic stationary blood flows in a vessel. The methods outperform the reduced adjoint method and show large speed‐up at the online stage. [ABSTRACT FROM AUTHOR]

Prediction of blood cell flow is known as the difficult research by reason of the complexity of blood vessel. In this study, considering the complex structure of blood vessels, a mechanical model for red blood cell (RBC) based on unstructured grid has been established to study the flow characteristics of RBCs in complex blood vessels. In the model, the strain‐energy function by Skalak is employed to model the shear elasticity and surface‐area conservation of the membrane, and the hinge spring is used to describe the forces originating from local bending of the membrane. The immersed boundary method is utilized to couple the interphase force. Using the model, the stretching test of RBC is compared with the experiment data, and the good agreement verified the validation of the present model. The morphology of red blood cell and the blood viscosity in micro‐vessel are studied. RBCs move with a symmetric shape (parachute shape) in small blood vessels, and the buckling instability is observed when the RBC flow slowly through a micro‐vessel or a converging–diverging capillary. When the vessel diameter is around 10 μm, the reverse Fahraeus‐Lindqvist effect is presented. The blood apparent viscosity shows linear increase with the blood hematocrit. In addition, Malaria infection can make the RBC deformability decreased and the blood apparent viscosity increased. [ABSTRACT FROM AUTHOR]

The article discusses Raynaud's phenomenon, a medical condition characterized by the constriction of small arterial vessels, resulting in reduced blood flow to the extremities. The condition is often triggered by exposure to cold or stressful conditions and primarily affects acral areas such as fingers and toes. The symptoms include numbness, tingling, discoloration, and, in severe cases, gangrene. Despite advancements in understanding the condition, there is still no effective treatment. The article also mentions recent research on vasomotion and the regulation of blood vessel tone in various vascular beds. Additionally, it highlights a genetic predisposition to Raynaud's phenomenon and proposes individual shear rate therapy as a potential non-invasive treatment option. The authors emphasize the need for further research and improved treatment options for patients with Raynaud's phenomenon. [Extracted from the article]

New Findings: What is the central question of this study?High‐intensity interval exercise (HIIE) is recommended for its favourable haemodynamic stimulation, but excessive haemodynamic fluctuations may stress the brain: is the cerebral vasculature protected against exaggerated systemic blood flow fluctuation during HIIE?What is the main finding and its importance?Time‐ and frequency‐domain indices of aortic–cerebral pulsatile transition were lowered during HIIE. The findings suggest that the arterial system to the cerebral vasculature may attenuate pulsatile transition during HIIE as a defence mechanism against pulsatile fluctuation for the cerebral vasculature. High‐intensity interval exercise (HIIE) is recommended because it provides favourable haemodynamic stimulation, but excessive haemodynamic fluctuations may be an adverse impact on the brain. We tested whether the cerebral vasculature is protected against systemic blood flow fluctuation during HIIE. Fourteen healthy men (age 24 ± 2 years) underwent four 4‐min exercises at 80–90% of maximal workload (Wmax) interspaced by 3‐min active rest at 50–60% Wmax. Transcranial Doppler measured middle cerebral artery blood velocity (CBV). Systemic haemodynamics (Modelflow) and aortic pressure (AoP, general transfer function) were estimated from an invasively recorded brachial arterial pressure waveform. Using transfer function analysis, gain and phase between AoP and CBV (0.39–10.0 Hz) were calculated. Stroke volume, aortic pulse pressure and pulsatile CBV increased during exercise (time effect: P < 0.0001 for all), but a time‐domain index of aortic–cerebral pulsatile transition (pulsatile CBV/pulsatile AoP) decreased throughout the exercise bouts (time effect: P < 0.0001). Furthermore, transfer function gain reduced, and phase increased throughout the exercise bouts (time effect: P < 0.0001 for both), suggesting the attenuation and delay of pulsatile transition. The cerebral vascular conductance index (mean CBV/mean arterial pressure; time effect: P = 0.296), an inverse index of cerebral vascular tone, did not change even though systemic vascular conductance increased during exercise (time effect: P < 0.0001). The arterial system to the cerebral vasculature may attenuate pulsatile transition during HIIE as a defence mechanism against pulsatile fluctuation for the cerebral vasculature. [ABSTRACT FROM AUTHOR]

Introduction: We aimed to describe physiological changes in endometrial blood flow (minute arterioles running through the endometrium) from ovulation to the mid‐luteal phase using superb microvascular imaging. Material and methods: The study involved 17 women (median age, 32.5 years; first to third interquartile range, 29.8–40.0 years) with regular menstrual cycles who were managed in our institute from 2020 to 2021. The uterus was delineated at the sagittal section using transvaginal ultrasonography incorporated with superb microvascular imaging. For each participant, a total of 28 cycles were observed; 17 cycles observed within one day of ovulation and the implantation period, 5–7 days (D5–7) after ovulation in the same cycle, and nine cycles in which only ovulation was observed, and two cycles in which only D5–7 was observed. Therefore, 26 and 19 images at ovulation and D5–7, respectively, were acquired. Endometrial blood flow was evaluated by depth of the vascular signal in the endometrium and categorized as follows: signals only in the basal layer of the endometrium (grade 1), reaching up to half the endometrium (grade 2), and covering the whole endometrium (grade 3). Changes in the grade of endometrial blood flow from ovulation to D5–7 after ovulation, and the relationship between the grade of endometrial blood flow and the endometrial thickness on ovulation and D5–7 after ovulation, were analyzed. Statistical significance was set at p < 0.05. Results: The endometrial blood flow from ovulation to D5–7 after ovulation during the same menstrual period showed a downgrade in 14 of 17 cycles (82.3%) and no change in the remaining three cycles (17.6%), indicating a decrease in the endometrial blood flow from ovulation to D5–7 after ovulation (p = 0.001). There were differences between the grade of endometrial blood flow and median endometrial thickness on ovulation (grade 1: 5.9 mm, grade 2: 9.1 mm, and grade 3: 11.2 mm); however, no differences in the endometrial thickness were found between the grades on D5–7 after ovulation. Conclusions: In the normal menstrual cycle, endometrial blood flow decreased from ovulation to the mid‐luteal phase, and the endometrial thickness in the ovulatory phase was related to the endometrial perfusion. [ABSTRACT FROM AUTHOR]

Networks of neurons are the primary substrate of information processing. Conversely, blood vessels in the brain are generally viewed to have physiological functions unrelated to information processing, such as the timely supply of oxygen, and other nutrients to the neural tissue. However, recent studies have shown that cerebral microvessels, like neurons, exhibit tuned responses to sensory stimuli. Tuned neural responses to sensory stimuli may be enhanced with experience‐dependent Hebbian plasticity and other forms of learning. Hence, it is possible that the microvascular network might also be subject to some form of competitive learning rules during early postnatal development such that its fine‐scale structure becomes optimized for metabolic delivery to a given neural micro‐architecture. To explore the possibility of adaptive lateral interactions and tuned responses in cerebral microvessels, we modelled the cortical neurovascular network by interconnecting two laterally connected self‐organizing networks. The afferent and lateral connections of the neural and vascular networks were defined by trainable weights. By varying the topology of lateral connectivity in the vascular network layer, we observed that the partial correspondence of feature selectivity between neural and hemodynamic responses could be explained by lateral coupling across local blood vessels such that the central domain receives an excitatory drive of more blood flow and a distal surrounding region where blood flow is reduced. Critically, our simulations suggest a new role for feedback from the vascular to the neural network because the radius of vascular perfusion determines whether the cortical neural map develops into a clustered vs. salt‐and‐pepper organization. [ABSTRACT FROM AUTHOR]

Cardiovascular disease (CVD) can progressively narrow arteries due to plaque accumulation on the inner walls of the blood vessels, which results in an obstructed blood flow, leading to heart attack, stroke, and even death if the obstruction is severe. A popular treatment for the disease is to use an intravascular mechanical device called the stent to achieve an immediate restoration of blood flow. However, the physical stimulation induced by the stent expansion can cause inflammation of the vessel tissue. As one of the most common post‐stenting complications, re‐narrowing of the vessel is the main pathology that leads to in‐stent restenosis (ISR), induced by the excess growth of the tissue over the deployed stent. The ISR is widely recognized as a significant cause of death globally if early symptoms are not detected. Hence, monitoring and early diagnosis indeed matter when it comes to treatment. The latest technologies for monitoring and treatments of ISR were reviewed in this work, and the potential issues and suggestions related to the reported technologies were presented. The target of this review aims to positively prompt researchers to develop an advanced stent system in terms of its electromechanical performance, size, functional feature, feasibility, and reliability. [ABSTRACT FROM AUTHOR]

In recent years, targeted drug delivery systems have been regarded as a promising solution to enhance the efficiency of treatments against clots in blood vessels. In this context, shear‐activated nanotherapeutics (SANTs) have been recently proposed. These are micrometric clusters of polymeric nanoparticles coated with a clot lysing agent. These drug carriers are stable under normal blood flow conditions, but they can be designed to undergo breakup right on the clot in response to the local increase in the hydrodynamic stress caused by the lumen restriction, effectively concentrating the active agent at the point of need. The aim of this work is to investigate the mechanical response of three potential drug carrier morphologies to the pathological flow field stress, typically encountered in obstructed blood vessels. Computational fluid dynamics simulations have been used to compare the viscous stress in arterial obstructions with the one in a microfluidic device, suitable for in vitro experimental tests. Discrete element method simulations built upon Stokesian dynamics were conducted to estimate the tensile stress distribution acting inside isostatic, random close packing, and hollow drug carriers. The results herein presented constitute a platform for a future experimental campaign and aim at establishing SANTs as a robust and broadly applicable targeting strategy. [ABSTRACT FROM AUTHOR]

Low‐flow vascular malformations are rare congenital anomalies due to errors in vascular development and may be associated with known pathogenic genetic variants. Slow flow through the blood vessels can lead to localized intralesional thromboses, which can cause debilitating pain and impair quality of life. We present a case of venous malformation due to a variant in the TEK gene in a 38‐year‐old woman in whom treatment with low dose rivaroxaban was successful in controlling symptoms of chronic localized intravascular coagulation. [ABSTRACT FROM AUTHOR]

Summary: The mechanism of many cardiovascular diseases can be understood by studying the pressure distribution in blood vessels. Direct pressure measurements, however, require invasive probing and provide only single‐point data. Alternatively, relative pressure fields can be reconstructed from imaging‐based velocity measurements by considering viscous and inertial forces. Both contributions can be potential troublemakers in pressure reconstruction: the former due to its higher‐order derivatives, and the latter because of the quadratic nonlinearity in the convective acceleration. Viscous and convective terms can be treated in various forms, which, although equivalent for ideal measurements, can perform differently in practice. In fact, multiple versions are often used in literature, with no apparent consensus on the more suitable variants. In this context, the present work investigates the performance of different versions of relative pressure estimators. For viscous effects, in particular, two new modified estimators are presented to circumvent second‐order differentiation without requiring surface integrals. In‐silico and in‐vitro data in the typical regime of cerebrovascular flows are considered, allowing a systematic noise sensitivity study. Convective terms are shown to be the main source of error, even for flows with pronounced viscous component. Moreover, the conservation (often integrated) form of convection exhibits higher noise sensitivity than the standard convective description, in all three families of estimators considered here. For the classical pressure Poisson estimator, the present modified version of the viscous term tends to yield better accuracy than the (recently introduced) integrated form, although this effect is in most cases negligible when compared to convection‐related errors. [ABSTRACT FROM AUTHOR]

Transcatheter arterial embolization (TAE) is wildly used in clinical treatments. However, the online monitoring of the thrombosis formation is limited due to the challenges of the direct visualization of embolic agents and the real‐time monitoring of dynamic blood flow. Thus, we developed a photochemical afterglow implant with strong afterglow intensity and a long lifetime for embolization and imaging. The liquid pre‐implant injected into the abdominal aorta of mice was rapidly transformed into a hydrogel in situ to embolize the blood vessel. The vascular embolism position can be observed by the enhanced afterglow of the fixed implant, and the long lifetime of afterglow can also be used to monitor the effect of embolization. This provides an excellent candidate in bio‐imaging to avoid the autofluorescence interference from continuous light excitation. The study suggests the potential usefulness of the implant as an embolic agent in TAE and artery imaging during a surgical procedure. [ABSTRACT FROM AUTHOR]

In this mini‐review, the main differences between spherical and spheroidal particles in terms of their size, surface area, morphology, and ability to penetrate biological membranes are described. The main routes of manufacturing of prolate spheroidal particles with controlled aspect ratio are reported. There are also shown exemplary results of computational and experimental studies of spheroids useful in biomedical applications, such as controlled drug delivery and numerical studies of the passage of spheroids through biological membranes. The relations of shape, size, aspect ratio of spheroidal particles and particle–biological membrane interactions, bioavailability, and flow in blood vessels are presented. The perspectives for future studies leading to resolve crucial problems and to explain basic issues related to acting of ellipsoidal particles in biological environment are also discussed. [ABSTRACT FROM AUTHOR]

In aortic dissections blood flows not only in the regular, true lumen but also between separated lamellae within the media of the aortic wall, in the so‐called false lumen. Both lumina are separated by a dissection membrane, which may move substantially during the cardiac cycle, linking blood flow and vessel deformation. We employ strongly coupled fluid‐structure interaction simulations incorporating an anisotropic, fiber‐reinforced, hyperelastic continuum including layer‐specific tissue parameters. [ABSTRACT FROM AUTHOR]

Purpose: To analyse retinal neurovascular coupling (NVC) in a plexus‐specific manner at baseline and during flicker light stimulation using optical coherence tomography angiography (OCTA) and to thereby use the retina as a model for non‐invasive microvascular assessment of NVC in humans. Methods: 22 healthy subjects were included in the study. Macular 10°x10° volume scans were acquired at baseline and during flicker light stimulation using the Spectralis OCTA module (Heidelberg Engineering, Heidelberg, Germany). Vessel densities (VDs) in the superficial (SCP), intermediate (ICP) and deep capillary plexus (DCP) as well as in the full retina (FR) were assessed after thresholding the respective slabs by mean values. Large vessels and resulting projection artefacts were removed using a threshold‐based approach. Capillary representation was optimized using a "Frangi filter". Volumetric blood flow and vessel diameters were measured using a Doppler‐OCT prototype. Results: Flicker light stimulation induced a significant FR VD increase from 39.7 ± 1.7 to 41.2 ± 1.6% (+3.8 ± 2.7%; p < 0.001). Upon separate analysis of the three retinal plexus, VD significantly increased by +9.9 ± 6.7% in SCP, by ±6.6 ± 1.7% in ICP and by +4.9 ± 2.3% in DCP (p<0.001 for all three). This increase was significantly higher in SCP than in ICP (p = 0.02) and DCP (p = 0.002). Arterial diameters increased by +3.7 ± 3.1% (p < 0.001), venous diameters rose by +4.5 ± 3.0% (p<0.001). Volumetric blood flow increased by +39.9±34.9% (p<0.001) in arteries and by +29.8 ± 16.8% (p < 0.001) in veins. Conclusions: In summary, a robust increase of retinal VD which was most pronounced in SCP could be observed upon flicker light stimulation. These data propose a plexus‐specific mechanism, to precisely meet the metabolic needs of retinal cells. The location of SCP in the inner retinal layers, where increase of metabolic demands is suggested to be greatest during flicker light stimulation, could be explanatory for the locally bigger response. [ABSTRACT FROM AUTHOR]