Research Phase

-Aneurysm Characterization

An aneurysm is a balloon-like swelling that weakens the wall of a blood vessel. This weakness predisposes the vessel to tear or rupture with potentially catastrophic consequences for the individual having the aneurysm. Aneurysm sites tend to be areas of mechanical stress concentration so that fluid flow seems to be the most likely initiating cause for the formation of these aneurysms.

-Thoracic Aorta Diameter

A thoracic aortic aneurysm refers to when the axial diameter of the aorta is greater than 5 cm; when the diameter is 4-5 cm it is called dilatation. A healthy aortic diameter should be less than 4 centimeters but not less than 3 centimeters.

-Blood Pressure Considerations

Blood viscosity refers to how resistant to flow blood is; the more viscous the blood, the greater resistance, which results in higher blood pressure.

Blood pressure readings have two values. Consider the average blood pressure of 120/80 mm Hg for an adult. The top number refers to “Systolic blood pressure”, which is the highest pressure achieved when the heart beats, and the bottom number refers to “diastolic blood pressure”, which is the lowest pressure achieved between heart beats.

-Intervention Device Technology

The device tested on our simulated vascular system will involve various lengths of GORE TEX® and nitinol to form a stent. The stent will bypass the thoracic aneurysm allowing little to no threat to the arterial walls with concern to blood pressure. The pressure within the aneurysm should theoretically decrease after the stent is deployed, which should be represented in our mock system.

-Measuring Fluid Flow

Flow meters are devices that measure the amount of liquid that pass through them.

Flow meters consist of a primary device, transducer and transmitter. The transducer senses the fluid that passes through the primary device. The transmitter produces a usable flow signal from the raw transducer signal.

With strategic deployment of two flow meters before and after our simulated aneurysm site, we will have an accurate estimation of the volume of fluid moving through our system.

-Measuring Fluid Pressure

A pressure transducer is a transducer that converts pressure into an analog electrical signal. Although there are various types of pressure transducers, one of the most common is the strain-gauge base transducer.

The conversion of pressure into an electrical signal is achieved by the physical deformation of strain gauges. Pressure applied to the pressure transducer produces a deflection of the diaphragm which introduces strain to the gauges. The strain will produce an electrical resistance change proportional to the pressure.

Deploying a single pressure sensor within the aneurysm wall will show the drop in pressure on the aneurysm once the stent device is in place

-Micro-Controllers

It was agreed with the team and Gore associates that we should use an Arduino Mega because it had the most I/O ports and our project would not have to be limited by how few ports we would be able to implement into our mock circulatory system.

-Microprocessors

Research on open source microprocessors include the BeagleBoard. IGEPv2, IOIO, MinnowBoard, OLinuXino, PandaBoard, RaspberryPi 3, and SAMA5D4 Xplained Ultra Evaluation Kit. These have been reviewed and the SAMA5D4 is the most powerful out of all the boards, but it seemed to have diminishing returns in our case. Support for the board is an aspect that was taken into account. With this in mind, the RaspberryPi 3, which has just recently been released with a quad-core processor and DDR3 RAM, seemed the most feasible out of all the boards researched. The forums on the boards are plenty enough to learn the basics about the board as well.

-System Requirements

Software requirements include a GUI that displays pressure in the aneurysm, flow rate from the simulated graft to the aneurysm, volume change in the aneurysm, and allows for general control of the models.

All parameters, which include flow rate and pressure inside the aneurysm, must output previously mentioned data to the user. This can be through mechanical output, onto a computer screen in real time, etc. The GUI is not limited to these parameters, but it is encouraged to design the recommended parameters before advancing onto optional requirements

Tools:

Phase One:

• Gantt Scheduling Software
• Microsoft PowerPoint
• Microsoft OneDrive
• Raspberry Pi 3
• Linux