(H-288) Medical IoT Device for Leak Detection & Monitoring Post Endovascular Aneurysm Repair

Introduction:: Abdominal Aortic Aneurysm (AAA) is an enlarged area in the lower part of the major vessel that supplies blood to the body (aorta). The aorta runs from the heart through the center of the chest and abdomen which is one of the largest blood vessels in the body. There is great demand in screening of the AAA, especially in patients who undergo endovascular aneurysm repair (EVAR) to prevent this fatal condition. Even after EVAR procedures, the stent graft can also experience complications and failures known as endoleaks that may also result in AAA rupture.

The research project discussed in this article focuses on the design methodology of a working prototype that features an integrated sensor that can monitor the pressure of an EVAR stent graft. The sensor can be monitored using a wireless transmission to a computer or cell phone. The patient and the doctors can monitor the buildup of pressure and manage emergency situations related to endoleaks that may occur with the EVAR device. This Medical Internet of Thing (M-IoT) device can continuously monitor the status and condition of the EVAR stent graft by detecting changes in the pressure sensor signal and the readings to communicate conditions that can be sent to the user and the health care provider wirelessly, without physically interacting with the stent device to determine the condition of the implanted device. The implementation of this feature on EVAR stent grafts can dramatically lower the cost of frequent hospital visits and computer tomography scanning post-surgery.


Materials and Methods:: The design concept was based on Innovation Base Learning phases: Gap for Survey to Define, Solution for Explore to Solve, and Impact for Draft to Share. In this reseach project we were building a working prototype to validate this continuous monitoring M-IoT concept for EVAR graft pressure monitoring. The prototype consisted of two parts and the design control flow chart was shown in Figure 1 Flow Chart. The first part was the close loop hydraulic flow system with pump, silicone tubing, and 3D printed AAA model. The flow circulation system was controlled by Arduino Uno R3 and the motor shield controller L293D. This part was to simulate the blood circulation through EVAR graft. The second part was the Force Sensing Resistor (FSR) sensor measuring the graft pressure and data transmission. The FSR sensor was specially packaged into a 3D printed housing that can fit into the AAA model as shown in Figure 2 Custom Made Sensor. The sensor was calibrated by various methods to ensure the accuracy. The FSR sensor was connected to signal conditioning circuit AD620 and analogue input of Arduino Uno R3 for data acquistion. The Arduino was also connected to HC-05 Bluetooth Board to communicate with the cell phone. An Android cell phone application was programmed by MIT App Inventor. The APP can connect with Arduino's Bluetooth and receive the pressure data from the FSR sensor for data analysis.


Results, Conclusions, and Discussions:: Results:
The custom-made sensor was calibrated by various calibration techniques to evaluate the uncertainly and accuracy and the result was shown in Figure 3 Calibration Result.


The Arduino-controlled prototype was functioning properly as shown in Figure 4 Prototype Picture. The hydraulic system with water flow through the tubing circulation system was properly controlled by pump controller program. The flow-pressure pulsation and pump control loop were analyzed with MATLAB Simulink. With additional pump and control sequence, the pressure pulsation can be simulated close to cardio cycle as shown in Figure 5 Pressure Cycle Result.

The second part of the model was using FSR sensor that could detect a small pressure pulse approximate 120mmHg. Another simplified model by air pressure pulse was used to demonstrate the measurement of pressure/resistance pulse. The resistance signal was converted into voltage and then connected to the ADC input of Arduino. The Arduino was programmed by Arduino IDE software and the signal was calculated into digital reading from 0-100. Android cell phone APP was programmed by MIT App Inventor. The APP can connect to the Arduino HC-05 Bluetooth. When the Bluetooth is connected to the Arduino, the digital reading will be sent to the cell phone. The APP can display the pressure reading (digital reading) every second. The APP can also display the measured pressure warning when the reading falls below 45 when the APP programmed setpoint at 45. This can alert the user when the presssure is abnormal.


Conclusions:
This prototype can be used to gather more data for the future implantable sensor design for post EVAR. This prototype is controlled by Arduino which is very flexible to program and simulate various blood circulation conditions such as stroke or heart attack.
This M-IoT device can continuously monitor the health status (pressure sensor signal) and the readings and conditions can be sent to the user and the health care provider via the internet. This dramatically lowers the cost of frequent hospital visits and computer tomography scanning post-surgery. Most importantly, this monitoring system can reduce the mortality rate post-surgery.




Acknowledgements (Optional): :

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