Research Papers

Hemodynamics in the Left Atrium and Its Effect on Ventricular Flow Patterns

[+] Author and Article Information
Vijay Vedula

Department of Mechanical Engineering,
Johns Hopkins University,
3400 N. Charles Street,
Baltimore, MD 21218

Richard George

Division of Cardiology,
Johns Hopkins University,
733 N. Broadway,
Baltimore, MD 21205

Laurent Younes

Department of Applied Mathematics
and Statistics,
Johns Hopkins University,
3400 N. Charles Street,
Baltimore, MD 21218

Rajat Mittal

Department of Mechanical Engineering,
Johns Hopkins University,
3400 N. Charles Street,
Baltimore, MD 21218
e-mail: mittal@jhu.edu

1Corresponding author.

Manuscript received April 1, 2015; final manuscript received August 22, 2015; published online September 16, 2015. Assoc. Editor: Ender A. Finol.

J Biomech Eng 137(11), 111003 (Sep 16, 2015) (8 pages) Paper No: BIO-15-1142; doi: 10.1115/1.4031487 History: Received April 01, 2015; Revised August 22, 2015

In the present study, we investigate the hemodynamics inside left atrium (LA) and understand its impact on the development of ventricular flow patterns. We construct the heart model using dynamic-computed tomographic images and perform simulations using an immersed boundary method based flow solver. We show that the atrial hemodynamics is characterized by a circulatory flow generated by the left pulmonary veins (LPVs) and a direct stream from the right pulmonary veins (RPVs). The complex interaction of the vortex rings formed from each of the PVs leads to vortex breakup and annihilation, thereby producing a regularized flow at the mitral annulus. A comparison of the ventricular flow velocities between the physiological and a simplified pipe-based atrium model shows that the overall differences are limited to about 10% of the peak mitral flow velocity. The implications of this finding on the functional morphology of the left heart as well the computational and experimental modeling of ventricular hemodynamics are discussed.

Copyright © 2015 by ASME
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Fig. 1

(a) Axial slice of contrast-enhanced CT data with highlighted chambers of left heart, (b) reconstructed chambers of the left heart model from the volume CT data with the indicated nomenclature, (c) time variation of LV volume (solid) and its time derivative (dotted) during the cardiac cycle, (d) 3D rendering and a flattened cylindrical projection of MV, and (e) measurement of MV leaflet angles with respect to the base or mitral annulus plane as shown in Figs. (a) and (b). LPVs/RPVs: left/right pulmonary veins; LA: left atrium; LAA: left atrial appendage; MV: mitral valve; AL: anterior leaflet; PL: posterior leaflet; LAL, LPL: maximum lengths of AL and PL; LV: left ventricle; Ao: Aorta; SV: stroke volume; and EF: ejection fraction.

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Fig. 2

(a) Schematic of volume registration of each target cardiac phase with respect to the template using large deformation diffeomorphic metric mapping (LDDMM) method. (b) An example mapping of the end-systolic state (template, red) with the end-diastolic state (target, blue) using LDDMM. (See online version for color versions of all figures.)

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Fig. 3

(a) Computational models used in the present study: (left) physiological left heart model with anatomically correct LA, LV, and Ao and (right) simplified atrium model where the filling into LV takes place from a pipe created by outward extrusion of MO along its axis. Both these models have identical MV configuration as highlighted. (b) Computational domain with the physiological model immersed into it. (c) Orthogonal cross-sectional planes (A-A and B-B) used for analysis of hemodynamic data together with transverse sections on B-B plane to probe velocity profiles. LA: left atrium; LV: left ventricle; MV: mitral valve; and Ao: Aorta.

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Fig. 4

Streamlines visualization in LA during diastole (a) and (c) and systole (b) and (d) in two different views. Streams emanating from the LPVs and RPVs are highlighted for better visualization and understanding of LA flow patterns. LPVs/RPVs: left/right pulmonary veins; MO: mitral orifice; and LAA; left atrial appendage.

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Fig. 5

Left atrial vortex dynamics and breakdown during ventricular systole. Instantaneous vortex structures are visualized using λci criterion [37] highlighted by the magnitude of velocity, and the numbers indicate nondimensional times during the third cardiac cycle.

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Fig. 6

Vortex structures in the physiological model highlighted by the magnitude of velocity. Numbers indicate various nondimensional times during the third cardiac cycle.

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Fig. 7

Same as Fig. 6 but for the simplified model

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Fig. 8

Comparison of averaged flow field between physiological (top) and simplified (bottom) models. (a) and (d) Phase-averaged velocity fields along B-B plane during mid-diastole. (c)–(f) Phase-time-averaged velocity field during entire diastole along the indicated reference planes (A-A and B-B). See Fig.3(c) for plane configuration.

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Fig. 9

Comparison of longitudinal velocity component profiles at various transverse sections (H1H12) of B-B plane during mid-diastole as shown in Fig. 3(c). The L1 norm of the difference in each profile is quantified as a percentage of peak mitral flow velocity (Up = 63 cm/s).

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Fig. 10

Comparison of vortex structures during late diastole of the third cycle (t* = 2.4) between the physiological model with MV (a) and without MV (b)




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