[TaylorAlexander]

The page isn’t loading so I’m not sure what they’ve got, but I’m still trying to get answers to a question I have. I did research Tuesday and it seems like ventilators are positive pressure only, and they cycle between a low pressure and a high pressure. If this is the case, could an air compressor with a regulator be used as the pressure source? If so, a small device with just two pressure regulators and an electronic valve could be used to cycle between high and low pressures for each patient. I keep seeing open source ventilators that use a fan and a motor, but those seem likely to fail. Air compressors are abundant and could literally be taken from construction sites to be used. You put a pressure regulator to go down to the (very low) pressures one might want as a maximum for any patient, then you can gang that up to a whole bunch of hoses. Finally a little box with a couple of regulators can adjust the per patient high and low levels.

This to me seems much simpler and more reliable than ventilators with their own fan. But I don’t have a good way of reaching anyone. I’ve created a thread on my website with my sources, thinking, and some questions. If anyone knows about this please reply here or there and let me know. Thanks.

https://reboot.love/t/coronavirus-towards-a-cheap-and-easy-t...

[IAmEveryone]

I believe hospitals do use systems with a single, central supply of pressurised air.

However, I'm also getting the sense from reading about these efforts that creating pressurised air is the easiest part of the setup. You need to control that pressure with a precision unlike any other application of air pressure. Just alternating high and low pressure isn't going to work, for example: you need to slowly ramp up pressure, then slowly release, on a specific schedule. Every patient also has individual needs, to the point where even for two people of the same gender and similar age/weight, the settings ideal for one might kill the other, and vice versa.

If I understand it correctly, these machines use feedback loops with sensors for blood oxidisation, acidosis, the elasticity of the lung, and other factors. Without such mechanisms, you'd be constantly adjusting the settings––consider a heating system or AC where you can't set the desired temperature, but only flow rate and power of the heating/cooling instrument. You need constant attention to keep such a setup within a comfortable range. And that attention will also be in short supply when hospitals are overrun.

[Mvandenbergh]

To quote an earlier comment of mine:

So there are four main ways for breathing machines to be powered: 1) By compressed air from a wall port (majority of ICU machines)

2) With bellows (anesthesia machines)

3) Turbine, either dynamic or constant speed with a proportional valve (home use or patient transport)

4) Piston

Let's assume that we use a pneumatic device driven by centrally purified air as that is simplest. The parts then are:

-Gas blending to mix O2 and HP air. In many designs this is done using two solenoid valves.

-A fast, precise, and accurate proportional solenoid valve. This turns the constant pressure into the desired waveform

-another valve for controlling exhalation pressure. Can be another proportional solenoid, alternatively a manually adjustable valve to ensure constant minimum end exhalation pressure (PEEP)

-Flow sensor (range of options, typically variable orifice or hot wire anemometer but other type exist)

-Pressure sensor (silicon waver transducer)

-Overpressure valve

-O2 sensor (highly desirable, arguably you can estimate from O2 blending settings but that will work better on a very well characterised design which this would not be. Anyway O2 sensors are widely used so this will never be a constraint.

-Piping to connect it all together

-A control and alarm system to drive desired waveform based on user settings and sensors

-Patient circuit: Humidifier / heat exchanger, patient valve (one time use), viral filters for intake and exhalation air (one time use), ET tubes (one time use) Probably the limiting factor as far as parts go are the valves since this is a niche application. Here's the problem: as a civilisation, if we had to make a hundred million vents by the end of the year it would be easy. Expensive, sure, but not that hard in an emergency. It is much harder to make an extra 50,000 in a few weeks because it just takes time to turn the machinery of mass production in a different direction.

Let me know if you want me to send my list of ventilator reading. I'm not an expert either, just trying to soothe my Corona-madness by thinking about building things.

[TaylorAlexander]

Thank you! I will copy your comment to the thread on my website and link back to your comment here. Feel free to share your reading, but the stress of feeling like I can help is a bit much. I’m going to collect information but for now I’m hoping the major manufacturers committed to ventilator manufacturing are going to pull through.