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Multi-Disciplinary Engineering Design Conference
Kate Gleason College of Engineering
Rochester Institute of Technology
Rochester, New York 14623
Project Number: 08026
HEMODYNAMIC FLOW SIMULATOR
Amanda Clark – ME
Charles Marion - IE
Jason Brown – ME
Jonathon Kelso – EE
Dan Wisniewski - EE
Matthew Hicks – EE
ABSTRACT
CONCEPTS
This project’s aim was to replicate the pressures and flows
associated with the cardiovascular system. A custom designed
hemodynamic flow simulator was constructed for the project.
LabView was used to collect the data and convert the raw
signal to a fluid property. The project is to be used as a test-bed
prototype for further projects. Tests were carried out in order to
investigate the response of the system as variables such as
compliance, resistance, and input waveform were varied.
Many designs were initially investigated. The main difference
between designs was whether the flow was pressure driven or
flow rate driven. In a pressure driven system the pressure is
controlled and the flow rate is variable. In a flow rate driven
system the flow rate is controlled and the pressure is variable.
INTRODUCTION
The design objective was to be able to accurately and reliably
replicate blood flow through the cardiovascular system. This
was to be accomplished by using a custom designed heart
chamber, a linear actuator to act as the drive system, a valve to
simulate vascular resistance within the system, and a
compliance chamber to take into effect the compliance of the
blood vessels during pulsatile flow.
Ideally, the system could also be used by researchers involved
with hemodynamic research in the testing of biomedical
devices such as heart valves and bypass grafts. The test stand
could also serve as a teaching tool for future biomedical
students so that they may have a better understanding of the
pressures and flows associated with the heart’s pulsatile flow
and various means of testing these properties. The system will
also be used as a demonstration illustrating biomedical
engineering during open houses and other institute events.
A bellows system was explored in which a linear actuator
would compress a bellows device to mimic the flow out of the
heart. This was not tested due to the nature that it is a flow
based system and the fact that the drawback part of the cycle
would cause a negative pressure within the heart chamber.
A piston based pump was considered, which would enable
accurate and linear volume displacement with high sensitivity
in flow control. After inspecting the friction involved and the
possibility of failure of the piston chamber and actuator, a
simpler method was implemented to ensure sustainability of the
pump mechanism.
A diaphragm based system was the final choice for the drive
system. This involves a rubber sheet secured to the top of an
open cylinder with an outlet at the bottom. The plunger
attached to a linear actuator applies pressure to the rubber
diaphragm which allows for a controlled volume displacement.
The rubber diaphragm is inexpensive and easily replaceable.
The design of the heart chamber and associated
electromechanical drive system was carried out by a contracted
company under the direction of Dr. Schwarz of Strong
Memorial Hospital and was donated to us for use in our project.
© 2005 Rochester Institute of Technology
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Proceedings of the Multi-Disciplinary Engineering Design Conference
stripping gasket material is used along the top edge in order to
provide an air-tight seal. Pressure is applied on the top piece by
pull-action toggle clamps.
Figure 1: Schematic of Flow Loop
CONSTRUCTION
Figure 3: Constructed Compliance Chamber
Compliance Chamber
The construction of the compliance chamber was a major part
of the project. Polycarbonate was chosen as the material for its
high strength and ability to be machined and enable threaded
fittings.
Drive System
The heart chamber was machined as part of Dr. Schwarz’s
previous research efforts. There are three openings to the
chamber. One is used to pressurize a chamber containing a
polyethylene bag representative of a ventricle and the other two
are the inlet and outlet to and from the simulated ventricular
cavity. The input and output ports have one way heart valves to
ensure there is no reversal of flow, similar to the situation in the
human circulatory system.
Figure 2: Schematic of Compliance Chamber Design
The inlet and outlet ports of both sides were drilled and tapped
using 1” National Pipe Thread standards. This allows for use of
standard fittings which are used for every component. Standard
screws with 6/32 thread count were used to affix the sides of
the chamber together.
A thin bead of silicone acts as a sealant around all joints in
order to make the chamber water and air tight. A weather-
Figure 4: Heart Chamber
Flow is created by modulating the volume of fluid surrounding
the polyethylene bag creating a change a volume and pressure
internal to the bag similar to that found in a human ventricle.
An increase in fluid surrounding the bag results in an increase
in its internal pressure and results in an ejection of its internal
fluid out of the output port and into the system. Since this is a
Paper Number 08026
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Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conference
closed system with a controlled compliance and resistance, the
volume of fluid ejected out the output port ends reentering the
bag via the input port, and thus refilling it for a another
compression/ejection cycle.
The linear actuator used was part of Dr. Schwarz’s system. It
was customized with the addition of an aluminum cylinder
similar in design to the plunger portion of syringe. This piece
applies pressure to and deflection of the diaphragm of the drive
cylinder which, in turn, produces an increase of fluid volume in
the fixed volume chamber in which the polyethylene bag is
contained. When the pressure outside the bag exceeds the
pressure inside due to the backpressure in the output port, a
volume of fluid is ejected through the output part in to the
simulated circulatory system.
Figure 6: Drive Cylinder
Tubing/Fittings
Figure 5: Drive System Assembly
The drive cylinder was an element of the original system
donated by Dr. Schwarz. It was customized for our use by
cutting a top plate piece which attached to the top of the
cylinder using screws. A rubber gasket material is sandwiched
between the plate and the drive cylinder chamber creating the
surface which is in contact with the actuator piston.
Standard 1” vinyl tubing was used throughout the system. All
fittings are 1” NPT thread, barbed style fittings. 1” hose-clamps
were used to provide a tight seal around the fitting. Threads are
wrapped with Teflon tape before being screwed in to prevent
leakage.
DATA ACQUISITION
The sensors were chosen to match the pressures and flows
within the circulatory system.
For this stage of the project, the signals from the sensors need
to be analyzed and displayed. LabView was chosen as the
platform to perform processing and display, due to its emphasis
on data collection and manipulation. The two types of input
result from pressure sensors and flow sensors. The pressure
sensors output a DC voltage shift corresponding to the pressure
change. The flow sensors output constant amplitude pulses with
increasing frequency as the flow increases. With the use of up
to 5 pressure sensors and 2 flow sensors in the system, the
amount of data being collected caused some concern about the
sampling rate of the initial DAQ given to the team (NI
USB6008, sampling rate of less then 10,000 samples/second for
all channels). Due to need for higher resolution in the sensor
data being collected, the Measurement Computing USB1208FS was chosen (sampling rate of 50,000 samples/second).
The pressure sensors will be connected to the analog inputs of
the DAQ since high resolution of the change in pressure will be
desired. The flow sensors were initially connected to the digital
input of the DAQ to enable measurement the frequency of the
pulses.
Copyright © 2005 by Rochester Institute of Technology
Proceedings of the Multi-Disciplinary Engineering Design Conference
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imported into LabView for real-time visual display as well as
being able to be exported in a standard file format.
RECOMMENDED FUTURE WORK
In terms of software, future work could involve the
development of an intuitive Graphical User Interface to
facilitate operation of the system for data acquisition and
control. In terms of hardware, future work will incorporate
electromechanical devices to enable computer controlled
operation of the system and modification of its operating
parameters.
ACKNOWLEDGMENTS
Figure 7: Preliminary LabView Interface
In LabView, the pressure sensor input data is converted from
millivolts to mmHg using the sensitivity of each sensor and a
conversion from PSI to mmHg. The flow sensors data is
collected into a if-statement loop which creates an artificial
small-scale buffer. After 50 milliseconds of data sampled, this
loop counts the pulses (frequency of pulses) and produces a
count, which is, then converted into flow rate (liters/min).. Both
the pressure sensor outputs and flow sensor outputs are
displayed via a custom user interface in LabView.
We would like to thank our Senior Design Guide, Dr. Daniel
Phillips (EE) as well as Dr. Karl Schwarz M.D. from Strong
Memorial Hospital. Their input was invaluable. Dr’s Day and
Kempski, both of Mechanical Engineering also provided
guidance. Thanks again go to Dr. Schwarz who also provided
the drive system used for the project. We would like to thank
Richard Wisniewski of Medline Industries, Inc for the donation
of various materials for the project. Thanks also go out to
Chamberlain Rubber who donated rubber sheets for our use.
TESTING
Three tests were carried out. The first was the validation of the
chosen drive system’s ability to adequately simulate a pressure
waveform similar to that out of the heart. This was completed
by measuring the pressure and flow rate on the outlet of the
heart chamber.
The second test concerned the simulated vascular resistance.
This was carried out by a globe valve placed between the two
parts of the compliance chamber. By closing the valve off at
specified angular displacements of the handle we were able to
test the effect of resistance on the pressure and flow.
The last test involved the custom built compliance chamber. By
varying the pressure and volume of air in the two sides of the
chamber we are able to change the level of compliance
simulated within the system.
RESULTS
The system adequately represented hemodynamic flows and
pressures. With the system operational, the pressure swing was
recorded as 120/80 mmHg, which represents normal
physiological blood pressure values. Data was acquired and
Paper Number 08026