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The current study is centered on the application of magnetically targeted drug delivery in a constricted vertical bifurcated artery utilizing Fe 3 O 4 nanoparticles. The arterial stenosis is characterized by a bell-shaped narrowing in the parent artery and overlapping narrowing in the daughter artery. The blood is regarded as exhibiting the rheological behavior of a Casson fluid. The temperature-dependent nature of blood viscosity is postulated, and Reynold's viscosity model describes it. This study examines the impact of electromagnetohydrodynamics (EMHD), body acceleration, Joule heating, and viscous dissipation. The assumption of a no-slip velocity condition is made at the walls of the artery. The governing equations are subjected to a process of non-dimensionalization and simplification, employing the mild-stenosis approximation. The resulting equations are subsequently solved in MATLAB by employing the finite-difference Crank–Nicolson technique. Entropy plays a significant role during any treatment or surgery; therefore, the present problem addresses entropy generation minimization. The results for velocity, temperature, wall shear stress, flow rate, impedance, heat transfer rate, entropy generation number, and Bejan number are represented graphically. The velocity contours illustrate that the flow velocity enhances with the Casson fluid and particle mass parameters. Furthermore, the number of trapped bolus also increases in the daughter artery. The nanofluid velocity and particle velocity decrease with an increase in the particle concentration parameter in the parent artery and the daughter artery. Entropy declines with the temperature difference parameter increment, whereas the Bejan number enhances. Magnetite (Fe 3 O 4) nanoparticles have various applications owing to their biocompatibility, elevated magnetic susceptibility, chemical stability, non-toxic nature, and cost-effectiveness. [ABSTRACT FROM AUTHOR]

Directional fluid flow in perivascular spaces surrounding cerebral arteries is hypothesized to play a key role in brain solute transport and clearance. While various drivers for a pulsatile flow, such as cardiac or respiratory pulsations, are well quantified, the question remains as to which mechanisms could induce a directional flow within physiological regimes. To address this question, we develop theoretical and numerical reduced-order models to quantify the directional (net) flow induceable by peristaltic pumping in periarterial networks. Each periarterial element is modeled as a slender annular space bounded internally by a circular tube supporting a periodic traveling (peristaltic) wave. Under reasonable assumptions of a small Reynolds number flow, small radii, and small-amplitude peristaltic waves, we use lubrication theory and regular perturbation methods to derive theoretical expressions for the directional net flow and pressure distribution in the perivascular network. The reduced model is used to derive closed-form analytical expressions for the net flow for simple network configurations of interest, including single elements, two elements in tandem, and a three element bifurcation, with results compared with numerical predictions. In particular, we provide a computable theoretical estimate of the net flow induced by peristaltic motion in perivascular networks as a function of physiological parameters, notably, wave length, frequency, amplitude, and perivascular dimensions. Quantifying the maximal net flow for specific physiological regimes, we find that vasomotion may induce net pial periarterial flow velocities on the order of a few to tens of μ m/s and that sleep-related changes in vasomotion pulsatility may drive a threefold flow increase. [ABSTRACT FROM AUTHOR]

In the present study, a Caputo–Fabrizio (C–F) time-fractional derivative is introduced to the governing equations to present the flow of blood and the transport of magnetic nanoparticles (MNPs) through an inclined porous artery with mild stenosis. The rheology of blood is defined by the non-Newtonian visco-elastic Jeffrey fluid. The transport of MNPs is used as a drug delivery application for cardiovascular disorder therapy. The momentum and transport equations are solved analytically by using the Laplace transform and the finite Hankel transform along with their inverses, and the solutions are presented in the form of Laplace convolutions. To display the solutions graphically, the Laplace convolutions are solved using the numerical integration technique. The study presents the impacts of different governing parameters on blood and MNP velocities, volumetric flow rate, flow resistance, and skin friction. The study demonstrates that blood and MNP velocities boost with an increase in the fractional order parameter, Darcy number, and Jeffrey fluid parameter. The volumetric flow rate decreases and flow resistance increases with enhancement in stenosis height. The non-symmetric shape of stenosis and the rheology of blood decrease skin friction, whereas enhancement in MNP concentration increases skin friction. A comparison of the present result with the previous work shows excellent agreement. The present study will be beneficial for the field of medical science to further study atherosclerosis therapy and other similar disorders. [ABSTRACT FROM AUTHOR]

The stenosis builds up and its progression in the artery causes serious damages, which may lead to death. This research aims to investigate the non-Newtonian properties of the pulsatile blood flow through the multi-stenotic inclined artery. The effect of external body acceleration is considered, and blood is taken as Rabinowitsch fluid in this work. The mathematical model representing the proposed problem is transformed into a dimensionless form by applying the assumption for mild stenosis. The dimensionless mathematical equations are solved using the perturbation method. The solutions of mathematical equations are investigated graphically to analyze the impacts of various physical constraints. We find that strong non-Newtonian effects lead to an increase in flow velocity and wall shear stress. The stenosis's presence and progression in the artery reduces the flow velocity. The stenotic artery (diseased artery) is found to have less flow rate than the healthy artery. It is noted that the vertically held conduit effectively has a larger flow velocity and wall shear stress than the horizontal one. External body acceleration is noted to have an impact that raises velocity and wall shear stress. [ABSTRACT FROM AUTHOR]

Purpose: Non‐contrast‐enhanced time of flight (TOF) is a standard method for magnetic resonance angiography used to depict vessel morphology. TOF is commonly performed with a 3D steady‐state acquisition, employing a short repetition time to support high resolution imaging. At 7 T, TOF exhibits substantial increase in SNR and contrast, improving its clinical value. However, one of the remaining challenges, exacerbated at 7 T, is the presence of artifacts due to pulsatile blood flow, especially near major blood vessels. In this study we examine a method to significantly reduce these artifacts. Methods: We recently introduced a new "local‐scrambling" approach that semi‐randomizes the acquisition order of the phase encodes, to achieve a controllable cutoff frequency above which the artifacts are drastically reduced. With this approach, artifacts resulting from fast local fluctuations such as cardiac pulsation are significantly reduced. In this study, we explore the ability of this local‐scrambling approach to reduce pulsatile blood flow artifacts in a 3D TOF acquisition. Cartesian line‐by‐line and center‐out ordering, with and without local‐scrambling, were compared in simulations and in human brain imaging at 3 and 7 T scanners. Results: In the simulations the artifact intensity showed a 10‐fold reduction using local‐scrambling compared to line‐by‐line and 4‐fold compared to center‐out ordering. In vivo results show that artifacts are much more pronounced at 7 T compared to 3 T, and in both cases they are effectively reduced by local‐scrambling. Conclusion: Local‐scrambling improves image quality for both line‐by‐line and center‐out ordering. This approach can easily be implemented in the scanner without any changes to the reconstruction. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive hemodynamic evaluation of two endovascular techniques for treating cerebral aneurysms. Using the finite volume method, we simulated pulsatile blood flow and heat transport dynamics in two saccular aneurysms of varying sizes and shapes. We assessed hemodynamic factors under two coiling conditions with different porosities and deformation stages to identify the most effective treatment for each case. Our computational analysis reveals that stent and coiling applications are more efficient for aneurysms with low-sac volume. Notably, stent placement proves to be more effective than coiling in treating saccular aneurysms. Our findings indicate that stent-induced deformation sufficiently diverts the main blood flow, thereby reducing the risk of aneurysm rupture near the ostium region. [ABSTRACT FROM AUTHOR]

Background Methods Results Conclusion This study evaluated the hemodynamic performance of arterial and venous cannulae in a compliant pediatric extracorporeal membrane oxygenation (ECMO) mock circuit in pulsatile and non‐pulsatile flow conditions.The ECMO setup consisted of an oxygenator, diagonal pump, and standardized‐length arterial/venous tubing with pressure transducers. A validated left‐heart mock loop was adapted to simulate pediatric conditions. The pulsatile flow was driven by a computer‐controlled piston pump set at 120 bpm. A roller pump was used for non‐pulsatile conditions. The circuit was primed with 40% glycerol‐based solution. The cardiac output was set to 1 L/min and the aortic pressure to 40–50 mmHg. Four arterial cannulae (8Fr, 10Fr, 12Fr, 14Fr) and five venous cannulae (12Fr, 14Fr, 16Fr, 18Fr, 20Fr) (Medtronic, Inc., Minneapolis, MN, USA) were tested at increasing flow rate in 12 combinations.The pulsatile condition required lower ECMO pump speeds for all cannulae combinations at a given flow rate, inducing a significantly smaller increase of flow in the mock loop. Under non‐pulsatile conditions, the aortic and arterial pressures in the cannulae were higher (p < 0.01) while no significant differences in pressure drop and pressure‐flow characteristics (M‐number) were observed. The total hemodynamic energy was higher in case of non‐pulsatile flow (p < 0.01).Under non‐pulsatile conditions, the system was characterized by overall higher pressures, resulting in higher support to the patient. The consequent increase of potential energy compensates for increases of kinetic energy, leading to a higher total hemodynamic energy. Pressure gradients and M number are independent of the testing conditions. Pulsatile testing conditions led to more physiological testing conditions, and it is recommended for ECMO testing. [ABSTRACT FROM AUTHOR]

The article explores the impact of deformable surfaces on oscillatory flow in a cylindrical tube, revealing complex secondary time-averaged flows. By analyzing the interaction under a long-wave theory, the research uncovers the exponential decay of oscillatory pressure along the length of a deformable channel, influenced by material properties and flow frequency. The study quantifies time-averaged secondary flow and highlights the interplay between fluid inertia and elastic deformations, offering valuable insights into fluid-structure interactions in diverse systems like cardiovascular physiology and microfluidic device design. [Extracted from the article]

Accurately identifying the onset of transitional and turbulent flow within any pipe flow environment is of great interest. Most often, the critical Reynolds number (Re) is used to pinpoint the onset of turbulence. However, the critical Re is known to be highly variable, depending on the specifics of the flow system. Thus, for flows (e.g., blood flows), where only one realization (i.e., one mean Re) exists, the presence of transitional and turbulent flow behaviors cannot be accurately determined. In this work, we aim to address this by evaluating the extent to which instantaneous time-frequency (TF)-based analysis of the fluctuating velocity field can be used to evaluate the onset of transitional and turbulent flow regimes. Because current TF analysis methods are not suitable for this, we propose a novel "wavelet-Hilbert time-frequency" (WHTF) method, which we validate herein. Using the WHTF method, we analyzed the instantaneous dominant frequency of three planar particle image velocimetry-captured pipe flows, which included one steady and two pulsatile with Womersley numbers of 4 and 12. For each case, data were captured at Re's spanning 800–4500. The instantaneous dominant frequency analysis of these flows revealed that the magnitude, size, and coherence of two-dimensional spatial frequency structures were uniquely different across flow regimes. Specifically, the transitional regime maintained the most coherent, but lowest magnitude frequency structures, while the laminar regime had the highest magnitude, lowest coherence, and smallest frequency structures. Overall, this study demonstrates the efficacy of TF-based metrics for characterizing the progression of transition and turbulent flow development. [ABSTRACT FROM AUTHOR]

This study employs extensive three-dimensional direct numerical simulations to investigate the hemodynamics around a bileaflet mechanical heart valve. In particular, this study focuses on assessing whether non-Newtonian rheological behaviors of blood, such as shear-thinning and yield stress behaviors, exert an influence on hemodynamics compared to the simplistic Newtonian behavior under both steady inflow and physiologically realistic pulsatile flow conditions. Under steady inflow conditions, the study reveals that blood rheology impacts velocity and pressure field variations, as well as the values of clinically important surface and time-averaged parameters like wall shear stress (WSS) and pressure recovery. Notably, this influence is most pronounced at low Reynolds numbers, gradually diminishing as the Reynolds number increases. For instance, surface-averaged WSS values obtained with the non-Newtonian shear-thinning power-law model exceed those obtained with the Newtonian model. At R e = 750 , this difference reaches around 67%, reducing to less than 1% at R e = 5000. Correspondingly, pressure recovery downstream of the valve leaflets is lower for the shear-thinning blood than the constant viscosity one, with the difference decreasing as the Reynolds number increases. On the other hand, in pulsatile flow conditions, jets formed between the leaflets and the valve housing wall are shorter than steady inflow conditions. Additionally, surface-averaged wall shear stress and blood damage (BD) parameter values are higher (with differences more than 13% and 47%, respectively) during the peak stage of the cardiac cycle, especially for blood exhibiting non-Newtonian yield stress characteristics compared to the shear-thinning or constant viscosity characteristics. Therefore, blood non-Newtonian behaviors, including shear-thinning and yield stress behaviors, exert a considerable influence on the hemodynamics around a mechanical heart valve. All in all, the findings of this study demonstrate the importance of considering non-Newtonian blood behaviors when designing blood-contacting medical devices, such as mechanical heart valves, to enhance functionality and performance. [ABSTRACT FROM AUTHOR]

This study explores hydraulic rams, a technology that exploits the effect of water hammer to pump water without the need for external artificial energy. Although first developed in the 18th century, a comprehensive numerical model elucidating the dynamics of each element, including valve manoeuvres, remains absent. Few authors have contributed specific models, often relying on simplistic approaches like rigid water column theory, or the method of characteristics (MOC) for water hammer equations with either instantaneous valve manoeuvre boundary conditions, or depicting the hydraulic ram as a single-node boundary condition. Some use sophisticated computational fluid dyamics (CFD) based models, primarily for optimizing individual components like the waste valve. Addressing this gap, this work introduces a novel comprehensive numerical model detailing full system dynamic – pipes, junctions, and valve behaviour. Analytical validation and experimental verification, using original laboratory-scale data, affirm the model's reliability. This advance improves understanding of hydraulic ram performance and encourages innovative, environmentally sustainable designs. [ABSTRACT FROM AUTHOR]

Heart disease is a leading cause of mortality, with calcific aortic valve disease (CAVD) being the most prevalent subset. Being able to predict this disease in its early stages is important for monitoring patients before they need aortic valve replacement surgery. Thus, this study explored hydrodynamic, mechanical, and hemodynamic differences in healthy and very mildly calcified porcine small intestinal submucosa (PSIS) bioscaffold valves to determine any notable parameters between groups that could, possibly, be used for disease tracking purposes. Three valve groups were tested: raw PSIS as a control and two calcified groups that were seeded with human valvular interstitial and endothelial cells (VICs/VECs) and cultivated in calcifying media. These two calcified groups were cultured in either static or bioreactor-induced oscillatory flow conditions. Hydrodynamic assessments showed metrics were below thresholds associated for even mild calcification. Young's modulus, however, was significantly higher in calcified valves when compared to raw PSIS, indicating the morphological changes to the tissue structure. Fluid–structure interaction (FSI) simulations agreed well with hydrodynamic results and, most notably, showed a significant increase in time-averaged wall shear stress (TAWSS) between raw and calcified groups. We conclude that tracking hemodynamics may be a viable biomarker for early-stage CAVD tracking. [ABSTRACT FROM AUTHOR]

Simple Summary: Doppler ultrasound is a commonly utilised non-invasive blood pressure measurement technique in dogs under general anaesthesia. This prospective clinical study compared the agreement of values obtained by audible return of pulsatile flow using Doppler ultrasound and visual sphygmomanometer needle oscillation with invasive arterial blood pressure in a clinical population of anaesthetised dogs. Visual sphygmomanometer needle oscillation (SNO) can occur before audible return of pulsatile flow (ARPF) when measuring blood pressure by Doppler ultrasound. The aim was to assess the agreement of SNO and ARPF with invasive blood pressure (iABP) in a clinical population of anaesthetised dogs. A total of 35 dogs undergoing surgery in dorsal recumbency necessitating arterial cannulation were included. Paired measurements of iABP and SNO, and iABP and ARPF, were collected. The agreement of non-invasive blood pressure (NIBP) and iABP measurements was analysed with concordance correlation coefficients (CCCs) and Bland–Altman plots. The proportions of SNO and ARPF measurements between 10 and 20 mmHg of iABP were compared. Both SNO and ARPF demonstrated greater agreement with invasive systolic (iSAP) than invasive mean (iMAP) pressures, and SNO demonstrated greater agreement with iSAP than ARPF measurements. The mean differences (95% limits of agreement) for SNO and APRF were −9.7 mmHg (−51.3–31.9) and −13.1 mmHg (−62.2–35.9), respectively. The CCC (95% CI) for SNO was 0.5 (0.36–0.64) and ARPF was 0.4 (0.26–0.54). A significantly greater proportion of SNO measurements were within 20 mmHg of iSAP compared to ARPF. Both NIBP techniques performed more poorly than veterinary consensus recommendations for device validation. Caution should be used clinically when interpreting values obtained by Doppler ultrasound in anaesthetised dogs. [ABSTRACT FROM AUTHOR]

The mechanism behind hemodialysis arteriovenous fistula (AVF) failure remains poorly understood, despite previous efforts to correlate altered hemodynamics with vascular remodeling. We have recently demonstrated that transitional flow induces high-frequency vibrations in the AVF wall, albeit with a simplified model. This study addresses the key limitations of our original fluid–structure interaction (FSI) approach, aiming to evaluate the vibration response using a more realistic model. A 3D AVF geometry was generated from contrast-free MRI and high-fidelity FSI simulations were performed. Patient-specific inflow and pressure were incorporated, and a three-term Mooney–Rivlin model was fitted using experimental data. The viscoelastic effect of perivascular tissue was modeled with Robin boundary conditions. Prescribing pulsatile inflow and pressure resulted in a substantial increase in vein displacement ( + 400 %) and strain ( + 317 %), with a higher maximum spectral frequency becoming visible above -42 dB (from 200 to 500 Hz). Transitioning from Saint Venant–Kirchhoff to Mooney–Rivlin model led to displacement amplitudes exceeding 10 micrometers and had a substantial impact on strain ( + 116 %). Robin boundary conditions significantly damped high-frequency displacement ( - 60 %). Incorporating venous tissue properties increased vibrations by 91%, extending up to 700 Hz, with a maximum strain of 0.158. Notably, our results show localized, high levels of vibration at the inner curvature of the vein, a site known for experiencing pronounced remodeling. Our findings, consistent with experimental and clinical reports of bruits and thrills, underscore the significance of incorporating physiologically plausible modeling approaches to investigate the role of wall vibrations in AVF remodeling and failure. [ABSTRACT FROM AUTHOR]

Hemodynamic analysis reveals a highly significant effect on the prevention, diagnosis, and treatment of human vascular diseases. This article goes deeply into the periodic pulsatile blood flow in the carotid artery with an elastic vessel wall. In view of blood rheological experimental data, the constitutive equation of fractional Maxwell power-law fluid with yield stress, which can describe the four characteristics of yield stress, viscoelasticity, shear thinning, and thixotropy is established. Meanwhile, drawing support from the data of pulsatile flow, the finite Fourier series of pressure gradient with a period of 1 s has been proposed. Leading into Hooke's law can build the fluid-structure coupling boundary condition of blood flow and elastic vessel wall. The numerical solutions are got hold of finite difference method integrated with the newly developed L1-algorithm, and their convergence and stability of which are verified. The axial velocities of blood under different constitutive relationships are compared. The results throw light that other constitutive relationships underestimate the velocity of blood. Furthermore, the flow rate and wall shear stress on different fluid are calculated. It can be concluded that compared with Bingham fluid, the maximum and minimum flow rate/wall shear stress of fractional Maxwell power-law fluid with yield stress increases by 19% and 32%, respectively. The flow rate lags behind the pressure gradient and has time delay effect, on the contrary, the velocity of blood vessel wall is keeping pace with the pressure gradient. The effects of relevant physical parameters on velocity are discussed. In addition, the spatiotemporal distribution of blood flow in cerebral artery and femoral artery are analyzed. HIGHLIGHTS: Fractional Maxwell power-law fluid is proposed to describe hemorheology property. Based on Hooke's law, the boundary condition of elastic wall is established. The finite Fourier series of pulsating pressure gradient has been fitted firstly. Blood flow promoted by the pressure gradient has a hysteresis effect. The velocity of blood vessel wall is keeping pace with the pressure gradient. [ABSTRACT FROM AUTHOR]

Smoking and hypertension are significant risk factors for atherosclerotic carotid artery disease, but also for intracranial aneurysms. The medical results suggest incidental intracranial aneurysms in patients with internal carotid artery (ICA) stenosis arteries. Which led to a study of the comparison between stenosis and aneurysm segments through the artery. A mathematical and numerical model for blood solidification and its rupture in a diseased artery is described in this paper. The interaction between the blood flow and a diseased arterial wall was formulated. The blood flow is formulated as a micropolar incompressible fluid with heat and mass transfer under the control of electro-osmotic and electromagnetic forces through an artery that contains stenosis and aneurysms. The approximation of mild stenosis is used to derive the governing flow equation, which is then solved using a method of finite difference. Particular attention is paid to the impact on axial velocity, flow rate, resistance impedance, and wall shear stress of geometrical parameters of the arterial wall and rheological blood parameters. In the instantaneous pattern of streamlines, the global behavior of blood is also investigated. Finally, the effect of all parameters on the blood flow through artery whose stenosis and aneurysm are investigated as a comparison of both segments. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) simulations are widely used to develop and analyze blood-contacting medical devices such as left ventricular assist devices (LVADs). This work presents an analysis of the transient behavior of two centrifugal LVADs with different designs: HeartWare VAD and HeartMate3. A scale-resolving methodology is followed through Large Eddy Simulations, which allows for the visualization of turbulent structures. The three-dimensional (3D) LVAD models are coupled to a zero-dimensional (0D) 2-element Windkessel model, which accounts for the vascular resistance and compliance of the arterial system downstream of the device. Furthermore, both continuous- and pulsatile-flow operation modes are analyzed. For the pulsatile conditions, the artificial pulse of HeartMate3 is imposed, leading to a larger variation of performance variables in HeartWare VAD than in HeartMate3. Moreover, CFD results of pulsatile-flow simulations are compared to those obtained by accessing the quasi-steady maps of the pumps. The quasi-steady approach is a predictive tool used to provide a preliminary approximation of the pulsatile evolution of flow rate, pressure head, and power, by only imposing a speed pulse and vascular parameters. This preliminary quasi-steady solution can be useful for deciding the characteristics of the pulsatile speed law before running a transient CFD simulation, as the former entails a significant reduction in computational cost in comparison to the latter. [ABSTRACT FROM AUTHOR]

Penn State University is developing a pediatric total artificial heart (TAH) as a bridge-to-transplant device that supports infants and small children with single ventricle anomalies or biventricular heart failure to address high waitlist mortality rates for pediatric patients with severe congenital heart disease (CHD). Two issues with mechanical circulatory support devices are thrombus formation and thromboembolic events. This in vitro study characterizes flow within Penn State's pediatric total artificial heart under physiological operating conditions. Particle image velocimetry (PIV) is used to quantify flow within the pump and to calculate wall shear rates (WSRs) along the internal pump surface to identify potential thrombogenic regions. Results show that the diastolic inflow jets produce sufficient wall shear rates to reduce thrombus deposition potential along the inlet side of the left and right pumps. The inlet jet transitions to rotational flow, which promotes wall washing along the apex of the pumps, prevents flow stasis, and aligns flow with the outlet valve prior to systolic ejection. However, inconsistent high wall shear rates near the pump apex cause increased thrombogenic potential. Strong systolic outflow jets produce high wall shear rates near the outlet valve to reduce thrombus deposition risk. The right pump, which has a modified outlet port angle to improve anatomical fit, produces lower wall shear rates and higher thrombus susceptibility potential (TSP) compared to the left pump. In summary, this study provides a fluid dynamic understanding of a new pediatric total artificial heart and indicates thrombus susceptibility is primarily confined to the apex, consistent with similar pulsatile heart pumps. [ABSTRACT FROM AUTHOR]

In this paper, we consider a one-dimensional model of blood flow along the compliant arteries. With the help of the invariant function, we construct and classify the optimal system of subalgebras. Next, we reduced the given system of partial differential equations (PDEs) to the system of ordinary differential equations (ODEs) for each subalgebra and subsequently solved them exactly. Further, we investigate the evolutionary behavior of the average blood flow velocity and the cross-sectional area of the arteries; under the influence of the physical parameter α graphically. Furthermore, we construct nonlocally related PDEs for the given system of PDEs, consisting of inverse potential systems (IPS) and potential systems. Finally, we classify the nonlocal symmetries arising from the potential system and IPS. [ABSTRACT FROM AUTHOR]

Murray’s law, as the best-known optimal relationship between bifurcation calibers, is obtained based on the assumption of steady-state Poiseuille blood flow and is mostly accurate in small vessels. In middle sized and large vessels such as the aorta and coronary arteries, the pulsatile nature of the flow is dominant and deviations from Murray law have been observed. In the present study, a general scaling law is proposed, which describes the optimum relationship between the characteristics of bifurcations and pulsatile flow. This scaling law takes into account the deviations from Murray law in large vessels, and proposes optimal flow (i.e. less flow resistance) for the full range of the vascular system, from the small vessels to large ones such aorta. As a general scaling law, it covers both symmetrical and asymmetrical bifurcations. One of the merits of this scaling law is that bifurcation characteristics solely depend on the Womersley number of parent vessels. The diameter ratios suggested by this scaling law are in acceptable agreement with available clinical morphometric data such as those reported for coronary arteries and aortoiliac bifurcations. A numerical simulation of pulsatile flow for several Womersley numbers in bifurcation models according to the proposed scaling law and Murray law has been performed, which suggests that the general scaling law provides less flow resistance and more efficiency than Murray law in pulsatile flow. [ABSTRACT FROM AUTHOR]

Background Coarctation of the aorta (CoA) is a common congenital heart defect that affects about 3–4 in every 10 000 live births. Despite clear signs on clinical examination, the diagnosis is sometimes not made until adulthood. An increasing number of patients with CoA are reaching child-bearing age. Unrepaired CoA or severe recurrent stenosis during pregnancy is a significant concern, as it poses a high risk of maternal and foetal complications and even death. Case summary A 21-year-old woman was referred to the cardiology department at 17 weeks' gestation for management of arterial hypertension and unexplained systolic murmur. She had been diagnosed with hypertension elsewhere the year before presentation, but unfortunately, this remained unexplored. She had been started on labetalol early in the pregnancy. Clinical examination showed a loud systolic heart murmur extending from parasternal to subclavicular and scapular areas. Pulses in the lower extremities were very weak, and blood pressure was slightly elevated with a significant gradient between the upper and lower extremities. Echocardiography showed remarkable absence of pulsatile flow in the abdominal aorta and narrowing just distal to the subclavian artery with typical diastolic tail pattern on suprasternal imaging. Cardiac magnetic resonance confirmed the presence of a severe coarctation distal to the subclavian artery and presence of multiple collaterals allocating this patient in the extremely high-risk category with a risk of up to 40%–100% of maternal cardiac event during pregnancy. An extensive multidisciplinary team meeting was convened. After initial medical optimization, increased claudication and signs of placental hypoperfusion necessitated an endovascular procedure under general anaesthesia at 23 weeks' gestation. A Bentley BeGraft Plus stent (16 × 38 mm) was successfully placed. Postoperative ultrasound showed biphasic placental perfusion and normalization of blood pressure and ankle-brachial indices. At 36 weeks' gestation, the patient gave birth to a healthy child. Discussion Coarctation of the aorta should be considered in any young patient with arterial hypertension. Altered maternal haemodynamics during pregnancy resulted in severe symptomatic CoA and reduced placental flow necessitating percutaneous intervention during pregnancy. A multidisciplinary pregnancy heart team is essential for optimal treatment management in these high-risk patients. [ABSTRACT FROM AUTHOR]

"Fluids" presents a Special Issue on "Image-Based Computational and Experimental Biomedical Flows," featuring thirteen research papers that explore the integration of medical imaging data and fluid dynamics for patient-specific cardiovascular flows. The Issue covers topics such as aneurysms, cardiac function, arterial flow, stenosis, and coronary artery interventions. The studies highlight the synergy between computational fluid dynamics, image-based simulations, and experimental setups, offering insights into cardiovascular physiology and pathology. The research aims to revolutionize cardiovascular disease management by providing personalized treatment strategies based on accurate simulations and advanced technologies. [Extracted from the article]

In ex vivo heart perfusion (EVHP), the control of aortic pressure (AoP) is critical for maintaining the heart's physiologic aerobic metabolism. However, the complexity of and variability in cardiac parameters present a challenge in achieving the rapid and accurate regulation of AoP. In this paper, we propose a method of AoP control based on deep reinforcement learning for EVHP in Langendorff mode, which can adapt to the variations in cardiac parameters. Firstly, a mathematical model is developed by coupling the coronary artery and the pulsatile blood pump models. Subsequently, an aortic pressure control method based on the Deep Deterministic Policy Gradient (DDPG) algorithm is proposed. This method enables the regulation of the blood pump and the realization of closed-loop control. The control performance of the proposed DDPG method, the traditional proportional–integral–derivative (PID) method, and the fuzzy PID method are compared by simulating single and mixed changes in mean aortic pressure target values and coronary resistance. The proposed method exhibits superior performance compared to the PID and fuzzy PID methods under mixed factors, with 68.6% and 66.4% lower settling times and 70.3% and 54.1% lower overshoot values, respectively. This study demonstrates that the proposed DDPG-based method can respond more rapidly and accurately to different cardiac conditions than the conventional PID controllers. [ABSTRACT FROM AUTHOR]

This paper presents a novel centrifugal microfluidic approach (so-called lab-on-a-CD) for magnetic circulating tumor cell (CTC) separation from the other healthy cells according to their physical and acquired chemical properties. This study enhances the efficiency of CTC isolation, crucial for cancer diagnosis, prognosis, and therapy. CTCs are cells that break away from primary tumors and travel through the bloodstream; however, isolating CTCs from blood cells is difficult due to their low numbers and diverse characteristics. The proposed microfluidic device consists of two sections: a passive section that uses inertial force and bifurcation law to sort CTCs into different streamlines based on size and shape and an active section that uses magnetic forces along with Dean drag, inertial, and centrifugal forces to capture magnetized CTCs at the downstream of the microchannel. The authors designed, simulated, fabricated, and tested the device with cultured cancer cells and human cells. We also proposed a cost-effective method to mitigate the surface roughness and smooth surfaces created by micromachines and a unique pulsatile technique for flow control to improve separation efficiency. The possibility of a device with fewer layers to improve the leaks and alignment concerns was also demonstrated. The fabricated device could quickly handle a large volume of samples and achieve a high separation efficiency (93%) of CTCs at an optimal angular velocity. The paper shows the feasibility and potential of the proposed centrifugal microfluidic approach to satisfy the pumping, cell sorting, and separating functions for CTC separation. [ABSTRACT FROM AUTHOR]

This paper presents a numerical solution to the problem of time-dependent blood flow via a w-shaped stenotic conduit, driven by pulsatile pressure gradient. The problem is formulated in cylindrical coordinates by employing the theoretical model of tangent hyperbolic fluid. The electro-osmotic effects are also taken into consideration. To simplify the non-dimensional governing equations of the flow problem, a mild stenosis assumption is utilized and the impact of the blood vessel wall is mitigated by employing a radial coordinate transformation. An explicit finite difference method is used to solve the resulting nonlinear system of differential equations, considering the auxiliary conditions specified at the boundary of the blood channel. After obtaining the numerical solution to the problem, an examination is carried out for various flow variables, such as axial velocity, temperature field, mass concentration, skin friction, Nusselt number, and Sherwood number. These results are presented graphically, and a concise explanation is provided using physical facts. An increase in flow rate and blood velocity leads to a rise in response, while an increase in stenosis height, Weissenberg number, and power-law exponent leads to a reverse response. Furthermore, the temperature field is significantly affected by the Brinkman number and the Prandtl number. [ABSTRACT FROM AUTHOR]

Introduction: Three-dimensional fractional moving blood volume (3D-FMBV) may provide superior noninvasive measurement of feto-placental perfusion compared to current methods. This study investigated the feasibility and repeatability of producing 3D-FMBV measurements of the placenta, fetal liver, kidney, and brain in a single ultrasound consultation. Methods: The placenta, fetal liver, kidney, and brain were scanned in triplicate using 3D power Doppler ultrasound (3D-PDU) in 48 women ≥22 weeks of gestation with healthy fetuses. 3D-FMBV was calculated by two analyzers. Feasibility was assessed as the percentage of cases where 3D-FMBV could be evaluated; repeatability (intraobserver and interobserver) using two-way mixed measure intraclass correlation coefficients (ICCs). Results: 3D-FMBV was calculated for 100% of scanned organs. Intraobserver ICCs (95% CI) were good to excellent; 0.93 (0.88–0.96) and 0.87 (0.78–0.92) for placenta, 0.95 (0.92–0.97) and 0.98 (0.96–0.99) for fetal liver, 0.96 (0.94–0.98) and 0.91 (0.85–0.95) for fetal kidney, and 0.98 (0.97–0.99) and 0.97 (0.95–0.98) for fetal brain. Interobserver ICCs (95% CI) were 0.50 (0.08–0.73), 0.92 (0.85–0.96), 0.89 (0.78–0.94), and 0.71 (0.46–0.85) for placenta, fetal liver, kidney, and brain. Conclusion: Feto-placental perfusion assessment with 3D-FMBV is highly reliable in healthy pregnancies ≥22 weeks of gestation and can be feasibly calculated in four feto-placental vascular beds in a single ultrasound consultation. Plain Language Summary: Throughout pregnancy the placenta provides the fetus with nutrients and oxygen. If blood flow to the fetus is impaired (i.e., in placental disease), the fetus adapts by directing more blood to its brain and less to peripheral organs, called "brain-sparing." This has consequences including impaired growth, stillbirth, and chronic adulthood disease. Brain-sparing is currently detected by measuring how pulsatile blood flow is in the fetal brain and placental vessels. However, in many cases, brain-sparing is detected too late for interventions to be implemented, or not at all. Three-dimensional fractional moving blood volume (3D-FMBV) is a new noninvasive technique that may be able to earlier detect brain-sparing by measuring blood flow in whole fetal organs. If successful, this technique could be used to define normal blood flow ranges in different organs throughout pregnancy, allowing for early detection, intervention, and optimization of fetal outcomes. To do this, it must first be practical to take 3D-FMBV measurements in a single ultrasound consultation (and not be too time intensive) and produce reliable measurements between patients. Our study found that it is practical to measure blood flow in four organs; placenta, fetal liver, kidney, and brain, in a single ultrasound consult, taking a median 10 min and 12 s for scanning and 41 min and 59 s for offline analysis. We were able to calculate 3D-FMBV for all organs scanned. Following our proposed protocol for scanning and analysis, 3D-FMBV measurements can be reliably calculated to a good to excellent degree by the same observer and between observers. [ABSTRACT FROM AUTHOR]

This study provides a critical understanding of controlling solute distribution in microfluidic systems by examining the effects of symmetric and asymmetric zeta potentials under magnetohydrodynamic (MHD) pulsatile electroosmotic flow. These findings are vital for enhancing the efficiency of microfluidic devices used in lab-on-a-chip applications. The aim of this study is to explore the modulation of solute transport in MHD pulsatile electroosmotic microchannel flow, focusing on both symmetric and asymmetric wall zeta potentials. Using the Debye–Hückel approximation, the Poisson–Boltzmann equation is obtained. Subsequently, the convection–diffusion equation is solved using the velocity profile, with Aris's method of moments to derive the moment equations. These equations are then solved using a finite difference scheme. The mean concentration is calculated employing Hermite polynomials. We examined the effects of key parameters such as the electroosmotic parameter (κ), the Hartmann number (Ha), and zeta potentials on the dispersion coefficient (DT), mean concentration distribution (Cm), skewness, and kurtosis. We consider three situations: symmetric ( ζ 1 = ζ 2 ), partially asymmetric ( ζ 1 = 1.0 , ζ 2 = 0.0), and fully asymmetric ( ζ 1 = 1.0 , ζ 2 = − 1.0) zeta potentials. Our results reveal that asymmetric zeta potentials lead to faster dispersion, with DT decreasing with increasing κ for symmetric potentials and increasing for asymmetric ones. As the Hartmann number increases, dispersion decreases for both symmetric and asymmetric zeta potentials while the peak of mean concentration rises. The mean concentration profile exhibits Gaussian behavior at both small and large times, with anomalous behavior in the intermediate region. For symmetric zeta potentials, Gaussianity is observed at t = 0.001 in the diffusive regime and at t = 10.0 in Taylor's regime, while for asymmetric potentials, Gaussianity occurs at t = 0.03 and t = 3.0, indicating that large-time Gaussian behavior is approximately 3.33 times faster and dispersion becomes transient for asymmetric potentials. [ABSTRACT FROM AUTHOR]

The study of blood flow in curved arteries aims to understand how hemodynamic behavior is affected by geometric factors, which is crucial for revealing the formation and progression of vascular diseases. Currently, most studies on blood flow in curved vessels have utilized computational fluid dynamics software. Numerical calculations have typically concentrated on the steady flow of Newtonian fluid in curved vessels with circular cross sections, while non-Newtonian fluid flow has predominantly been calculated in curved pipes with rectangular cross sections. In this paper, the governing equation of Carreau fluid flow in a curved cerebral artery with constant curvature is established using a curvilinear coordinate system, with the flow driven by a physiological pulsatile pressure gradient. Deriving support from finite difference method, numerical solutions are acquired, whose convergence and validity are verified. It is concluded that time-averaged wall shear stress peaks at the inner side of the artery, resulting in the risk of atherosclerosis, while relative residence time peaks at the outer side, causing the likelihood of cerebral infarction there. While an increase in δ amplifies the amplitude of both, it has barely any effect on their values at θ = π/2 and θ = 3π/2. Time-averaged Dean number is first defined to evaluate the development of secondary flow in curved arteries over a cardiac cycle. Near the wall, it peaks at the inner side of the vessel and escalates markedly with larger δ. This study can provide an effective reference for the early prevention and diagnosis of cerebral artery infarction. [ABSTRACT FROM AUTHOR]

Solute transport in pulsatile viscoelastic fluid flow is relevant in nutrient transport and drug delivery in blood flow. Previous studies have extensively analyzed the effect of the shear-thinning nature of the blood but neglected the elastic property. The present study aims to fill this lacuna by analyzing the role of blood viscoelasticity on solute transport. To accomplish this, we study solute transport for a non-uniformly distributed solute slug in the pulsatile flow of an Oldroyd-B fluid through a tube in the presence of wall absorption. We employ Gill's procedure and Aris' method of moments to compute the transport coefficients K m (t) (m ≤ 4). We also numerically solve the species transport equation using a finite difference scheme to directly determine local solute concentration C (t , z , r). Consistent results for a non-viscoelastic fluid predict a negative convection coefficient K1 and a positive effective diffusivity K2 for realistic values of the parameters. However, the present analysis predicts positive K1 and negative K2 for small tubes due to flow reversal caused by the fluid elasticity. For high Λ 1 , the amplitude of oscillation for K1 and K2 exhibits scaling K 1 ∼ Λ 1 1.5 and K 2 ∼ Λ 1 2 indicating an enhancement in the dispersion due to fluid elasticity, where Λ 1 is the dimensionless relaxation time. The analysis of the skewness and (excess) kurtosis coefficients reveals inconsistency in previous studies on Newtonian fluids. Thus, we present consistent results not only for a viscoelastic fluid but also for a Newtonian fluid subjected to a pulsatile pressure gradient. In addition, the solute dispersion is significantly influenced by the non-uniformity of a solute slug. As the radius of a slug increases, solute dispersion reduces in short and moderate times; however, at large times, it is independent of the radius of a slug. [ABSTRACT FROM AUTHOR]

The establishment of a peripheral ECMO circuit can lead to significant arterial and venous complications in 10–30% of patients. Vascular complications, particularly acute limb ischemia, are associated with worsening overall outcomes. Limb ischemia occurs significantly more frequently in the early stages of VA ECMO than in VV ECMO. Mechanisms of limb ischemia include arterial obstruction, cannulation injury, loss of pulsatile flow, thromboembolism, venous stasis from compressive obstruction with large venous cannulas, and systemic vasoconstriction due to shock and pharmacologic vasoconstriction. The care team may use several mitigation strategies to prevent limb ischemia. Arterial and venous complications can be mitigated by careful access site selection, minimizing cannula size, placement of distal perfusion and/or outflow catheter(s), and continuous NIRS monitoring. Rapid intervention, when ischemia or compartment syndrome occurs, can reduce limb loss but may not affect the mortality and morbidity of the ECMO patient in the long term due to their underlying conditions and the etiology of the ECMO need. [ABSTRACT FROM AUTHOR]

In this study, a computational analysis has been made for a steady, incompressible, MHD flow of the SWCNT-blood and the MWCNT-blood nanofluids past a non-linear stretching sheet of variable thickness. Darcy porous medium has been considered for fluid flow. Consequences of homogeneous-heterogeneous chemical reactions on heat and mass transfer along with Joule heating and viscous dissipation have been explored. Appropriate similarity transformations have been applied to convert the governing equations of nanofluid flow into non-linear ordinary differential equations. Galerkin finite element scheme has been used to examine the resulting system with corresponding boundary conditions. Numerical solutions of equations are demonstrated via graphs for various physical parameters, and these graphs have also been analyzed. Comparison of velocity, thermal, and concentration profiles of SWCNT-blood and MWCNT-blood nanofluids has been established. It is concluded that flow profiles of MWCNT-blood nanofluid dominate. Concentration profile declines with homogeneous and heterogeneous reaction parameters whereas increases with the Schimdt number for both nanofluids. Then, a comparison between present and the existing results was made, and they are in good agreement. After that, several physical quantities such as the local Nusselt number, skin friction coefficient, and concentration rate are exhibited in a table. [ABSTRACT FROM AUTHOR]

The study of biological fluids in the presence of a magnetic field is known as biomagnetic fluid dynamics (BFD). The research work in BFD has been rapidly growing due to its applications in developing magnetic devices used for cell separation, targeted drug delivery and cancer tumor treatment. This study aims to examine the biomagnetic fluid flow with pulsatile conditions through a channel when subjected to a magnetic field that varies in space. The nondimensional continuity and momentum equations are solved with the effect of the magnetic field added as a body force. A two-dimensional computational model is developed using the finite volume method and is implemented on a staggered grid system with the help of the semi-implicit fractional step method. The code is written using MATLAB. Numerical simulations are performed by varying the Magnetic, Reynolds and Womersley numbers. Pulsatile flow results indicate the periodic growth and decay of vortices near the source of the magnetic field. With an increase in the magnetic number from 100 to 150, 250 and 500, the maximum vorticity increases by 48.04%, 149.84% and 402.68%. A similar relation is found when varying the Reynolds number, while almost no change is found when varying the Womersley number. [ABSTRACT FROM AUTHOR]

This paper represents a detailed and systematic review of one of the most ongoing applications of computational fluid dynamics (CFD) in biomedical applications. Beyond its various engineering applications, CFD has started to establish a presence in the biomedical field. Cardiac abnormality, a familiar health issue, is an essential point of investigation by research analysts. Diagnostic modalities provide cardiovascular structural information but give insufficient information about the hemodynamics of blood. The study of hemodynamic parameters can be a potential measure for determining cardiovascular abnormalities. Numerous studies have explored the rheological behavior of blood experimentally and numerically. This paper provides insight into how researchers have incorporated the pulsatile nature of the blood experimentally, numerically, or through various simulations over the years. It focuses on how machine learning platforms derive outputs based on mass and momentum conservation to predict the velocity and pressure profile, analyzing various cardiac diseases for clinical applications. This will pave the way toward responsive AI in cardiac healthcare, improving productivity and quality in the healthcare industry. The paper shows how CFD is a vital tool for efficiently studying the flow in arteries. The review indicates this biomedical simulation and its applications in healthcare using machine learning and AI. Developing AI-based CFD models can impact society and foster the advancement towards responsive AI. [ABSTRACT FROM AUTHOR]

Introduction: Bony surface cleaning using a pulse lavage device (PLD) is essential for modern cementation of hip and knee arthroplasties. This costly single-use device is a medical waste and unaffordable for some patients. Reprocessing is a worldwide standard strategy to solve this problem. To determine the technical properties and biological safety of a reprocessed PLD handpiece and compare its performance under different power supplies. Materials and methods: Eight brand-new disposable PLDs were tested for baseline technical properties (flow rate, pulse frequency, and peak pressure). Thereafter, they were reprocessed and retested for 10 rounds using two different power supplies. An adenosine triphosphate (ATP) swab test was performed on the PLD accessory parts after cleansing and disinfection. Passed-through isotonic sodium chloride solution ejected from the reprocessed PLD underwent aerobic bacterial culture. The unit costs of production were analysed. Results: The mean flow rate of the disposable PLD (1.5±0.1 L/min) was less than that of reprocessed PLD using DC15V battery (2.5±0.3 L/min, p

Murray’s law, as the best-known optimal relationship between bifurcation calibers, is obtained based on the assumption of steady-state Poiseuille blood flow and is mostly accurate in small vessels. In middle sized and large vessels such as the aorta and coronary arteries, the pulsatile nature of the flow is dominant and deviations from Murray law have been observed. In the present study, a general scaling law is proposed, which describes the optimum relationship between the characteristics of bifurcations and pulsatile flow. This scaling law takes into account the deviations from Murray law in large vessels, and proposes optimal flow (i.e. less flow resistance) for the full range of the vascular system, from the small vessels to large ones such aorta. As a general scaling law, it covers both symmetrical and asymmetrical bifurcations. One of the merits of this scaling law is that bifurcation characteristics solely depend on the Womersley number of parent vessels. The diameter ratios suggested by this scaling law are in acceptable agreement with available clinical morphometric data such as those reported for coronary arteries and aortoiliac bifurcations. A numerical simulation of pulsatile flow for several Womersley numbers in bifurcation models according to the proposed scaling law and Murray law has been performed, which suggests that the general scaling law provides less flow resistance and more efficiency than Murray law in pulsatile flow.

Background: Our primary goal was to utilize pulmonary arterial stiffness (PAS) to demonstrate the early alterations in the pulmonary vascular area in individuals with prior COVID-19 illness who had not undergone hospitalization. Methods: In total, 201 patients with prior COVID-19 infection without hospitalization and 195 healthy, age- and sex-matched individuals without a history of COVID-19 disease were included in this prospective analysis. The PAS value for each patient was calculated by dividing the mean peak pulmonary flow velocity by the pulmonary flow acceleration time. Results: The measured PAS was 10.2 ± 4.11 Hz/msec in post–COVID-19 participants and 8.56 ± 1.47 Hz/msec in healthy subjects (P < 0.001). Moreover, pulmonary artery acceleration time was significantly lower in patients with a prior history of COVID-19. Multivariable logistic regression analysis revealed that PAS was significantly connected to a prior COVID-19 illness (odds ratio, 1.267; 95% confidence interval, 1.142–1.434; P < 0.001). The optimal cutoff point for detecting a prior COVID-19 disease for PAS was 10.1 (sensitivity, 70.2%; specificity, 87.7%). Conclusions: This might be the first investigation to reveal that patients with a history of COVID-19 had higher PAS values compared to those without COVID-19. The results of the investigation may indicate the need of regular follow up of COVID-19 patients for the development of pulmonary arterial hypertension, especially during the post–COVID-19 interval. [ABSTRACT FROM AUTHOR]

Oscillatory flow in confined spaces is central to understanding physiological flows and rational design of synthetic periodic-actuation based micromachines. Using theory and experiments on oscillating flows generated through a laser-induced cavitation bubble, we associate the dynamic bubble size (fluid velocity) and bubble lifetime to the laser energy supplied—a control parameter in experiments. Employing different channel cross-section shapes, sizes and lengths, we demonstrate the characteristic scales for velocity, time and energy to depend solely on the channel geometry. Contrary to the generally assumed absence of instability in low Reynolds number flows ( < 1000 ), we report a momentary flow distortion that originates due to the boundary layer separation near channel walls during flow deceleration. The emergence of distorted laminar states is characterized using two stages. First the conditions for the onset of instabilities is analyzed using the Reynolds number and Womersley number for oscillating flows. Second the growth and the ability of an instability to prevail is analyzed using the convective time scale of the flow. Our findings inform rational design of microsystems leveraging pulsatile flows via cavitation-powered microactuation. [ABSTRACT FROM AUTHOR]

Hemodialysis (HD) is a treatment supporting decreased kidney function, via a catheter inserted into the heart’s Right Atrium (RA). Recirculation is a source of inefficiency for treatment, where blood is dialyzed again due to poor catheter design. Lab-testing is still relatively unexplored, hence, a mechanical testing system was designed with the intention of providing a consistent and repeatable environment for testing HD catheters. System geometry was composed using a Computer-Aided Design (CAD) model of a heart, with the RA scaled to appropriate dimensions, and a PolyDiMethylSiloxane (PDMS) model produced through 3D printing and negative wax casting. Pulsatile blood flow was mimicked by peristaltic pumps driving a blood analogue (BA). Recirculation was induced by adding dyed BA to the system via the catheter and measured using a colorimeter. The developed platform was initially evaluated using two catheters, demonstrating the capability to accurately replicate atrial hemodynamic conditions. Two step-tipped catheters, A and B, were tested at 350 ml/min, producing recirculation values of 13.11% and 18.58%, respectively. The results exhibit the ability of the system developed to evaluate HD catheter performance, with the potential to explore a wider range of tip geometries relevant to clinical preference. Furthermore, this advancement towards an anatomically accurate lab-based test system could be paired with computational methods to progress the evaluation of such medical devices and enhance their development. [ABSTRACT FROM AUTHOR]

In the present work, the impact of periodic body acceleration on the unsteady flow of blood in an inclined artery has been investigated. The blood is represented by an incompressible, viscous, non-Newtonian Jeffrey fluid. The artery is assumed to have mild overlapping stenoses inside its lumen. The perturbation method is used to solve the governing nonlinear coupled partial differential equations. Here, the Womersley frequency parameter is considered small enough for blood flow through arteries. Analytic expressions for the wall shear stress, stress at the critical height of stenosis, velocity profile, volumetric flow rate, pressure drop, resistive impedance, and effective viscosity are obtained using the perturbation technique. Regarding different flow parameters, the effects of body acceleration, pulsatility, the non-Newtonian character of blood, and velocity slip are examined and graphically depicted. It is concluded from the present analysis that the flow impedance rises when the stenosis reaches its critical height, but it falls as the velocity slip at the wall increases. It is also observed that when body acceleration increases, flow rate, velocity, and shear stress near the critical height of stenosis all rise, whereas wall shear stress decreases as body acceleration rises. Here, we also analyzed the flow pattern of the non-Newtonian Jeffrey fluid when it passes through the overlapped stenosed artery with the help of streamlines. The results of the present problem have been verified with the previous existing results in the literature. [ABSTRACT FROM AUTHOR]

OBJECTIVES The use of ventricular assist devices (VADs) in children is increasing. However, absolute numbers in individual centres and countries remain small. Collaborative efforts such as the Paedi-European Registry for Patients with Mechanical Circulatory Support (EUROMACS) are therefore essential for combining international experience with paediatric VADs. Our goal was to present the results from the fourth Paedi-EUROMACS report. METHODS All paediatric (<19 years) patients from the EUROMACS database supported by a VAD were included. Patients were stratified into a congenital heart disease (CHD) group and a group with a non-congenital aetiology. End points included mortality, a transplant and recovery. Cox proportional hazard models were used to explore associated factors for mortality, cerebrovascular accident and pump thrombosis. RESULTS A total of 590 primary implants were included. The congenital group was significantly younger (2.5 vs 8.0 years, respectively, P  < 0.001) and was more commonly supported by a pulsatile flow device (73.5% vs 59.9%, P  < 0.001). Mortality was significantly higher in the congenital group (30.8% vs 20.4%, P  = 0.009) than in the non-congenital group. However, in multivariable analyses, CHD was not significantly associated with mortality [hazard ratio (HR) 1.285; confidence interval (CI) 0.8111–2.036, P  = 0.740]. Pump thrombosis was the most frequently reported adverse event (377 events in 132 patients; 0.925 events per patient-year) and was significantly associated with body surface area (HR 0.524, CI 0.333–0.823, P  = 0.005), CHD (HR 1.641, CI 1.054–2.555, P  = 0.028) and pulsatile flow support (HR 2.345, CI 1.406–3.910, P  = 0.001) in multivariable analyses. CONCLUSIONS This fourth Paedi-EUROMACS report highlights the increasing use of paediatric VADs. The patient populations with congenital and non-congenital aetiologies exhibit distinct characteristics and clinical outcomes. [ABSTRACT FROM AUTHOR]

Average-sized microfluidic artificial lungs consisting of rows and columns of fiber bundles with different column to row aspect ratios (AR) are numerically analyzed for flow characteristics, maximum gas transfer performance, minimum pressure drop, and proper wall shear stress (WSS) values in terms of biocompatibility. The flow is fully laminar and assumed to be incompressible and Newtonian. The transport analysis is performed using a combined convection-diffusion model, and the numerical simulations are carried out with the finite element method. The inlet volumetric flow is modeled as a sinusoidal wave function to simulate the cardiac cycle and its effect on the device performance. The model is first validated with experimental studies in steady-state condition and compared with existing correlations for transient conditions. Then, the validated model is used for a parametric study in both steady and pulsatile flow conditions. The results show that increasing the aspect ratio in fiber configuration leads to converging gas transfer, higher pressure drop, and higher WSS. While determining the optimum configuration, the acceptable shear stress levels play a decisive role to ensure biocompatibility. Also, it is observed that the steady analysis underestimates the gas transfer for higher aspect ratios. [ABSTRACT FROM AUTHOR]

Amplified MRI (aMRI) is a promising new technique that can visualize pulsatile brain tissue motion by amplifying sub-voxel motion in cine MRI data, but it lacks the ability to quantify the sub-voxel motion field in physical units. Here, we introduce a novel post-processing algorithm called 3D quantitative amplified MRI (3D q-aMRI). This algorithm enables the visualization and quantification of pulsatile brain motion. 3D q-aMRI was validated and optimized on a 3D digital phantom and was applied in vivo on healthy volunteers for its ability to accurately measure brain parenchyma and CSF voxel displacement. Simulation results show that 3D q-aMRI can accurately quantify sub-voxel motions in the order of 0.01 of a voxel size. The algorithm hyperparameters were optimized and tested on in vivo data. The repeatability and reproducibility of 3D q-aMRI were shown on six healthy volunteers. The voxel displacement field extracted by 3D q-aMRI is highly correlated with the displacement measurements estimated by phase contrast (PC) MRI. In addition, the voxel displacement profile through the cerebral aqueduct resembled the CSF flow profile reported in previous literature. Differences in brain motion was observed in patients with dementia compared with age-matched healthy controls. In summary, 3D q-aMRI is a promising new technique that can both visualize and quantify pulsatile brain motion. Its ability to accurately quantify sub-voxel motion in physical units holds potential for the assessment of pulsatile brain motion as well as the indirect assessment of CSF homeostasis. While further research is warranted, 3D q-aMRI may provide important diagnostic information for neurological disorders such as Alzheimer's disease. [ABSTRACT FROM AUTHOR]

In the present exploration, entropy production on hydromagnetic pulsating flow of Au + SWCNT/blood and Au + MWCNT/blood-based Jeffrey hybrid nanofluid in a vertical porous channel with Cattaneo-Christov theory has been inspected. The impacts of Ohmic heating, viscous dissipation, and thermal radiation are considered. The transformation of the governing partial differential equations into a system of ordinary differential equations is made by applying the perturbation method and then numerically solved by the fourth-order Runge-Kutta method aided by bvp4c shooting technique built-in MATLAB software. The effects of various emerging parameters and variables on velocity, temperature, entropy generation, and the Bejan number are displayed through graphs. The consequences of physical parameters on heat transfer rate are prearranged in a table. This analysis demonstrates that the velocity of both hybrid nanofluids is intensified with an upsurge in the Grashof number, while it is decreasing by giving higher values in an applied magnetic field. The temperature of both hybrid nanofluids increases with an increment in the radiation parameter, and Eckert number. The entropy generation is an increasing function of Eckert number and radiation parameter. The heat transfer rate has a higher impact in the case of (Au + MWCNT/blood) hybrid nanofluid as compared to (Au + SWCNT/blood) hybrid nanofluid and mono nanofluid. [ABSTRACT FROM AUTHOR]

The intermittency characteristics in transitional and turbulent flows can provide critical information on the underlying mechanisms and dynamics. While time–frequency (TF) analysis serves as a valuable tool for assessing intermittency, existing methods suffer from resolution issues and interference artifacts in the TF representation. As a result, no suitable or accepted methods currently exist for assessing intermittency. In this work, we address this gap by presenting a novel TF method—a Fourier-decomposed wavelet-based transform—which yields improved spatial and temporal resolution by leveraging the advantages of both integral transforms and data-driven mode decomposition-based TF methods. Specifically, our method combines a Fourier-windowing component with wavelet-based transforms such as the continuous wavelet transform (CWT) and superlet transform, a super-resolution version of the CWT. Using a peak-detection algorithm, we extract the first, second, and third most dominant instantaneous frequency (IF) components of a signal. We compared the accuracy of our method to traditional TF methods using analytical signals as well as an experimental particle image velocimetry (PIV) dataset capturing transition to turbulence in pulsatile pipe flows. Error analysis with the analytical signals demonstrated that our method maintained superior resolution, accuracy, and, as a result, specificity of the instantaneous frequencies. Additionally, with the pulsatile flow dataset, we demonstrate that IF components of the fluctuating velocities extracted by our method decompose energy cascade components in the flow. Additional investigations into corresponding spatial frequency structures resulted in detailed observations of the inherent scaling mechanisms of transition in pulsatile flows. [ABSTRACT FROM AUTHOR]

The motion of a deformable compound droplet flowing within a confined channel in response to a pulsatile flow is numerically investigated. Toward this, an in-house solver based on the level-set method is developed. It is shown that a low Strouhal number leads to significant oscillation in flow velocity and a greater deformation of the compound droplet, driving it periodically along the streamwise direction resulting in an increased residence time, as compared to steady imposed flow. Conversely, high Strouhal number results in smaller amplitude oscillations in flow velocity leading to smoother droplet motion and lower deformation. Expectedly, a decrease in the pulsatile flow amplitude yields smoother and more uniform flow with reduced droplet deformation. Importantly, hitherto unreported cross-stream migration of an off-centered compound droplet under pulsatile flow is investigated. An off-centered compound droplet migrates toward the center of the channel, with its core being eccentric toward the wall it was initially close to. The influence of other key parameters such as density ratio, size ratio of the core, and the viscosity ratio of the shell in shaping the dynamics of the compound droplet is systematically explored. It is revealed that the eccentricity of the core can be manipulated by tuning inlet flow and density of core fluid. A more viscous shell results in a marginally higher film thickness near the wall and a higher droplet residence time within the channel. A higher Bond number results in a larger droplet deformation, resulting in a streamlined shape and significantly higher droplet speed. [ABSTRACT FROM AUTHOR]

In the present study, we investigate the flow dynamics of non-Newtonian blood, focusing on the distribution of wall shear stress (WSS) and hematocrit levels, which is the volume percentage of red blood cells in whole blood. We analyze these factors under pulsatile conditions, in vascular anomalies such as stent channels and intracranial aneurysms. To achieve this, a three-dimensional computational approach based on the lattice Boltzmann method (LBM) with a multiple relaxation time (MRT) collision operator is employed. To represent the blood's shear-thinning properties, we developed a constitutive model inspired by the Carreau–Yasuda model. This model considers the variability in blood viscosity with shear rate correlated with hematocrit levels based on experimental data documented in the literature. The accuracy of the employed MRT-LBM is demonstrated by the consistency of results with analytical solutions for steady state and experimental data for pulsatile WSS distributions in non-Newtonian and Newtonian fluids. Results indicate that, in areas narrowed by stenosis or expanded by aneurysms, hematocrit levels affect flow dynamics. Higher hematocrit levels intensify pulsatile flow through stenotic regions, increasing WSS cyclic variations. We derived a density distribution function to demonstrate how shear rates vary in vascular anomalies, revealing blood viscosity changes and non-Newtonian properties. These properties complicate flow patterns, resulting in non-linear WSS distributions, which are essential for understanding endothelial cell reactions and disease pathways. Pulsatile blood flow and altered rheological properties due to increased hematocrit affect saccular aneurysm fluid dynamics over time and space, causing vorticities to change shape, size, and intensity. [ABSTRACT FROM AUTHOR]

Aortic valve disease is a significant health issue. Research on the effects of aortic sinus geometry and aortic valve motion during a heartbeat is imperative, as numerous valvular diseases are associated with blood flow near the heart valve. Changes in the internal space of the sinus and the formation of blood clots have been reported after the implantation of a transcatheter aortic valve, an artificial heart valve. Although the sinus shape and leaflet motion significantly affect the hemodynamic characteristics and platelet aggregation, the blood flow behaviors near the heart valve associated with clot formation have not been fully elucidated. This study conducted in vitro experiments to investigate the flow behavior near an aortic sinus model based on the sinus shape. Additionally, hemodynamic changes associated with variations in the aortic sinus geometry and leaflet length within an aortic sinus model under pulsatile-flow conditions were elucidated. In a curved sinus model, a large single vortex formed near the center of the sinus region. Meanwhile, the center of the vortex in the sinus region shifted during a cycle in an expanded sinus model. Furthermore, a small vortex remained where the leaflet was initiated, thus increasing the likelihood of thrombus formation. Thus, the curved sinus model is advantageous for preventing material accumulation by maintaining a large vortex structure. The experimental results confirmed that the aortic sinus shape and leaflet length affect the likelihood of thrombus formation inside the aortic sinus. [ABSTRACT FROM AUTHOR]

Background: The implanted non-vascular stent is prone to fatigue fracture due to the periodic cyclic load caused by long-term physiological motion in the non-vascular lumen. Objective: To effectively study and predict the fatigue performance of non-vascular stents, an experimental setup was designed to simulate and conduct fatigue performance tests on non-vascular stents under various loads. This design simplified the periodic cyclic loads generated within non-vascular lumens, in accordance with the physiological motion patterns of non-vascular lumens, into pulsatile loads. Methods: To meet the requirements of different stents and various fluctuating load conditions during testing, the relationship between test conditions and the fatigue load of the stent was studied based on Fluent. Results: A fatigue test device with a special load module was built and used to complete the fatigue performance test of a group of esophageal stents. It can be found that the experimental device can satisfy the control and application of the fatigue load of the stent, and can effectively realize the testing requirements of the fatigue performance of the stent. Conclusion: In this paper, a non-vascular stent fatigue in vitro test device that can simulate the fluctuating load of a non-vascular lumen is designed. The results of flow field simulation, fatigue simulation, and actual fatigue test show that the device can meet the needs of fatigue test and has good versatility and operability. [ABSTRACT FROM AUTHOR]

Idiopathic intracranial hypertension (IIH) is a disorder that primarily affects obese women of reproductive age. The exact pathogenesis of IIH is unknown though multiple etiologies have been proposed. We report a case of IIH triggered by first-time Ramadan intermittent fasting (RIF) in an 18-year-old woman. Our patient developed new onset headaches, diplopia, and pulsatile tinnitus with examination notable for bilateral papilledema and lumbar puncture revealing an elevated opening pressure. Her symptoms resolved after cessation of RIF, apart from persistent left sided tinnitus which later resolved with acetazolamide administration. This case report uniquely illustrates that RIF may provoke symptomatic IIH. We hypothesize that a decreased concentration of glucagon-like peptide-1 (GLP-1) induced by fasting results in decreased GLP-1 receptor activation in the choroid plexus, allowing for increased CSF secretion into the ventricles invoking increased intracranial pressure (ICP). This theoretical mechanism provides further insight as to the possible underlying pathophysiology of IIH. [ABSTRACT FROM AUTHOR]