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Capnometer - DIY Solution?

Discussion in 'Monitoring Vitals' started by DrJ, Nov 27, 2015.

  1. DrJ

    DrJ Member

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    Probably like many people here, I've looked into buying a capnometer to monitor CO2 levels in my exhaled breath. Of course, they are very expensive! Looks like at least $1000 USD or more. Since I had some free time with the Thanksgiving holiday, I thought I'd look into what it would take to make one...

    And it seems quite possible! As far as I can tell, you can buy an integrated circuit CO2 sensor, solder some wires between it and something like an Arduino to read the sensor output; power can probably be supplied by the Arduino. It seems an adequate sensor runs about $155USD in qty 1, and then an Arduino is about $25USD. Some misc wiring and solder would be needed, as well as some sort of tubing scheme to direct your breath to the sensor, and I would assume people have a computer to talk to the Arduino, but seems possible to build a basic but functional capnometer for under $225USD and a little programming. Still not exactly cheap, but more approachable than buying one.

    Anyone see any problems with this? Or has ever tried it or know of someone who has? I don't really have a feel for the accuracy required, nor exactly how to go about calibrating the thing. It seems human exhaled breath has about 300,000ppm CO2, and I would guess you would want 1-2% accuracy on that number. Background air CO2 levels seem to be about 350ppm. Do these numbers sound right?
     
  2. Such_Saturation

    Such_Saturation Member

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    Vernier makes one for the classroom. You just need that and the mouthpiece along with their basic computer connector and software.
     
  3. OP
    DrJ

    DrJ Member

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    The only one I find from Vernier can only read up to 100,000ppm CO2, which would not be a large enough range for exhaled breath :( Is there another?
     
  4. tara

    tara Member

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    Interesting project.

    This looks very high to me - 30% CO2? Or is my maths badly off today? What's your source?

    From Rakhimov's normalbreathing site, quoting Buteyko, normal breathing parameters include:
    "- CO2 concentrations in the alveoli or arterial blood – 6.5% or about 46 mm Hg (at sea level)."

    And on this page about end-tidal CO2, it looks as though the CO2 level is typically in the order of 5%.
    http://www.normalbreathing.com/d/etco2-capnography.php

    If this is true, then 100 000ppm (10%, right?) should be plenty?

    Do you expect to be able to graph continuous changes, or just get a few point values?

    Out of curiosity, if you feel like telling, have you experimented with measurig your control pause? Learn anything interesting?
     
  5. OP
    DrJ

    DrJ Member

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    The source is the manual for the CO2 sensor I'm looking to use. It says don't breathe near the sensor during calibration because human breath can contain 300,000ppm CO2. Maybe that is wrong! That is why I post, to see where I might be wrong.... Thanks for the link! So maybe 5% is much more reasonable. Also allows for a cheaper sensor closer to $100USD.

    As long as the sampling rate of the sensor is enough, "continuous" changes should be no problem to graph.

    I haven't measured control pause. I am just trying to learn more specifics about CO2 monitoring as a proxy to metabolism monitoring.
     
  6. tara

    tara Member

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    I haven't done anything to verify Rakhimov's info, but I think Buteyko was a leading expert in the field.
    I can't see how 30% could be right - air is only 20% oxygen, and we don't generally use it all up and replace it all with CO2 at every breath. We'd be in danger of asphyxiating ourselves quite quickly whenever we got in confined spaces, too. :)

    Maybe they made a typo, and meant 30 000ppm? Maybe email them and ask where the number comes from?
     
  7. ecstatichamster

    ecstatichamster Member

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    The Buteyko control pause gives you a great indication of carbon dioxide.and it's free.
     
  8. OP
    DrJ

    DrJ Member

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    Haha, yeah. But I need an excuse to build something :). Doing is living.

    But yes it seems that that the 300k ppm is high. Like I said, will save about $50 on a sensor. If I get this to work out I can post instructions in case anyone want to build their own.
     
  9. NathanK

    NathanK Member

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    Anybody ever try VoS' build?
     
  10. Parsifal

    Parsifal Member

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    What is that?
     
  11. tara

    tara Member

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    CO2 cannister (eg the kind used for paintball) with regulator and mask for breathing supplemental CO2. He said he used it regularly and reported good results. There was some discussion of potential risks - not all of us think his method is necessarily safe for every one depending on details of logistics and what else is going on with one's health. I can imagine it could be of benefit in some situations.
     
  12. ecstatichamster

    ecstatichamster Member

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    VoS = VisionofStrength, a since banned member here...search out his threads, they're VERY good
     
  13. Lore

    Lore Member

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    I'm very interested in this build. Please let me know.
     
  14. cdg

    cdg Member

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    Where exactly can we find out?? Can you send link? Thanks.
     
  15. Light

    Light Member

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    @DrJ did you ever make it?
     
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