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Wednesday, March 11, 2020

Design for a Positive Pressure Pandemic Ventilator





I am developing this at:  https://app.jogl.io/project/121 
Helpful Engineering  - you can join up to help

This is my first new ventilator design in 12 years.
I have been told that a pressure control ventilator design would be more useful for caring for patients with ARDS from such a pandemic as we are experiencing now.  “These  designs use extremely high RPM turbine blowers to generate high flow at high pressure. Driven by electric motors that can stop, start and adjust flow in milliseconds. Small package, high reliability and tough construction. A flow sensor is mandatory for measuring the flow into the patient and to calculate the Tidal Volume (Vt). “
 So I looked for these tiny blowers.  The reason they are small is not just so that they can be compact.  They need to be high RPM with low mass of motor and impeller so that they can change the speeds very quickly so as to provide the desired pressure profile. 
 Such a pump is available, say from Digikey, but only a few dozen are in stock and then multiple weeks to order more.  That won’t work for us.  You could also get them from China.  There are obvious supply chain problems there.  One of my original requirements for the Pandemic Ventilator Project was that it be able to be built from parts that we already have around because I assumed supply chains would be disrupted by the pandemic as well.  Well, that turned out to be true.

So here it is:

·         The blower in this design is a big one that runs on AC and not a nice little low voltage brushless.  (Sorry, no intrinsic battery backup here.)  The blower runs full on all the time.  (Will be noisy too.)
·         In order to rapidly change the pressure there is a valve arrangement that opens the pressure control valve and closes the waste gate with the linear actuator shutting down the outlet flow to rapidly bring up the pressure to start the cycle. The motor operates a turning arm that is connected to the valves to rotate them so as increase or decrease the opening in the pipes.  The motor could be a stepper or a fast turning motor with gear reduction and some method of angle feedback.  (I am sure the RC model car guys can figure this out - it’s fundamentally like the steering part.)
·         Pressure is then controlled by feedback from the feed pressure sensor adjusting the servo motor and additional fine tuning from the linear actuator controlled slot valve.
·         The flow meter monitors the inspiratory volume and when the conditions are met to exhale, the pump pressure is cut off by the servo motor and the linear actuator opens he slot valve to control the flow to the outlet.  The linear actuator then adjusts the slot valve position to maintain a prescribed PEEP pressure utilizing feedback from the patient pressure sensor.
·         With the right software, you could control rates, tidal volumes, minute volumes, pressure profiles, PEEP to whatever you want, and also offer patient controlled breath initiation.
·         I added a filter to reduce cross contamination and protect workers.  I don’t know, that may be optional if everyone is wearing PPE in any case.

·         What you actually now see is version 2.  I reaarranged the layout to minimize dead space, I added the input tube for humidified oxygen increased air, and added a recirculation loop to minimize the waste of oxygen.

Anyway, this is my first shot at a design for this style.  Actually, looking at it, it seems too simple a design to me.  I must have left something out.  I am sure readers will find flaws and maybe offer some design improvements.  Any maker group, anywhere please feel free to use whatever you want from this.

Next Steps:

  • The design should be reviewed by experts in ventilator use as well as engineers with experience in device control to be sure it is adequate and relatively optimized.
  • Need to come up with a list of potential parts and interface criteria for sensors
  • Specify control system processor, drivers etc.
  • Specification list (state table) for all modes of the device to aid in programming
  • Basic machine control program is written,
  • Interface program for operator control, alarms and setup
  • Modify interface look and feel to clone an existing popular ventilator design
  • Functional, safety and usability testing
  • Operators manual.
  • All of these steps are of course iterative and involve testing and user feedback at each level

Parts List


Name 
Web Link
Part #
Price
Blower



Feed Pres Sensor
https://www.st.com/en/mems-and-sensors/lps27hhw.html
LPS27HHb
4,6€
Patient Pres Sensor
LPS27HHB
4,6€
Servo Motor



Flow meter
SFM3300-D
40 €
Linear Actuator



Gate Valves










39 comments:

  1. Will you post some specs on air pressure numbers and also what type of flow meters and pressure sensors would be appropriate? Also wondering if it would be practical to adapt a bag valve mask... maybe not as precise but a mechanical bellows compressed by a cam seems like it could do some amount of similar work more simply. Thanks.

    ReplyDelete
    Replies
    1. I agree, upper and lower pressure values are very important I think which can ultimately leads to the suitable pressure sensor.

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  2. Starting a build of this today in concert with a few other homefab people. Please let me know how to get in touch directly.

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  3. There should be a contact form at the bottom of the page. I am collaborating this design right now with a group on https://app.jogl.io/project/121 I added the start of a parts list. This list is in no way definitive or proven. it is just a starting point.

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  4. I showed your project to a doctor, and he said you need to use an electric motor, NEVER a gas motor, since a gas motor would get carbon monoxide in the air stream.

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    Replies
    1. That is good advice. Electric motor should be fine.

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  5. I am a PA in an emergency department. This must have a filter. I just got a note from a partner in Washington and they are already running bout of N95s.

    Two, has anyone looked at using raspberry Pi for the controller?

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    Replies
    1. Good point Brendan. Filter stays in. I guess it is just not just Coronavirus that is concern but all the bacteria from anyone that has pneumonia as well.

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    2. HME units (heat moisture exchange) are plentiful and cheap. Coviduen DAR ate used in the firm I work at and mitigate the need for heated humidifiers.

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    3. Arduino is a better choice for a controller than Raspberry Pi. The Arduino comes with analog/digital converter, and is cheaper. Raspberry Pi is kind of overkill for this.

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    4. I agree, Arduino is easier to program for control functions and has less overhead. Simpler control design is probably more stable. The Raspberry could be used just for the control interface to an HDMI screen so that it could look very similar ro other commercial ventilator control screens and be easier to learn for medical personnel.

      Delete
    5. Thinking about the combination of Pi and Arduino the one board that comes to mind is the BBB or even the BBE which has more memory, extra sensors, WiFi and Bluetooth. It would allow the GPIO control with analog inputs and can drive a touchscreen display.
      We are willing to support this effort with boards. Get in contact with us https://www.sancloud.co.uk/contact-us

      Delete
  6. I'm soon to be internal medicine resident. One consideration I was having with this is that feasibility of repurposing CPAP hardware as a improvised ventilator. We have a ton of them in the US, and they already have most of a medical grade pressure control ventilation system set up inside them.

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    Replies
    1. C-PAP units do not provide assistance in exhalation, though. In fact, the biggest concern that I can see with any DIY vents is that patients may end up with CO2 retention and given their already compromised condition, these devices will cause more harm than benefit.

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  7. Wow what a coincidence. I was just writing a comment on your slack post in Helpful Engineering. Good idea. Where do you think we should start to look to get them?

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  8. Engineer with a 3d printer and experience with arduinos, raspis, etc. Not sure how to help but there are enormous numbers of 3d printer enthusiasts online looking to do something for the next month. If each component could be spruced scalably, standardized firmware developed for Arduino, there could be many, many ventilators manufactured. It's not as good as hacking something existing but entirely plausible that we could make an army of these things

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    Replies
    1. Hi, thank you- can you recommend how to connect with 3D printer operators? Mallin dot Andrew at g mail

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  9. couldn't a double spoolingsolution (like in a turbo)+actuator swap between in and out gasing?

    The blower would be constantly working, but come of the time forcing air in, pause , help air out

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    Replies
    1. Possibly, I am not an airflow specialist. Can that be done using simple components? Any design we use has to be something that could be made from readily available components or very easily manufactured at large scale in a short time.

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  10. Thinking of using a CPAP machine as a blower feeding two zeolite-filled tubes alternately on a pressurize/exhaust cycle to oxygenate air. Would need valves and control mechanism. Patient would get either pressurized oxygenated air or just atmospheric pressure alternately as it cycles.

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    Replies
    1. If you figure this out, I'd love to know more. I have a bipap that seems like it just needs to be hacked to do what a ventilator does, but I'm just guessing.

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  11. Anybody jumping into this should probably read this book about the subject: Medical Ventilator System Basics to get an understanding of the problems. https://www.docdroid.net/gval5gc/medical-ventilator-system-basics-a-clinical-guide-by-yuan-lei.pdf

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  12. Many hoses to one rigid gang machine are indicwAted

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  13. How about adapting / using a vacuum cleaner, is this possible? Also on the news I seem to remember an Italian emergency doc saying that most virus patients didn't need oxygen, just ventilation. Can anyone confirm?

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  14. Hello, I have done a project of a mechanical ventilation machine with low resources, I hope it would help someone, works like a aquarium coffer. Watch it https://youtu.be/X-5Uwbz5yO8

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  15. Thses guys are 3D printing valves in italy. I wish I could be more helpful.

    https://www.theverge.com/2020/3/17/21184308/coronavirus-italy-medical-company-threatens-sue-3d-print-valves-treatments

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  16. In an emergency situation, wouldn't an Iron Lung device be easier to build and operate ? Or maybe a wearable cuirass ventilator of sorts.

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    Replies
    1. Thanks, Yes That will work. Not useful for people with COVID symptoms but can be used for other people in the hospital that will be triaged and competing for remaining ventilators. This is what you mean. https://www.youtube.com/watch?v=pvrUQCMa3a8
      I am talking to this guy

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  17. I also came here after reading about the people 3D printing the valves because when I read the parts list for the original Instructables project (which pointed me here) it seemed like the valves are the part that is most expensive and hardest to acquire... is that true, or am I misunderstanding something? Is there a spec that could be distributed to 3D printing hobbyists in order to diversify the supply chain? If the valve is a known component, and we theoretically need hundreds of thousands of them, shouldn't we just start making as many of as possible them ASAP even if the final kit design is still being tested? Or is it just a pipe dream to think that people can print ones that will work?

    Thanks for all the time and effort you have clearly put into this... sucks to be called back to the front lines after 11 years... I am heartened by the energy and just trying to figure out if there is any way I can help.

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    Replies
    1. I am working on developing the ventilators and other designs at:
      Helpful Engineering
      You can access the discussion channels once you sign in at:
      https://app.jogl.io/project/121
      It is an ongoing effort to develop open-source designs for ventilators and other required equipment to save lives that could otherwise have been lost due to shortages of this equipment.  Also to provide engineering support wherever it is required.  We also welcome people with medical skills to advise us and also people with resources and skills in building or manufacturing devices within a very short time frame.

      Delete
  18. *Limpia tus pulmones del Coronavirus*
    Sí, el *vinagre* 🍶es natural y no es tóxico; y al limpiar la lechuga con vinagre se desinfecta de bichos, además, si frotamos con un paño superficie donde hay *Coronavirus*🔅🧫 se logra desinfectar (lo dijeron en las noticias de Colombia y el mundo).
    *Entonces… ¿con vinagre también se logra desinfectar nuestros pulmones?*
    Como dice DaVinci 🧙🏼‍♂️✨ *"El Poder de lo Simple"*
    Con un vaporizador o difusor, mezclar una taza de vinagre con una taza de Agua🥛.
    Si no lo tienes, puedes poner a hervir una taza de agua en una olla, cuando hierva, le aplicas la taza de vinagre y aspiras por boca y nariz sus vapores (puedes repetir y volverla a calentar las veces que sean necesarias en el día♻️).
    Instala el vaporizador o difusor en el baño de la casa o de la oficina💨, cuando regresemos a casa u oficina o cuando nos visite un amigo o un cliente, prendemos el dispositivo y aspiramos su vapor profundamente por las fosas nasales y también por la boca👃👄.
    *¡La solución para mantener tus pulmones sin Coronavirus es simple!✨*
    *El reto verdadero es cambiar el inconsciente colectivo del miedo y pánico*, para que volvamos a florecer la unión desde los pilares de la familia y trabajo en equipo🌤️.
    ¡Sé siempre positivo!🙏✨

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  19. It is not obvious to me that a cuirass ventilator would NOT work with COVID patients. It is about as simple a device as we could hope for. I will discuss with an MD friend who is a pulmonary specialist and report back tomorrow. Interestingly, they are currently in production and allegedly available. I just wonder if it has FDA approval. Check out this website and video: Hayekmedical.com

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  20. This is the same direction that I’ve been thinking. Positive pressure ventilation is decades old tech, so there can be no serious obstacles that couldn’t be overcome with arduino, 3D printer components, and commercial off the shelf parts.

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  21. Centrifugal blowers generally are fine with being deadheaded, so you likely don't need the waste gate. If you felt some circulation was needed when the pressure control valve was closed you could have manual valve in place of the waste gate to allow a small continous recirculation.

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  22. A final use for the air suspension componentes used in new and old Rangerovers. Mainly Dunlop parts. Something to look into. I have plenty of p38 parts to do it

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  23. Hi I just join https://app.jogl.io/project/121
    Which channels are you in ? Slack use hashtag for channels ?

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  24. https://web.mit.edu/2.75/projects/DMD_2010_Al_Husseini.pdf

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  25. I read a couple of papers recently including:
    1)"Modelling the ventilator-patient interaction:
    a pressure-cycled control strategy"
    2) "https://link.springer.com/article/10.1186/s40635-018-0195-0"

    I assume you have a way to model the patient's lung , perhaps with spirometry readings.

    I think the basic problem is that the lung must be part of the system as a whole - you could call it the "load". The characteristics of elasticity of the lung will affect the pressure wave. Perhaps input could be gentle at first to measure the system response from the patient's lung, then a system model could be dynamically deduced in controller software.

    There is a MATLAB model :
    https://www.mathworks.com/help/physmod/simscape/examples/medical-ventilator-with-lung-model.html

    That looks very promising as it gives you output as waves, also allows you to set Otis frequency and to change the lung model.

    Often systems have a digital controller running alongside the hardware, giving estimations for the expected output, and taking feedback variable measurements to adjust parameters. Simulink can be converted into C quite easily (if I remember correctly).

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  26. Do you need some type of differential pressure sensor?

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