PnAIR

Inspiration

We need to have several possible solutions to make a lot of cheap and reliable ventilators to meet the demand caused by covid-19.

I believe the total need is best met by having several different solutions: some advanced for cases needing that, and a lot of simpler but reliable units for most cases.

Another reason for different machines is that it is then less risk of running out of supply of some critical components, like sensors or "ambu" bags.

I here envision a design completely free of electronics, supplied by air/oxygen mix, from another module also described below.

What it does

The core part switches between directing air to and from patient.

The miniature version of it may be positioned immediately at patient intubation, and switched between maximum pressure and PEEP pressure. Nothing more.

The full core part can be positioned up to three metres form patient, and is connected to patient through two tubes, one for inspiration, the other for expiration. They are connected to patient intubation/mask/helmet by a simple Y-connection. It have two valves; one for inspiration and one for expirations. It can thus maintain an inspiration plateau pressure. It acts on pressure in the currently unused tube, and thus pressure control is not deteriorating from flow resistance in tubes, so the may be longer / cheaper.

Add-on level 1: Expiration and inspiration pause timers.

Add-on level 2: Trig: During expiration pause, if pressure fall below PEEP: start inspiration immediately.

Add-on level 3: alarms: 1) Measure exhale volume - If under a set level, alarm. 2) Measure cycle time - If too long, alarm!

The alarm is a "neon" coloured very visible warning sign. It also have an electric switch, so a battery, buzzer, flashing light may be added.

All functions can be realised by pneumatic designs: delays, pressure triggers, logic, in combination with mechanical parts, and of course pressure mechanically activated valves and safety valves.

Feeder

The idea above is to have a machine operating solely on any kind of air pump giving enough pressure: high pressure vortex fan, a couple cheap centrifugal fan, a stack of even cheaper axial fans, a vacuum cleaner fan on lower voltage than designed give enough power and last long (or a complete standard vacuum cleaner of the kind that can be reverse connected, and adjusted.)

Buffer, Humidifier, Oxygen mixing

In the most simple setup, the feeder is a stack of small fans connected directly to the PnAIR unit.

But i suggest a buffer that can also moisturise and mix in oxygen.

A design like a gas golder https://en.wikipedia.org/wiki/Gas_holder made to supply a constant 40 cm water pressure.

Both inlet air and oxygen air may enter by bubbling through the water.

Level switches switches on and off both air and oxygen simultaneously, controlled by the level of accumulator top part.

A good inlet filter is to be used to stop contaminants and dust to get into the water - possible microbe buildup!

The air supply buffer/humidifier/air-oxygen mixing unit can like the fans be used several times, and made big to supply several PnAIR concurrently. Using only one air pump and oxygen supply (if all patients on that unit can use same concentration) several PnAIR can be run from a single air supply unit, thus lowering cost per patient. That supply by design in a reliable way keep pressure close to max safety pressure, ( i.e 40 cm water) so that function is offloaded from PnAIR main device.

For oxygen and flow logging external equipment is to be used when needed.

Materials and manufacturing

3D-printing is the thing today and suitable or mid scale production or distributed large scale. Of course some part like frame and flat sheets are faster and cheaper to produce traditionally. I aim to make the design also being able to be made from wood pieces, plastic bottles and boxes, etc - which is the plan for the prototype model. For the membranes for valves, pressure detectors, and actuators the common disposable gloves are usable, or condoms can be used, some part of bicycle tyre.

How I built it

Coming to that stage i hope ...

Challenges I ran into

... I spent all free time on https://devpost.com/software/ch-air

Accomplishments that I'm proud of

I actually think it works - when finished ;-)

What I learned

I think i already know a lot about this kind of pneumatics, mechanics, fluids, and prototype building :)

It have come to my attention that there is an old design that sound similar, web search "Bird Mark 7 Pneumatic Respirator Ventilator", but i plan more functionality than that have.

What's next for PnAIR

Drawings and prototyping