Medical Ventilator Design

[dietert1]

We have a working 3D printer that could have printed hundreds of parts during February and March. It didn't and probably it won't. I think the reasons have been mentioned already.
Global enterprises will sell clean water and fresh air if you let them and they will use their money to create by lobby work/corruption a legal situation that protects that business, disregarding any social or ecological toll. And it's everywhere. On German TV they showed a couple who said they recently bought an icecream machine for € 50 000 (!) and didn't know how to continue now that their place is closed.
I am a freelancer in the medical sector and received several inquiries about our monitoring solutions. In the end i'm left with doubts. How come those professors and most experienced experts with lot's of academical resources and government money are unable to provide a solution on their own? Are they just trying to waste my time?

Regards, Dieter

[Gandalf_Sr]

So, instead of stuff like:

If you have money, I can help or
Americans (in general) are incapable of self help

How about some practical ideas for how to make a ventilator?  As has been been said, all we need is:

1. An air pump that can be controlled - I prefer a brushless DC motor, I have many that are used for RC models.
2. Sensors that measure PaCO2, TcCO2, SpO2, FiO2 in addition to flow and pressure
3. A microcontroller that can connect all the parts together (with some interface circuitry)
4. Code that controls it all

I can cover 2 & 3 (although I'd like suggestions for sensors) and I can write code.  Some input on 1 would be useful.

[profdc9]

What if you just started with a conventional air compressor and tank, perhaps one that is quieter than the usually noisy type that is used to inflate tires, and then a computer controlled pressure regulator valve?  I supposed a simple version of this could be a solenoid valve with a diaphragm and pressure sensor.  The control of pressure would be coarse.

[KaneTW]

The spec was already posted: https://www.gov.uk/government/publications/coronavirus-covid-19-ventilator-supply-specification/rapidly-manufactured-ventilator-system-specification. Even just the pneumatic system is a headache and a half.

[Ground_Loop]

AFAIK ventilators (same as other medical equipment) are so expensive not because they are expensive to manufacture. It's to recoup the astronomical costs of safety and regulatory compliance testing.

Of course the price is also driven by the 'because we can' factor.

My dad has been working in radiotherapy field for ~30 years. I recall him telling some stories, about how Varian wanted >200€ for a replacement lightbulb for an accelerator, which they were forced to buy, because otherwise the xxx k€ machine would lose certification o.O.

Manufacturers are also covering the costs of liability insurance and litigation risk.

[Gandalf_Sr]

Guys,

We know that, in the land of litigation (aka USA) that manufacturers of healthcare equipment carry massive insurance overheads which they pass on to their customers in the form of extra equipment cost.  Now imagine that we are in a Wild West situation where people in your town are dying for the lack ventilators and you are the only engineer - that's where the USA seems to be going over the next month or 2.

Enginerding has PMd me with information that is exactly what I was trying to do and his/her work is way ahead of what I could ever do so I'm following that rather than trying to compete.  The main thread of interest is here, scroll down a little bit to find Known Open-Source Projects: under which you'll find a link to a summary of all known (to the writer) efforts in the respect of low cost ventilators; I particularly liked the suggestion of making a PAPR (powered air purifying respirator) which is mentioned in this github thread that would be used to protect the care givers rather than their patients with Covid-19

[Kilo Tango]

Some thoughts on the Ventilator project.

Motors, I would avoid brushless model motors, they are built down to a price, not up to a spec. I doubt they could run continuously for long without wearing out. I wonder if Dyson is going to use a standard hoover motor in his ?, I would worry about reliability. UK Gov spec says run for 14 days plus, that's 336 hrs. The average hoover is used once a week for 20mins, and fails after 3 years, that's 52 hrs.

I would stick with standard, well engineered, Industrial grade blower fans. They last for a long time, some are still going after 10 years plus.

Shame we couldn't use a computer fan, they generally run for years without problems, modify a standard cooling fan ?.

Battery, I would choose lead acid, its a mature technology been around for 30+ years so no surprises. easily available in quantity if you stick to burglar alarm sizes. Li-ion potentially better, however charging requirements are complicated, and they still go off with a bang if not treated properly. Also sourcing good quality ones in the 1000's would be difficult.

Standard compressor - no they use oil to lubricate the pump, and put oil mist into the air stream. It tastes crap (! ) and would need a lot of filtering to clear it. However maybe those used to recharge aqualungs would do ?, could they run 24/7, or use a reservoir system and feed 10 people at once ?.

Reliability and notifying faults. Well start with a hardware watchdog system, a retriggerable monostable that has to be reset every sec or so else it causes a hardware reset and sounds the alarm, will ensure the processor doesn't fall asleep. Next every so often the program checks that all sensors are giving allowable values. I remember one 3D printer trying to heat the bed of an unattended printer, nearly caused a fire cause the sensor cable had broken. You could even use a 2nd processor to keep a check on things and if it dissagreed with the current machine state it could also sound the alarm.

I think the Medtronics documents are very useful. Not as a set of DIY build it yourself plans, everyone builds one in their garage and dashes down the hospital with it, but all the clever stuff, the thinking about how it has to work is all done for us. Basically al we got to do is engineer something to meet their spec, and we would be home free, no need to spend years verifying performance is what is needed.

Thoughts ?

[profdc9]

Looking around at some CPAP designs, it looks like brushless motors are used in those for the blowers.

Perhaps a 3-D printed shell enclosure and internal wheel could be designed around a common brushless motor.  If they're good enough for CPAP perhaps they are good enough for an improvised ventilator.  A method of pressure regulation could be to actively commutate the motor to vary its speed/torque.  Perhaps look at a HVAC fan?

[max_torque]

Once again, people are missing the actual problem!

The problem is NOT designing a new ventilator, the problem is designing a new ventiliator of which you can make lets say 50,000 in less than 3 weeks.

So what motor you want to use is not governed by any engineering factor, no it's governed by "who has 50,000 motors on the shelf i can get delivered to me tomorrow"

This is a "Buying" problem, not an "engineering" problem.........

[AndyC_772]

For such a unique specification, and set of circumstances, the NHS spec is missing some really important information:

- estimated quantity required
- time scale for delivery
- details of regulatory approvals that will be required
- (if they're trying to attract manufacturers that aren't usually in the business of designing life critical medical equipment): some kind of guarantee or other reasonable assurance that, when very sick people inevitably die whilst attached to these machines, the manufacturer won't be held liable.

Without that information, the technical requirements are moot. Nobody capable of actually developing a viable product and bringing it to mass production would do so without it.

[Kilo Tango]

Thanks for the info regarding brushless motors, I tend to automatically think of drone motors, not up to date with recent developments.

However after some Googling, I think the problem is not an engineering one. I read somewhere that Phillips had developed a new low cost ventilator, the Trilogy Evo, it was launched last year.

A report in Propublica.org says that the US paid for its development, and gave them a 10,000 unit contract. It received FDA approval in July 2019. However Phillips are not due to ship any units under this contract until 2022, and are not yet making that model. However they are currently selling a more expensive version, and have been doing so since approval date.

Ken

[Gandalf_Sr]

Great inputs from the Brits

I used to be into model airplane / helicopter flying and have many small brushless motors; I also have many ESCs (electronic speed controllers) which control the motor speed based off the width of the pulsed signal coming onto the control input.  A 3D-printed case with fan would make a good ventilator fan plus they have no brushes to wear out.  The bearings would ideally need to be ceramic to last but an off the shelf motor would probably be fine for a cheap ventilator.  These brushless motors and ESCs are dirt cheap and widely available.

[nardev]

You'll get no argument from me that the American health care system is rapacious and inefficient.

Even in a well-functioning, properly incentivized health care system, emergency preparedness can be a problem.  There was an attempt to create a reserve of ventilators, however, the company with the contract to produce the ventilators was bought by a major medical conglomerate which had no interest in providing a low cost, emergency device.  If you demonstrate that the function of a device can be performed at a lower cost, then that puts pressure on the prices of the entire market for ventilators.   As the market has significantly consolidated there is little competition left.

Anyways, we now are reaping the consequences, and the true tragedy is that it may be only tragedy that can galvanize any change to this situation.

Quite some time have passed, not much changed but we can see what's happening. People with up to a 1.1 milion hospital bill are coming home.

Ok, i don't know enough, it was pretty subjective from my side. But there is a huge flow in your conclusion IMHO.

The health care system is not divided in "well-functioning, properly incentivized" and those that are not.

There is countries that have more social approach to a public health or as in USA, "it's just a business" and than we package it, sell and resell it, add plenty of middleman between the patient and the doctor.

It's pretty clear that Germany, Spain and UK had very different consequences in all of this. Germany have pretty decent, at least rudimentary elements of public health and in USA, Spain, UK you don't have that.



But, anyway, right now, in my country, the situation is getting back to "normal".

Few months ago, we were very organized and now, tests are made primarily through corrupt doctors, some non covid-19 urgent patients are ignored because they don't have right tests, which are impossible to make unless you have covid-19 test, just today, one guy dies in Sarajevo, hew was waiting for hearth surgery and he was denied several times to make the COVID-19 test, although there was no legal way to deny him but they did, without explanation, which actually means "we are waiting your dumb ass to bring us some money and gifts". Sadly, it was fatal for him.

Since, corruption here is pretty normal, that was the reason i said "everything is back to normal".