Mechanical Ventilator
With the recent COVID-19 outbreak, mechanical ventilators are in high demand. In order to supply rural towns with a solution, I worked with a team of undergrad ME students to design a low cost, easy to manufacture ventilator for emergency response use.
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Our objective is to produce a low-cost mechanical ventilator that is easy to use, lightweight, and easy to assemble. In addition, it must be made up of parts that are easily accessible and are for the most part off the shelf. It should be portable and allow access for the bag valve mask to be taken in and out with ease. The ventilator should be reliable, easy to clean, and abide by CFR codes and standards.
Full assembly of the seat belt ventilator using both and Ambu bag and a Raspberry Pi powered display.
When we were approached to work on a low cost mechanical ventilator, we wanted to build a product that could be reproduced anywhere. With an increase in demand due to COVID-19, we decided try to use off the shelf parts from various stores. Starting with the main source of the ventilator itself, we used an Ambu bag. This is commonly found in ambulances and allows air to be given to the patient by compressing it at a certain depth and rate. This will help determine the air output from the bag to the patient.
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Working with various professors who had been doing research building their own ventilator, we were able to get a lot of information regarding the respiratory rate, tidal volume, and inspiratory/expiration ratio required to properly provide to the patient. Along with the information regarding air flow, we also were recommended parts such as motors, motor controllers, and controls. This not only allowed us to focus on the mechanical system, but also helped us figure out what was plausible in designing a ventilator.
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Rather than compress the bag with a single or multiple arms, we decided to use a belt across the top of the bag fixed at a single point and attached to a motor at the other. We needed to ensure the bag was easy and quick for an operator to set up so a buckle is used on the fixed side of the belt allowing a user to switch from a manually operated bag to a machine and vice versa.
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Along with the belt fastening system we also provided and adjustable cradle to fit different sized Ambu bags. The same can be seen for the seat belt to accommodate different belt sizes and Ambu bag lengths. We are using a Neo brushless motor to contract the belt around and axle. As the belt wraps around the axle, the belt tightens and compresses the bag. Based on the rate and depth of the compression, we can determine the IE ratio best fit for the patient. The belt is attached to a 3D printed part that secures it inside of a PVC pipe attached to the transmission. It is also supported by a bearing to prevent the system from moving from its linear position.
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The outer box is made up out of stainless steel that is laser cut and assembled in a machine shop. By using one piece of sheet metal, it reduces the assembly time while also reducing cost. Shown on the right is the bottom of the ventilator. The display for the device is a 7 in screen compatible with a raspberry pi 4. This will control the system and determine the rates that will compress the bag. It is attached to a 12V rechargeable battery that can be used both plugged into a wall and up to a 2 hour battery life on its own. Everything else is attached using mounts and fasteners making the overall ventilator easy and simple to assemble.
Expanded view of the motor system used in the ventilator.
Above is the final version of the Mechanical Ventilator. Attached to the Ambu bag is a flow sensor to measure the amount of air going through the tube and into the balloon on the end. The balloon is used to simulate the inflation of lungs during the inhale and exhale process.