Elsevier

Medical Engineering & Physics

Volume 82, August 2020, Pages 58-69
Medical Engineering & Physics

Does the inflow velocity profile influence physiologically relevant flow patterns in computational hemodynamic models of left anterior descending coronary artery?

https://doi.org/10.1016/j.medengphy.2020.07.001Get rights and content

Highlights

  • Computational hemodynamics in coronary arteries is affected by uncertainties.

  • The velocity profile applied as inflow boundary condition is a source of uncertainty.

  • A framework is developed to generate analytical, realistic 3D velocity profiles.

  • The velocity profile impacts local hemodynamics in the proximal segment only.

  • The velocity profile impact length is generally shorter than the theoretical entrance length.

Abstract

Patient-specific computational fluid dynamics is a powerful tool for investigating the hemodynamic risk in coronary arteries. Proper setting of flow boundary conditions in computational hemodynamic models of coronary arteries is one of the sources of uncertainty weakening the findings of in silico experiments, in consequence of the challenging task of obtaining in vivo 3D flow measurements within the clinical framework. Accordingly, in this study we evaluated the influence of assumptions on inflow velocity profile shape on coronary artery hemodynamics. To do that, (1) ten left anterior descending coronary artery (LAD) geometries were reconstructed from clinical angiography, and (2) eleven velocity profiles with realistic 3D features such as eccentricity and differently shaped (single- and double-vortex) secondary flows were generated analytically and imposed as inflow boundary conditions. Wall shear stress and helicity-based descriptors obtained prescribing the commonly used parabolic velocity profile were compared with those obtained with the other velocity profiles. Our findings indicated that the imposition of idealized velocity profiles as inflow boundary condition is acceptable as long the results of the proximal vessel segment are not considered, in LAD coronary arteries. As a pragmatic rule of thumb, a conservative estimation of the length of influence of the shape of the inflow velocity profile on LAD local hemodynamics can be given by the theoretical entrance length for cylindrical conduits in laminar flow conditions.

Introduction

The marked predisposition to develop atherosclerosis makes coronary arteries of paramount clinical relevance. Although atherosclerosis initiation and progression results from the interplay of many systemic factors [1], its development at specific, geometrically predisposed locations such as branching and bifurcations [2] suggested the involvement of local hemodynamics [3,4]. In particular, the role of wall shear stress (WSS) was extensively investigated over the last years [5], [6], [7], [8], while more recently the role of intravascular helical patterns on coronary atherosclerosis initiation and progression was demonstrated [9,10]. In this context, the combined use of medical imaging and computational fluid dynamics (CFD) has proven to be a valuable tool in the study of possible associations between local hemodynamics and coronary artery disease as it makes available highly resolved hemodynamic flow patterns inside anatomically realistic, patient-specific geometries [11], [12], [13]. However, in silico methods require assumptions that introduce uncertainties, weakening CFD findings at a level that could limit their translation to clinics [14], [15], [16], [17], [18], [19], [20]. As recently highlighted, the uncertainties in cardiovascular modelling should not compromise its added value with respect to standard clinical measurement and therefore they should be carefully assessed.

While anatomically realistic geometries can be reconstructed with satisfactory accuracy using in vivo imaging tools, acquiring non-defective patient-specific boundary conditions, as required to perform reliable computational hemodynamics, is not always feasible. This is particularly true for the coronary arteries, for which (1) the measurable (whenever possible) inflow rates can be imposed only in terms of idealized velocity profiles, and (2) the possibility to use realistic three-dimensional (3D) velocity profiles measured directly in vivo as inflow boundary condition is still challenging, due to issues related to resolution and cardiac motion [21]. To be clearer, when only the integral quantity flow rate is available, its translation to inflow Dirichlet boundary condition in terms of 3D velocity profiles in CFD applications necessarily undergoes an idealization process based on a priori hypotheses to fill the gap of information. For these reasons, most of the previous computational studies on coronary arteries, including those accounting for the presence of coronary stents, starting from in vivo flow rate measurements/estimations, prescribed the inflow boundary conditions in terms of flat (e.g. [22], [23], [24], [25]) or fully developed (e.g. [26], [27], [28], [29], [30]) velocity profiles. Such a priori hypotheses on the velocity profiles to be used as conditions at inflow boundaries represent a source of uncertainty in the estimation of helical and WSS patterns [31], potentially masking their relationship with atherosclerosis initiation and progression. Moreover, in vitro and in silico hemodynamic studies revealed the presence of skewed velocity profiles in the left coronary artery [32], [33], [34], with a not negligible presence of secondary flows in the entire coronary tree, as it can be expected by considering the vessel tortuosity and the presence of bifurcations and branching.

In this context, the aim of this study was to evaluate the budget of uncertainty associated with assumptions on the shape of the velocity profiles imposed as inflow boundary conditions in coronary artery CFD models. To this end, a framework was developed enabling the generation of artificial velocity profiles by means of generalized analytical formulations able to (1) generate 3D velocity profiles with secondary flows, and (2) fit the non-circular cross-section of blood vessels. The developed framework was then applied to left anterior descending (LAD) coronary artery models to evaluate the impact that the shape of inflow velocity profiles used as inlet boundary condition has on WSS distribution at the luminal surface and intravascular flow features, focusing on helical flow patterns.

Section snippets

Image data collection and 3D vessel reconstruction

Ten subjects (8 males and 2 females, age = 58.6 ± 6.5) that underwent invasive coronary cineangiography after heart transplant with no sign of atherosclerosis were selected for this study. Clinical images were acquired at Città della Salute e della Scienza hospital (Turin, Italy) with the monoplane X-ray system Allura Xper (Philips Medical Systems, Amsterdam, The Netherlands). Two cranial, end-diastolic angiographic projections, with a minimum angle of 25° between them were used to reconstruct

Near-wall hemodynamics

The impact that the shape of the inflow velocity profile has on WSS was firstly evaluated in terms of AWSS percentage differences with respect to the reference (TP-only parabolic) velocity profile. In the box plot of Fig. 3, the analysis is presented aggregating AWSS data from all the 10 LAD models on the basis of the specific velocity profile used as inflow boundary condition and considering the whole vessel and its division in three segments. Overall, the largest percentage differences from

Discussion

In computational hemodynamics, when dealing with patient-specific models, the imposition of in vivo measured 3D velocity profiles as inflow boundary condition leads to more realistic simulations. However, velocity profiles are often not measurable in vivo, and their idealized versions, based upon assumptions needed to fill a gap of knowledge, are prescribed to model blood flow.

In coronary arteries, blood flow velocity values can be derived in vivo from Doppler flow velocity or thermodilution

Conclusions

In this study, the impact of the shape of blood velocity profiles, prescribed as inflow boundary conditions in image-based computational models of LAD coronary arteries, on local hemodynamics was evaluated. Our findings highlighted that the hemodynamic impact of considering realistic 3D features, such as eccentricity and differently shaped secondary flows, as a part of the inflow velocity profile is limited to the proximal LAD segment. Furthermore, the findings suggested that the problem of the

Declaration of Competing Interest

The authors have no professional or financial conflicts of interest to disclose.

Funding

None.

Ethical approval

The study was approved by the Ethics Committee of the Città della Salute e della Scienza hospital in Turin. Informed consent was obtained from the patients for being included in the study. The Ethical approval was given April 4th, 2019 with protocol number 0036571.

References (61)

  • U. Morbiducci et al.

    Inflow boundary conditions for image-based computational hemodynamics: impact of idealized versus measured velocity profiles in the human aorta

    J Biomech

    (2013)
  • E. Doutel et al.

    Experimental and numerical methodology to analyze flows in a coronary bifurcation

    Eur J Mech B/Fluids

    (2018)
  • E. Wellnhofer et al.

    Flow simulation studies in coronary arteries-Impact of side-branches

    Atherosclerosis

    (2010)
  • Y. Li et al.

    Impact of Side Branch Modeling on Computation of Endothelial Shear Stress in Coronary Artery Disease: coronary Tree Reconstruction by Fusion of 3D Angiography and OCT

    J Am Coll Cardiol

    (2015)
  • C. Chiastra et al.

    Healthy and diseased coronary bifurcation geometries influence near-wall and intravascular flow: a computational exploration of the hemodynamic risk

    J Biomech

    (2017)
  • A.G. van der Giessen et al.

    The influence of boundary conditions on wall shear stress distribution in patients specific coronary trees

    J Biomech

    (2011)
  • U. Morbiducci et al.

    Helical flow as fluid dynamic signature for atherogenesis risk in aortocoronary bypass

    A numeric study. J Biomech

    (2007)
  • D. Gallo et al.

    Helical flow in carotid bifurcation as surrogate marker of exposure to disturbed shear

    J Biomech

    (2012)
  • L. Shtilman et al.

    On the role of helicity in complex fluid flows

    Phys Lett A

    (1985)
  • H. Everaars et al.

    Doppler Flow Velocity and Thermodilution to Assess Coronary Flow Reserve: a Head-to-Head Comparison With [15O]H2O PET

    JACC Cardiovasc Interv

    (2018)
  • A. Kumar et al.

    High Coronary Shear Stress in Patients With Coronary Artery Disease Predicts Myocardial Infarction

    J Am Coll Cardiol

    (2018)
  • M. Malvè et al.

    Unsteady blood flow and mass transfer of a human left coronary artery bifurcation: FSI vs

    CFD. Int Commun Heat Mass Transf

    (2012)
  • A.P. Antoniadis et al.

    Impact of local flow haemodynamics on atherosclerosis in coronary artery bifurcations

    EuroIntervention

    (2015)
  • A.M. Malek et al.

    Hemodynamic Shear Stress and Its Role in Atherosclerosis

    JAMA

    (1999)
  • U. Morbiducci et al.

    Atherosclerosis at arterial bifurcations: evidence for the role of haemodynamics and geometry

    Thromb Haemost

    (2016)
  • H. Samady et al.

    Coronary artery wall shear stress is associated with progression and transformation of atherosclerotic plaque and arterial remodeling in patients with coronary artery disease

    Circulation

    (2011)
  • J.J. Wentzel et al.

    Endothelial shear stress in the evolution of coronary atherosclerotic plaque and vascular remodelling: current understanding and remaining questions

    Cardiovasc Res

    (2012)
  • B.R. Kwak et al.

    Biomechanical factors in atherosclerosis: mechanisms and clinical implications

    Eur Heart J

    (2014)
  • A. Hoogendoorn et al.

    Multidirectional wall shear stress promotes advanced coronary plaque development: comparing five shear stress metrics

    Cardiovasc Res

    (2020)
  • G. De Nisco et al.

    The Atheroprotective Nature of Helical Flow in Coronary Arteries

    Ann Biomed Eng

    (2019)
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