Ann Thorac Surg 2009;87:993-994. doi:10.1016/j.athoracsur.2009.02.045
© 2009 The Society of Thoracic Surgeons
Editorial
The Use of Computational Flow Modeling (CFD) to Determine the Effect of Left Ventricular Shape on Blood Flow in the Left Ventricle
Liang Ge, PhD,
Mark Ratcliffe, MD*
San Francisco Veterans Affairs Medical Center, San Francisco, California
* Address correspondence to Dr Ratcliffe, VAMC Surgery 112D, San Francisco Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121 (Email: mratcliffe{at}hotmail.com).
Doenst and colleagues [1] present a computational fluid dynamics (CFD) study of blood flow in the normal left ventricle (LV) and in the LV with anteroapical myocardial infarction before and after surgical ventricular remodeling (SVR). CFD simulates fluid flow by solving the Navier-Stokes equations (essentially Newton's second law of motion for fluid flow) using advanced numeric methods. Typically, a set of boundary conditions, including inlet and outlet pressures or flow velocity and conduit shape, are input to a CFD solver, which then calculates the corresponding flow field.
The authors performed magnetic resonance imaging (MRI) studies on a single healthy volunteer and on a single patient with ischemic cardiomyopathy before and after SVR. In each case, the endocardial surface was traced (contoured) throughout the cardiac cycle, and those contours were used as boundary conditions in a CFD model of blood flow in the LV. Calculation of flow in the normal LV showed a ring vortex that progressed in a clockwise fashion. In the LV of the patient with ischemic cardiomyopathy, the ring vortex that formed during diastole was distorted (branched), although outflow was normal. After SVR, the inflow and outflow appear even less organized and there is stagnation at the LV apex. The principal finding of the authors' study is that LV shape has a profound effect on the pattern of blood flow in the LV [1].
 |
Flow in the LV
|
|---|
Kilner and colleagues [2] suggest that the normal human LV has been fine-tuned by evolution to pump blood efficiently. The human LV and mitral valve are geometrically arranged so that an asymmetric vortex forms during diastole, with flow continuing toward the LV outflow track during systole. This presumably enhances the pump function of the LV [2]. The normal human LV operates within a small range of vortex formation time (T), a dimensionless parameter that is proportional to the time-averaged velocity of flow through the mitral valve (MV) and inversely proportional to MV size [3]. Vortices are optimized around T = 4, the largest possible vortex without formation of a trailing jet [3]. Vortex formation time [3] and the kinetic energy of flow [4] are both decreased in dilated cardiomyopathy.
|
CFD and the Need for Validation
|
|---|
Given the complexity and the number of assumptions that go into CFD models, we believe that validation of model results with measured flow is especially important. CFD has previously been used to study flow in the normal LV [5–7]. Most of those previous studies [5, 6] and the current study by Doenst and colleagues [1] measured LV shape with cardiac MRI. MRI can also be used to measure flow in the LV [4, 8], however, and validation of results with MRI-measured flow would seem appropriate. For instance, Saber and colleagues [7] compared the CFD model output from their simulation with MRI-measured flow. Mitral valve inflow velocity measured with Doppler echo and LV pressure gradients could also be used to validate model output.
|
Fluid Structure Interaction
|
|---|
The value of the study by Doenst and colleagues [1] could have been enhanced if fluid (blood) flow in the LV cavity had been coupled to the mechanical behavior of the LV wall. LV pump function is the result of the initial conversion of chemical energy to mechanical energy at the myocyte level and then conversion of mechanical energy in the LV wall to blood flow. A stand-alone CFD fluid dynamics study, as conducted by Doenst and colleagues [1], models only the blood flow part of this system. It is possible to model both structure and flow using finite element techniques. This is typically referred to as a fluid structure interaction (FSI) simulation. For instance, Cheng and colleagues [5] previously performed FSI of the LV wall, and LV blood flow although the model was limited to diastole.
Guccione and colleagues [9, 10] have developed three-dimensional constitutive relations for active contraction in cardiac muscle. Finite element models of that type have been used to simulate the effect of SVR on fiber stress, LV chamber stiffness, and pump function [11]. FSI simulations that incorporated those constitutive relations would be extremely powerful. For instance, an FSI simulation of the LV would allow investigators to quantify the effect of myocardial infarction and surgical therapy on regional and global LV function and the subsequent effect of those parameters on blood flow in the LV chamber.
|
References
|
|---|
- Doenst T, Spiegel K, Reik M, et al. Fluid-dynamic modeling of the human left ventricle: methodology and application to surgical ventricular reconstruction Ann Thorac Surg 2009;87:1187-1195.[Abstract/Free Full Text]
- Kilner PJ, Yang GZ, Wilkes AJ, Mohiaddin RH, Firmin DN, Yacoub MH. Asymmetric redirection of flow through the heart Nature 2000;404:759-761.[Medline]
- Gharib M, Rambod E, Kheradvar A, Sahn DJ, Dabiri JO. Optimal vortex formation as an index of cardiac health Proc Natl Acad Sci U S A 2006;103:6305-6308.[Abstract/Free Full Text]
- Bolger AF, Heiberg E, Karlsson M, et al. Transit of blood flow through the human left ventricle mapped by cardiovascular magnetic resonance J Cardiovasc Magn Reson 2007;9:741-747.[Medline]
- Cheng Y, Oertel H, Schenkel T. Fluid-structure coupled CFD simulation of the left ventricular flow during filling phase Ann Biomed Eng 2005;33:567-576.[Medline]
- Saber NR, Gosman AD, Wood NB, Kilner PJ, Charrier CL, Firmin DN. Computational flow modeling of the left ventricle based on in vivo MRI data: initial experience Ann Biomed Eng 2001;29:275-283.[Medline]
- Saber NR, Wood NB, Gosman AD, et al. Progress towards patient-specific computational flow modeling of the left heart via combination of magnetic resonance imaging with computational fluid dynamics Ann Biomed Eng 2003;31:42-52.[Medline]
- Houlind K, Schroeder AP, Stodkilde-Jorgensen H, Paulsen PK, Egeblad H, Pedersen EM. Intraventricular dispersion and temporal delay of early left ventricular filling after acute myocardial infarction. Assessment by magnetic resonance velocity mapping. Magn Reson Imaging 2002;20:249-260.[Medline]
- Guccione JM, McCulloch AD. Mechanics of active contraction in cardiac muscle: Part I—Constitutive relations for fiber stress that describe deactivation J Biomech Eng 1993;115:72-81.[Medline]
- Guccione JM, Waldman LK, McCulloch AD. Mechanics of active contraction in cardiac muscle: Part II—Cylindrical models of the systolic left ventricle J Biomech Eng 1993;115:82-90.[Medline]
- Dang AB, Guccione JM, Zhang P, et al. Effect of ventricular size and patch stiffness in surgical anterior ventricular restoration: a finite element model study Ann Thorac Surg 2005;79:185-193.[Abstract/Free Full Text]
Related Article
-
Fluid-Dynamic Modeling of the Human Left Ventricle: Methodology and Application to Surgical Ventricular Reconstruction
- Torsten Doenst, Kathrin Spiegel, Michael Reik, Michael Markl, Jürgen Hennig, Stefan Nitzsche, Friedhelm Beyersdorf, and Herbert Oertel
Ann. Thorac. Surg. 2009 87: 1187-1195.
[Abstract]
[Full Text]
[PDF]
This article has been cited by other articles:
|
|
|
|
 
C. J. Carlhall and A. Bolger
Passing Strange: Flow in the Failing Ventricle
Circ Heart Fail,
March 1, 2010;
3(2):
326 - 331.
[Full Text]
[PDF]
|
|
|
Top
Flow in the LV
CFD and the Need...