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Overview

VentCU ultimately aims to create a realistic, clinically viable option for medical professionals working in the field. With the information gathered from the numerous engineers and medical professionals we consulted in our design process, we have learned additional requirements that will push our concept beyond the scope of Columbia Engineering's DIY Ventilator design challenge, to a standard that will be considered acceptable for hospital use.

Mechanical

The intent of our mechanical construction was to be as simple as possible. We have achieved this goal save a few small parts which need physical testing and iteration (such as which pulley and rope we will choose). Additionally, we need to verify our theoretical calculations and ensure that the real world capabilities of our parts meet the standards defined in theory. For instance, testing is required to ensure the spring on the compression arm correctly allows the arm to reach its fully open position as desired. Additionally, aspects like mounting the rope to the pulley and the pulley itself still require iteration. Refining these aspects will require physical testing. Following these refinements, we will reduce weight and part count on VentCU.

We also acknowledge our price is higher than some other DIY ventilator designs. However, we decided to prioritize the the availability of commercial off the shelf parts to ensure that VentCU can be built at a large scale and be rapidly assembled without the need for manufactured parts, even if it does result in a higher price. We plan to reach out to companies supplying a significant amount of the parts required for VentCU, such as McMaster-Carr and Digikey, for sponsorship so we can further reduce the price.

Electrical

Though the specifications of Columbia Engineering's DIY Ventilator design challenge specify the assumption that battery operation is not needed, after speaking with a number of senior New York hospital clinicians, we plan to include a battery in our design capable of powering VentCU for a minimum of 30 minutes. Disconnecting a ventilator increases the possibility of contagious spread, so when patients must be transported through the hospital it is preferable to leave the ventilator in place during transit. As seen in the diagram below, a computer battery backup can easily be inserted in the bottom level of the ventilator.

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We will also switch our alarm to a variable volume model, so the volume can be lowered if the physician is in the room.

The electrical system could be greatly condensed using a custom designed PCB including the majority of required electronics, but in order to make sourcing of materials readily accessible, it was decided to favor a design with multiple components even if it takes more time to construct. This decision may be reevaluated.

Control System

From a meeting with the anesthesiologist who is leading New York Presbyterian's ventilation strategy, we learned that a number of sensing and control necessities are missing in our current design and in Columbia Engineering's DIY Ventilator design challenge specifications.

At a minimum, a field-usable ventilator must be able to measure Peak Inspiration Pressure, set the Tidal Volume, set the Inspiration/Expiration Ratio, and set the Respiration Rateーthese are currently part of our design. However, the ventilator must be also able to detect Positive End-Expiratory Pressure (PEEP). COVID-19 patients are particularly susceptible to the danger of auto-PEEP, a condition in which the lungs fail to fully exhale the total ventilator-delivered tidal volume before the next machine breath is delivered. If this situation goes unrecognized, the peak inspiration pressure and total volume pushed into the lungs can raise to dangerous levels, possibly leading the lung to rupture. To detect auto-PEEP, the ventilator must have a more complex flow profile which includes inspiratory and expiratory pauses, allowing the pressure in the lungs to equalize and to measure plateau pressure and PEEP respectively.

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(source:

https://veteriankey.com/advanced-mechanical-ventilation/⁠

)

More drastically, we learned that sedating patients enough to fully suppress their brain's signals to breathe is extremely difficult, and appropriate medications are already running in short supply. For this reason, our previous assumptions of having an intubated, completely sedated and paralyzed patient may not be reasonable. Continuous Mechanical Ventilation (CMV), the term describing our current strategy of un-triggered ventilation, can cause significant damage to the patients lungs if they are not completely sedated, especially when their lungs are already damaged. Most Bag Valve Masks (BVM's) include Expiratory Valves to allow outside air in during the event of a spontaneous breath, but medical professionals conveyed that these valves are not completely reliable.

The only true solution to the problems presented by CMV is to implement some variant of patient triggered ventilation or assist control ventilation (ACV). This is a far more complex control problem, but a pressure triggered ventilation system, where breaths are triggered by pressure deviations caused by a patients intent to breathe, is not beyond reach with our current sensor suite.

Generally, more complex flow profile control and more detailed readouts are expected for any clinically used ventilator. To account for these additional desired control and sensing capabilities, and in aims of producing a clinically viable device as quickly as possible, we have connected with a team from Columbia who are working to recreate the Philips NM3 monitoring device. Our mechanical design has the ability to finely control the speed and duration of compression, allowing the implementation of complex flow profiles with sufficient sensing data. Such a device would provide all monitoring capabilities needed to create a hospital-ready ventilator.

Funding

Most importantly, the design must be built and tested extensively to identify mechanical and electrical issues. We will need materials and testing equipment to verify its capabilities and robustness. To do this we are requesting 3,000 dollars. These funds will be used to build at least two versions of the device for simultaneous testing and to purchase testing equipment such as different sized Ambu-bags, artificial lungs and sensors. Additionally, although our design does not require 3D-printed parts, we plan to buy a 3D printer to rapidly prototype mechanical components during iteration, preventing supply and shipping time from becoming a hindrance.

Design Process

Throughout VentCU's creation, we have adhered to the principles of the engineering design process. For more information and notes about the process of the ventilators design, visit the following sections:

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