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Modeling the Cardiovascular Inferior Venous System
Jim Clear, Chase Houghton, Meghan Murphy
Biomedical Engineering, Vanderbilt University, Nashville, TN 37235
ABSTRACT
Purpose
To develop a model of the inferior venous cardiovascular system for the purpose of
visualizing catheterizations and testing new catheter technologies.
Methods
Considering model specifications presented by Vanderbilt University Cardiology
Fellow Dr. Michael Barnett, the relevant technology available, the design flaws of a
previous prototype, and machine constraints presented by machinist John
Fellenstein, a prototype was established and a final model was constructed.
Results
The model achieved demands presented by Dr. Michael Barnett and functioned in the
catheterizations identified as specific device objectives.
Conclusion
The model constructed has potential in commercial use. Addition of a superior vena
cava and a pulmonary vein would be functional in following the progression of an air
embolism if introduced during catheterization.
BACKGROUND
Problem Statement
There currently exists a need for a commercially available model offering an
unobstructed view of in vitro catheterizations. This model will have functions in:
- Proof of concept experimentation and demonstration for developing catheter
technology.
- Clinical training, more specifically for detecting the introduction of air
embolisms during catheter insertions.
Specific Device Functions
- Demonstrate catheters used as optical scopes in the heart: for proof of concept
- Demonstrate Swan-Ganz catheters used to measure blood pressure in the heart
Currently Available Technology
There exist three types of cardiac models used today
in catheterizations:
- Mentice VIST: Life like simulation of catheterizations
Figure 1. Mentice VIST
used exclusively for clinical training.
catherization simulation
- Opaque Heart Model: Hard plastic model of the heart
for visualizing intracardiac catheter movement- anatomically incorrect.
- Device Specific Models: There exist several models for testing various aspects of
cardiac medical devices.
- Patented model for fatigue testing of prosthetic tricuspid valve
replacements
- Agar Gel Model for ultrasound imaged flow dynamics through bicuspid
valve
- Model testing ventricle assist devices pumping performance and
quantifying flow dynamics
Adapting a Recent Prototype
Previously established prototype
was established with several design
flaws we wished to address:
1. Leaking at joints
2. No flow potential
3. Difficulty emptying
4. Anatomically incorrect heart
Figure 2. Prototype established by 2009 senior design
team based on Dr. Michael Barnett’s design specifications
OBJECTIVES
Meeting Device Objectives
1. Clear visibility of catheter movement
2. Water tight system
3. Anatomically correct flow
RESULTS CONT’D
Achieved Anatomically Representative Heart
4. Anatomically correct heart
5. Meet size constraints of carry-on
luggage: 22” x 14” x 9”
Symmetrical between Left
and Right
Separated by self healing
polymer representing
septum
METHODOLOGY
Creating a Closed Circuit
- Bended ½” acrylic tubes 180° using heat gun
- Put sand in tubes for a good bend
- Failed due to grains being imbedded in tube
- Used a metal cylinder to standardize bend radius
- Also used acrylic grease to prevent melted acrylic
from sticking to the metal
Preventing Leaking at Inferior Vena Cava Bifurcation
- Made 2 Y-connectors:
Figure 3. From left to right, a
progression of attempted bended
- One with 1” output to heart
½” tubes.
- One with ½” input from pump
Sealing the Joints
- Used acrylic tubing for veins and acrylic blocks for heart
- Allowed us to use dichloroethylene glue instead of
silicone glue
- Built double o-rings into Y-connectors
Generating Flow Throughout Model
Figure 4. Bifurcation of the
- Included a metering bellows pump into the closed circuit
inferior vena cava.
- Placed underneath the model in order to be anesthetically
pleasing
Creating Catheter Insertion Points
- Cut short angled acrylic tubes and glued them to
femoral vein using melding acrylic adhesive
- Used rubber stoppers to prevent leaking at entry point
- Drilled various sized holes in different stoppers in
order to prevent leaking while allowing various diameter
catheter insertions
Figure 5. Single metering bellows
Making the Heart Anatomically Correct
pump used to create pulsatile,
- Designed so that the inferior vena cava directly entered
venous pressure in model.
into right atrium
- Attempted casting the heart with urethane
- Failed due to lack of clarity and inability to release
urethane from mold
- Built heart as 4 blocks to model the interior of the heart
Decrease Weight, Increase Portability
- Removed all tubing which represented veins above the
heart in the body
- Designed model to fit inside a 22” x 14” x 9” suitcase
Figure 6. Failed attempt of
casting a half of a spherical heart
- Double o-rings in Y-connector allow the bended tubes to
with a hemispherical press.
be removed during transportation
Figure 7. Cost analysis for various
models used in visualizing
catheterizations
Model
Our Prototype
Mentice VIST
Opaque Heart
Total Cost
$1380.00
$40,000.00
$5,000.00
Ellipsoid Chambers
Atria: R: .7” H: .75”
Ventricle: R: .75” H: 1.2”
Figure 8. Left: Design of heart as modeled in ProE depicting the dorsal half of the heart with
simulated septum. Right: Mid esophageal Echocardiogram depicting dorsal half of the heart
Femoral Vein
IVC
Length IVC
RA Volume
Ventricle Volume
Model
.5 in. ID
1 in. ID
9 in.
1.53 in3
2.82 in3
Body (Avg)
~0.41 in (11 mm)
~0.81 in (20mm)
~14 in (37cm) *includes SVC
~2.37 in3 (39 ml)
~3.6 in3 (60 ml)
Figure 9. Comparing
ventricular sizes for
model and average male
estimated between
diastole and systole.
CONCLUSIONS
In measuring the success of our model, Dr. Barnett is able to interface
successfully with the device, visualizing cardiac procedures with catheters of
various diameters and lengths. Design objectives have been successfully
implemented including the addition of an anatomically accurate flow gradient,
interior heart design and vasculature diameters. The model has improved
from the previous prototype with the elimination of leaking and the addition
of transportability.
FUTURE WORK
Future work will involve establishing a means of casting the heart to achieve an
anatomically correct exterior in addition to an anatomically correct interior.
This casting will potentially involve plaster paris and a cadaver heart . A second
avenue of further work will involve adding a modular superior venous system
as well as a pulmonary vein for visualizing the path of an air embolism if
introduced during catheterization.
REFERENCES
• Appartus for Testing Prosthetic Heart Valve Hinge Mechanism. More RB et al., inventors.
United States Patent US5531094. http://www.freepatentsonline.com/5531094.pdf
accessed 12 Nov 2009.
• Durand LG, Garcia D, Sakr F, et al. A New Flow Model for Doppler Ultrasound Study of
Prosthetic Heart Valves. Journal of Heart Valve Disease. [Internet] 2006 Nov 4 [cited 12
November 2009]; 17. Available from: http://www.icr-heart.com/journal/.
• Hertzberg BS, Kliewer Ma, Delong DM et al. Sonographic Assessment of Lower Limb
Vein Diameters: Implications for the Diagnosis and Characterization of Deep Venous
Thrombosis. AJR. May 1997; 168:1253-1257.
• Pantalos GM, Koenig SC, Gillar KJ, Giridharan GA, Ewert DL. Characterization of an
adult mock circulation for testing cardiac support devices. ASAIO. Feb 2004; 50(1):37-46.
ACKNOWLEDGEMENTS
Special thanks to Dr. King, John Fellenstein and the Machine Shop, Dr. Barnett, Alex
Makowski, Andrew Cross, Ray Booker and the Vanderbilt Simulation Center