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Thread: CO2 production results

  1. #11
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    Re: CO2 production results

    during the test, how was your WOB? Any increase would also tend to drive the co2 up. I don't know what all the measurements are, but I think the co2 measurements bear some consideration.
    The WOB was fairly consistent, I was using a USD Artic 2nd stage reg that had been modified to reclaim my exhaled gas.

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    Re: CO2 production results

    Quote Originally Posted by iain-hsm
    VE Ventilation Rate usually described in BPM Breath Per Min referenced to BTPS. iain
    Hi Iain,

    I think VE is the expired volume in one minute rather than the rate. This is probably the next most important statistic to the actual CO2 production because it will influence flow rates / contact times etc. The combination of high CO2 production coupled with high flow (volume and rate) is what will challenge a CO2 scrubber as you know. Of interest, notice how the end tidal CO2 does not change... demonstrating how efficient we are at maintaining arterial CO2 during heavy exercise provided there is no excessive breathing resistance and we do not rebreathe the stuff.

    Simon M

  3. #13
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    Re: CO2 production results

    Quote Originally Posted by diverrob
    I also would like to know how AP determined CO2 production value of 1.6l/min as a bench mark? From what I see in this report 1.6 seems low, I was able to produce 1.6 early on in the test.
    APD used 1.6l/min because that is what is specified in EN14143:2003. Section 6.6.2 and Table 4.
    The test is for scrubber endurance - keeping up 1.6l/min for the life of the scrubber requires quite a feat: to keep this level of exertion up to several hours.

    Alex
    Last edited by AD_ward9; 4th August 2006 at 07:08.

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    Re: CO2 production results

    As all these tests keep seeming to show, I think rebreather manufacturers need to show more absorbent capacity test data, under different protocols. i.e. lower co2 rates coupled with short high co2 bursts, which seems a LOT closer to acctual diving scenarios. No one can keep up 1.6lpm for over 20 mins, heck no one can keep up 1.35 lpm for over 20 mins, but they can do bursts of up to 5 lpm of CO2.

    My bits of useless data I'll throw in

    VO2 = volume of O2 consumed
    VCO2 = volume of CO2 produced
    VE = Volume exhaled (RMV)
    RER = Respitory quotiont (Co2 produced per L of O2 consumed)
    RR = Respitory rate (breaths per min (bpm))
    Vt = Tidal Volume
    FEO2 = Fraction exhaled O2
    FECO2 = fraction exhaled CO2

    VE(RMV) is derived from RR (BPM) * Vt(Tidal Volume)

    RER (Respitory Quotient) is usually assumed to be ~0.85 CO2 produced to O2 consumed (i.e. 1.6lpm = 2lpm of O2 consumed)

    The CE spec tests (used by AP, et al) are at 1.6lpm CO2, 40 RMV (20 RR(BPM) and 2L Vt(Tidal Volume)) which equates to 4% FeCO2

  5. #15
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    Re: CO2 production results

    Quote Originally Posted by teksimple  View Original Post
    In the second reference, it indicates that the metabolism of alcohol produces even less CO2 than fat. As far as scrubber time, then, a good pre-dive meal would be steak cooked in butter and a sour cream omelette chased with a nice cold glass of vodka.
    OMG! Can I go diving with you sometime! We can stop for breakfast...

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    Re: CO2 production results

    Quote Originally Posted by E-man  View Original Post
    No one can keep up 1.6lpm for over 20 mins, heck no one can keep up 1.35 lpm for over 20 mins, but they can do bursts of up to 5 lpm of CO2.
    When I said 1.6lpm for several hours is quite a feat, I was not suggesting it was impossible - in fact, it is quite easy: the feat is to do it without being clobbered by your buddy who would be trying to keep up.

    A man running a marathon in 3 hours 15 minutes, generates 3.6 litres of CO2 per minute. This not a record time at all: when I was 25 years younger than now, I used do a marathon in 2 hours 36 minutes, but so could thousands of others - there is a world of difference between 2hrs 30mins and 2 hours 10 mins (now it is 2 hours 4 mins for the best male time). If I had been born a century earlier, then I could have been a great runner! Fact is, 3 hours 15 is nothing more than a respectable time nowadays for a weekend runner entering one of the city marathons. This is probably why NORSOK U-101 requires testing at 3.6 litres per minute of CO2.

    Some divers I know are like clockwork mice: they get in the water, and trying to follow them is hopeless. I am sure they are doing a marathon underwater. For this reason, rebreathers should be tested at high rates of CO2 production as well as low rates.

    On your general point, I agree: it is more realistic to test for short durations at high work rates, but the results would be very hard to interpret. Doing tests from 0.3 litres of CO2 to 3.6 litres of CO2 per minute is the best approach, IMHO.

    5lpm is just beyond most people: the Vo max would be very high, though for short sprints the Respiratory Quotient increases from around 0.8 to almost 2 due to lactic acid dumping in anabolic exercise.

    For those interested in this area, Verhs et. all. in their paper "Submaximal Treadmill Exercise Test to Predict VO2max in Fit Adults", in the journal Measurement in Physical Education and Exercise Science 2007, Vol. 11, No. 2, Pages 61-72, give the equation:

    VO2max (mL · kg-1 · min-1) = 58.687 + (7.520 × Gender; 0 = woman and 1 = man) + (4.334 × mph) — (0.211 × kg) — (0.148 × HR) — (0.107 × Age)

    So, an 80kg male (divers tend to be plumper than average), 35 years old, running a marathon in 3 hours 15, uses 4.6 l/min of O2. At an RQ of 0.8 is 3.68 litres/min of O2. A fitter chap at 70kg is just under this.

    Alex
    Last edited by AD_ward9; 15th March 2008 at 21:44.

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    Re: CO2 production results

    Quote Originally Posted by E-man  View Original Post
    No one can keep up 1.6lpm for over 20 mins, heck no one can keep up 1.35 lpm for over 20 mins, but they can do bursts of up to 5 lpm of CO2.
    actually it is not a problem to keep up 1.6lpm for quite some time... even some hours
    question is if you do this under water.

    paul
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    .... radial scrubbers give longer dwell time than axials...
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  8. #18
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    Re: CO2 production results

    Hi Rob,
    excellent post.
    Looking at the data, you will see that at the end of each period, with the highest exertion, there happens the following:

    -hyperproportional rise of respiration frequency, due to exertion and probably pH-changes ( CO2 blood level rising, causing increased respiration, as well as oxygen debt, causing same)

    -higher percentage of _expired_ oxygen! How come ?
    --You were breathing so fast that the whole of it had no chance to enter the bloodstream
    -- your blood was loaded with too much CO2 to give room for the needed oxygen

    -lower percentage of expired CO2!
    -- Well, since there were some straits in the gas exchange ( velocity and blood load, the CO2 had to go/stay somewhere.
    Part of it stays in the blood, part of it is stowed away in muscles, and in the stomach.
    The fitter an athlet is, and the more anaerobic training he has, the greater his capability to stow away CO2.

    I'd like to see your lactate values after these tests.

    Greets,
    Matthias

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