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A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: closed (30 June 2019) | Viewed by 57815

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Special Issue Editors

Dr. Andrew Cookson

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Guest Editor

Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK
Interests: perfusion imaging; vascular devices; computational modelling; laminar mixing

Prof. Michael W. Plesniak

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Guest Editor

Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
Interests: experimental biofluid dynamics; bioinspired engineering; stent fractures; secondary flows in arteries

Special Issue Information

Dear Colleagues,

The flow of blood in the cardiovascular system is a multi-scale, non-Newtonian, pulsatile flow phenomenon, with complex mechanical and biological interactions in both health and disease. Our understanding of this system has advanced tremendously in the past few decades, and with exciting developments in medical imaging technology, numerical methods, and experimental techniques, we would like to present the very latest progress in cardiovascular flow research.

Though cardiovascular flow covers a broad range of topics, the aim of this Special Issue is to collect together papers that demonstrate and enable fundamental insights into cardiovascular flow. In particular, we are seeking to highlight the state-of-the–art, as well as new theoretical and experimental representations of the cardiovascular system, methods for assimilating and combining experimental and medical imaging data with computational simulations, as well as novel methods for extracting meaningful information from flow data, whether in the form of visualisations, data/model reduction, or biologically meaningful indices.

Dr. Andrew Cookson
Prof. Michael W. Plesniak
Guest Editors

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Keywords

haemodynamics
computational modelling
flow visualization
data assimilation
experimental methods
flow biomarkers
reduced modelling

Published Papers (11 papers)

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Research

20 pages, 7942 KiB

Open AccessArticle

Blood Flow Dynamics at the Pulmonary Artery Bifurcation

by Francesco Capuano, Yue-Hin Loke and Elias Balaras

Fluids 2019, 4(4), 190; https://doi.org/10.3390/fluids4040190 - 01 Nov 2019

Cited by 14 | Viewed by 12662

Abstract

Knowledge of physiologic hemodynamics is a fundamental requirement to establish pathological findings. However, little is known about the normal flow fields in the pulmonary arteries, especially for children. The purpose of this study is to characterize flow patterns in the pulmonary artery bifurcation of healthy pediatric subjects using direct numerical simulations. A realistic geometry is obtained via statistical shape modeling, by averaging five subject-specific digital models extracted from cardiovascular magnetic resonance datasets of healthy volunteers. Boundary conditions are assigned to mimic physiological conditions at rest, corresponding to a peak Reynolds number equal to 3400 and a Womersley number equal to 15. Results show that the normal bifurcation is highly hemodynamically efficient, as measured by an energy dissipation index. The curvature of the pulmonary arteries is sufficiently small to prevent flow separation along the inner walls, and no signs of a turbulent-like state are found. In line with previous imaging studies, a helical structure protruding into the right pulmonary artery is detected, and its formation mechanism is elucidated in the paper. These findings might help to identify abnormal flow features in patients with altered anatomic and physiologic states, particularly those with repaired congenital heart disease. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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18 pages, 4200 KiB

Open AccessArticle

Injection of Deformable Capsules in a Reservoir: A Systematic Analysis

by Alessandro Coclite and Alberto M. Gambaruto

Fluids 2019, 4(3), 122; https://doi.org/10.3390/fluids4030122 - 03 Jul 2019

Cited by 4 | Viewed by 2451

Abstract

Motivated by red blood cell dynamics and injectable capsules for drug delivery, in this paper, a computational study of capsule ejection from a narrow channel into a reservoir is undertaken for a combination of varying deformable capsule sizes and channel dimensions. A mass-spring membrane model is coupled to an Immersed Boundary–Lattice Boltzmann model solver. The aim of the present work is the description of the capsules’ motion, deformation and the response of the fluid due to the complex particles’ dynamics. The interactions between the capsules affect the local velocity field and are responsible for the dynamics observed. Capsule membrane deformability is also seen to affect inter-capsule interaction. We observe that the train of three particles locally homogenises the velocity field and the leading capsule travels faster than the other two trailing capsules. Variations in the size of reservoir do not seem to be relevant, while the ratio of capsule diameter to channel diameter as well as the ratio of capsule diameter to inter-capsule spacing play a major role. This flow set-up has not been covered in the literature, and consequently we focus on describing capsule motion, membrane deformation and fluid dynamics, as a preliminary investigation in this field. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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17 pages, 4508 KiB

Open AccessArticle

Image-Guided Fluid-Structure Interaction Simulation of Transvalvular Hemodynamics: Quantifying the Effects of Varying Aortic Valve Leaflet Thickness

by Anvar Gilmanov, Alexander Barker, Henryk Stolarski and Fotis Sotiropoulos

Fluids 2019, 4(3), 119; https://doi.org/10.3390/fluids4030119 - 29 Jun 2019

Cited by 16 | Viewed by 5078

Abstract

When flow-induced forces are altered at the blood vessel, maladaptive remodeling can occur. One reason such remodeling may occur has to do with the abnormal functioning of the aortic heart valve due to disease, calcification, injury, or an improperly-designed prosthetic valve, which restricts the opening of the valve leaflets and drastically alters the hemodynamics in the ascending aorta. While the specifics underlying the fundamental mechanisms leading to changes in heart valve function may differ from one cause to another, one common and important change is in leaflet stiffness and/or mass. Here, we examine the link between valve stiffness and mass and the hemodynamic environment in aorta by coupling magnetic resonance imaging (MRI) with high-resolution fluid–structure interaction (FSI) computational fluid dynamics to simulate blood flow in a patient-specific model. The thoracic aorta and a native aortic valve were re-constructed in the FSI model from the MRI data and used for the simulations. The effect of valve stiffness and mass is parametrically investigated by varying the thickness (h) of the leaflets (h = 0.6, 2, 4 mm). The FSI simulations were designed to investigate systematically progressively higher levels of valve stiffness by increasing valve thickness and quantifying hemodynamic parameters known to be linked to aortopathy and valve disease. The computed results reveal dramatic differences in all hemodynamic parameters: (1) the geometric orifice area (GOA), (2) the maximum velocity

V_{\max}

of the jet passing through the aortic orifice area, (3) the rate of energy dissipation

{\dot{E}}_{diss} (t)

, (4) the total loss of energy

E_{diss}

, (5) the kinetic energy of the blood flow

E_{kin} (t)

, and (6) the average magnitude of vorticity

Ω_{a} (t),

illustrating the change in hemodynamics that occur due to the presence of aortic valve stenosis. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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27 pages, 30652 KiB

Open AccessArticle

Near-Wall Flow in Cerebral Aneurysms

by Vahid Goodarzi Ardakani, Xin Tu, Alberto M. Gambaruto, Iolanda Velho, Jorge Tiago, Adélia Sequeira and Ricardo Pereira

Fluids 2019, 4(2), 89; https://doi.org/10.3390/fluids4020089 - 16 May 2019

Cited by 12 | Viewed by 4964

Abstract

The region where the vascular lumen meets the surrounding endothelium cell layer, hence the interface region between haemodynamics and cell tissue, is of primary importance in the physiological functions of the cardiovascular system. The functions include mass transport to/from the blood and tissue, and signalling via mechanotransduction, which are primary functions of the cardiovascular system and abnormalities in these functions are known to affect disease formation and vascular remodelling. This region is denoted by the near-wall region in the present work, and we outline simple yet effective numerical recipes to analyse the near-wall flow field. Computational haemodynamics solutions are presented for six patient specific cerebral aneurysms, at three instances in the cardiac cycle: peak systole, end systole (taken as dicrotic notch) and end diastole. A sensitivity study, based on Newtonian and non-Newtonian rheological models, and different flow rate profiles, is effected for a selection of aneurysm cases. The near-wall flow field is described by the wall shear stress (WSS) and the divergence of wall shear stress (WSSdiv), as descriptors of tangential and normal velocity components, respectively, as well as the wall shear stress critical points. Relations between near-wall and free-stream flow fields are discussed. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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16 pages, 1886 KiB

Open AccessArticle

Impact of Inflow Boundary Conditions on the Calculation of CT-Based FFR

by Ernest W. C. Lo, Leon J. Menezes and Ryo Torii

Fluids 2019, 4(2), 60; https://doi.org/10.3390/fluids4020060 - 28 Mar 2019

Cited by 18 | Viewed by 4814

Abstract

Background: Calculation of fractional flow reserve (FFR) using computed tomography (CT)-based 3D anatomical models and computational fluid dynamics (CFD) has become a common method to non-invasively assess the functional severity of atherosclerotic narrowing in coronary arteries. We examined the impact of various inflow boundary conditions on computation of FFR to shed light on the requirements for inflow boundary conditions to ensure model representation. Methods: Three-dimensional anatomical models of coronary arteries for four patients with mild to severe stenosis were reconstructed from CT images. FFR and its commonly-used alternatives were derived using the models and CFD. A combination of four types of inflow boundary conditions (BC) was employed: pulsatile, steady, patient-specific and population average. Results: The maximum difference of FFR between pulsatile and steady inflow conditions was 0.02 (2.4%), approximately at a level similar to a reported uncertainty level of clinical FFR measurement (3–4%). The flow with steady BC appeared to represent well the diastolic phase of pulsatile flow, where FFR is measured. Though the difference between patient-specific and population average BCs affected the flow more, the maximum discrepancy of FFR was 0.07 (8.3%), despite the patient-specific inflow of one patient being nearly twice as the population average. Conclusions: In the patients investigated, the type of inflow boundary condition, especially flow pulsatility, does not have a significant impact on computed FFRs in narrowed coronary arteries. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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26 pages, 12066 KiB

Open AccessArticle

Efficiently Generating Mixing by Combining Differing Small Amplitude Helical Geometries

by Andrew N. Cookson, Denis J. Doorly and Spencer J. Sherwin

Fluids 2019, 4(2), 59; https://doi.org/10.3390/fluids4020059 - 27 Mar 2019

Cited by 9 | Viewed by 3452

Abstract

Helical geometries have been used in recent years to form cardiovascular prostheses such as stents and shunts. The helical geometry has been found to induce swirling flow, promoting in-plane mixing. This is hypothesised to reduce the formation of thrombosis and neo-intimal hyperplasia, in turn improving device patency and reducing re-implantation rates. In this paper we investigate whether joining together two helical geometries, of differing helical radii, in a repeating sequence, can produce significant gains in mixing effectiveness, by embodying a ‘streamline crossing’ flow environment. Since the computational cost of calculating particle trajectories over extended domains is high, in this work we devised a procedure for efficiently exploring the large parameter space of possible geometry combinations. Velocity fields for the single geometries were first obtained using the spectral/hp element method. These were then discontinuously concatenated, in series, for the particle tracking based mixing analysis of the combined geometry. Full computations of the most promising combined geometries were then performed. Mixing efficiency was evaluated quantitatively using Poincaré sections, particle residence time data, and information entropy. Excellent agreement was found between the idealised (concatenated flow field) and the full simulations of mixing performance, revealing that a strict discontinuity between velocity fields is not required for mixing enhancement, via streamline crossing, to occur. Optimal mixing was found to occur for the combination

R = 0.2 D

and

R = 0.5 D

, producing a

70 %

increase in mixing, compared with standard single helical designs. The findings of this work point to the benefits of swirl disruption and suggest concatenation as an efficient means to determine optimal configurations of repeating geometries for future designs of vascular prostheses. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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19 pages, 4824 KiB

Open AccessArticle

Stenosis Indicators Applied to Patient-Specific Renal Arteries without and with Stenosis

by Alexander Fuchs, Niclas Berg and Lisa Prahl Wittberg

Fluids 2019, 4(1), 26; https://doi.org/10.3390/fluids4010026 - 15 Feb 2019

Cited by 9 | Viewed by 2765

Abstract

Pulsatile flow in the abdominal aorta and the renal arteries of three patients was studied numerically. Two of the patients had renal artery stenosis. The aim of the study was to assess the use of four types of indicators for determining the risk of new stenosis after revascularization of the affected arteries. The four indicators considered include the time averaged wall shear stress (TAWSS), the oscillatory shear index (OSI), the relative reference time (RRT) and a power law model based in platelet activation modeling but applied to the endothelium, named endothelium activation indicator (EAI). The results show that the indicators can detect the existing stenosis but are less successful in the revascularized cases. The TAWSS and, more clearly, the EAI approach seem to be better in predicting the risk for stenosis relapse at the original location and close to the post-stenotic dilatation. The shortcomings of the respective indicators are discussed along with potential improvements to endothelial activation modeling and its use as an indicator for risks of restenosis. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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19 pages, 4201 KiB

Open AccessArticle

Use of Computational Fluid Dynamics to Analyze Blood Flow, Hemolysis and Sublethal Damage to Red Blood Cells in a Bileaflet Artificial Heart Valve

by Madison E. James, Dimitrios V. Papavassiliou and Edgar A. O’Rear

Fluids 2019, 4(1), 19; https://doi.org/10.3390/fluids4010019 - 29 Jan 2019

Cited by 18 | Viewed by 5674

Abstract

Artificial heart valves may expose blood to flow conditions that lead to unnaturally high stress and damage to blood cells as well as issues with thrombosis. The purpose of this research was to predict the trauma caused to red blood cells (RBCs), including hemolysis, from the stresses applied to them and their exposure time as determined by analysis of simulation results for blood flow through both a functioning and malfunctioning bileaflet artificial heart valve. The calculations provided the spatial distribution of the Kolmogorov length scales that were used to estimate the spatial and size distributions of the smallest turbulent flow eddies in the flow field. The number and surface area of these eddies in the blood were utilized to predict the amount of hemolysis experienced by RBCs. Results indicated that hemolysis levels are low while suggesting stresses at the leading edge of the leaflet may contribute to subhemolytic damage characterized by shortened circulatory lifetimes and reduced RBC deformability. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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13 pages, 3368 KiB

Open AccessArticle

Cardiac Triangle Mapping: A New Systems Approach for Noninvasive Evaluation of Left Ventricular End Diastolic Pressure

by Niema M. Pahlevan and Ray V. Matthews

Fluids 2019, 4(1), 16; https://doi.org/10.3390/fluids4010016 - 22 Jan 2019

Cited by 6 | Viewed by 6237

Abstract

Noninvasive and practical assessment of hemodynamics is a critical unmet need in the treatment of both chronic and acute cardiovascular diseases. Particularly, the ability to monitor left ventricular end-diastolic pressure (LVEDP) noninvasively offers enormous benefit for managing patients with chronic congestive heart failure. Recently, we provided proof of concept that a new cardiac metric, intrinsic frequency (IF), derived from mathematical analysis of non-invasively captured arterial waveforms, can be used to accurately compute cardiovascular hemodynamic measures, such as left ventricle ejection fraction (LVEF), by using a smartphone. In this manuscript, we propose a new systems-based method called cardiac triangle mapping (CTM) for hemodynamics evaluation of the left ventricle. This method is based on intrinsic frequency (IF) and systolic time interval (STI) methods that allows computation of LVEDP from noninvasive measurements. Since the CTM method only requires arterial waveform and electrocardiogram (ECG), it can eventually be adopted as a simple smartphone-based device, an inexpensive hand-held device, or perhaps (with future design modifications) a wearable sensor. Such devices, combined with this method, would allow for remote monitoring of heart failure patients. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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16 pages, 29547 KiB

Open AccessArticle

An Experimental Study of Pulsatile Flow in a Compliant Aortic Root Model under Varied Cardiac Outputs

by Ruihang Zhang and Yan Zhang

Fluids 2018, 3(4), 71; https://doi.org/10.3390/fluids3040071 - 04 Oct 2018

Cited by 9 | Viewed by 4477

Abstract

The fluid dynamics of a natural aortic valve are complicated due to the highly pulsatile flow conditions, the compliant wall boundaries, and the sophisticated geometry of the aortic root. In the present study, a pulsatile flow simulator was constructed and utilized to investigate the turbulent characteristics and structural deformation of an intact silicone aortic root model under different flow inputs. Particle image velocimetry and high-frequency pressure sensors were combined to gather the pulsatile flow field information. The results demonstrated the distributions and the variations of the jet flow structures at different phases of a cardiac cycle. High turbulence kinetic energy was observed after the peak systole phase when the flow started to decelerate. Deformations of the aortic root upstream and downstream of the valve leaflets under normal boundary conditions were summarized and found to be comparable to results from clinical studies. The cardiac output plays an important role in determining the strength of hemodynamic and structural responses. A reduction in cardiac outputs resulted in a lower post-systole turbulence, smaller circumferential deformation, a smaller geometric orifice area, and a shortened valve-opening period. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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13 pages, 1582 KiB

Open AccessArticle

Sinus Hemodynamics in Representative Stenotic Native Bicuspid and Tricuspid Aortic Valves: An In-Vitro Study

by Hoda Hatoum and Lakshmi Prasad Dasi

Fluids 2018, 3(3), 56; https://doi.org/10.3390/fluids3030056 - 06 Aug 2018

Cited by 21 | Viewed by 4367

Abstract

(1) The study’s objective is to assess sinus hemodynamics differences between stenotic native bicuspid aortic valve (BAV) and native tricuspid aortic valve (TrAV) sinuses in order to assess sinus flow shear and vorticity dynamics in these common pathological states of the aortic valve. (2) Representative patient-specific aortic roots with BAV and TrAV were selected, segmented, and 3D printed. The flow dynamics within the sinus were assessed in-vitro using particle image velocimetry in a left heart simulator at physiological pressure and flow conditions. Hemodynamic data calculations, vortex tracking, shear stress probability density functions and sinus washout calculations based on Lagrangian particle tracking were performed. (3) (a) At peak systole, velocity and vorticity in BAV reach 0.67 ± 0.02 m/s and 374 ± 5 s⁻¹ versus 0.49 ± 0.03 m/s and 293 ± 3 s⁻¹ in TrAV; (b) Aortic sinus vortex is slower to form but conserved in BAV sinus; (c) BAV shear stresses exceed those of TrAV (1.05 Pa versus 0.8 Pa); (d) Complete TrAV washout was achieved after 1.5 cycles while it was not for BAV. (4) In conclusion, sinus hemodynamics dependence on the different native aortic valve types and sinus morphologies was clearly highlighted in this study. Full article

(This article belongs to the Special Issue Cardiovascular Flows)

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