1. Hemodynamics of Patient-Specific Aortic Root Geometries
Ryan W. Oba, Amirsepehr Azimian, Atieh Yousefi, Hoda Hatoum,
Jennifer Dollery, Juan Crestanello, Lakshmi P. Dasi
The Ohio State University
Introduction
Intoduction
Intoduction
Data and Discussion
Results and Discussion
Calcific aortic valve disease (CAVD) is the most common form of valve disease in the Western World, yet its etiology remains unclear.
Clinical factors such as smoking or aging are associated with increased risk of CAVD, but more work is needed to identify the contribution of other factors in its progression. Groups previously studied effects of coronary flow and sinus geometry [1], calcification shape [2], and calcification in bicuspid aortic valves [3], but little can be said about the contribution of the leaflet opening itself, in a patient-specific manner to the onset of valvular disease.
The objective of this study is to investigate the influence of changes to aortic valve leaflet geometry on hemodynamic performance and the onset of CAVD.
Patient Geometry
Segmentation artifacts removed using filtering smoothing.
Average of 100k, 150k tetrahedral elements for solid and fluid domains, respectively.
Computational Fluid Dynamics
Boundary conditions for the transient simulations of peak systole included a 25 kg/min mass flow inlet, and zero pressure outlets.
Orifice jet becomes angled and vorticity magnitudes increase with level of leaflet stenosis.
Experimental
Printed geometries appeared durable enough to withstand physiological cardiac output of 5.0 L/min and aortic pressures of 120/80 mmHg.
Calcified leaflet openings in vitro resemble levels seen in vivo.
Printed model testing in flow loop system, and PIV visualization illustrate jet formation of similar magnitude to in vivo values.
Pressure tap ports
Right coronary
Outlet
RCC
NCC
Inlet
Specific Aims
LCC
Left coronary
To achieve this, computational and experimental methodologies were developed, namely computational fluid dynamics (CFD) simulations, and testing of novel 3D printed patient-specific models within a flow loop system.
Figure 4: 3D printed geometry, with ventricular/aortic views.
Materials and Methods
Patient Geometry
Patient aortic root CT images were acquired from The Ohio State University Wexner Medical Center.
Segmentation and 3D geometry reconstruction was performed using Mimics Research Tissue types filtered using pixel thresholding.
Computational Fluid Dynamics
Leaflet positions were varied using ANSYS Mechanical’s structure modeling.
Four distinct leaflet configurations for each patient were used; uncalcified - fully open, partially open, stenotic, and calcified – stenotic.
Fluid simulations of patient geometries were performed using ANSYS CFX.
Experimental
Patient-specific calcified and idealized uncalcified 3D models were printed on a Stratasys Connex 350 printer using Tango+ material for the soft tissue, and VeroWhite for calcified.
Printed models were tested in an in-house left heart simulator flow loop, similar to systems described previously [4], and exposed to physiological flows; 5.0 L/min flow rate, and 120/80mmHg. Flow visualization was performed using a DaVis particle image velocimetry (PIV) system.
Figure 2: Thresholding of CT images and smoothed geometry, and example wall/fluid meshes used in CFD simulations.
Figure 5: CT vs. experimental openings, PIV velocity vectors and jet formation.
Conclusions
This study observed flow pattern changes which may indicate a “tipping point” level of reduced leaflet opening which could favor the onset of CAVD.
This study provides new insight into which valve configurations are most likely to result in a specific pattern of calcification, as well as flow stagnation, and thrombosis.
Acknowledgements
The authors gratefully acknowledge funding from the DHLRI Trifit Challenge and National Institutes of Health (NIH) under award number R01HL
References
[1] Moore, BL. Ann Biomed Eng (9):
[2] Halevi, R. Med Biol Eng Comput Epub (ahead of print).
[3] Chandra, S. Circulation : A12887.
[4] Leo, HL. Ann Biomed Eng (6):
Figure 3: Velocity and Vorticity plots during peak systole for 4 valve configurations.
Figure 1: In-house flow loop system schematic.