Beating Heart Simulator:Oral Report 3Ashley WhitesideNicole RiceJacob Bauer

1

Question and Thesis• Can a user interface be created on a computer that can link

and affect different aspects of a heart simulator?

• The user will input a heart rate. This input will then cause a sample heart to beat at that rate and simulate an ECG that will display the blood pressure and heart rate.

• The point of this simulation is to mimic real problems that may be observed in the operating room and train students to react accordingly.

2

Jonathan C. Nesbitt• Graduated from University of Virginia

with a BA in Biology• Attended the Georgetown University

School of Medicine in 1981• Completed postgraduate training at

Vanderbilt in 1986• Was a surgeon on the USNS Comfort

during operation Desert Storm/Shield • Joined department of thoracic surgery

at Vanderbilt University Medical Center in 2008

• Specializes in the treatment of esophageal cancer, lung cancer, thymoma and thymic carcinoma 3

Background

Current System in use by Dr. Nesbitt:• Utilizes a windshield wiper motor to cyclically pump a plastic

bellows.• The bellows forces air through surgical tubing connected to

party balloons placed in right and left ventricles of a porcine heart.

• Does not allow for variable BPM or real time control• Does not produce a simulated ECG display• Does not displace enough air to accurately represent the

magnitude of contraction in a healthy heart

4

Diagram of Current System

5

Silicone Well

Plastic Bellows

Piston

Motor

Engineering Requirements• The simulator must be controlled by a computer software

package.• The software must drive a physical heartbeat in a porcine

heart based on the user provided heart rate data.• The software must also produce an ECG display that

corresponds to the user provided data.• The simulated heartbeat must be dynamically alterable• The physical palpitation of the porcine heart must mimic real-

life motion.

6

Methods

We have segmented our design process according to our system’s three main components

1. Computer Software2. Physical Heartbeat3. Simultaneous ECG output

7

Computer SoftwareThe computer interface currently consists of a simple Graphical User Interface (GUI) which allows for the user to input a heart rate value.

Based on this value the software programs an Arduino Uno microcontroller to produce a voltage signal in order to control the physical heart beat. The heart rate variable is also used to generate the ECG display.

The GUI can be easily updated and will feature a dropdown menu for selecting desired arrhythmia once the ECG display has been completed.

8

Computer SoftwareWe plan on displaying the corresponding ECG as a dynamic graph which updates its data from an array, storing the currently selected arrhythmia and heart rate values.

The ECG will feature a traditional 5-6 second scrolling display and will be presented in a separate GUI window that can be displayed on a connected “dual monitor”.

We are also considering using the Arduino to generate a signal that will produce an ECG on a peripheral oscilloscope or actual ECG. 9

10

Simulator

Pump Driver (main())

ECG Driver

USB Port

Computer Program (C++)

1. Pump Driver input -> Pin 12. ECG Driver input -> Pin 2

Arduino Program (C++)

Output to Pump

ClassesSingleton• Stores heart rate and arrhythmia values• Allows for dynamic access to variables• Ensures single instance of class (Singleton GoF

Pattern)Pump Driver• Operates as a helper function to main() (for

now)• Accesses heart rate value from Simulator class• Outputs instructions to pump through Arduino

board• Initializes ECG driverECG Driver• Operates within unique thread• Accesses heart rate and arrhythmia values from

Simulator class• Builds graph data for ECG display• Builds and updates ECG display

Computer SoftwareThe Arduino Microcontroller• “Arduino is an open source electronics

prototyping platform based on flexible, easy to use hardware and software.” – www.arduino.cc

• The software and electronic hardware needed to construct a serial port or USB output are incredibly complex to design.

• The Arduino has a built in USB connection through which the user can program the board.

• Also, the Arduino is programmed using a derivative of C++, meaning we could program it directly from our software. 11

Image courtesy of http://mc202.com/synthesizers/arduino-glitch-box-machinedrum/

Developing A Beating Heart

We met with Dr. Barnett, an

associate professor of mechanical

engineering, on February 2nd to

discuss several means of creating

the mechanical force we need

and to learn more about the

application of hydraulic and

pneumatic devices to our system.

12

Developing a Beating HeartMeeting with Dr. Barnett• Dr. Barnett informed us that while hydraulics are more

versatile pneumatics respond more rapidly, which is essential because we need to produce heart rates of over 100 bpm.

• Additionally, a leak of hydraulic fluid would create significant problems for our system while a pneumatic leak would be less of an issue.

• Having decided that pneumatics would indeed be ideal for our project, Dr. Barnett agreed that using a three-way solenoid valve would be best as it would allow us to integrate use of both compressed air and a vacuum pump. 13

Developing a Beating Heart

We plan on using a three-way solenoid valve to regulate the flow of compressed air into balloons placed in each ventricle.

Image courtesy of http://www.yourheartvalve.com/heartbasics/heartanatomy.htm

14

Developing a Beating Heart

• We chose to use a three-way solenoid valve because they are cheap, reliable, and capable of switching rapidly.

• We have purchased a 3 way, 3 position, 2 port single solenoid valve from automationstore.com for approximately $20. 15

Three-Way Pneumatic Solenoid Valve

Developing a Beating Heart

Specifications of our solenoid valve:• Manufactured by AirTAC• 3 port, 2 position, single solenoid

valve• Controlled by 12 VDC input.• Maximum pressure of 114 Psi• Power consumption of 2.5W• Maximum frequency of 5

cycles/second• Minimum activation time is 0.05

seconds16

Developing a Beating Heart

The Arduino’s output will control the pneumatic valve, causing it to alternate between compressed air and the vacuum pump to produce the physical heartbeat.Balloon

Vacuum Pump

Arduino

Air Compressor

17

Control Valve

Diagram of Solenoid Valve Setup

Simultaneous ECG Output

An ECG that corresponds to the user-provided heart rate will also be generated by our software.

The ECG output and beating heart prototype will operate simultaneously but completely independently of one another.

Image from: http://www.swharden.com/blog/images/simple_ecg_circuit_output.png

18

Simultaneous ECG Output

We are currently generating our plots using formula that was developed for a MATLAB program. The formula creates a sinusoid that roughly approximates the shape of an ECG.

19

Simultaneous ECG Output• We have also just obtained access

to a Laerdal HeartSim-200 simulator. This is a battery powered ECG rhythm simulator. We are working on a way to gather our ECG source data from the signal it generates.

• This would make our ECG display much more accurate and would allow us to plot a wide range of arrhythmias.

20

Image from: hthttp://www.laerdal.com/us/doc/177/HeartSim-200

Additional Goals

Once we have developed a successful prototype we will contemplate endowing the system with additional capabilities to increase functionality. These include:

• Plot of arterial pressure• Simulation of the effects of anesthesia• Simulation of common arrhythmias

21

Status and Results• We have developed our basic software program including a

usable Graphical User Interface. • We have ordered our three-way solenoid valve and are

awaiting its shipment.• We have found an algorithm which generates an approximate

ECG waveform.• We have obtained an ECG rhythm generator capable of

simulating multiple arrhythmias.• We have begun to work on using these resources to develop

our software-driven ECG display.

22

Conclusion

Our goal is to develop a prototype for a cardiac surgery simulator that will permit dynamic alteration of variables during surgery.

We have ordered all raw materials that we foresee needing in order to develop a working prototype. The last of these materials should arrive within the next week. Upon their arrival we will begin prototyping our simulator hardware.

We plan to meet again with Dr. Nesbitt following spring break to discuss our progress.

23