Showing papers on "Pulsatile flow published in 2022"
TL;DR: A strategy to autonomously navigate a miniature helical robot in dynamic blood flow under ultrasound Doppler imaging guidance provides simultaneous robot navigation and localization in complex dynamic biological environments, providing an intelligent approach toward real-time targeted delivery and diagnostic applications in vivo.
Abstract: Untethered small-scale robots offer great promise for medical applications in complex biological environments. However, challenges remain in the control and medical imaging of a robot for targeted delivery inside a living body, especially in flowing conditions (e.g., blood vessels). In this work, we report a strategy to autonomously navigate a miniature helical robot in dynamic blood flow under ultrasound Doppler imaging guidance. A magnetic torque and force-hybrid control approach is implemented, enabling the actuation of a millimeter-scale helical robot against blood flow under a rotating magnetic field with a controllable field gradient. Experimental results demonstrate that the robot (length 7.30 mm; diameter 2.15 mm) exhibits controlled navigation in vascular environments, including upstream and downstream navigation in flowing and pulsatile flowing blood with flow rates up to 24 mL/min (mean flow velocity: 14.15 mm/s). During navigation, the rotating robot-induced Doppler signals enable real-time localization and tracking in flowing and pulsatile flowing blood environments. Moreover, the robot can be selectively navigated along different paths by actively controlling the robot's orientation. We apply this autonomous strategy for localizing thrombus and accelerating thrombolysis rate. Compared with conventional tissue plasminogen activator (tPA) thrombolysis, the robot-enhanced shear stress and tPA convection near the clot-blood interface increase the unblocking and thrombolysis efficiency up to 4.8- and 3.5-fold, respectively. Such a medical imaging-guided navigation strategy provides simultaneous robot navigation and localization in complex dynamic biological environments, providing an intelligent approach toward real-time targeted delivery and diagnostic applications in vivo.
31 citations
TL;DR: In this article , the authors used a CNN autoencoder to reconstruct the arterial pulse signal independent of sensing location from a group of six Bio-Z sensors within the sensor array.
Abstract: Continuous monitoring of blood pressure (BP) is essential for the prediction and the prevention of cardiovascular diseases. Cuffless BP methods based on non-invasive sensors integrated into wearable devices can translate blood pulsatile activity into continuous BP data. However, local blood pulsatile sensors from wearable devices suffer from inaccurate pulsatile activity measurement based on superficial capillaries, large form-factor devices and BP variation with sensor location which degrade the accuracy of BP estimation and the device wearability. This study presents a cuffless BP monitoring method based on a novel bio-impedance (Bio-Z) sensor array built in a flexible wristband with small-form factor that provides a robust blood pulsatile sensing and BP estimation without calibration methods for the sensing location. We use a convolutional neural network (CNN) autoencoder that reconstructs an accurate estimate of the arterial pulse signal independent of sensing location from a group of six Bio-Z sensors within the sensor array. We rely on an Adaptive Boosting regression model which maps the features of the estimated arterial pulse signal to systolic and diastolic BP readings. BP was accurately estimated with average error and correlation coefficient of 0.5 ± 5.0 mmHg and 0.80 for diastolic BP, and 0.2 ± 6.5 mmHg and 0.79 for systolic BP, respectively.
20 citations
TL;DR: In this article , the role of slow waves in the generation of CSF pulsations was investigated across the full sleep-wake cycle and during a waking respiratory task, which revealed a novel generating mechanism that relies on the autonomic regulation of cerebral vascular tone without requiring slow electrocortical activity or even sleep.
18 citations
TL;DR: In this paper , the velocity, temperature, heat transfer rate, and isothermal lines are produced using the perturbation approach to evaluate coupled equations with the nonlinear problem, and the response surface method is executed to probe the sensitivity of effective flow field parameters on the heat transfer rates.
16 citations
TL;DR: In this paper, the cellular and molecular mechanisms underlying the pulsatile release of gonadotropin-releasing hormone (GnRH) to regulate gametogenesis and steroidogenesis in mammals are discussed.
15 citations
TL;DR: In this paper , the cellular and molecular mechanisms underlying the pulsatile release of gonadotropin-releasing hormone (GnRH) to regulate gametogenesis and steroidogenesis in mammals are discussed.
15 citations
TL;DR: In this paper , a shape-adaptively controlled locomotion in phantoms emulating the physiological conditions of the M4 segment of the middle cerebral artery was investigated, where the lumen diameter shrinks from 1.5 mm to 1 mm, the radius of curvature of the tortuous lumen gets as small as 3 mm, and the bifurcation angle goes up to 120 ° , and pulsatile flow speed reaches up to 26 cm/s.
Abstract: Abstract Microcatheters have enabled diverse minimally invasive endovascular operations and notable health benefits compared with open surgeries. However, with tortuous routes far from the arterial puncture site, the distal vascular regions remain challenging for safe catheter access. Therefore, we propose a wireless stent-shaped magnetic soft robot to be deployed, actively navigated, used for medical functions, and retrieved in the example M4 segment of the middle cerebral artery. We investigate shape-adaptively controlled locomotion in phantoms emulating the physiological conditions here, where the lumen diameter shrinks from 1.5 mm to 1 mm, the radius of curvature of the tortuous lumen gets as small as 3 mm, the lumen bifurcation angle goes up to 120 ° , and the pulsatile flow speed reaches up to 26 cm/s. The robot can also withstand the flow when the magnetic actuation is turned off. These locomotion capabilities are confirmed in porcine arteries ex vivo. Furthermore, variants of the robot could release the tissue plasminogen activator on-demand locally for thrombolysis and function as flow diverters, initiating promising therapies towards acute ischemic stroke, aneurysm, arteriovenous malformation, dural arteriovenous fistulas, and brain tumors. These functions should facilitate the robot’s usage in new distal endovascular operations.
14 citations
TL;DR: An overview of the dynamics of the human heart is presented and the main goal is the discussion of its fluid mechanic features, particularly the interaction with the systemic and pulmonary circulations with which it is strongly connected.
Abstract: Abstract This article presents an overview of the dynamics of the human heart and the main goal is the discussion of its fluid mechanic features. We will see, however, that the flow in the heart can not be fully described without considering its electrophysiology and elastomechanics as well as the interaction with the systemic and pulmonary circulations with which it is strongly connected. Biologically, the human heart is similar to that of all warm-blooded mammals and it satisfies the same allometric laws. Since the Paleolithic Age, however, humans have improved their living conditions, have modified the environment to satisfy their needs and, more recently, have developed advanced medical knowledge which has allowed triple the number of heartbeats with respect to other mammals. In the last century, effective diagnostic tools, reliable surgical procedures and prosthetic devices have been developed and refined leading to substantial progress in cardiology and heart surgery with routine clinical practice which nowadays cures many disorders, once lethal. Pulse duplicators have been built to reproduce the pulsatile flow and ‘blood analogues’, have been realized. Heart phantoms, can attain deformations similar to the real heart although the active contraction and the tissue anisotropy still can not be replicated. Numerical models have also become a viable alternative for cardiovascular research: they do not suffer from limitations of material properties and device technologies, thus making possible the realization of truly digital twins. Unfortunately, a high-fidelity model for the whole heart consists of a system of coupled, nonlinear partial differential equations with a number of degrees of freedom of the order of a billion and computational costs become the bottleneck. An additional challenge comes from the inherent human variability and the uncertainty of the heart parameters whose statistical assessment requires a campaign of simulations rather than a single deterministic calculation; reduced and surrogate models can be employed to alleviate the huge computational burden and all possibilities are currently being pursued. In the era of big data and artificial intelligence, cardiovascular research is also advancing by exploiting the latest technologies: equation-based augmented reality, virtual surgery and computational prediction of disease progression are just a few examples among many that will become standard practice in the forthcoming years.
14 citations
TL;DR: The results indicate that the proposed model, involving a limited number of parameters, can serve as a basis for future quantitative analyses targeting predictions of ICP temporal fluctuations based on MRI measurements of spinal-canal anatomy and CSF flow rate.
Abstract: Abstract The monitoring of intracranial pressure (ICP) fluctuations, which is needed in the context of a number of neurological diseases, requires the insertion of pressure sensors, an invasive procedure with considerable risk factors. Intracranial pressure fluctuations drive the wave-like pulsatile motion of cerebrospinal fluid (CSF) along the compliant spinal canal. Systematically derived simplified models relating the ICP fluctuations with the resulting CSF flow rate can be useful in enabling indirect evaluations of the former from non-invasive magnetic resonance imaging (MRI) measurements of the latter. As a preliminary step in enabling these predictive efforts, a model is developed here for the pulsating viscous motion of CSF in the spinal canal, assumed to be a linearly elastic compliant tube of slowly varying section, with a Darcy pressure-loss term included to model the fluid resistance introduced by the trabeculae, which are thin collagen-reinforced columns that form a web-like structure stretching across the spinal canal. Use of Fourier-series expansions enables predictions of CSF flow rate for realistic anharmonic ICP fluctuations. The flow rate predicted using a representative ICP waveform together with a realistic canal anatomy is seen to compare favourably with in vivo phase-contrast MRI measurements at multiple sections along the spinal canal. The results indicate that the proposed model, involving a limited number of parameters, can serve as a basis for future quantitative analyses targeting predictions of ICP temporal fluctuations based on MRI measurements of spinal-canal anatomy and CSF flow rate.
13 citations
24 Feb 2022
TL;DR: Categorizing the myriad causes of pulsatile tinnitus into structural, metabolic, and vascular groups ensures that dangerous causes are not missed, and that patients receive the appropriate care from the proper specialist when needed.
Abstract: Importance
Pulsatile tinnitus is a debilitating symptom affecting millions of Americans and can be a harbinger of hemorrhagic or ischemic stroke. Careful diagnostic evaluation of pulsatile tinnitus is critical in providing optimal care and guiding the appropriate treatment strategy.
Observations
An underlying cause of pulsatile tinnitus can be identified in more than 70% of patients with a thorough evaluation. We advocate categorizing the myriad causes of pulsatile tinnitus into structural, metabolic, and vascular groups. Structural causes of pulsatile tinnitus include neoplasms and temporal bone pathologic abnormalities. Metabolic causes of pulsatile tinnitus include ototoxic medications and systemic causes of high cardiac output. Vascular causes of pulsatile tinnitus include idiopathic intracranial hypertension and dural arteriovenous fistulas. This categorization facilitates a practical evaluation, referral, and treatment pattern.
Conclusions and Relevance
Categorizing the underlying cause of pulsatile tinnitus ensures that dangerous causes of pulsatile tinnitus are not missed, and that patients receive the appropriate care from the proper specialist when needed.
11 citations
TL;DR: In this article , a photoplethysmographic (PPG) retinal venous pulse amplitude measurement system was used to measure amplitudes in 30 subjects undergoing invasive ICP measurements by lumbar puncture (LP) or external ventricular drain (EVD).
Abstract: Intracranial pressure (ICP) includes the brain, optic nerve, and spinal cord pressures; it influences blood flow to those structures. Pathological elevation in ICP results in structural damage through various mechanisms, which adversely affects outcomes in traumatic brain injury and stroke. Currently, invasive procedures which tap directly into the cerebrospinal fluid are required to measure this pressure. Recent fluidic engineering modelling analogous to the ocular vascular flow suggests that retinal venous pulse amplitudes are predictably influenced by downstream pressures, suggesting that ICP could be estimated by analysing this pulse signal. We used this modelling theory and our photoplethysmographic (PPG) retinal venous pulse amplitude measurement system to measure amplitudes in 30 subjects undergoing invasive ICP measurements by lumbar puncture (LP) or external ventricular drain (EVD). We estimated ICP from these amplitudes using this modelling and found it to be accurate with a mean absolute error of 3.0 mmHg and a slope of 1.00 (r = 0.91). Ninety-four percent of differences between the PPG and invasive method were between - 5.5 and + 4.0 mmHg, which compares favourably to comparisons between LP and EVD. This type of modelling may be useful for understanding retinal vessel pulsatile fluid dynamics and may provide a method for non-invasive ICP measurement.
TL;DR: In this paper , the authors investigate core-shell pulsatile tablets by combining the advantages of FDM 3D printing and traditional pharmaceutical technology, which are suitable for a patient's individual medication and chronopathology.
Abstract: The aim of the study was to investigate core–shell pulsatile tablets by combining the advantages of FDM 3D printing and traditional pharmaceutical technology, which are suitable for a patient’s individual medication and chronopathology. The tablets were designed and prepared with the commercial verapamil hydrochloride tablets as core inside and the fused deposition modelling (FDM) 3D-printed shell outside. Filaments composed of hydroxypropylmethyl cellulose (HPMC) and polyethylenglycol (PEG) 400 were prepared by hot melt extrusion (HME) and used for fabrication of the shell. Seven types of printed shells were designed for the tablets by adjusting the filament composition, geometric structure and thickness of the shell. A series of evaluations were then performed on the 3D-printed core–shell tablets, including the morphology, weight, hardness, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), in vitro drug release and CT imaging. The results showed that the tablets prepared by FDM 3D printing appeared intact without any defects. All the excipients of the tablet shells were thermally stable during the extruding and printing process. The weight, hardness and in vitro drug release of the tablets were affected by the filament composition, geometric structure and thickness of the shell. The pulsatile tablets achieved personalized lag time ranging from 4 h to 8 h in the drug release test in phosphate-buffered solution (pH 6.8). Therefore, the 3D-printed core–shell pulsatile tablets in this study presented good potential in personalized administration, thereby improving the therapeutic effects of the drug for circadian rhythm disease.
TL;DR: In this paper , a photoplethysmographic (PPG) retinal venous pulse amplitude measurement system was used to measure amplitudes in 30 subjects undergoing invasive ICP measurements by lumbar puncture (LP) or external ventricular drain (EVD).
Abstract: Intracranial pressure (ICP) includes the brain, optic nerve, and spinal cord pressures; it influences blood flow to those structures. Pathological elevation in ICP results in structural damage through various mechanisms, which adversely affects outcomes in traumatic brain injury and stroke. Currently, invasive procedures which tap directly into the cerebrospinal fluid are required to measure this pressure. Recent fluidic engineering modelling analogous to the ocular vascular flow suggests that retinal venous pulse amplitudes are predictably influenced by downstream pressures, suggesting that ICP could be estimated by analysing this pulse signal. We used this modelling theory and our photoplethysmographic (PPG) retinal venous pulse amplitude measurement system to measure amplitudes in 30 subjects undergoing invasive ICP measurements by lumbar puncture (LP) or external ventricular drain (EVD). We estimated ICP from these amplitudes using this modelling and found it to be accurate with a mean absolute error of 3.0 mmHg and a slope of 1.00 (r = 0.91). Ninety-four percent of differences between the PPG and invasive method were between - 5.5 and + 4.0 mmHg, which compares favourably to comparisons between LP and EVD. This type of modelling may be useful for understanding retinal vessel pulsatile fluid dynamics and may provide a method for non-invasive ICP measurement.
TL;DR: This article showed that coupling theoretical and simulated flows to more realistic end boundary conditions, using resistance and compliance values measured in mice instead of using periodic boundaries, results in velocities that match observations more closely in phase and relative amplitude of oscillation, while preserving the existing agreement in mean flow speed.
TL;DR: In this article , the authors investigated the hemodynamic and bio-mechanical changes occurring during the growth stages of abdominal aortic aneurysms using fluid structure interaction (FSI) studies.
TL;DR: In this article , the impact of coiling and blood hematocrit on the risk of intracranial aneurysm rupture was investigated using computational fluid dynamic (CFD) simulations.
Abstract: The precise evaluations of intracranial aneurysms (IAs) are highly prominent for the treatment and control of aneurysm rupture. Computational fluid dynamic (CFD) simulations based on angiography image is a reliable tool for the recognition of high-risk region and aneurysm status in recent years. In our study, the CFD is used to investigate the impacts of blood hematocrit and coiling techniques on the risk of aneurysm rupture. To do this, wall shear stress (WSS), oscillatory shear index (OSI) and pressure distribution on the wall of an aneurysm are comprehensively evaluated in various coding porosities and blood viscosities. One-way Fluid Solid Interaction (FSI) technique is applied to investigate the non-Newtonian, pulsatile blood stream inside the sac of the aneurysm. Impacts of two coiling porosities and blood hematocrits of 0.3 and 0.5 on blood features inside the sac are also analyzed. The influence of the blood mass flow rate in four different time instants of blood cycles on the size of the high-risk region on the aneurysm wall is demonstrated. Our results show that more than 40% reduction is noticed when the hematocrit (HCT) of blood is reduced from 0.5 to 0.3 in different time instants. Our findings also reveal that decreasing the porosity from 0.96 to 0.74 in the peak systolic stage results in a 28% reduction in the maximum OSI at specific HCT = 0.4.
TL;DR: It is demonstrated that pulsatile release is governed by a sudden increase in porosity of the polymeric matrix, leading to the formation of a porous path connecting the core to the environment and contributing to the understanding and design of advanced drug delivery systems.
Abstract: Next-generation therapeutics require advanced drug delivery platforms with precise control over morphology and release kinetics. A recently developed microfabrication technique enables fabrication of a new class of injectable microparticles with a hollow core-shell structure that displays pulsatile release kinetics, providing such capabilities. Here, we study this technology and the resulting core-shell microstructures. We demonstrated that pulsatile release is governed by a sudden increase in porosity of the polymeric matrix, leading to the formation of a porous path connecting the core to the environment. Moreover, the release kinetics within the range studied remained primarily independent of the particle geometry but highly dependent on its composition. A qualitative technique was developed to study the pattern of pH evolution in the particles. A computational model successfully modeled deformations, indicating sudden expansion of the particle before onset of release. Results of this study contribute to the understanding and design of advanced drug delivery systems.
TL;DR: In this paper , the effects of different patterns of coronary artery tortuosity (CAT) on the stress concentration of the plaques and the blood flow pattern inside an atherosclerotic artery to predict the risk of plaque rupture and progression were investigated.
TL;DR: In this paper, the authors used the fourth order Runge-Kutta method (RK4) to solve the force balance equation and presented the influence of pertinent parameters such as Reynolds number, pulsatile frequency, magnetic field strength, Darcy number and fractional-order parameters.
TL;DR: In this article, the authors investigated the hemodynamic and bio-mechanical changes occurring during the growth stages of abdominal aortic aneurysms using fluid structure interaction (FSI) studies.
TL;DR: In this article , the authors used the fourth order Runge-Kutta method (RK4) to solve the force balance equation and presented the influence of pertinent parameters such as Reynolds number, pulsatile frequency, magnetic field strength, Darcy number and fractional-order parameters.
TL;DR: In this article , the authors used computational fluid dynamics to investigate the hemodynamic conditions that may predispose to false lumen enlargement in this patient population, and they found no correlation between the rate of lumen growth and blood pressure, immediate post-op aortic diameter, or the number of fenestrations.
TL;DR: Age and aortic stiffness are significant predictors of cerebral artery pulsatility index in healthy adults and this study highlights the importance of targeting aorti stiffness in the increasingly aging population to reduce the burden of age-related changes in cerebral hemodynamics.
Abstract: The central arteries dampen the pulsatile forces from myocardial contraction, limiting the pulsatility that reaches the cerebral vasculature, although there are limited data on this relationship with aging in humans. The purpose of this study was to determine the association between aortic stiffness and cerebral artery pulsatility index in young and older adults. We hypothesized that cerebral pulsatility index would be associated with aortic stiffness in older adults, but not in young adults. We also hypothesized that both age and aortic stiffness would be significant predictors for cerebral pulsatility index. This study included 23 healthy older adults (aged 62 ± 6 years) and 33 healthy young adults (aged 25 ± 4 years). Aortic stiffness was measured using carotid-femoral pulse wave velocity (cfPWV), while cerebral artery pulsatility index in the internal carotid arteries (ICAs), middle cerebral arteries (MCAs), and basilar artery were assessed using 4D Flow MRI. Cerebral pulsatility index was calculated as (maximum flow – minimum flow) / mean flow. In the combined age group, there was a positive association between cfPWV and cerebral pulsatility index in the ICAs (r = 0.487; p < 0.001), MCAs (r = 0.393; p = 0.003), and basilar artery (r = 0.576; p < 0.001). In young adults, there were no associations between cfPWV and cerebral pulsatility index in any of the arteries of interest (ICAs: r = 0.253; p = 0.156, MCAs: r = −0.059; p = 0.743, basilar artery r = 0.171; p = 0.344). In contrast, in older adults there was a positive association between cfPWV and cerebral pulsatility index in the MCAs (r = 0.437; p = 0.037) and basilar artery (r = 0.500; p = 0.015). However, the relationship between cfPWV and cerebral pulsatility index in the ICAs of the older adults did not reach the threshold for significance (r = 0.375; p = 0.078). In conclusion, age and aortic stiffness are significant predictors of cerebral artery pulsatility index in healthy adults. This study highlights the importance of targeting aortic stiffness in our increasingly aging population to reduce the burden of age-related changes in cerebral hemodynamics.
TL;DR: Cell resolved blood flow simulations are used to study the pulsatile flow of whole blood through a segmented retinal microaneurysm to resolve the impact of rigid red blood cells, as a result of diabetes, in blood flow.
Abstract: Abstract Blood flow within the vasculature of the retina has been found to influence the progression of diabetic retinopathy. In this research cell resolved blood flow simulations are used to study the pulsatile flow of whole blood through a segmented retinal microaneurysm. Images were collected using adaptive optics optical coherence tomography of the retina of a patient with diabetic retinopathy, and a sidewall (sacciform) microaneurysm was segmented from the volumetric data. The original microaneurysm neck width was varied to produce two additional aneurysm geometries in order to probe the influence of neck width on the transport of red blood cells and platelets into the aneurysm. Red blood cell membrane stiffness was also increased to resolve the impact of rigid red blood cells, as a result of diabetes, in blood flow. Wall shear stress and wall shear stress gradients were calculated throughout the aneurysm domains, and the quantification of the influence of the red blood cells is presented. Average wall shear stress and wall shear stress gradients increased due to the increase of red blood cell membrane stiffness. Stiffened red blood cells were also found to induce higher local wall shear stress and wall shear stress gradients as they passed through the leading and draining parental vessels. Stiffened red blood cells were found to penetrate the aneurysm sac more than healthy red blood cells, as well as decreasing the margination of platelets to the vessel walls of the parental vessel, which caused a decrease in platelet penetration into the aneurysm sac.
TL;DR: Compression-coated pulsatile tablets' optimized composition exhibited a lag time of 9’h and released 95% of the ketorolac tromethamine in 17.42 h and validation of the mathematical model assured the reliability of QBD in formulation design.
Abstract: Abstract Pulsatile drug delivery systems have drawn attention in contemporary research for designing chronotherapeutic systems. The current work aims to design pulsatile ketorolac tromethamine tablets using compression coating for delayed delivery with a lag time suitable for the treatment of morning stiffness in arthritis. Rapidly disintegrating core tablets of ketorolac tromethamine were formulated using super-disintegrants, and the optimized formulation was compression using PEO WSR coagulant and Eudragit RLPO for delaying the release. The central composite design and response surface methodology were employed to optimize the formulation and process parameters namely PEO WSR Coagulant (X1), Eudragit RLPO (X2), and Hardness (X3). The dependent variables optimized were lag time and time required for 95% drug release. Analysis using response surface graphs and mathematical modeling of the results allowed identifying and quantifying the formulation variables active on the selected responses. A polynomial equation fitted to the data was used to predict the composition with optimum responses. Compression-coated pulsatile tablets’ optimized composition exhibited a lag time of 9 h and released 95% of the ketorolac tromethamine in 17.42 h. Validation of the mathematical model assured the reliability of QBD in formulation design. In vivo X-ray imaging and pharmacokinetic studies established a strong relationship between the coated polymers maintaining the desired lag time for delayed delivery of the active to coincide with the chronobiology for enhanced bioavailability at the right time when needed.
TL;DR: In this article , the authors analyzed the impact of magnetic field on the unsteady blood flow pass a small vessel with a pulsatile pressure gradient by treating blood as a non-Newtonian fluid, which can be described by Maxwell fluid model with fractional derivative.
TL;DR: In this article , the authors measured the viscoelastic properties of human descending thoracic aorta segments at three different pulse rates to identify the aortic dynamic stiffness ratio, defined as the ratio between the stiffness in case of pulsatile pressure and the stiffness measured for static pressure at the same value of pressure.
Abstract: Healthy human descending thoracic aortas, obtained during organ donation for transplant and research, were tested in a mock circulatory loop to measure the mechanical response to physiological pulsatile pressure and flow. The viscoelastic properties of the aortic segments were investigated at three different pulse rates. The same aortic segments were also subjected to quasi-static pressure tests in order to identify the aortic dynamic stiffness ratio, which is defined as the ratio between the stiffness in case of pulsatile pressure and the stiffness measured for static pressurization, both at the same value of pressure. The loss factor was also identified. The shape of the deformed aorta under static and dynamic pressure was measured by image processing to verify the compatibility of the end supports with the natural deformation of the aorta in the human body. In addition, layer-specific experiments on 10 human descending thoracic aortas allowed to precisely identify the mass density of the aortic tissue, which is an important parameter in cardiovascular dynamic models.
TL;DR: Numerical results indicate that larger PFRs and bifurcated shunt ratios can cause higher wall shear stress (WSS) in some local regions of the aneurysmal dome that may increase the probability of small/secondary aneurYSm generation than under smaller P FRs, and CFD simulations show that the vortex location plays a major role in the temporal and spatial distribution of the WSS on the luminal wall, varying significantly with the cardiac period.
Abstract: The pulsatile flow rate (PFR) in the cerebral artery system and shunt ratios in bifurcated arteries are two patient-specific parameters that may affect the hemodynamic characteristics in the pathobiology of cerebral aneurysms, which needs to be identified comprehensively. Accordingly, a systematic study was employed to study the effects of pulsatile flow rate (i.e., PFR−I, PFR−II, and PFR−III) and shunt ratio (i.e., 75:25 and 64:36) in bifurcated distal arteries, and transient cardiac pulsatile waveform on hemodynamic patterns in two internal carotid artery sidewall aneurysm models using computational fluid dynamics (CFD) modeling. Numerical results indicate that larger PFRs can cause higher wall shear stress (WSS) in some local regions of the aneurysmal dome that may increase the probability of small/secondary aneurysm generation than under smaller PFRs. The low WSS and relatively high oscillatory shear index (OSI) could appear under a smaller PFR, increasing the potential risk of aneurysmal sac growth and rupture. However, the variances in PFRs and bifurcated shunt ratios have rare impacts on the time-average pressure (TAP) distributions on the aneurysmal sac, although a higher PFR can contribute more to the pressure increase in the ICASA−1 dome due to the relatively stronger impingement by the redirected bloodstream than in ICASA−2. CFD simulations also show that the variances of shunt ratios in bifurcated distal arteries have rare impacts on the hemodynamic characteristics in the sacs, mainly because the bifurcated location is not close enough to the sac in present models. Furthermore, it has been found that the vortex location plays a major role in the temporal and spatial distribution of the WSS on the luminal wall, varying significantly with the cardiac period.
TL;DR: Pulsatile flows are demonstrated to be a promising method to delay clogging at both the pore and system scale in a microfluidic array using a dilute suspension of colloidal particles.
Abstract: Clogging is a common obstacle encountered during the transport of suspensions and represents a significant energy and material cost across applications, including water purification, irrigation, biopharmaceutical processing, and aquifer recharge. Pulsatile pressure-driven flows can help mitigate clogging when compared to steady flows. Here, we study experimentally the influence of the amplitude of pulsation 0.25P0 ≤ δP ≤ 1.25P0, where P0 is the mean pressure, and of the frequency of pulsation 10-3 Hz ≤ f ≤ 10-1 Hz on clog mitigation in a microfluidic array of parallel channels using a dilute suspension of colloidal particles. The array geometry is representative of a classical filter, with parallel pores that clog over time, yielding a filter cake that continues to grow and can interact with other pores. We combine flow rate measurements with direct visualizations at the pore scale to correlate the observed clogging dynamics with the changes in flow rate. We observe that all pulsatile amplitudes at 0.1 Hz yield increased throughput compared to steady flows. The rearrangement of particles when subject to a dynamic shear environment can delay the clogging of a pore or even remove an existing clog. However, this benefit is drastically reduced at 10-2 Hz and disappears at 10-3 Hz as the pulsatile timescale becomes too large compared to the timescale associated with the clogging and the growth of the filter cakes in this system. The present study demonstrates that pulsatile flows are a promising method to delay clogging at both the pore and system scale.
TL;DR: In this paper , the authors investigated the role of pulsatile flow within stenosed arteries in myocardial infarction, a medical condition that incorporates high mortality rates, and established the spatio-temporal evolution of vortices influencing the disease.