Medical Ventilator Challenge

One of my friends sent me the link to this, knowing that I recently got into “functional” 3D printing. I’d like to share some first thoughts on the Code Life Ventilator Challenge:

To design a low-cost, simple, easy-to-use and easy-to-build ventilator that can serve the COVID patients, in an emergency timeframe.

Note that I am not a medical professional, and most of what I write here I just learned about myself. The rest is speculation.

**** SEE BELOW FOR UPDATES ****

Initially I was confused because the German word for fan is Ventilator. It turns out a medical ventilator has (almost) nothing in common with the thing you use to cool you down on hot days.The list of requirements is short, but packs quite a punch. There is a reference to ISO 80601-2-12:2020, but it is not mentioned explicitly to comply with this norm.

So let’s start and build this thing…

Fan*

It is called ventilator, because it pushes air into the patients lungs, so we need a fan capable of doing this: 40 cm water column of pressure (about 0.04 bar) is a considerable pressure for a fan. CPAPs are machines that do remotely the same thing, and they use a kind of centrifugal fan. (See the insides of CPAP here) I would assume that ventilators use the same principle. Laying out this kind of fan is work for specialist in fluid dynamics. A flow optimized geometry of the fan and housing is a typical case for a 3D printer. The fan itself will be spinning at a high RPM, so in order to minimize the balancing, I would see if it could be resin printed. The housing could be printed with widely available FDM printing.

Fan Motor*

A fan needs a motor, probably a brushless electronic motor to be able to control the speed, and by that the pressure created by the fan. In terms of availability, this is one of the most critical parts, together with the electronics. An interesting approach would be to design around a commonly available motor like a heater fan from a car, but this kind of motor would require more components to control the speed, and lose the advantage of availability.

Control

A major part of the design will be electronics and programming. The task is to check present flow and pressure, compare them to the set values: how often per minute should the patient breathe, how much, at which pressure and so on. The board would then adjust the RPM of the fan. Then there is the oxygen concentration to measure and the oxygen valve to control. Finally, the board has to put out an alert on a number of occasions. Given that these tasks are important but not too demanding, I assume an Arduino board would have the necessary calculation power, and they (and their clones) are also widely available. The “eyes and ears” of your control board would be electronic pressure sensors. They can be used to measure the air flow in a Venturi tube. There is a project about this on hackaday.io. I would consider electronic pressure sensors as another critical component.

Power Supply

Since backup batteries are required, I would opt for 12 V lead acid batteries for availability reasons. Worst case you can get a spare from every car standing around.

Team

A minimal team would certainly include an electrical engineer for circuitry and a mechanical engineer (fluid dynamics) for 3D modelling and the manufacturing process, both working together closely with the medical professional.

So far my first thoughts, maybe some finds something useful.

*) Updates

CPAP stands for Continuous Positive Airway Pressure, so the pressure is continuous. That means that the fan of a CPAP is likely not speed controlled.

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