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The Role of Shape and Heart Rate on the Performance of the Left Ventricle

[+] Author and Article Information
Zeying Song

Mechanical and Aerospace Engineering Department,
University at Buffalo,
State University of New York,
Buffalo, NY 14260

Iman Borazjani

Mechanical and Aerospace Engineering Department,
University at Buffalo,
State University of New York,
Buffalo, NY 14260
e-mail: iman@buffalo.edu

1Corresponding author.

Manuscript received October 30, 2014; final manuscript received August 21, 2015; published online September 16, 2015. Assoc. Editor: Alison Marsden.

J Biomech Eng 137(11), 114501 (Sep 16, 2015) (6 pages) Paper No: BIO-14-1542; doi: 10.1115/1.4031468 History: Received October 30, 2014; Revised August 21, 2015

The left ventricle function is to pump the oxygenated blood through the circulatory system. Ejection fraction is the main noninvasive parameter for detecting heart disease (healthy >55%), and it is thought to be the main parameter affecting efficiency. However, the effects of other parameters on efficiency have yet to be investigated. We investigate the effect of heart rate and left ventricle shape by carrying out 3D numerical simulations of a left ventricle at different heart rates and perturbed geometries under constant, normal ejection fraction. The simulation using the immersed boundary method provide the 3D flow and pressure fields, which enable direct calculation of a new hemodynamic efficiency (H-efficiency) parameter, which does not depend on any reference pressure. The H-efficiency is defined as the ratio of flux of kinetic energy (useful power) to the total cardiac power into the left ventricle control volume. Our simulations show that H-efficiency is not that sensitive to heart rate but is maximized at around normal heart rate (72 bpm). Nevertheless, it is more sensitive to the shape of the left ventricle, which affects the H-efficiency by as much as 15% under constant ejection fraction.

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Figures

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Fig. 1

The computational setup: The LV and the mitral opening are discretized with triangular elements required for the immersed boundary method. The LV does not move above S0, and completely moves below S1. The motion is constrained between S0 and S1 for a smooth transition between fixed and fully moving sections.

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Fig. 2

The volume of the LV from the lumped parameter model and the he nondimensional flow rate (nondimensionalized by Q0=UD2=5.019×10−4 m3/s =30.1 L/min) for different flow rates during one cycle. The positive values denote the flow out of the LV during systole, and negative values denote the flow into the LV during diastole. The flow during diastole shows two peaks: an early peak (E-wave) and a later peak (A-wave).

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Fig. 3

The H-efficiency is plotted against the heart rate for 40, 72, and 120 bpm. Simulations at 72 bpm show that global geometric perturbation of the left ventricle (LV) can affect the hydrodynamic efficiency (while ejection fraction and VFT remains unchanged).

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Fig. 4

The 3D vortical structures are visualized at different time instants in the cycle (marked on Fig. 2) using the iso-surfaces of q-criteria for heart rates 40, 72, and 120 bpm and the LVs with perturbed geometries at 72 bpm

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