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Research Papers

Dynamic Hemodynamic Energy Loss in Normal and Stenosed Aortic Valves

[+] Author and Article Information
Choon-Hwai Yap

Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0535

Lakshmi P. Dasi

Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523

Ajit P. Yoganathan1

Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0535ajit.yoganathan@bme.gatech.edu

1

Corresponding author.

J Biomech Eng 132(2), 021005 (Jan 28, 2010) (10 pages) doi:10.1115/1.4000874 History: Received July 27, 2009; Revised November 30, 2009; Posted December 22, 2009; Published January 28, 2010; Online January 28, 2010

Aortic valve (AV) stenosis, if untreated, leads to heart failure. From a mechanics standpoint, heart failure can be interpreted as the failure of the heart to generate sufficient power to overcome energy losses in the circulation. Thus, energy efficiency-based measures for evaluating AV performance and disease severity have the advantage of being a direct measure of the contribution of the AV hydrodynamic characteristics toward heart failure. We present a new method for computing the rate of energy dissipation as a function of systolic time, by modifying the Navier–Stokes momentum equation. This method preserves the dynamic term of the Navier–Stokes momentum equation, and allows the investigation of the trend of the rate of energy dissipation over time. This method is applied to a series of in vitro experiments, where a trimmed porcine valve is exposed to various conditions: varying stroke volumes (50 ml to 90 ml) at the fixed heart rate; varying heart rates (60–80 beats/min) at fixed stroke volume; and varying stenosis levels (normal, mild stenosis, moderate stenosis). The results are: (1) energy dissipation waveform has a distinctive pattern of being skewed toward late systole, due to flow instabilities during deceleration phases; (2) increasing heart rate and stroke volume increases energy dissipation, but the normalized shape of the energy dissipation waveform is preserved across heart rates and stroke volumes; (3) increasing stenosis level increases energy dissipation, and also alters the normalized shape of the energy dissipation waveform. Since stenosis produces a signature energy dissipation waveform shape, dynamic energy dissipation analysis can potentially be extended into a clinical tool for AV evaluation.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Control volume around the aortic valve for the derivation of the dynamic energy loss equation

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Figure 2

Valve mounting chamber and control volume for experimental measurement of energy dissipation

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Figure 10

Energy loss during the three equally divided durations of systole, normalized by the total energy loss for the entire systole. With increasing stenosis, the percentage of energy lost during midsystole (2/3) increases, while the percentage of energy lost during late systole (3/3) decreases. Data are average of ten cardiac cycles. p∗<0.01.

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Figure 11

Energy dissipation waveforms over systole normalized by systolic duration and peak dissipation value for various conditions for (a) mild stenosis and (b) moderate stenosis

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Figure 12

Percentage energy loss during the three equally divided durations of systole for (a) normal valve, (b) mild stenosis, and (c) moderate stenosis. Condition (1): 60 beats/min heart rate, 70 ml stroke volume; condition (2): 70 beats/min heart rate, 70 ml stroke volume; condition (3): 80 beats/min heart rate, 70 ml stroke volume; condition (4): 70 beats/min heart rate, 50 ml stroke volume; condition (5): 70 beats/min heart rate, 90 ml stroke volume. Data are average of ten cardiac cycles p∗<0.01.

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Figure 13

(a) Total systolic energy loss over different stroke volumes for different stenosis levels; (b) total systolic energy loss over different heart rates for different stenosis levels

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Figure 14

Relationship of EOA and mean gradient with stroke volume, heart rate, and stenosis level

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Figure 15

(a) Plot of mean gradient versus average energy dissipation and (b) of EOA versus average energy dissipation. Mean gradient demonstrates a good trend with energy dissipation across different levels of stenosis, while EOA distinguishes different levels of stenosis well.

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Figure 16

(a) Plot of kinetic energy within the control volume over time for assumptions of the Womersley, plug, and parabolic flow profiles. (b) Plot of the kinetic energy ratio between different flow profiles over time.

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Figure 3

Valve model constructed from native porcine aortic valve. The aortic root is first excised from the heart (left), the sinus walls are then excised (middle), and the remaining tissue is trimmed and sutured to a tristented metal ring (right). The valve model is later inserted into the valve chamber.

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Figure 4

Schematic of the pulsatile flow loop for experimental measurement of energy dissipation

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Figure 5

Pressure and flow waveforms and energy dissipation over systole. Vertical lines demarks various systolic phases: acceleration phase (Acc. phase), peak flow phase, and deceleration phase (Decc. phase).

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Figure 6

Energy budget plot for normal condition over systole: acceleration phase (Acc. phase) and deceleration phase (Dec. phase)

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Figure 7

Energy dissipation waveforms over systole for (a) different stroke volumes and (b) the same plot after normalization for systolic duration and peak dissipation value

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Figure 8

Energy dissipation trends over systole for (a) different heart rates and (b) the same plot after normalization for systolic duration and peak dissipation value

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Figure 9

Energy dissipation waveforms over systole for (a) various stenosis conditions under the same heart rate (70 beats/min) and stroke volume (70 ml), and (b) the same plot after normalization for systolic duration and peak dissipation value

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