1
Table of Contents
Abstract ............................................................................................................................................... 3
Background ........................................................................................................................................ 4
Pericarditis ........................................................................................................................................ 4
Pericardial Effusion .......................................................................................................................... 5
Pericardiocentesis .............................................................................................................................. 6
Simulation.......................................................................................................................................... 7
Currently Available Task Trainers ................................................................................................... 7
Patents .......................................................................................................................................... 11
Customer Request ........................................................................................................................... 12
Simulife Innovations........................................................................................................................ 12
Mission Statement ........................................................................................................................... 12
Member Expectations ..................................................................................................................... 13
Initial Customer Meeting to Define Project ................................................................................... 13
Problem Statement .......................................................................................................................... 14
Defining the Project......................................................................................................................... 14
Observing Simulation.................................................................................................................... 14
Design ................................................................................................................................................ 15
Functional Requirements ............................................................................................................... 16
Engineering and Client Constraints and Limitations ................................................................ 19
Procedures and Manufacturing ...................................................................................................... 19
Box design .................................................................................................................................... 19
Sternum/Ribs ................................................................................................................................ 20
Heart and Pericardium ................................................................................................................... 23
Other Internal Organs .................................................................................................................... 25
Ultrasoundable Skin ...................................................................................................................... 27
Heart Movement and Variable Fluid .............................................................................................. 28
Performance Testing ....................................................................................................................... 29
Project Timeline ............................................................................................................................... 33
Budget ................................................................................................................................................ 34
Future Steps ...................................................................................................................................... 34
Acknowledgements .......................................................................................................................... 36
References ......................................................................................................................................... 37
2
Abstract
Pericardiocentesis, the removal of excessive fluid from the pericardium under ultrasound
guidance, can be a life-saving intervention in critically ill patents if performed correctly.
Commercially available pericardiocentesis task trainers have been shown to decrease the
occurrence of associated complications. Unfortunately, most task trainers are prohibitively
expensive and are not physiologically accurate. The most limiting features of current trainers
include the lack of a beating heart, limited number of times the procedure can be performed, and
excessive amount of time and cost for maintenance. To address these issues, the team developed
a method of using a battery filling siphon bulb connected to a syringe which simulates heart
movement in the bulb. A relatively low cost pericardium was made from Silastic® MDX4-4210,
which is both flexible and resistant to multiple punctures. Finally, to reduce the cost of the
trainer, the team used a 15.2cm x 24.8cm x 11.4cm Plexiglas box, instead of modeling an entire
torso. Additional physiologic features, including Ecoflex® 00-30 gel to simulate body tissue,
sponges for lungs, and barriers to simulate the stomach and liver were added to increase
physiological accuracy. The entire trainer is ultrasoundable, reusable, and affordable, meeting
the most important criteria set forth by the project.
3
Background
Pericarditis
Pericarditis (PC) is inflammation of the pericardium, the sac that holds the heart, and can
lead to pericardial effusion, which is when the pericardium fills with fluid. PC can be caused by
infections, renal failure, cancer, trauma, medications, tuberculosis, AIDS, and many other
conditions [1-3]. For a complete list of causes see Table 1 [2]. Any person can be affected by
PC and pericardial effusion, but it is more commonly diagnosed in adults, unless there is a preexisting condition such as cancer (Dr. Holder). Symptoms of PC are abnormal heart rhythm,
muffled heart tones, chest pain, fever, malaise, myalgias, swelling of the veins in the neck,
change in skin color from pink to blue, friction rub, and abnormal breathing rate. [1-4].
Diagnosis is performed through use of electrocardiography (ECG), which shows non-specific
ST-T wave changes, blood work showing elevated white blood cell count and red blood cell
death, or chest radiography showing enlarged heart size when more than 250mL of fluid is
accumulated [1-3]. Patients exhibiting enlarged neck veins, tachycardia, hypotension, and
elevated enzyme levels are usually hospitalized [1].
For mild cases, anti-inflammatory medications may be used to relieve pericardial
inflammation [1]. If the condition worsens, corticosteroids may help to reduce inflammation [1].
If not treated, calcification of the pericardium or death may occur [1]. In very rare cases, removal
of the pericardium may be required [3]. Mortality for tuberculosis-related PC is near 85% [1].
Pericarditis can cause pericardial effusion, which will require pericardiocentesis (PCC).
4
Pericardial Effusion
Pericardial effusion is the accumulation of fluid in the pericardium. This is usually the
result of a lack of fluid drainage due to an imbalance in the resorption and production rate of the
5
fluid [4]. Normally, the volume of the pericardial liquid, which is needed to lubricate cardiac
motion, is 15-20mL [1]; when this volume reaches 50mL [4, 5], or when the pericardium
thickness reaches 3mm [3], it is considered excessive. This fluid can be exudates, water, or
blood. As the condition progresses, the heart cannot effectively produce needed cardiac output
due to the surrounding pressure, which is known as cardiac tamponade, and requires emergency
PCC [4, 5].
Pericardiocentesis
PCC was first used to treat pericardial effusion in the early 18th century [5]. At first this
was a blind procedure, which incurred a very high complication rate [5]. In the 1970s,
echocardiography (ultrasound) was introduced for visualization of the procedure [5]. ECG can
be used to show improper heart rhythm if the needle punctures the heart [1, 3]. These advances
greatly enhanced procedure safety [5]. With echocardiography, success rate of PCC was 97%
with a total complication rate of 4.7%, whereas prior to use of echocardiography, morbidity rates
reached 20% and mortality approached 6% [5]. To limit recurrence of pericardial effusion,
extended catheter drainage is used [5].
PCC is performed by medical professionals in emergency situations, most often in
hospital emergency rooms. During the procedure, the patient is placed at a 45-60° angle so that
the heart is close to the left interior chest wall [1, 6]. The ultrasound transducer is placed on the
left interior chest wall and is set at a frequency range of 2.5-3.5mHz for imaging of needle
placement [6]. A 16-18 gauge [7] needle is inserted adjacent to the transducer below the
xyphoid process, into the intercostal space, or in a position for the easiest access to the
pericardium for optimal fluid collection [6, 8]. The needle is inserted into the chest cavity
toward the left shoulder and into the pericardium [1]. Some of the fluid is aspirated, and the
6
needle is sometimes replaced by a catheter to allow for extended drainage. ECG is used to alert
the medical professional if the heart itself has been punctured [6, 8].
Current studies consistently emphasize a need for experienced personnel in performing
this procedure [1, 8, 9]. In at least 10% of all PCC attempts, more than one needle insertion is
required to access the pericardium [5] and 3-5% of patients will suffer from a complication
associated with the procedure [5, 8]. Fatal complications include chamber lacerations requiring
surgery, injury to intercostal vessel requiring surgery, pneumothorax requiring chest tube
placement, ventricular tachycardia, and bacteremia [5]. Alternatively, minor complications
include transient chamber entries, small pneumothorax, vasovagal response with transient
decrease in blood pressure, non-sustained supraventricular tachycardia, pericardial catheter
occlusion, and probable pleuropericardial fistulas [5].
Simulation
Experience greatly affects a physician’s performance. For instance, patients are more
likely to die from cardiac arrest on nights and weekends, when experienced staff are not present
[10]. Simulation is “the emersion of a trainee in a realistic situation created within a physical
space or a task trainer that replicates a real environment” [10]. It has been shown that training on
task trainers decreases the occurrence of complications resulting from medical errors because of
the increased experience of the medical professional [10, 11]. Additionally, a more realistic
trainer results in more effective training and better patient care [10].
Currently Available Task Trainers
There are task trainers for PCC currently on the market. A very simple model is
produced by Life/Form® (Figure 1, A, B) [12]. The model consists of a headless torso without a
heart [12]. It has a fluid filled sac in the chest cavity and allows for variable fluid volume,
viscosity, and color [12]. The task trainer must lie flat, which is unlike normal patient
7
orientation during this procedure, when the patient is placed at a 45-60° angle[12]. The model is
not useable with external monitoring devices such as ultrasound or ECG [12]. The fluid is
controlled by an I.V. bag near the task trainer, and allows for training of needle placement, fluid
removal, and chest tube maintenance [12]. This model is very limited in that it only allows for
puncture of the model and fluid removal [12]. Most institutions can afford the price of $1,500,
but because of its limited physiological relevance and interaction, it cannot prepare medical
professionals adequately.
Another simplistic task trainer for PCC was designed by physicians at Advocate Christ
Medical Center in Illinois (Figure 1, C) [13]. This task trainer uses gelatin from a Tupperware®
mold as ultrasoundable skin, a golf ball that acts as the center of the heart, and a balloon for the
pericardial sac. It costs approximately $20, and takes around ninety minutes to assemble. The
trainer will last for two weeks at room temperature, and can last for over two months if
refrigerated. However, the model is very temporary and does not simulate complications or heart
movement [13].
Blue Phantom™ is another task trainer that uses an ultrasoundable fluid in the pericardial
sac (Figure 1, D). The model is a torso, and a head can be bought separately [14]. Compared to
the Life/Form® model, Blue Phantom™ allows the physician to develop necessary skills in
using ultrasound system controls, in transducer placement, in recognition of structures, and in
guiding needles and catheters into the pericardial space [14]. The model can be used with any
ultrasound system [14]. It can be used repeatedly without high cost for part replacement as with
other models [14]. Blue Phantom™ claims that the model has self-healing skin tissue that can be
punctured multiple times without fluid leakage [14]. Major limitations of the model are a lack of
8
a beating heart and error indicator on an EKG [14]. The price of the Blue Phantom™ model is
$15,000, which is costly for an unrealistic task trainer.
The most realistic task trainer that is used for PCC, as well as many other medical
emergency situations, is iStan, produced by Medical Education Technologies, Inc. (METI)
(Figure 1, E,F) [15]. iStan interacts with the user much in the same way a real patient would [11,
15]. iStan has arms and legs, as well as a torso and head, is adult size, talks, cries, bleeds, has
thumb twitches, heart sounds, bowl sounds, and blinks its eyes [11, 15]. The model has carotid,
femoral, popliteal, and pedal pulses, and correct anatomical landmarks [11, 15]. The model’s
chest rises with breathing and it can simulate breathing difficulties [11, 15]. Limitations are
constrained to fake plastic skin and the need to use an oxygen tank for breathing simulation [11,
15]. However, its cost of $250,000 makes it prohibitively expensive for almost all institutions
[11, 15]. For a summary comparing each task trainer’s properties, see Table 2.
x
x
x
x
x
x
x
x
x
x
x
x
x
x
ts
oi
n
ac
ce
ss
p
Co
st
pl
e
ul
ti
M
pl
e
ul
ti
ri
nd
ic a
to
s
x
Er
ro
us
ag
e
x
M
ab
le
Du
r
od
y
ll
b
Fu
ca
te
m
ee
li
ng
od
el
sk
i
n
r(
EK
G)
ce
Re
ali
sti
cf
ki
x
De
li
op
pr
sti
cs
Re
ali
x
x
na
pp
ea
ra
n
ert
ies
e
id
flu
le
Va
ria
b
le
Va
ria
b
wi
th
ul
flu
id
tra
x
Us
e
He
art
be
at
Br
ea
th
ing
ll
ica
An
a
x
vo
lu
m
so
un
d
ar
k
an
dm
rec
t
co
r
lly
Advoacte
Christ
Medical
Center
tom
ica
tom
An
a
Blue
Phantom
Model
METI
iStan
Life/form
Simulator
s
he
ar
t
Table 2. Comparison of current pericardiocentesis simulation models on the market.
x
x
$15,000
x
x
$250,000
x
x
$1,450
x
$20
9
(A)
(B)
(C)
(D)
(E)
(F)
Figure 1. Current training models on the market. (A) Life/Form® model. (B) Life/Form® model
parts inside the chest cavity. (C) Advocate Christ Medical Center gelatin task trainer. (D) Blue
Phantom™ model with ultrasound transducer. (E) METI’s iStan with listed capabilities. (F)
METI’s iStan simulation.
10
Patents
A preliminary patent search found similar task trainers and task trainer components to those
used in Simulife Innovation’s design [16]. Simulife Innovation’s design does not explicitly
infringe on any one of these patents.
1. #6,780,016 by Toly, entitled “Human surgical trainer and methods for training.”
Disclosed is a surgical trainer comprised of elastomeric simulated human tissue
structures. The chest area is designed to allow for PCC training; other areas of the task
trainer allow for practice of other surgical procedures. Anatomical features include a
sternum, ribs, inflatable lungs, a simulated pericardium (which is replaceable), and a
heart. The heart and pericardium can be filled with simulated body fluid of different
colors to indicate the progress of the procedure. The heart and pericardium are spherical
elastomeric material; the pericardium can be made out of a balloon. They are filled with
different colors of fluid to indicate laceration of the myocardium. The body tissue is
made of layers of various materials to simulate the layers of tissue in the body.
2. #7,857,626 by Toly, entitled “Medical physiological simulator including a conductive
elastomer layer.” Disclosed is a continuation of the patent described above. The
improvement focuses on the conductive elastomer layer, which allows for feedback to the
user as to the progress of the procedure. During PCC training, the sensors near the skin
can determine if the user punctured the correct area, depth, and angle to perform the
procedure.
3. #5,947,744 by Izzat, entitled “Training apparatus and method for coronary artery
anastomoses featuring simulated pulsating heart.” Discloses a method using a cam-shaft
motor connected to a moving platform to induce pump-like motion in a simulated heart.
11
4. #6,685.481 by Chamberlain, entitled “Cardiac surgical trainer and method for making
same.” Discloses a model of a heart with natural organ motion connected to a control
device to determine speed of motion. It has two sections; an inner cast simulating the
myocardium and an outer shell simulating the pericardium. Both are preferably made of
silicone rubber. The inner is made by making a mold from a sculpture of the heart.
Tubes are embossed in the heart model and coiled around the orthogonal and longitudinal
axes; a control device changes the pressure within the tubes so that natural movement is
induced.
Customer Request
There is a need for a cost effective task trainer that will appropriately mimic advanced
medical emergency situations for optimal physician training. Austen BioInnovation Institute in
Akron (ABIA) requested a design team from The University of Akron’s Department of
Biomedical Engineering to design and create a task trainer for PCC that can fulfill these
requirements.
Simulife Innovations
Simulife Innovations was created on October 7, 2010. The design team, consisting of
five members, Laura G. Smith, Swata Patel, Katie Hasenstab, Rachel Manthe and Mary Beth
Wade, was tasked with creating a simulation device that can be used with hospital devices, such
as EKG and ultrasound, to adequately simulate PCC in an emergency situation.
Mission Statement
Simulife Innovations’ mission is to provide exemplary customer satisfaction and
education through state of the art physiological simulation systems for medical advancement in a
12
cost efficient manner while keeping in mind the interests of our stakeholders, employees, and
community.
Member Expectations
All members are required to come to every meeting on time and stay till the end of the
meeting, and must inform another team member if she is running late or will be unable to attend.
As a working member of the group, everyone must be open to accepting follow-up assignments
and work, and complete any work or assignments from the last meeting before attending the next
meeting. All members are expected to do quality work on all individual and group tasks.
Everyone must adhere to the agenda/objectives and participate and contribute at every meeting.
Every member will support and encourage one another during meetings, respect other team
members and their ideas, and listen actively to one another and ask questions if confused. Social
talk during meetings must be kept at a minimum. All members are expected to be open to all
ideas, and should state opinions on other’s ideas tactfully. Any conflicts will be managed by an
unbiased arbitrator, either within or outside of this group.
Initial Customer Meeting to Define Project
The team met with Dr. Michael Holder, Vice President and Director of the Center for
Simulation and Integrated Healthcare Education at ABIA on October 28, 2010. In this meeting,
the team was able to ask any questions regarding the procedure and simulation device that would
be necessary for further understanding. Dr. Holder explained that while PC is normally the
result of trauma or cardiac arrest, it can also occur due to some pre-existing condition, such as
cancer, lupus, and arthritis. He further explained that PC is diagnosed by labored chest
movement, or an abnormal heart beat. He emphasized that immediate and fast fluid removal is
required.
13
The team also discussed the simulation model and expectations from ABIA. Dr. Holder
is aware of currently available task trainers on the market, and has stated his reasons for
declining to purchase these models. While it would be ideal to fully create a trainer that will
adequately mimic every contributing variable to PCC in a traumatic situation, this goal is beyond
the scope of this project. After the meeting, the team immediately began in-depth research on
PCC and task trainers, and began defining the obtainable objectives for this project.
Problem Statement
Pericardiocentesis allows for immediate alleviation of potentially life threatening
symptoms when performed correctly. However, due to the complexity of the procedure and lack
of experience, physicians may make detrimental errors. Practicing with task trainers allows
physicians to develop expertise, and reduces patient complications, recovery time, and cost of
treatment. Unfortunately, currently available task trainers are prohibitively expensive and
limited in their scope of realistic characteristics. There is a need for a physiologically accurate,
easily maintained, and cost effective task trainer.
Defining the Project
Observing Simulation
In order to better understand the procedure, Dr. Holder recommended a meeting with Mr.
Scott Atkinson, Program Coordinator/Simulation Technologist and Paramedic at the Simulation
Lab at Summa Health Systems. On December 3, 2010, Mr. Atkinson showed the team the
current PCC task trainer, and all of the other trainers that are used by Summa and Children’s
Hospital residents and staff. Of these models, there is no working practical task trainer for PCC.
The group observed simulation devices for paracentesis, thoracentesis, and subclavian vein
access. The models showed signs of wear and tear, and there were many circumstances where
14
leaking had begun after numerous punctures. The most durable models were self-healing due to
glue within the material. This material would still leak after approximately 150 punctures. Mr.
Atkinson explained that hospitals prefer task trainers with replaceable components for cost
effectiveness. He emphasized the importance of replaceable component parts and durability of
materials while still allowing use with ultrasound in a new PCC trainer. While talking with Mr.
Atkinson and viewing the task trainers, the team realized that their initial project scope was far
too large to be completed within the given timeframe of four months. Instead, the team changed
the main focus to be on reusability of an ultrasoundable, beating heart model through
development of better materials.
Design
Based on the first meetings with Dr. Holder and Mr. Atkinson, Simulife changed the
focus of the PCC task trainer project. Most significantly, the team decided to use a box design
containing the mechanical heart, rather than an entire manikin torso. The group also decided to
focus on a heart that will move with respect to fluid volume. By increasing the volume of fluid
in the pericardium, the degree of movement of the heart will decrease. Heart and pericardium
material also became priority over skin material. The material should be self-sealing after
repeated needle punctures without leakage, and flexible for movement. The team used
ultrasoundable gel recommended by Austin BioInnovation and created a mold for forming the
skin. The design of each component of the task trainer is discussed in detail in future sections.
The team met with Dr. Holder at ABIA on January 12, 2011 to discuss these changes. His
preference was still for a model that would include a warning signal on EKG. While the group
did not intend to include this parameter in the final design, Simulife considered designing a
closed loop electrical circuit that could simulate the requested warning signal.
15
Functional Requirements
The original list of functional requirements was created on November 10, 2010, and was
summarized in an objective tree (Table 3A). Items that were required by this team were
highlighted in red, while all further requirements from the client were highlighted in blue. This
list was re-evaluated in January 2011, and the objective tree was updated to reflect those changes
(Table 3B).
16
Table 3. (A) Original objective tree. (B) Project necessities are red, client wants are in blue.
Stars denote completed items.
(A)
17
(B)
18
Engineering and Client Constraints and Limitations
Clients for this project are the hospital administration, physicians, medical students,
EMTs, EMT trainees, nurses, nursing students, maintenance technicians, ABIA, Summa, Dr.
Holder, Mr. Atkinson, and patients requiring the procedure. The team decided to limit the
parameters of the design to be cost efficient, be adult sized, have a beating heart, have realistic
skin, adapt to variable fluid amounts contained within the pericardium, be easy to move and
maintain, and be reusable. The constraints of this project include cost of no more than $15,000,
maintainable and easily prepared for simulation by any medical professional with a limited
amount of training. The size of the model should be adequate for portability through the
hospital. The materials must mimic native tissues in the body. The skin must be able to be
punctured at least 150 times without leaking, and the heart must be visible by ultrasound.
Procedures and Manufacturing
Box design
The group chose to make the box out of Plexiglas since it was readily available, cheap,
and was echolucent on ultrasound as determined on March 14, 2011 at the Summa Simulation
Lab. Mr. Manthe constructed the box for the group using 0.6cm thick, clear Plexiglas. The walls
of the box were glued together with Oatey® All Purpose Cement. The bottom of the box was left
unglued for easy access to the parts after filling the model with the Ecoflex® 00-30 gel. The
inner dimensions of the box required to contain the left portion of the upper ribcage (including
the entire sternum and ribs 1-7) were 15.2cm (W) x 24.8cm (L) x 11.4cm (D). The box was
modeled in SolidWorks (Figure 2). A 2.9cm hole was also carefully drilled for the heart fluid
lines to exit the box.
19
Figure 2. SolidWorks model of box (dimensions in mm).
Sternum/Ribs
Anatomical landmarks are crucial for correct needle placement and insertion during the
procedure. To construct physiologically accurate ribs, the dimensions of the sternum and ribs
were determined by measuring a model skeleton in Dr. Verstraete’s gait analysis lab supported
by measurements obtained from literature [17-19]. Using these measurements, models were
created in SolidWorks (see Figures 3 and 4).
The prototype ribcage was created using Sculpey 3 oven-bake modeling clay from Pat
Catan’s Craft Centers (Figure 5). The entire clay mold of the ribs and sternum was baked in one
piece at 275°F for 15 minutes. The piece was then carefully screwed in correct anatomical
position into the sides of the box (Figure 6).
For future manufacturing, a hard plastic would be used in an injection mold to make a
consistently accurate ribcage.
20
Figure 3. SolidWorks model of the sternum (dimensions in mm).
Figure 4. SolidWorks model of ribs 1-7 (dimensions in mm).
21
Figure 5. Sculpey 3 oven-bake modeling clay prior to baking.
Figure 6. Baked clay ribs screwed into the Plexiglas box.
22
Heart and Pericardium
The pericardium is a thin elastic sac surrounding the heart that can reach a thickness of
3mm when affected by PC. In order to model this, the material for the pericardium must imitate
basic functions of the normal pericardium, be flexible, and be self-healing. Further, the
prototype heart should be approximately the same size as average adult heart, which is12cm in
length and 8-9cm in width [20]. A battery filling siphon bulb purchased from Ace Hardware was
found to be appropriate; the size of this bulb was measured to be 10.8cm long and 7.4cm wide.
This bulb also exhibited self-healing and simplicity in filling the cavity, but again, the wall was
too thick for realistic simulation of the pericardium. The group then decided to search for selfhealing materials with similar thickness and elasticity to a real pericardium that would encase the
bulb and hold fluid.
A latex punching ball was tested as a potential simulated pericardium over the larger
siphon bulb and modeled using finite element analysis (see Testing Procedures). However, this
material did not exhibit self-healing properties and was difficult to fill with fluid. While the
material would be sufficient, cheap and easy to replace, the group decided to search for a more
durable and moldable material.
A Biomedical Grade Elastomer produced by Dow Corning, Silastic® MDX4-4210, was
found in the Olson Biomedical Engineering workshop. After researching the material properties
online and comparing to the latex punching ball on finite element analysis (see Testing
Procedures), it was decided that this elastomer would be more effective. To create a Silastic®
pericardium, the material was formed by thoroughly mixing 1 part of the curing agent with 10
parts by weight of the base elastomer. Approximately 165g of Silastic® was made and poured
onto a preformed template of wax paper with a 1mm thickness (Figure 7). The material was then
23
allowed to cure for approximately eighteen hours. The material was then shaped around the
heart bulb and fluid inlet line (diameter= 4mm), and was sealed with more Silastic® (Figure 8).
The material then fully cured in approximately three days at room temperature. The heart and
pericardium were also modeled in SolidWorks (Figure 9).
For future manufacturing, it would be beneficial to use an injection mold for shaping the
Silastic® around the heart bulb during curing.
Figure 7. Template for molding Silastic® MDX4-4210 (dimensions in mm).
Figure 8. Ace Hardware battery filling siphon bulb wrapped in Silastic® MDX4-4210 for
final curing.
24
(A)
(B)
Figure 9. SolidWorks model of the heart (A) and the pericardium (B) (dimensions in mm).
Other Internal Organs
Some complications of PCC include puncturing the organs surrounding the heart.
Puncturing the lung is one of the most common complications. When performing the procedure,
the syringe is pulled back as the needle enters the skin. The tissue creates a resistance on the
syringe. When the lung is punctured, air in the lung creates minimal resistance on the syringe
(Dr. Holder). In order to simulate the lung, a porous dry sponge was cut to shape and placed in
the correct anatomical location (Figure 11) using images from Google and Gray’s Anatomy [21].
25
Other complications of the procedure include puncturing the stomach and liver. In order
to simulate this, the group injected different colored dyes into a liver-shaped sponge and a
stomach-shaped sponge to serve as warnings of incorrect needle placement. As with the lung, the
liver and stomach were cut into the correct anatomical shape and positioned appropriately within
the box (Figure 11).
For future manufacturing, inlet lines could be placed into the sponges for easier filling.
A final complication of the procedure is puncturing the heart. Usually, this is monitored
on EKG and displays a spike in the reading. Dr. Holder suggested that an electrical circuit
should be grounded at the heart. A positive electrode on the metal of the needle would then
sufficiently simulate a spike on the EKG caused by a voltage difference when the loop is closed.
The group decided that this component exceeded limitations due to time constraints, and that
there were increased difficulties due to the fluid components in the system. It is expected that
this part of the project could be easily added at a later time.
Figure 11. Placement of the internal organs.
26
Ultrasoundable Skin
Samantha Stucke, an engineer at ABIA, found an ultrasoundable and self-healing
material from Smooth-On called Ecoflex® 00-30. The material was purchased and tested for
reactions to the Silastic® and other materials used in the task trainer. The only adverse reaction
of this material is the inability to cure next to latex, which is not an issue in this project.
To prepare the Ecoflex® 00-30 gel, it is mixed at a 1:1 ratio of components A and B by
weight or by volume. With all the components of the task trainer in place, the remaining space in
the box was filled with the gel (Figure 12). Normally, the gel cures at room temperature after
approximately four hours with negligible shrinkage. However, 2L were required to fill the entire
box with the gel. Since the gel is approximately 11.4cm thick, it required three days to
completely cure. This material is ideal for this application because it is self-healing and
ultrasoundable.
For future manufacturing, the gel could be dyed to match skin pigment and should be
poured in layers to minimize curing time and allow for easy access to other components.
(A)
(B)
Figure 12. (A) Box with ribs, internal organs, and Ecoflex® 00-30. (B) Completed
SolidWorks model.
27
Heart Movement and Variable Fluid
The group intended to control movement of the sac using a cam-shaft/piston motor
attached to the plunger-end of a 100mL syringe (Figure 13). The syringe is connected to rubber
tubing (diameter=1cm and length of tubing=132.1cm), which is attached to the siphon bulb inlet
line (diameter=1.1cm). Pumping the syringe creates a pressure difference in the heart bulb that
adequately simulates heart movement (Figure 13). This motion also produces chest movement,
making the task trainer more realistic.
An animal respirator motor found in the Department of Biomedical Engineering
workshop would be suitable for automating the heart movement. The motor is controlled by a
dimmer that can be changed to match any desired heart rate. The system could be modified to
pull the syringe plunger to the appropriate distance that would produce an average adult stroke
volume of 70mL/beat [22]. Unfortunately, due to time constraints the group could not complete
this device. However, manual pumping of the syringe was adequate to test the prototype.
Mr. Atkinson also provided the group with I.V. bags for filling the pericardial cavity with
approximately 250mL of saline (Figure 14).
(A)
(B)
Figure 13. (A) Heart bulb attached to tubing and syringe. (B) Cam-shaft/piston device.
28
Figure 14. Simulated heart and pericardium filled with approximately 250mL of fluid. The
arrow points to the fluid line.
Performance Testing
Tensile testing was required to obtain material properties of the latex punching balloon
and Silastic® MDX4-4210 for finite element analysis. Two samples of each material were tested
in Dr. Saunder’s tensile testing machine using a 10lb load cell (Figure 15). Cross sectional areas
were measured, before and after loading, using calipers. The samples were pulled at a rate of
1.165mm/sec. The data was collected at a rate of 10Hz, and was converted to SI units in
Microsoft Excel. Once the linear region of the stress-strain curve was determined, the elastic
modulus was calculated.
29
Figure 15. Tensile testing of Silastic® MDX4-4210.
Finite element analysis was performed using the calculated latex punching balloon and
Silastic® MDX4-4210 properties on the SolidWorks model of the pericardium. These results
were compared to finite element analysis of real heart pericardium properties with a 0.005N/mm2
maximum pressure that is normally seen in the heart [23, 24] using Autodesk® Algor®
Simulation software (Figure 16, Table 4). These results confirmed that Silastic® MDX4-4210 is
the best material to use for simulating a heart pericardium.
Table 4. Tensile Testing and FEA results
FEA Max.
Area
Peak
Peak Disp.
Peak Stress
(mm2)
Load (N)
(mm)
(N/mm2)
Sample
Avg. Modulus
Thickness
(N/mm2)
(mm)
Strain
Stress
(N/mm2)
Silastic® 1
21.45
0.29
0.86
0.01
0.03
Silastic® 2
17.31
0.98
2.61
0.06
0.21
Latex 1
5.55
0.57
1.18
0.10
0.09
Latex 2
5.52
0.67
1.63
0.12
0.12
Heart
N/A
N/A
N/A
N/A
N/A
0.37
1.00
0.30
1.09
1.00
0.89
20.4x106
1
0.34
30
Figure 16. Finite element analysis results.
Fatigue testing of the Silastic® MDX4-4210 material was performed by repeatedly
puncturing the material in the same hole with an 18 gauge needle, to mimic the worst-case
scenario. After each puncture, the Silastic® was examined for leakage; none was observed, even
after 30 punctures in the same location. This was taken to indicate that the Silastic® could be
used in the task trainer for many uses, especially because each attempt would be in a slightly
different location.
Extracting fluid with an 18 gauge needle was performed to assure the realistic
performance of the Silastic® MDX4-4210. A Silastic® pouch was filled with water and
punctured with an 18 gauge needle. Fluid was successfully withdrawn, and the Silastic®
provided the correct amount of resistance, according to Mr. Atkinson.
Material compatibility testing was performed to show that Ecoflex® 00-30 gel and
Silastic® MDX4-4210 bond together during curing, but are compatible after both materials have
completely cured.
31
Mr. Atkinson performed ultrasound testing of all materials and the final device on April
14, 2011 (Figure 17). The materials did appear on ultrasound; however, the fluid in the
pericardium was not as echolucent as desired. It is possible that this is due to density of the
materials (Silastic® and Ecoflex®) or incompatibility of the materials on ultrasound. While
previous testing of each material individually showed adequate compatibility under ultrasound,
the other materials in the completed prototype may have caused some interference. Further, one
feature that is notably missing from the task trainer is the differentiation between the chambers
of the heart. Future designs should include this feature.
Mr. Atkinson gave feedback in the form of human factors testing while testing for
ultrasound capabilities. There were some difficulties in finding which direction the model was
oriented, and in ultrasonography over the protruding ribs. For future designs, the box will be
placed in a full torso, so direction will not be a problem. The ribs will also need to be flatter in
the front so that the ultrasound transducer can be flush with the flesh.
Figure 17. Ultrasound testing of completed prototype.
32
Project Timeline
A timeline of goals was outlined in a gantt chart. Team members were assigned separate
tasks. The end date to complete the prototype was set to be Friday April 15, 2011. A final
update of this gantt chart reflects any changes to the timeline and completion of different tasks
(Table 5).
Table 5. Final gantt chart with updates and completed tasks.
33
Budget
Table 6. Budget
Future Steps
While the current design of the PCC task trainer adequately meets the requirements of the
customer, there are many simple improvements that would greatly enhance the design.
The current box design is useful for portability and is adequate for the scope of this
project, but is not compatible with other task trainers. Ideally, the final design would be shaped
to fit into the torso of any task trainer to provide more realistic simulation.
During testing of the final prototype, leakage of the saline from the pericardial cavity
entered the heart bulb, which slightly disrupted pumping action. Fortunately, the fluid is easily
removed by dumping the fluid prior to use. However, in the future, the nozzle to the siphon bulb
should be sealed. This problem was not anticipated, and an appropriate sealant would need to be
found since the latex in the siphon bulb prevents use of Silastic® or Ecoflex® 00-30 as sealants.
The customer requested an electrical system that would provide an EKG warning for the
complication of puncturing the heart. However, due to the fluid in the system and time
34
constraints, this component was not implemented. This is a component that could be designed
and added at a later time.
The heart and pericardium need to be improved to better match the size and shape of an
anatomically accurate heart. As previously described in manufacturing, the pericardium could be
improved by creating a curing mold that would match the shape of the heart it would surround.
The heart could also be molded out of a rubber material to be more anatomically correct.
Part of this project includes variable fluid volume within the pericardium. Currently,
there is an inlet line for the fluid into the pericardium, but there is no outlet line for simple and
quick variations in fluid. Also, inlet and outlet fluid lines to fill the stomach and liver would
simplify repeated use of the trainer.
For simple replacement and easy access to the heart, it would be beneficial to form the
Ecoflex® gel in fully cured layers, so that they could be easily peeled away from the internal
components. This should also be done so that the Ecoflex® and Silastic® do not bond together
while curing.
35
Acknowledgements
We would like to thank the following people for assistance in the design and manufacture
of this project. Our customers, Dr. Holder and Mr. Atkinson, gave invaluable advice and
information about PCC and simulation. Dr. Verstraete provided the group with guidance and the
use of her lab and skeleton for modeling purposes. Dr. Yun provided the group with lab space
and materials for creating the final prototype. Kush Shah gave advice for potential materials.
Mr. Manthe donated materials and made the Plexiglas box for the final prototype. Samantha
Stucke assisted in materials for the ultrasoundable skin. Jeff Long in Polymer Engineering gave
ideas for molding the ribs. Dr. Saunders provided tensile testing equipment, the use of Dr.
Saunder’s lab, and assistance in tensile testing. Dr. Gao in Mechanical Engineering assisted
group members in performed finite element analysis. Rick Nemer helped in designing the heart
motion. Many thanks to all those who provided guidance to Simulife Innovations throughout the
design of this project!
36
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