scholarly journals Non-Newtonian Patient-specific Simulations of Left Atrial Hemodynamics

2021 ◽  
Author(s):  
Alejandro Gonzalo ◽  
Manuel Garcia-Villalba ◽  
Lorenzo Rossini ◽  
Eduardo Duran ◽  
David Vigneault ◽  
...  
Keyword(s):  
Blood Flow ◽  
Left Atrial ◽  
Flow Behavior ◽  
Blood Rheology ◽  
Patient Specific ◽  
Shear Rates ◽  
Wide Range ◽  
History Of ◽  
Slow Blood Flow ◽  
Cell Aggregations

Atrial fibrillation (AF) is the most common arrhythmia, affecting ~35M people worldwide. The irregular beating of the left atrial (LA) caused by AF impacts the LA hemodynamics increasing the risk of thrombosis and ischemic stroke. Most LA thrombi appear in its appendage (LAA), a narrow sac of varied morphology where blood is prone to stagnate. In the LAA, the combination of slow blood flow and low shear rates (<100 [1/s]) promotes the formation of red blood cell aggregations called rouleaux. Blood experiences a non-Newtonian behavior when rouleaux formed that has not been considered in previous CFD analysis of the LA. We model the anatomy and motion of the LA from 4D-CT images and solve the blood flow inside the LA geometry with our CFD in-house code, which models Non-Newtonian rheology with the shear-hematocrit-dependent Carreau-Yasuda equation. We cover a wide range of non-Newtonian effects considering a small and a large hematocrit, including an additional constitutive relation to account for themrouleaux formation time, and we compare our results with Newtonian simulations. Blood rheology influence in LAA hemostasis is studied in 6 patient-specific anatomies. Two subjects had an LAA thrombus (digitally removed before running the simulations), another had a history of TIAs, and the remaining three had normal atrial function. In our simulations, the shear rate remains below 50 [1/s] in the LAA for all non-Newtonian models considered. This triggers an increase of viscosity that alters the flow behavior in that site, which exhibits different flow patterns than Newtonian simulations. These hemodynamic changes translate into differences in the LAA hemostasis, calculated with the residence time.

Rheology of Plastisols of Poly(Vinyl Chloride)

1979 ◽  
Vol 52 (3) ◽  
pp. 676-691 ◽  
Author(s):  
E. A. Collins ◽  
D. J. Hoffmann ◽  
P. L. Soni
Keyword(s):  
Flow Behavior ◽  
Basic Mechanism ◽  
Particle Sizes ◽  
Solvent Interaction ◽  
Factors Affecting ◽  
Shear Rates ◽  
Wide Range ◽  
Size Of Particles ◽  
Increasing Temperature ◽  
Future Work

Abstract The viscosity of PVC plastisols is seen to be affected by numerous variables. Increase in concentration of the resin causes the viscosity to rise, with the increase being more abrupt at the higher concentrations. Deviation from Newtonian behavior also increases with concentration. Decrease in the size of particles results in an increase in viscosity, the effect being more pronounced at low shear rates. Broadening the distribution of particle sizes results in a decrease in viscosity. Porous particles yield plastisols with higher viscosity as compared to nonporous compact particles. The type of plasticizer also affects the viscosity. A plasticizer which is a better solvent for PVC (low value of polymer-solvent interaction parameter, χ) results in a higher viscosity due to an increase in the amount of dissolved polymer. Additives such as alcohols and soaps affect the viscosity in an, as yet, unknown way. Fillers, heat stabilizers, and pigments also increase the viscosity. With increasing temperature, the viscosity first decreases, passes through a minimum and then increases until gelation. With further rise in temperature the viscosity again decreases and then levels out before degradation occurs. In future work, particular emphasis needs to be given to the understanding of the basic mechanism involved in the effect of additives on the flow behavior. Systematic experiments with a range of well-defined particle sizes and over a wide range of shear rates are also needed. A better understanding of the factors affecting the behavior of plastisols will go a long way in changing the art of plastisol formulation to a science.

Nonnewtonian Flow of Poly(Dimethyl Siloxane)

1967 ◽  
Vol 40 (5) ◽  
pp. 1483-1491
Author(s):  
Yoshio Ito
Keyword(s):  
Shear Rate ◽  
Polymer Solutions ◽  
Flow Behavior ◽  
Degree Of Polymerization ◽  
High Shear ◽  
Newtonian Viscosity ◽  
Shear Rates ◽  
Molecular Weights ◽  
Dimethyl Siloxane ◽  
Wide Range

Abstract Nonnewtonian flow of poly(dimethyl siloxanes) of various molecular weights has been studied with a short capillary viscosimeter. The experiment covered a wide range of shear rate, from 10−1 to 3×106sec−1. Results were as follows: (1) Flow behavior of the sample changes with the degree of polymerization. For siloxanes with degrees of polymerization less than 1.55×102, flow of the fluid is newtonian throughout the whole range of shear rates; for siloxanes with degrees of polymerization from 3.22×102 to 2.63×103, flow is nonnewtonian at moderate shear rates; it again becomes newtonian at high shear rates. With degrees of polymerization more than 3.31×103, the spiral flow rises to a high shear rate. (2) Plow behavior of the samples is expressed by modifying Shishido's equation proposed for nonnewtonian polymer solutions. (3) When the observed flow curve contains its inflection point, the upper newtonian viscosity can be estimated by a new method proposed here. (4) The relations among the end correction of capillary, the pressure loss, and the shear stress proposed by Shishido for polymer solutions are applicable to poly(dimethy! siloxane) also.

scholarly journals Therapeutic potential of intranasal photobiomodulation therapy for neurological and neuropsychiatric disorders: a narrative review

2020 ◽  
Vol 31 (3) ◽  
pp. 269-286 ◽  
Author(s):  
Farzad Salehpour ◽  
Sevda Gholipour-Khalili ◽  
Fereshteh Farajdokht ◽  
Farzin Kamari ◽  
Tomasz Walski ◽  
...  
Keyword(s):  
Blood Flow ◽  
Therapeutic Potential ◽  
Blood Rheology ◽  
Potential Method ◽  
Cerebrovascular Diseases ◽  
Photobiomodulation Therapy ◽  
Light Sources ◽  
Novel Approach ◽  
Home Based ◽  
Wide Range

AbstractThe application of photobiomodulation therapy (PBMT) for neuronal stimulation is studied in different animal models and in humans, and has shown to improve cerebral metabolic activity and blood flow, and provide neuroprotection via anti-inflammatory and antioxidant pathways. Recently, intranasal PBMT (i-PBMT) has become an attractive and potential method for the treatment of brain conditions. Herein, we provide a summary of different intranasal light delivery approaches including a nostril-based portable method and implanted deep-nasal methods for the effective systemic or direct irradiation of the brain. Nostril-based i-PBMT devices are available, using either lasers or light emitting diodes (LEDs), and can be applied either alone or in combination to transcranial devices (the latter applied directly to the scalp) to treat a wide range of brain conditions such as mild cognitive impairment, Alzheimer’s disease, Parkinson’s disease, cerebrovascular diseases, depression and anxiety as well as insomnia. Evidence shows that nostril-based i-PBMT improves blood rheology and cerebral blood flow, so that, without needing to puncture blood vessels, i-PBMT may have equivalent results to a peripheral intravenous laser irradiation procedure. Up to now, no studies were conducted to implant PBMT light sources deep within the nose in a clinical setting, but simulation studies suggest that deep-nasal PBMT via cribriform plate and sphenoid sinus might be an effective method to deliver light to the ventromedial part of the prefrontal and orbitofrontal cortex. Home-based i-PBMT, using inexpensive LED applicators, has potential as a novel approach for neurorehabilitation; comparative studies also testing sham, and transcranial PBMT are warranted.

On the Relative Importance of Rheology for Image-Based CFD Models of the Carotid Bifurcation

2006 ◽  
Vol 129 (2) ◽  
pp. 273-278 ◽  
Author(s):  
Sang-Wook Lee ◽  
David A. Steinman
Keyword(s):  
Blood Rheology ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Newtonian Viscosity ◽  
Cfd Simulations ◽  
Shear Rates ◽  
Cfd Models ◽  
Geometric Precision ◽  
Simplifying Assumptions ◽  
Constant Viscosity

Background: Patient-specific computational fluid dynamics (CFD) models derived from medical images often require simplifying assumptions to render the simulations conceptually or computationally tractable. In this study, we investigated the sensitivity of image-based CFD models of the carotid bifurcation to assumptions regarding the blood rheology. Method of Approach: CFD simulations of three different patient-specific models were carried out assuming: a reference high-shear Newtonian viscosity, two different non-Newtonian (shear-thinning) rheology models, and Newtonian viscosities based on characteristic shear rates or, equivalently, assumed hematocrits. Sensitivity of wall shear stress (WSS) and oscillatory shear index (OSI) were contextualized with respect to the reproducibility of the reconstructed geometry, and to assumptions regarding the inlet boundary conditions. Results: Sensitivity of WSS to the various rheological assumptions was roughly 1.0dyn∕cm2 or 8%, nearly seven times less than that due to geometric uncertainty (6.7dyn∕cm2 or 47%), and on the order of that due to inlet boundary condition assumptions. Similar trends were observed regarding OSI sensitivity. Rescaling the Newtonian viscosity based on time-averaged inlet shear rate served to approximate reasonably, if overestimate slightly, non-Newtonian behavior. Conclusions: For image-based CFD simulations of the normal carotid bifurcation, the assumption of constant viscosity at a nominal hematocrit is reasonable in light of currently available levels of geometric precision, thus serving to obviate the need to acquire patient-specific rheological data.

scholarly journals Red cells’ dynamic morphologies govern blood shear thinning under microcirculatory flow conditions

2016 ◽  
Vol 113 (47) ◽  
pp. 13289-13294 ◽  
Author(s):  
Luca Lanotte ◽  
Johannes Mauer ◽  
Simon Mendez ◽  
Dmitry A. Fedosov ◽  
Jean-Marc Fromental ◽  
...  
Keyword(s):  
Flow Direction ◽  
Flow Behavior ◽  
Blood Rheology ◽  
Shear Thinning ◽  
Shear Stresses ◽  
Flow Conditions ◽  
Shear Rates ◽  
Volume Fractions ◽  
Microcirculatory Flow ◽  
Morphological Transitions

Blood viscosity decreases with shear stress, a property essential for an efficient perfusion of the vascular tree. Shear thinning is intimately related to the dynamics and mutual interactions of RBCs, the major component of blood. Because of the lack of knowledge about the behavior of RBCs under physiological conditions, the link between RBC dynamics and blood rheology remains unsettled. We performed experiments and simulations in microcirculatory flow conditions of viscosity, shear rates, and volume fractions, and our study reveals rich RBC dynamics that govern shear thinning. In contrast to the current paradigm, which assumes that RBCs align steadily around the flow direction while their membranes and cytoplasm circulate, we show that RBCs successively tumble, roll, deform into rolling stomatocytes, and, finally, adopt highly deformed polylobed shapes for increasing shear stresses, even for semidilute volume fractions of the microcirculation. Our results suggest that any pathological change in plasma composition, RBC cytosol viscosity, or membrane mechanical properties will affect the onset of these morphological transitions and should play a central role in pathological blood rheology and flow behavior.

An Approach on Fluid-Structure Interaction for Hemodynamics of Carotid Arteries

2012 ◽  
Author(s):  
Sang Hyuk Lee ◽  
Seongwon Kang ◽  
Nahmkeon Hur
Keyword(s):  
Blood Flow ◽  
Carotid Artery ◽  
Solid Mechanics ◽  
Fluid Structure Interaction ◽  
Blood Rheology ◽  
Numerical Approach ◽  
Patient Specific ◽  
Circulation System ◽  
Fluid Structure ◽  
Structure Interaction

In the present study, a problem of the hemodynamic fluid-structure interaction (FSI) in the carotid artery was analyzed using a numerical approach. To predict the blood flow and arterial deformation, a framework for the FSI analysis was developed by coupling computational fluid dynamics (CFD) and solid mechanics (CSM) approaches. Using this framework, the hemodynamics of the carotid artery was simulated with the patient-specific clinical data of the arterial geometry, pulsatile blood flow and blood rheology. It is found that the hemodynamic characteristics of the carotid artery are significantly affected by its geometric factors and flow conditions, and relatively low values of the wall shear stress were observed in the post-plaque dilated region of the carotid bifurcated area. Since these characteristics of the carotid artery are affected by the cerebral circulation system, the effects of the cardiac output and the distal vascular resistance on hemodynamics were also analyzed.

Experimental and theoretical investigations on the viscosity of heterogeneous asphalt binders

2017 ◽  
Vol 50 (4) ◽  
pp. 354-371 ◽  
Author(s):  
Aboelkasim Diab
Keyword(s):  
Flow Behavior ◽  
Ethylene Vinyl Acetate ◽  
Hydrated Lime ◽  
Crumb Rubber ◽  
Asphalt Binders ◽  
Zero Shear Viscosity ◽  
Shear Rates ◽  
Wide Range ◽  
Theoretical Investigations ◽  
Pavement Construction

The inherent multiphase structure of heterogeneous asphalt binders (additives containing binders) may complicate viscosity understanding and predictions in the Newtonian or non-Newtonian response. The objective of this article is to understand the viscosity characteristics of heterogeneous asphalt binders based on experimental and theoretical investigations over a wide range of conditions the matter may encounter in the field (temperatures and oxidative aging). Selected materials representing the generic additives commonly used for pavement construction including styrene–butadiene–styrene block copolymer and ethylene–vinyl acetate copolymer, crumb rubber, and two mineral fillers, namely hydrated lime and fly ash, were utilized separately at different concentrations to produce the heterogeneous materials under study. The effects of varied temperatures as well as short- and long-term aging processes were studied for the materials over a wide range of shear rates. A further theoretical investigation was carried out by addressing the capability of Tscheuschner model to predict the flow behavior under the aforementioned conditions. In addition, the zero shear viscosity said to be an intrinsic characteristic of asphalt binders was evaluated using the regression analysis of data predicted from Tscheuschner model. Overall, the shear thinning behavior of heterogeneous asphalt binders occurred at low shear rates as compared to the base binder, especially at low temperatures. Emphasis was placed on the repeatability of the model predictions under different conditions, which could be an initiative to provide a simple but accurate representation of the viscosity of heterogeneous asphalt binders.

Endocardial left atrial appendage occlusion in atrial fibrillation: computational fluid dynamics simulations to assess stroke risk

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
A Masci ◽  
N D"alessandro ◽  
A Scivoletto ◽  
S Severi ◽  
F Ansaloni ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Atrial Fibrillation ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Left Atrial ◽  
Left Atrial Appendage ◽  
Blood Stasis ◽  
Atrial Appendage ◽  
Patient Specific ◽  
Hemodynamic Changes

Abstract Funding Acknowledgements Type of funding sources: None. Background Percutaneous endocardial left atrial appendage (LAA) occlusion (LAAO) in non-valvular atrial fibrillation (AF) seems comparable to anticoagulation therapy (OAC) as regards thromboembolic risk reduction with a possible additional decrease in major bleeding. LAAO is currently limited to patients with contraindications to OAC, due to its high costs and procedural risks, but better pre-procedural planning and operative techniques might improve the outcome widening practical indications. Computational fluid dynamics (CFD) represents a valuable non-invasive approach to estimate physiologically significant hemodynamic parameters in a complex fluid dynamics system. It might provide a helpful in silico simulation of blood flow patterns within the LA and LAA by using 3D patient-specific models, allowing LAAO planning and effects prediction. Purpose This study’s aim was to simulate the fluid dynamics effects of LAAO in AF patients to predict patient-specific hemodynamic changes caused by applying the two most popular devices. Methods LAAO was simulated on the 3D LA anatomical models obtained from CT data in 5 AF patients, considering the device specific shape. CFD simulations in AF condition were performed both on the whole LA model and on the models with the LAAO performed with the two devices. Significant fluid dynamics indices (blood velocity, vortex structures, LAA ostium velocity, LA blood stasis) were computed to evaluate the changes in the flow patterns after LAAO in relation to the thrombogenic risk. Results Overall we found a more effective washout within the LA after LAAO, in terms of a different spatial distribution of velocities (see figure for a qualitative evaluation of LA blood flow velocity in one patient: (A) model with LA and LAA; models after LAAO applying the Amulet (B) and the Watchman (C) device) and vortex structures (after LAAO, they were decreased in number and increased in size). Moreover, a higher velocity at the mitral valve and at the LAA ostium (peak velocity: 12-17 cm/s in the models with LAA, 40-60 cm/s in LAAO_A and 35-65 in LAAO_W) was detected together with  a slightly improved washout effect in terms of blood stasis with the Watchman device (stasis: 3.1-5.7% in the models with LAA, 1.9-4.1% in LAAO_A, 1.7-3.7% in LAAO_W). Conclusions A workflow for simulating the fluid dynamics effects of endocardial LAAO in AF was developed and tested. CFD provides a valuable tool to quantify hemodynamic changes after LAAO and assess thrombogenic risk in patient-specific LA and LAA. Our preliminary results suggest that endocardial LAAO favourably affects blood fluid dynamics in the LA. Abstract figure

scholarly journals Demonstration of Patient-Specific Simulations To Assess Left Atrial Appendage Thrombogenesis Risk

2020 ◽  
Author(s):  
Manuel García-Villalba ◽  
Lorenzo Rossini ◽  
Alejandro Gonzalo ◽  
Davis Vigneault ◽  
Pablo Martinez-Legazpi ◽  
...  
Keyword(s):  
Left Atrial ◽  
Left Atrial Appendage ◽  
Bleeding Risk ◽  
Atrial Appendage ◽  
Patient Specific ◽  
Immersed Boundary ◽  
Moving Wall ◽  
History Of ◽  
Small Cohort ◽  
And Function

AbstractAtrial fibrillation (AF) alters left atrial (LA) hemodynamics, which can lead to thrombosis in the left atrial appendage (LAA), systemic embolism and stroke. A personalized risk-stratification of AF patients for stroke would permit improved balancing of preventive anticoagulation therapies against bleeding risk. We investigated how LA anatomy and function impact LA and LAA hemodynamics, and explored whether patient-specific analysis by computational fluid dynamics (CFD) can predict the risk of LAA thrombosis. We analyzed 4D-CT acquisitions of LA wall motion with an in-house immersed-boundary CFD solver. We considered six patients with diverse atrial function, three without a LAA thrombus (LAAT/TIA-neg), and three with either a LAA thrombus (removed digitally before running the simulations) or a history of transient ischemic attacks (LAAT/TIA-pos). We found that blood inside the left atrial appendage of LAAT/TIA-pos patients had marked alterations in residence time and kinetic energy when compared with LAAT/TIA-neg patients. In addition, we showed how the LA conduit, reservoir and booster functions distinctly affect LA and LAA hemodynamics. While the flow dynamics of fixed-wall and moving-wall simulations differ significantly, fixed-wall simulations risk-stratified our small cohort for LAA thrombosis only slightly worse than moving-wall simulations.

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