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Study of Crossflow in Total Cavopulmonary

Connectionby

Sandesh RajputGuide:

Prof. S.D.Sharma

Department of Aerospace EngineeringIIT Bombay

26 June 201326 June 2013

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Topics to be covered

IntroductionFontan OperationTotal Cavopulmonary ConnectionComputational Models MethodologyResultsConclusionReference

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Introduction

Congenital Heart diseases (CHD)

o defects in the structure of the heart at the time of birth

o 8 out of 1000 live births

o 2,00,000 children born with such defects and accounts for 10%

infant mortality rate in

Single ventricular deficiencies

o refers to defect where the heart has only one effective or

functional pumping chamber e.g. Tricuspid atresia, Hypoplastic

left heart syndrome etc.26 June 2013

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Fontan operation

In 1971, Fontan and Baude successfully by-passed right heart

Tricuspid atresia ( complete absence of tricuspid valve )

Development of hypoplastic (undersized) or absent right ventricle

Purpose was to drain the whole vena cava

blood to the pulmonary arteries.

Connection between superior vena cava

(SVC) and right pulmonary artery (RPA)

Atriopulmonary connection (APC)

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SVC connected directly to right pulmonary artery (RPA)IVC can be connected to PA through right atrium or outside the

heart

Total cavopulmonary Connection

Intra-atrial conduit Fonta Extra-cardiac conduit Fonta

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Computational Models

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LPA

IVC

SVC

RPA

SVC- Superior Vena CavaIVC - Inferior Vena CavaRPA- Right Pulmonary ArteryLPA- Left Pulmonary Artery

Base Model

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Computational 2D Models

a) Model 1, straight zero offset b) Model 2, Flared zero offset26 June 2013

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Computational 2D Models continued…

c) Model 3, Flared 0.5 diameter offset

d) Model 4, Flared 1 diameter offset (2D)26 June 2013

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Computational Models

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offset

2 cm Offset Model

• Offset model prepared for offset value of 1 cm, 1.5 cm and 2 cm

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Computational 3D Models

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22% Blockage Plate

Blockage Model Control case

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Computational 3D Models

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Optiflo ModeHalf( SVC) Optiflo

Half( IVC) Optiflo

• Bifurcation of SVC or IVC or both

• Avoid head-on collision• Growth problem

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Methodology

Ansys WorkbenchPre-processing

1. DesignModeler

2. MeshingTetrahedral and Triangular

elements180,000-200,000 nodesMesh Quality

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Methodology continued…

Ansys FLUENT 2D Model Simulation

1. Flow split RPA:LPA (30:70, 40:60, 50:50, 60:40 and 70:30)

2. Flow rate , SVC : IVC = 40:60

3. Boundary Condition- Velocity at inlet and Outflow at Outlet3D Model Simulation

1. Flow rate and

2. SVC : IVC =

3. Boundary Condition- Velocity at inlet and Outflow at pressureAssumptions (Flow, Fluid and Vessel walls)

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Methodology

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• Convergence Criteria- Residual• 1200 iteration• RMS =0.00001

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The total pressure and volume flow was calculated using area-weighted average at the boundaries

Hydraulic dissipated power,

It is difference between the total energy rate at the inlet and at the outlet of the model.

Total Energy-loss coefficient

It is the ratio of the hydraulic dissipated power and the inlet

kinetic energy.

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Methodology

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Results- 2D Models

power loss in the flared model was on an average 20% less than in model with straight connection

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Effect of flaring (equal flow split)

Effect of offset (at equal flow split )

Flared zero offset Flared 0.5 diameter offset1726 June 2013

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power losses decreases with increase in the offset valueshead-on collision in zero offset models results inaccurate

Effect of offset (at equal flow split ) continued…

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Comparison with previous studies for flared 1 dia. model

similar patterns in the trends of energy loss as a function of RPA flow split ratio

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3D Model Results

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Power loss through offset models for Q =3 Lit/min

• the power loss goes on decreasing with increasing offset values• Power losses are reduced by almost 9 % when the model is offset

by 2 cm.

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Power loss comparison of various TCPC models

Application of turbulent modeling on zero offset shows maximum power loss while Optiflo [7] is found to most energy efficient

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Velocity Contours for Blockage and Control Model

The velocity magnitude increased tremendously at the blockage due to least cross sectional

The plate kept at the center does not allow the head-on collision of flows from IVC and SVC

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Velocity contour for Optiflo Model

Due to inertia of the caval flow entering the bifurcation, the majority of the follow could not follow the outer curved of the model.

This caused large low flow regions and flow separation region contributing to the power loss

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Turbulence ModelingSimulation on Control model and Base model using turbulence

modeling

Realizable k-epsilon model was used with 5% of turbulence intensity

The Turbulent kinetic energy variable determines the scale of the

turbulence while epsilon variable determines the energy in the

turbulence

The power losses relatively higher than the laminar model

vortex main source of turbulence in the central region

the plate does not allow head-on collision, hence no vortex is formed

causing less turbulence.

As a result of this, the power loss in control model is 30% lesser than

in Base model26 June 2013

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Conclusion

Flaring at the connection site reduced power losses by 20%

when compared to model with straight connections

The energy losses are minimum in all the models for equal flow

split to both the pulmonary arteries

The offset enhances the hemodynamics of the connection and

power losses reduce with increasing offset values

The power loss in Control model is 30% lesser than in Base

model

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References

[1] A. Saxena, “Congenital heart disease in India: a status report,” Indian journal of pediatrics,

vol. 72, no. 7, pp. 595–8, Jul. 2005.

[2] F. Fontan and E. Baudet, “Surgical repair of tricuspid atresia,” Thorax, vol. 26, no. 3, pp.

240–8, May 1971.

[3] M. R. de Leval et al. “Total cavopulmonary connection: a logical alternative to

atriopulmonary connection for complex Fontan operation. Experimental studies and early

clinical experience,” The Journal of thoracic and cardiovascular surgery, vol. 96, no. 5, pp.

682–95, Nov. 1988.

[4]H. D. Puga et al. “Modifications of the Fontan operation applicable to patients with left

atrioventricular valve atresia or single a atrioventricular valve,” Circulation, vol. 76, no. (3 Pt 2),

pp. III53–60, 1987.

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References

[5] Ann E. Ensley et al. “Toward designing the optimal total cavopulmonary

connection: an in vitro study,” The Annals of thoracic surgery, vol. 68, no. 4, pp.

1384–90, Oct. 1999

[6] K. Ryu, et al. “Importance of Accurate Geometry in the Study of the Total

Cavopulmonary Connection: Computational Simulations and In Vitro Experiments,”

Annals of Biomedical Engineering, vol. 29, no. 10, pp. 844–853, Oct. 2001.

[7] D. D. Soerensen, K. Pekkan, D. de Zélicourt, S. Sharma, K. Kanter, M. Fogel,

and A. P. Yoganathan, “Introduction of a new optimized total cavopulmonary

connection.,” The Annals of thoracic surgery, vol. 83, no. 6, pp. 2182–90, Jun. 2007.

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Thank You

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Energy Indices

1. Hydraulic dissipated power,

It is calculated using following expression:

where,

2. Total Energy-loss coefficient It is the ratio of the hydraulic dissipated power and the inlet kinetic energy.

It is calculated using following expression:26 June 2013

and as a function of the offset

et al., “Use of computational fluid dynamics in the design of surgical procedures : application to the study of competitive flows in cavopulmonary connections,” Journal of Thoracic Cardiovascular Surgery, vol. 111, pp. 502–13, 1996.

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Pulmonary Flow distributions among offset models

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