Modeling blood flow through Bioengineered heart valves

Modeling blood flow through Bioengineered heart valves

How to choose?

[9]

Heba Osman

Aziz Rana

Ahmed Elmeligi

References

Types of Modelling

[15]

1D

• Simple to use
• Can obtain pressure & volume curve but can't provide the flow field inside LV chambers

2D

• Simulate idealized LV models
• Their extension to simulate realistic LV flow in patient-specific geometries is difficult

3D

• 3D LV geometry, with the wall motion prescribed either through analytical functions or using patient-specific data
• Not only account for the interaction of blood flow with the heart wall but also the interaction of the heart with organs

Fluid Flow

[12]

1. "How the Heart Valves Work." Heart Valves. Web. 20 Oct. 2014.

2. Carson, Claire. "Prosthetic Heart Valves."The Physics Behind Artificial Heart Valves. Web. 22 Oct. 2014.<http://www.ipass.net/tonyg/HeartValvesWeb.html>

3. "Valves of the Heart: Circulation of Blood."Cardiothoracic Surgery. Web. 21 Oct. 2014.<http://www.cts.usc.edu/hpg-valvesoftheheart-circulationofblood1.html>

4. "Heart Valve Disease Symptoms, Causes, Treatment." MedicineNet. 1 Jan. 2014. Web. 24 Oct. 2014. <http://www.medicinenet.com/heart_valve_disease/page2.htm>

5. " Mitral Stenosis." Multimedia Encyclopedia. Web. 27 Oct. 2014. <http://keckmedicine.adam.com/content.aspx?productId=117&pid=1&gid=000175>.

6.“Leaking Heart Valve Symptoms” Heart Valve Surgery. Web 25 Oct. 2014 <http://www.heart-valve-surgery.com/leaking-heart-valve-symptoms.php>.

7.“Valvular Heart Disease” Circulation. Web 26 Oct. 2014. <http://circ.ahajournals.org/content/119/7/1034.full>.

8. "Cardiac Valve Replacement Surgery." We Care Health Services. Web. 26 Oct. 2014. <http://www.indiasurgerytour.com/heart/india-surgery-valve-replacement.html>.

9. Khan, SS, A. Trento, and M. DeRobertis. "Twenty-year Comparison of Tissue and Mechanical Valve Replacement." J Thorac Cardiovasc Surgery 122.2 (2001). Pubmed. Web. 25 Oct. 2014. <http://www.ncbi.nlm.nih.gov/pubmed/11479498>.

10. Yun, B. Min, Jingshu Wu, Helene A. Simon, Shiva Arjunon, Fotis Sotiropoulos, Cyrus K. Aidun, and Ajit P. Yoganathan. "A Numerical Investigation of Blood Damage in the Hinge Area of Aortic Bileaflet Mechanical Heart Valves During the Leakage Phase." Annals of Biomedical Engineering (2012): 1468-485.Pubmed. Web. 1 Nov. 2014. <http://www.ncbi.nlm.nih.gov/pubmed/22215278>.

11. "Heart Valve Surgery." MedlinePlus. Web. 4 Nov. 2014. <http://www.nlm.nih.gov/medlineplus/ency/article/002954.htm>.

12. Sotiropoulos, Fotis, and Iman Borazjani. "A Review of State-of-the-art Numerical Methods for Simulating Flow through Mechanical Heart Valves." Medical & Biological Engineering & Computing (2009): 245-56. Web. 4 Nov. 2014. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2717171/>.

13. Sotiropoulos, Fotis, and Iman Borazjani. "A Review of State-of-the-art Numerical Methods for Simulating Flow through Mechanical Heart Valves." Medical & Biological Engineering & Computing (2009): 245-56. Web. 4 Nov. 2014. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2717171/>.

14. Le, Trung Bao, and Fotis Sotiropoulos. "Fluid–structure Interaction of an Aortic Heart Valve Prosthesis Driven by an Animated Anatomic Left Ventricle." Journal of Computational Physics (2012): 41-62. Print.

Loon, Raoul Van. Eindhoven, 1 Jan. 2007. Web. 2 Nov. 2014. <http://wwwf.imperial.ac.uk/ssherw/bioflow/people/Raoul_van_Loon/Figs/thesis2.pdf>.

15.Alemu, Y. "Mmechanical Heart Valve." Web. 1 Nov. 2014. <http://www.ic.sunysb.edu/Stu/yalemu/Doc6.htm>.

16. Choi, Choeng Ryul, Chang Nyung Kim, Young Joo Kwon, and Jae Won Lee. "Pulsatile Blood Flows Through a Bileaflet Mechanical Heart Valve with Different Approach Methods of Numerical Analysis."KSME International Journal 17.7 (2006). Web. 1 Nov. 2014. <http://link.springer.com/article/10.1007/BF02982992>.

17 http://www.cell.com/cms/attachment/2007962848/2030694701/gr1.jpg

[13]

• Blood flow - modeled as pulsatile, laminar, incompressible, and Newtonian flow
• Lattice Boltzmann methods
• Navier-Stokes Equation
• Fluid Turbulence:
• Reynolds number
• Could vary depending on whether patient is an infant, child or adult

Aortic Position

[12]

Fluid and Solid

[12]

Treatment Options

[5]

• Moving grid methods are methods in which the computational grid is fitted to and moves/deforms with the moving boundary
• Moving methods: Arbitrary Lagrangian Eulerian --> Challenging
• Fixed methods: a cartesian mesh is used as a fixed background mesh

Coupling of Fluid and Structure:

• Methods used to enforce the couple of the fluid and solid solutions
• Loosely coupled or strongly coupled
• Depends level of interaction between the fluid and the structure solutions

Structural Dynamics

[14][16]

• Most BMHV simulations have been carried out in the aortic position
• Pulmonary and tricuspid valve flows are similar to aortic and mitral valve flows respectively (but lower overall velocity)
• Shear stresses are higher in the aortic and mitral positions compared to the triscuspid and pulmonary positions. Because the potential of BMHV induced blood cell damage is greater in the left ventricle we model in the left ventricle.
• Geometry/ movement of the aorta is less complicated relative to the left ventricle downstream of the mitral valve so the simulations are less challenging in the aortic position, which is why we use the aortic position over the mitral position
• Therefore, most models mainly focuses on the BMHV flows in the aortic position basically modeling for worst case scenario.

For Next Time:

• Surgical Valve Repair
• Surgical Valve Replacement
• Tissue Valve
• Mechanical Valve

• Valve leaflets are free to pivot around their hinges and open and close in response to the cardiac cycle --> Account for the motion using Angular Momentum Equations
• Assumptions:
• Aortic wall is rigid & only leaflets are free to move

[16]

Anatomy

[1]

The heart has 4 valves:

• The mitral valve and tricuspid valve, which control blood flow from the atria to the ventricles
• The aortic valve and pulmonary valve, which control blood flow out of the ventricles

• Walk through a Computational Fluid Dynamic design for a Bileaflet Mechanical Heart Valve
• Mathematical models that are used for Fluid Flow and Structural dynamics
• Assumptions
• Future Applications

Need for Mathematical Modeling

[17]

Problems cont'd

[6] [7]

Assessing Valves

[2]

What to take into account?

Complications with non-physiologic flow patterns

• Blood squeezed out through small gaps between leaflets --> strong jets
• Jets cause higher shear stresses --> RBC damage and platelet activation
• Anticoagulant related bleeding
• Thrombotic complication
• Hemolytic anemia (hemolysis)
• Turbulence

Complications with function of valve:

• Valve failure (wear and tear, blockage)
• Stuck leaflets
• Trans-valvular pressure gradient
• Leakage
• Forward/Backward shear
• Leakage Shear
• Foreign material

• Mechanical stimuli such as pressure, strain or shear are important with respect to damage or rupture of tissue
• Consider endothelial cells are very susceptible to (changes in) shear stress, which has a link to thrombosis
• Difficult to obtain this knowledge in vivo
• Difficult as well in vitro due to the complex three dimensional shape and the high resolutions that are required
• As a result computational models and as a consequence numerical modeling is becoming a substantial part in the developing process of new prosthetic heart valves.

A normal, healthy heart valve minimizes any obstruction and allows blood to flow smoothly and freely in one direction. It closes completely and quickly, not allowing any blood to flow back through the valve.

What physicians look when assessing the hemodynamic performance of a particular valve design:

The valve should:

• (1) function efficiently and present the minimum load to the heart
• (2) be durable and maintain its efficiency for the patient's entire lifespan
• (3) not cause damage to molecular or cellular blood components or stimulate thrombus formation (blood clotting).

Thank You!

Valve Diseases

[3] [4]

Fluid Mechanics

Need for Mathematical Modelling

[5]

[10][12]

Physiology

[2]

Problems (with Heart Valves)

[10]

Types of Artificial Valves

Stenosis

[7]

Monoleaflet Mechanical Valve

Stented Porcine Bioprosthesis

[6]

• Branch of physics which involves the study of fluids(liquids, gases, and plasmas) and the forces on them.
• Computational Fluid dynamics (CFD) is a branch of fluid mechanics that helps solve problems that involve fluid flows.
• Simulations can model 3D bileaflet mechanical heart valve (BMHV) flows with high spatiotemporal resolution where the smallest scales of fluid motion can be resolved.

Aorta Block

There are many complications that can arise as a result of getting a prosthetic heart valve implant.

The complications that arise are summarized below:

Direct Consequence of Surgery

• Scar tissue ingrowth
• Complications not directly related to the implant
• Arrhythmia, fluid in lungs, infections in heart cavity, inflammation of lining of the lung etc
• Infection of prosthetic heart valve

Bileaflet Mechanical Valve

Caged Ball Valve

• For the purposes of Modeling, we are able to look at and address issues associated with the complex, non-physiologic blood flow patterns
• Understanding flow patterns in the heart and physiologic conditions is difficult
• Especially at the scales sufficiently fine for establishing quantitatively links between heart disease and patient-specific hemodynamics
• This challenge becomes even more formidable when prosthetic heart valves are implanted

LV Block

Regurgitation

Cardiac valves have 3 functional properties:

• (1) Preventing regurgitation of blood flow from one chamber to another
• (2) Permitting rapid flow without imposing resistance on that flow
• (3) Withstanding high-pressure loads.

Aortic Valve- 3D Fluid Structure Interaction

Valve closure, valve motion and the corresponding fluid dynamics are the three main points of interest in dynamical heart valve analysis.

Congenital valve disease

• Wrong size, malformed leaflets, or leaflets that are not attached correctly

Acquired valve disease - develop with valves that were normal

• Diseases or infections

Stented Pericardial Bioprosthesis

Percutaneous Bioprosthesis expanded over a balloon

Self-expandable Percutaneous Bioprosthesis

Stentless Porcine Bioprosthesis

What are they made of?

[11]

Mechanical Valves

• Stainless Steel
• Titanium
• Ceramic

Biological Valves

• Homograft valves - donated human aortic valves
• Porcine [pig] aortic heart valve tissue

Valve we will focus on

[10]

Bileaflet Mechanical Heart Valve

• Two semicircular occluders called leaflets.
• Most popular and accounts for 80% of implanted mechanical heart valves
• Its popularity over other prosthetic heart valves is due to its superior durability, function, and bulk flow hemodynamics.

Questions?