Executive summary

    Children with congenital heart disease have a higher probability of developing pulmonary hypertension. This causes the already malfunctioning heart to work harder to pump blood through the hardened arteries eventually leading to the weakening and possible failure of the heart. To better understand the coupling of these diseases, the endothelial cells that line the interior of the artery should be studied. These cells can sense circumferential stretching, shear stress caused by the blood flow, and normal stress caused by the blood pressure. Current products can test these three parameters but only one combination at a time. With each test taking one day to perform, this system is very inefficient. Therefore a system must be developed for simultaneous tests at different parameter combinations while still fitting inside an incubator to keep cells alive.

4 Channel Device Layout

The product that was developed is able to vary shear stress and blood pressure. It contains four channels connected by tubing. Each of these channels are at the same shear stress which is determined through the use of a pulsatile pump with the ability to replicate a heartbeat. This device is shown above. 

    The pressure is then controlled through self-designed valves as shown in the first figure above. These valves constrict the tubes through the use of servo motors which are connected to an electronics box. This constriction causes the pressures within the channels to change. The electronic box then reads and displays the pressure within each channel while also having the ability to control the motors. Users are able to turn knobs to change the position of the motors which changes the pressure within each channel while having the device within the incubator. The final layout of the system during use is shown in the second figure above.

    With this new device, scientists are able to greatly decrease the time needed to test the parameters. The time per test does not change. However, with 4 channels and valve automation, scientists can test the whole range of normal stresses at once while only needing to perform multiple tests to change shear stress. With this increase in test efficiency, a solution to the coupling of diseases in children can be developed at a far quicker rate.

Performance:

Due to unexpected circumstances, channel 4 was cracked during the process of testing. Thus, this channel and valve 3 were left out of the final experiment in order for the leak to not affect the performance of the device. Overall, the team were able to vary pressures within the device as shown in the graph of the pressures within the channels above. This graph shows each channel at different pressures and does not exceed a pressure drop of 70mmHg. In addition, the team was able to control the inlet pressure to be 50mmHg using a master valve at the request of our sponsor. The table above also shows us varying the deformation of the valves. From this data it can be observed that as valve 1 deformed, denoted at V1, channel 2 pressure decreased which was what was designed for. Unexpected data starts when V2 starts deforming where a sudden pressure increase in channel 3 from 9.9 to 19.3mmHg can be observed. The team believes that this may be caused by the slowing down of the fluid causing a higher net pressure on the outlet but due to time restrictions are not able to further test this theory.. However, despite this, the device is still able to perform optimally and adhere to the constraints that were placed and thus is successful.