8 ms·

what is so complicated about ventilators? Serious question as I don’t know enough about this. I see a lot of DIY posts that are probably not 100% the same thing

by lukevp 7y ago

what is so complicated about ventilators? Serious question as I don’t know enough about this. I see a lot of DIY posts that are probably not 100% the same thing but are they even close? This opens up a bigger question too, is there such a thing as a path for open source medical devices to be built and certified and deployed? Is there a company that supports something like this? I follow Scott hanselman, a Microsoft employee who’s diabetic, and there is a big movement within that community to build open source artificial pancrea, using insulin pumps and software and such. Is there a play like that for ventilators? And other critical medical devices?

toomuchtodo 7y ago
There is a narrow range of pressure where you're not damaging the alveoli from underpressure, but not bursting the lungs from overpressure. You need a mechanical scalpel, not a butcher's knife.
- Nambia 7y ago
  Honest question: is the pressure range actually that narrow? People can survive at high altitudes, which will see pressure of 70% sea level (or less, especially when considering mountain climbing). Additionally, when SCUBA diving, something like 30 feet of depth = 1 atmosphere. I feel like I'm missing something here. Any ideas?
  - gregoriol 7y ago
    It's really a complicated subject. One of the best reads I've seen these days is https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/ https://hackaday.com/2020/03/25/ventilators-101-what-they-do... and they explain how many factors there is to consider: it's actually "very" complicated to make right.
  - gjhan 7y ago
    As you point out, the body can tolerate significant variation in absolute pressure, corresponding to the temperature, composition, and density of the gas you breathe. The pressure that must be narrowly controlled in a ventilator application is the relative pressure: the difference between the absolute pressure outside the lung (in the room) and the absolute pressure inside the lung. This relative pressure is what does all the work --- mechanically opening airways and alveoli --- and could cause all the injury.
  - landryraccoon 7y ago
    Covid patients in the ICU probably don’t have healthy lungs. The people you’re talking about at those pressure ranges are probably all young, healthy and athletic. I know a bit about scuba diving, and you absolutely are not supposed to go diving if you have a lung injury. I would speculate that if you put a person with serious covid on a mountain top or 30 meters under the ocean it would kill them pretty quickly..
  - refurb 7y ago
    People can survive at high altitudes... That's because the pressure outside their body is the same as inside. With a ventilator, the pressure going in is higher than atmospheric pressure. That can cause damage.
  - nradov 7y ago
    Scuba divers are at ambient pressure and breathe through demand valve regulators. Pressures inside their lungs are almost exactly the same as outside so there's no extra stress. Increasing pressure with depth does increase work of breathing due to higher gas viscosity. Beyond a certain depth, divers can no longer ventilate enough to take in O2 and remove CO2. This problem can be mitigated to an extent by breathing lower density gasses such as helium. Occasionally hospitals even have patients with severely impaired lung function breathe heliox just to get better gas flow. In theory it's possible to use a 2nd-stage scuba regulator as an improvised mechanical ventilator by partially blocking the exhaust valve with your hand and pressing the purge button. In practice it's unlikely to work, but if I was trying to rescue someone who had stopped breathing in the water and had no way to get them back to shore or a boat quickly then I might try it as a last-ditch effort.
  - jacquesm 7y ago
    Yes, it's pretty narrow. I've had double pneumonia somewhere in my 20's. Just playing a reed instrument (sax) was over-pressuring my lungs to the point that it led to more damage over time. And that's only a tiny little bit of pressure.
- lukevp 7y ago
  What’s the limiting factor there? The pressure regulation, pressure production, measurement accuracy? There’s open source ECUs that measure dozens of sensors at 1000hz+ and keep an engine perfectly timed using a $35 raspberry pi. Is this problem harder somehow?
  - toomuchtodo 7y ago
    Validation and quality assurance in my opinion.
- jmole 7y ago
  There is evidence that positive pressure ventilation results in worse outcomes than the negative pressure iron-lung-style ventilators: https://www.atsjournals.org/doi/full/10.1164/rccm.200707-1004OC https://www.atsjournals.org/doi/full/10.1164/rccm.200707-100...
- rasz 7y ago
  How could we archive that? its not like almost disposably cheap actuators moving with 0.1mm precision guaranteed for >10K hours MTBF was a solved problem over 30 years ago (floppy drive). /s
gregoriol 7y ago
Here is an interesting read on the subject: https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/ https://hackaday.com/2020/03/25/ventilators-101-what-they-do...
- lukevp 7y ago
  Thanks for the link, I’ll read up on it!
DanBC 7y ago
Partly this is a problem with jargon. When healthcare professionals talk about "beds" or "ventilators" they mean "the bed and all the staff needed for the patient in that bed", or "the ventilator and all the staff needed to put a patient on, and take a patient off, the ventilator". Ventilators turn out the be pretty complicated. Here's a useful thread: https://twitter.com/aroradrn/status/1243091107149418496 https://twitter.com/aroradrn/status/1243091107149418496 And another simplified cheat sheet for people who use machines in one setting which are now being used in other settings, but it has replies from doctors asking questions that give some hints at the complexity: https://twitter.com/aroradrn/status/1244134454001635329?s=20 https://twitter.com/aroradrn/status/1244134454001635329?s=20 Then you have all the "human factors" stuff caused by machines having different layouts.
- canada_dry 7y ago
  > caused by machines having different layouts This is going to be a huge issue with the onslaught of different manufacturers. I liken it somewhat similar to helping troubleshoot router/switch issues... yes at a high level they're all the same but, at the same time, each one has it quirks and peculiarities and even use slightly different nomenclature that make it a non-trivial exercise.
SkyPuncher 7y ago
My wife is a doctor (I am not). I've been following COVID closely and discussing with her/peers. I'm not an expert (but feel I have an above average understanding, thanks to my wife) > I see a lot of DIY posts that are probably not 100% the same thing but are they even close? I have yet to see (though I haven't looked extensively) a DIY ventilator that has the fine tune control many doctors are suggesting are required for COVID patients. My understanding is most of the DIY vents are comparable to emergency or transport vents. They'll keep a patient breathing for minutes/hours until they can be transferred to a proper ventilator. After a short period of time, you really need to transfer a patient to a proper ventilator to continue to support life. Two big challenges with COVID patients in particular: * They require ventilation for DAYS or even weeks. Over durations of that long, you really need precise control over a vent. A tech analogy is using floating point numbers for finance. Over a small number of transactions, a floating point number may be sufficient. Over time, though, the inaccuracies of floating point numbers will become apparent. * Many COVID patients needing ventilation also have Acute Respiratory Distress Syndrome (ARDS). The simple explanation is their lungs are functioning so poorly that you can't simply stuff oxygen into them and hope it works. You need to be extremely particular with how you control breathing. * Bonus, related to point two, many doctors are reporting using pretty crazy ventilation settings as a baseline. They're basically overclocking a CPU/GPU by default then hoping they can keep overclocking as CPU/GPU load increases (not fully accurate, but it's an analogy).
- deleted 7y ago
  [deleted]
- rasz 7y ago
  There is nothing complicated about air pressure/volume control loop. If $5 arduino can control a V8 engine (Speeduino) it can control a small air pump.
deleted 7y ago
[deleted]
db48x 7y ago
They're really not very complicated; the requirements can be written out in a few pages. I'd say they're a bit more complicated than your fridge, but a lot less complicated than a car. Generally the primary barrier to entry for manufacturing medical devices is not their complexity but the onerous requirements of certification by the FDA. On the whole that's a good thing, since it means that properly certified medical devices are rarely built by fly-by-night organizations that disappear once they have your money.

by lukevp 7y ago

toomuchtodo 7y ago

There is a narrow range of pressure where you're not damaging the alveoli from underpressure, but not bursting the lungs from overpressure. You need a mechanical scalpel, not a butcher's knife.

Nambia 7y ago
Honest question: is the pressure range actually that narrow? People can survive at high altitudes, which will see pressure of 70% sea level (or less, especially when considering mountain climbing). Additionally, when SCUBA diving, something like 30 feet of depth = 1 atmosphere. I feel like I'm missing something here. Any ideas?
- gregoriol 7y ago
  It's really a complicated subject. One of the best reads I've seen these days is https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/ https://hackaday.com/2020/03/25/ventilators-101-what-they-do... and they explain how many factors there is to consider: it's actually "very" complicated to make right.
- gjhan 7y ago
  As you point out, the body can tolerate significant variation in absolute pressure, corresponding to the temperature, composition, and density of the gas you breathe. The pressure that must be narrowly controlled in a ventilator application is the relative pressure: the difference between the absolute pressure outside the lung (in the room) and the absolute pressure inside the lung. This relative pressure is what does all the work --- mechanically opening airways and alveoli --- and could cause all the injury.
- landryraccoon 7y ago
  Covid patients in the ICU probably don’t have healthy lungs. The people you’re talking about at those pressure ranges are probably all young, healthy and athletic. I know a bit about scuba diving, and you absolutely are not supposed to go diving if you have a lung injury. I would speculate that if you put a person with serious covid on a mountain top or 30 meters under the ocean it would kill them pretty quickly..
- refurb 7y ago
  People can survive at high altitudes... That's because the pressure outside their body is the same as inside. With a ventilator, the pressure going in is higher than atmospheric pressure. That can cause damage.
- nradov 7y ago
  Scuba divers are at ambient pressure and breathe through demand valve regulators. Pressures inside their lungs are almost exactly the same as outside so there's no extra stress. Increasing pressure with depth does increase work of breathing due to higher gas viscosity. Beyond a certain depth, divers can no longer ventilate enough to take in O2 and remove CO2. This problem can be mitigated to an extent by breathing lower density gasses such as helium. Occasionally hospitals even have patients with severely impaired lung function breathe heliox just to get better gas flow. In theory it's possible to use a 2nd-stage scuba regulator as an improvised mechanical ventilator by partially blocking the exhaust valve with your hand and pressing the purge button. In practice it's unlikely to work, but if I was trying to rescue someone who had stopped breathing in the water and had no way to get them back to shore or a boat quickly then I might try it as a last-ditch effort.
- jacquesm 7y ago
  Yes, it's pretty narrow. I've had double pneumonia somewhere in my 20's. Just playing a reed instrument (sax) was over-pressuring my lungs to the point that it led to more damage over time. And that's only a tiny little bit of pressure.
lukevp 7y ago
What’s the limiting factor there? The pressure regulation, pressure production, measurement accuracy? There’s open source ECUs that measure dozens of sensors at 1000hz+ and keep an engine perfectly timed using a $35 raspberry pi. Is this problem harder somehow?
- toomuchtodo 7y ago
  Validation and quality assurance in my opinion.
jmole 7y ago
There is evidence that positive pressure ventilation results in worse outcomes than the negative pressure iron-lung-style ventilators: https://www.atsjournals.org/doi/full/10.1164/rccm.200707-1004OC https://www.atsjournals.org/doi/full/10.1164/rccm.200707-100...
rasz 7y ago
How could we archive that? its not like almost disposably cheap actuators moving with 0.1mm precision guaranteed for >10K hours MTBF was a solved problem over 30 years ago (floppy drive). /s

gregoriol 7y ago

Here is an interesting read on the subject: https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/ https://hackaday.com/2020/03/25/ventilators-101-what-they-do...

lukevp 7y ago
Thanks for the link, I’ll read up on it!

DanBC 7y ago

Partly this is a problem with jargon. When healthcare professionals talk about "beds" or "ventilators" they mean "the bed and all the staff needed for the patient in that bed", or "the ventilator and all the staff needed to put a patient on, and take a patient off, the ventilator". Ventilators turn out the be pretty complicated. Here's a useful thread: https://twitter.com/aroradrn/status/1243091107149418496 https://twitter.com/aroradrn/status/1243091107149418496 And another simplified cheat sheet for people who use machines in one setting which are now being used in other settings, but it has replies from doctors asking questions that give some hints at the complexity: https://twitter.com/aroradrn/status/1244134454001635329?s=20 https://twitter.com/aroradrn/status/1244134454001635329?s=20 Then you have all the "human factors" stuff caused by machines having different layouts.

canada_dry 7y ago
> caused by machines having different layouts This is going to be a huge issue with the onslaught of different manufacturers. I liken it somewhat similar to helping troubleshoot router/switch issues... yes at a high level they're all the same but, at the same time, each one has it quirks and peculiarities and even use slightly different nomenclature that make it a non-trivial exercise.

SkyPuncher 7y ago

My wife is a doctor (I am not). I've been following COVID closely and discussing with her/peers. I'm not an expert (but feel I have an above average understanding, thanks to my wife) > I see a lot of DIY posts that are probably not 100% the same thing but are they even close? I have yet to see (though I haven't looked extensively) a DIY ventilator that has the fine tune control many doctors are suggesting are required for COVID patients. My understanding is most of the DIY vents are comparable to emergency or transport vents. They'll keep a patient breathing for minutes/hours until they can be transferred to a proper ventilator. After a short period of time, you really need to transfer a patient to a proper ventilator to continue to support life. Two big challenges with COVID patients in particular: * They require ventilation for DAYS or even weeks. Over durations of that long, you really need precise control over a vent. A tech analogy is using floating point numbers for finance. Over a small number of transactions, a floating point number may be sufficient. Over time, though, the inaccuracies of floating point numbers will become apparent. * Many COVID patients needing ventilation also have Acute Respiratory Distress Syndrome (ARDS). The simple explanation is their lungs are functioning so poorly that you can't simply stuff oxygen into them and hope it works. You need to be extremely particular with how you control breathing. * Bonus, related to point two, many doctors are reporting using pretty crazy ventilation settings as a baseline. They're basically overclocking a CPU/GPU by default then hoping they can keep overclocking as CPU/GPU load increases (not fully accurate, but it's an analogy).

deleted 7y ago
[deleted]
rasz 7y ago
There is nothing complicated about air pressure/volume control loop. If $5 arduino can control a V8 engine (Speeduino) it can control a small air pump.

deleted 7y ago

[deleted]

db48x 7y ago

They're really not very complicated; the requirements can be written out in a few pages. I'd say they're a bit more complicated than your fridge, but a lot less complicated than a car. Generally the primary barrier to entry for manufacturing medical devices is not their complexity but the onerous requirements of certification by the FDA. On the whole that's a good thing, since it means that properly certified medical devices are rarely built by fly-by-night organizations that disappear once they have your money.