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Research Papers

Steady Flow Hemodynamic and Energy Loss Measurements in Normal and Simulated Calcified Tricuspid and Bicuspid Aortic Valves

[+] Author and Article Information
Clara Seaman

Department of Aerospace
and Mechanical Engineering,
University of Notre Dame,
Notre Dame, IN 46556

A. George Akingba

Department of Surgery
and Biomedical Engineering,
Indiana University School of Medicine,
Indianapolis, IN 46202

Philippe Sucosky

Department of Aerospace
and Mechanical Engineering,
University of Notre Dame,
143 Multidisciplinary Research Building,
Notre Dame, IN 46556-5637
e-mail: Philippe.Sucosky@nd.edu

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received February 18, 2013; final manuscript received January 14, 2014; accepted manuscript posted January 27, 2014; published online March 24, 2014. Assoc. Editor: Francis Loth.

J Biomech Eng 136(4), 041001 (Mar 24, 2014) (11 pages) Paper No: BIO-13-1087; doi: 10.1115/1.4026575 History: Received February 18, 2013; Revised January 14, 2014; Accepted January 27, 2014

The bicuspid aortic valve (BAV), which forms with two leaflets instead of three as in the normal tricuspid aortic valve (TAV), is associated with a spectrum of secondary valvulopathies and aortopathies potentially triggered by hemodynamic abnormalities. While studies have demonstrated an intrinsic degree of stenosis and the existence of a skewed orifice jet in the BAV, the impact of those abnormalities on BAV hemodynamic performance and energy loss has not been examined. This steady-flow study presents the comparative in vitro assessment of the flow field and energy loss in a TAV and type-I BAV under normal and simulated calcified states. Particle-image velocimetry (PIV) measurements were performed to quantify velocity, vorticity, viscous, and Reynolds shear stress fields in normal and simulated calcified porcine TAV and BAV models at six flow rates spanning the systolic phase. The BAV model was created by suturing the two coronary leaflets of a porcine TAV. Calcification was simulated via deposition of glue beads in the base of the leaflets. Valvular performance was characterized in terms of geometric orifice area (GOA), pressure drop, effective orifice area (EOA), energy loss (EL), and energy loss index (ELI). The BAV generated an elliptical orifice and a jet skewed toward the noncoronary leaflet. In contrast, the TAV featured a circular orifice and a jet aligned along the valve long axis. While the BAV exhibited an intrinsic degree of stenosis (18% increase in maximum jet velocity and 7% decrease in EOA relative to the TAV at the maximum flow rate), it generated only a 3% increase in EL and its average ELI (2.10 cm2/m2) remained above the clinical threshold characterizing severe aortic stenosis. The presence of simulated calcific lesions normalized the alignment of the BAV jet and resulted in the loss of jet axisymmetry in the TAV. It also amplified the degree of stenosis in the TAV and BAV, as indicated by the 342% and 404% increase in EL, 70% and 51% reduction in ELI and 48% and 51% decrease in EOA, respectively, relative to the nontreated valve models at the maximum flow rate. This study indicates the ability of the BAV to function as a TAV despite its intrinsic degree of stenosis and suggests the weak dependence of pressure drop on orifice area in calcified valves.

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References

Figures

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Fig. 1

Porcine valve models: normal TAV (a), type-I BAV (b), calcified TAV (c), and calcified type-I BAV (d)

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Fig. 2

Placement and characterization of glue-simulated calcific lesions on the leaflets: idealized leaflet representation and geometric parameters (a) and glue beads deposited on an actual leaflet (b)

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Fig. 3

Experimental setup: valve chamber (a) (arrow indicates flow direction), cross-sectional view of the sinus region (b), valve mount (c), and schematic of the PIV flow loop (d) (arrows indicate flow direction; x: axial direction; y: transverse direction)

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Fig. 5

Ensemble-averaged vorticity ((a); red and blue regions corresponding to counter-clockwise and clockwise rotation, respectively), viscous shear stress (b) and Reynolds shear stress (c) fields captured in the TAV, BAV, CTAV, and CTAV models at a flow rate of 20 L/min (Re = 3946; x: axial direction; y: transverse direction)

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Fig. 4

Velocity field characteristics: Ensemble-averaged velocity contour and vector fields captured in the TAV, BAV, CTAV, and CTAV models at six flow rates (a) (x: axial direction; y: transverse direction; inset: camera position and field of view) and average orifice jet skewness in the four valve models at six flow rates (b).

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Fig. 9

Dependence of EL on EOA at six flow rates, for the four valve models (results reported as mean ± standard error; n = 4)

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Fig. 8

Comparison of the ELI measured in the four valve models at six flow rates (results reported as mean ± standard error; *: p < 0.05; n = 4)

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Fig. 7

Comparison of the pressure drop (ΔP) on flow rate for the four valve models (results reported as mean ± standard error; *: p < 0.05; n = 4)

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Fig. 6

Valvular orifice characterization: typical orifice image captured by camera 2 in the TAV (a), BAV (b), CTAV (c), and CBAV (d) models at a flow rate of 20 L/min, comparison of the GOA measured in the four valve models at six flow rates (e) and valvular eccentricity expressed as a percentage of the aortic root diameter in the four valve models at six flow rates (f) (results reported as mean ± standard error; *p < 0.05 versus TAV; #p < 0.05 versus BAV;∼p < 0.05 versus CTAV; + : p < 0.05 versus CBAV; n = 10)

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