Low-Cost Open-Source Ventilator-ish Device

In the event that COVID-19 hospitalizations exhaust the availability of FDA approved ventilators. This project documents the process of converting a low-cost CPAP (Continuous Positive Airway Pressure) blower into a rudimentary ventilator that could help with breathing during an acute respiratory attack.

WARNING/DISCLAIMER: Whenever possible, please seek professional medical care with proper equipment setup by trained individuals. Do not use random information you found on the internet. I am not a medical professional, just a random person on the internet.

This rudimentary design could provide a target breathing rate, and a positive end-expiratory pressure (PEEP). It can't guarantee a specific tidal volume, and doesn't regulate specific fractional oxygen (FiO2). With an attached O2 tank, it could provide 100%. Without a tank, it just pushes atmospheric air of 21% O2. Any other ratio would require manual guess work on the O2 supply flow. It is lacking in many ways, but it is possible this limited functionality could help when better care is not possible.

Here's a youtube video walking through the components as of 2020/03/17:

There are also many other efforts in this direction. Here's a short list of them Thanks! discussion

To Do's (aka. things that I could use help with):

1. A pulmonologist that (while understanding this is not an FDA approved device) is willing to advise on how to make this more effective as a last resort.
2. A supply chain person that can help us find good suppliers of parts. If there is desire to make these, I don't have a supply chain setup. The few parts I have on hand may not be easily sourcable in any volume quickly.
3. Figure out how to reprogram an existing CPAP. If this operating mode is helpful, there's a large number of these device's already in the field which could be enabled. I don't have good stats on the popularity of different makes/models. There could be on the order of a 1M devices worldwide?
4. Test with a simple inflator pump and achieve the same pressure control.
5. Develop Arduino compatible algorithms to align blower cycle the breathing cycle by looking at backpressure load on the blower.
6. Develop a better solution to the mouth guard. Current solution would require a bunch of tape to create a sufficent forward pressure.
7. Solutions to prevent the system from becoming unsafe if power is lost. It's not obvious to me on how to do this. Ideas welcome.
8. A 3D model for an inline air filter with link to common filter supply such as this

To provide comments/feedback/offer help, create a new issue on the project. Thanks!

References about the supply and potential shortage of ventilators:

Here we will briefly summarize information on the supply and potential shortage. Key numbers that will affect this:

1. The current numbers for supply of ventilators (# of ventilators currently)
2. The demand for ventilators, over time (# of ventilators needed over time)
3. The ability to increase supply of ventilators (# of ventilators able to be manufactured over time)

Additionally, the numbers above will vary based on each region's need globally.

Some preliminary data (we can continue to update) on some of these areas:

Region	# ventilators, current supply	# ventilators, needed
Globe
U.S.	46,000 [1]	200,000 or more [1]
California	7,587 and "buying more" now [2]
U.K.	5,000 [3]	> 30,000 [3]
... add more...	...	...

References

• [1] Text from my friend who is a doctor at Stanford, let's replace with citable sources if possible. "Estimated 46,000 vent beds across US with anticipated need of 200,000, maybe more if more severe than we know"
• [2] Gavin Newsom press conference, March 15, 2020 (add link)
• [3] https://www.ft.com/content/7ebb238c-67c7-11ea-a3c9-1fe6fedcca75

References from doctors specifically about ventilator technical requirements

Specifically for COVID-19

Tweets from Vamsi Aribindi, MD (March 13, 2020) https://mobile.twitter.com/aribindi/status/1238629714069032961

Specifically for ARDS (which is associated with COVID-19)

Journal article about treating ARDS (2017): https://www.nejm.org/doi/full/10.1056/NEJMra1608077

References about CPAP/BiPAP/PEEP ventilator modes

Lung Mechanics: PEEP,PEP,ACMV

Ventilator Modes Explained! PEEP, CPAP, Pressure vs. Volume

Materials

1. Continuous Positive Airway Pressure (CPAP) devices are commonly used by individuals to treat sleep apnea. As a result, CPAP blower components are fairly abundant. Used ones are available on eBay and new ones on Alibaba. In many of these devices, the blower is a simple BLDC motor that can be driven with an Electronics Speed Controller (ESC) used by quadrotors and RC cars. The one I used is pulled from a Respironics REMStar. In volume, these blower components can be under $20.

• Alternative: test a 12v inflator pump which is even more abundant.
• Alternative: print a blower [discussion]

2. Arduino Compatible Nano/Clone to control the motor speed, breathing cycles, and handle user input. Download the Arduino IDE to program the microcontroller software.

3. Brushless DC Motor Electronic Speed Controller capable of at least 10A.

4. Button or swtich for input control. The code cycles through 5 levels of pressure, and double click to swtich between CPAP and BiPAP/Fixed PEEP mode.

5. 12v DC power supply that can handle at least 5A. The blower works pretty had, and the breathing cycles can create voltage drops which will reset the Arduino if the supply if not strong enough.

6. Tubing and face mask. If you search for CPAP face mask, you'll find many options/suppliers. The full face mask that covers both the mouth and nose and enabled pressure buildup in the lungs. As an alternative, see below for draft 3D printable parts.

7. Optional inline 12v battery backup.

Building

This is the full system, with mask, tubing, pump, 12v battery, and swtich for input. However, I would strongly recommend running with a DC power supply since the battery will only last about 3-4 hours. Wearing the mask with a dead battery could cause dangerous CO2 build up. This particular battery can charge and supply power at the same time, acting as an inline battery backup to wall power.

Below is a close up of the extracted blower. It simply an BLDC motor driving a blower fan. A small ESC and Arduino attached (technically a Teensy2.0++, but the code has now been changed to an Arduino Nano). It has a 3d printed tapered hose adpater on it to fit in the hose. The microcontroller software can be programmed with the Arduino IDE. The software goes through a short initialization sequence to configure the ESC, and then starts at the lowest CPAP setting. You can use the switch to cycle through pressure levels, and double click to cycle through operating modes.

Here is the schematic for the electronics. As you can see, it's very simple with only a few parts. A slightly modifed version that is able to sense the blower current is here.

Face mask / Tube Adapter

Since I have CPAP, I happen to have a Resmed AitFit F20 mask that I can use. This is quite comfortable and covers both the nose and mouth to make a good seal. However if you can't get a mask, below is a prototype mouthguard that fit in the category of not-so-great-but-usable-if-you-have-a-lot-of-tape. I am using some elastic straps as head gear. But to get an good air seal to get enough positive pressure would require some tape. A little bit of leakage is actually desirable to allow CO2 to escape near the mouth nose and flushes out the air over time, rather than being stuck in the tube. WARNING: wearing this sealed to the mouth with tape without power may cause dangerous CO2 build up.

Download the [3D model] [Fusion 360 link].

Pressure Testing

This is a picture of my test rig to measure the output pressure. It's a U-shaped tube with attached measuring tape to check displacement of water. The actual liquid displacement is 2x the measured line since liquid is being push downwards on the other side of the U an equal amount, doubling the displacement. (I think this is the correct way to measure). At full blast at 12v, it is achieving 45cm/H20. Guidance on ventilators for COVID-19 patients require upto 20cm/H20. So, these blowers are plently powerful.

Here are some images showing the dislacement of the liquid at differen speeds. I happen to have Diet Dr. Pepper on hand which makes it easier to see the liquid level rather than just plain water.

Here's a video of the blower pushing a breathing cycle of 16 cycles/min oscilating between 12 and 22cm/H20.

Air Filtration - Optional

An open air blower into someone's airway isn't great. If possible, some filtration is preferred. These parts were originally used for a DIY Powered Air Purifying Respriator (PAPR). However, adding a filter will definitely affect the output pressure. It will depend on the blower you have if the motor can handle the additional load. Given the headroom of the blower I tested, these CPAP blowers can probably handle the filter and still hit the target pressure. However, I haven't done longterm thermal testing at high pressure and a strong filter. These adapter plates can be attached with liberal amounts of hot glue, and wrapping the unit in vinyl tape to get a reasonably airtight seal. My blower's enclosure was not air-tight, so it is difficult to guarantee that 100% of the air is coming only through the filter.

• This is an adapter plate for a 3M P100 or N95 face mask filter cartridge. Download [3D model] [Fusion 360 link]

• This is an adapter plate for a NATO 40mm gas mask filter cartridge. These fitlers are available with CBRN ratings which are needed for viral and bacterial defense similar to those approved by the CDC/NIOSH. Download [3D model] [Fusion 360 link]

• This is an option for an inline filter [discussion] that looks easy to install, and would be helpful for non-CPAP blowers.

Updates:

2020-03-18-9AM PST: added to do about reprogramming CPAPs

2020-03-18-3AM PST: added youtube video

2020-03-17-11PM PST: added current/breathing datasets, plots, and wiki for discussing analysis, and this update section