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Thread: Is it Hypercapnia or Hypoxia?

  1. #31
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    Re: Is it Hypercapnia or Hypoxia?

    Interesting topic.

    Improvement in the gas diffusion model seems to be the stumbling block for any correlation that faciliates advancement, whether regarding the effects of CO2 or decompression.

    It is a wonder, for example, that the accepted gas diffusion model for decompression is limited to a parallel 16 compartment model. This is positively daft. Even the latest models do not consider modelling the the coupling between tissue compartments. It is amazing that we anoint ourselves with being above animals when a model refuses to take the giant leap of modelling bodily arrangments of functions. Every science is represented in this field, yet there isn't a meeting of the minds.

    Second year engineering students typically engage in the formulation of transfer functions for complex systems that incorporate several levels of coupling including feedback, gain, filtering... This level of applied science is considered trivial. The accepted higher-order analysis of such transfer functions includes stability, Bode plots and other methods to gauge the fidelity, accuracy and practical use of such modelling techniques.

    The gas diffusion models, in comparison, can't even model skin bends, one of the most common manifestations of the condition. Repetitive diving is also considered voodoo with regard to the model, completely unpredictable. This would be the most basic form of testing for any transfer function, step analysis. Yo-yo diving also not modeled, yet this is a basic step toward frequency analysis. Instead, we find ourselves constantly inundated with all manner of studies and nobody bothers to go back to change or improve the model. Sure it is innacurate, physiological changes, individual differences, the weather, hydration, navel lint and so forth. However, it doesn't mean that the model can't be improved.

    A first step in modelling could lead to further model sophoistication to account for cardiovascular effects, even dual-loop cardio-pulmonary and cardio-vascular coupling.

    So, how would the model be improved? One quick improvement would be to calculate tissue compartment loading based on the physical arrangment of the phisical tissue arrangments. Thus, lung tissue (if such a compartment exists) and blood would be in series as would muscle and bone. Organs would be in parallel with muscles however decoupled from the bone. The lymphatic system could be modelled in series with muscle. An activity index during the deep portion of the dive versus the decompression phase could add a dimension of physical reality to the model, particularly with the skin in series to the lymphatic system.

    An example such as this may result in more insightful products given that it will not behave in a linear fashion as might the usual parallel compartment model. Yes, it would be nice to dabble with this, but the O2 cell project is still preoccupying at the moment. The coupling issue with the model has been nagging at me for years. Maybe in the future...

    Getting back to the CO2 issues, such a gas diffusion model may explain the quirks encountered by the freediving community when counterintuitive observations are made.

    During the frowned upon but sometimes necessary practice of skip-breathing, better gas efficiency can be realized by maintaining average-empty lungs rather that average-full lungs. Is this because the often empty lungs cause more CO2 to diffuse to out of the body and into the lungs, as opposed to maintaining full lungs on the hold that forces CO2 to remain in the tissues? Surely the mechanics of the lungs, whether full or empty, influence the flow or diffusion of gas? Perhaps this physical coupling mechanism can be modelled as well.

    It is not a perfect way to proceed, however it is different from the status quo.

    Thank you for tuning in to this rant.

  2. #32
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    Re: Is it Hypercapnia or Hypoxia?

    Quote Originally Posted by zzzzzzzz  View Original Post
    Interesting topic.

    During the frowned upon but sometimes necessary practice of skip-breathing, better gas efficiency can be realized by maintaining average-empty lungs rather that average-full lungs. Is this because the often empty lungs cause more CO2 to diffuse to out of the body and into the lungs, as opposed to maintaining full lungs on the hold that forces CO2 to remain in the tissues? Surely the mechanics of the lungs, whether full or empty, influence the flow or diffusion of gas? Perhaps this physical coupling mechanism can be modelled as well.
    The whole reason myself and a few others have pioneered the art of 'exhale' freediving is to avoid the CO2 problems that occur at great depth. A freediver who holds his breath on an exhale never achieves any high level of CO2. I never get narcosis on exhale dives.

    The urge to breathe on an exhale breath-hold is thus much lower than on an inhale breath-hold. The reason is debatable. I have a hypothesis as to why that is, but it seems useless to even post it as it would probably be once again said to be a fantasy.

    However, this phenomenon might have some relevance to skip breathing in scuba.

    Regards to research published by Peter Lindholm, he is a personal friend whom I've been corresponding with for years. In fact he sent me his PhD thesis even before it was published, for feedback. He is probably the researcher who is the closest to the cutting edge of breath-hold diving, but even his research lags a bit.


    Eric Fattah
    Liquivision Products

  3. #33
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    Re: Is it Hypercapnia or Hypoxia?

    For some of the best years of my life, I was a competition Judo player. One of the ways you can win a Judo bout is by securing a submission from your opponent with a strangle. The trick is to make sure that your opponent doesn't see it coming: you use the blade of your hands to press on your opponent's jugular veins on either side, while avoiding restricting his breathing. That way he is breathing normally, feeling only a tighness on his neck. Then you distract him, perhaps by going for a hold down. If you're good at a strangle, he will lose consciousness after only a few seconds: it's stunning how fast it works in the hands of a skillful practitioner. The interesting thing is that an experienced Judo player can feel unconsciousness coming on: it's hard to describe, but it's like a sizzling in the tongue - yes, perhaps some tunnel vision, but it's the sizzling you really notice.

    I nearly knocked myself out with my rebreather a year back. I was walking up a slope towards the dive site with my 'breather on my back. I must have been a bit spaced out, because for some reason I thought "why don't I breathe off the loop while walking along, to save time kitting up?" But I didn't turn on my O2. Suddenly, I felt that sizzling sensation, stopped, closed the loop and took it out of my mouth. The PO2 was right down around 0.08. My normal pre-flight check routine has prevented me from getting in the water with the gas turned of, but it didn't prevent me being a dung-brain out of the water.

    Clearly, if you know what to look for, you can sense hypoxia, even when the PCO2 is low. It also appears you can endure a very low level of PO2 for a short time, though I'm not sure how much to trust the precise reading when I closed the loop. Obviously, the most important lesson is to engage your brain before connecting to the loop..

  4. #34
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    Re: Is it Hypercapnia or Hypoxia?

    Quote Originally Posted by tdzao  View Original Post
    The whole reason myself and a few others have pioneered the art of 'exhale' freediving is to avoid the CO2 problems that occur at great depth. A freediver who holds his breath on an exhale never achieves any high level of CO2. I never get narcosis on exhale dives.

    The urge to breathe on an exhale breath-hold is thus much lower than on an inhale breath-hold. The reason is debatable. I have a hypothesis as to why that is, but it seems useless to even post it as it would probably be once again said to be a fantasy.

    However, this phenomenon might have some relevance to skip breathing in scuba.

    Regards to research published by Peter Lindholm, he is a personal friend whom I've been corresponding with for years. In fact he sent me his PhD thesis even before it was published, for feedback. He is probably the researcher who is the closest to the cutting edge of breath-hold diving, but even his research lags a bit.


    Eric Fattah
    Liquivision Products

    There is a technique for relaxation that involves "waiting" before inhalation until the body's natural response is triggered. This often results in slow controlled breathing cycles that enhance relaxation.

    Pausing on "full" lungs in the breathing cycles doesn't seem to yield the same result. Instead, it seems to result in hyperventilation or dizzyness or erratic breathing.

    These relaxation techniques are not part of western thinking.

    Perhaps there is more at work than meets the eye.

  5. #35
    RBW Member MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV is a jewel in the rough MatV's Avatar
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    Re: Is it Hypercapnia or Hypoxia?

    Quote Originally Posted by tdzao  View Original Post
    According to the Duke study, CO2 blackout occurs around PCO2=90mmHg.

    I have done 'air' breath-holds with my CO2 monitor where I have exhaled PCO2>=85mmHg, suffered CO2 narcosis sitting on dry land, still having TONS of O2 left (SaO2=80-85%). A usual breath-hold ends around SaO2=45%. So it is totally possible to go way over 90mmHg CO2 on a breath-hold. The main decisive factor is how much deep breathing is done before hand. To get such a high CO2 value I must start the breath-hold without much breathing before hand. This parallels the new paradigm in deep freediving which calls for 'no warm up, no breathe up.'

    Further, if I can routinely reach over 85mmHg PCO2 on land, then imagine what an impossibly high level that would convert to at 100m. With my lungs crushed to 1/11th of their sea level volume, and there being the same number of CO2 molecules in 1/11th the space, the PCO2 level would be drastically higher than at sea level, perhaps 50% higher or more, with the remainder being forcefully dissolved in the plasma, bound to hemoglobin, or dissolved in other tissues.


    Eric Fattah
    Liquivision Products
    Eric,
    from results gathered by German Drs. C.M. Muth and Rademacher, it follows that pCO2 in well trained free divers will not follow Boyle's law, as your statements imply.
    Dr. Muth's lab provided means to take blood samples while the athletes were doing breathhold dives. Blood CO2 levels --were at the edge of being detectable--Edit: only rose from ca. 3 kPa to 5.8kPA. This indicates that other CO2 retaining and storing mechanisms were involved. Still he blood was reasonably depleted of oxygen, which somewhat invalidates your allusion to the Bohr mechanism paired with a generally low side oxygen supply. on the other side, a high blood ppO2 may hinder CO2 to be eliminated, IMHO.

    It was found out as well, that on ascent, the blood's oxygen content balanced out with the declining ppO2 in the lungs, thus leading to additional depletion of blood ppO2
    by O2 crossing from he blood into the lungs.


    regards,
    Matthias
    Last edited by MatV; 3rd January 2009 at 20:14.

  6. #36
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    Re: Is it Hypercapnia or Hypoxia?

    Mine came in the mail today.

    Bruce

    Quote Originally Posted by Simon Mitchell  View Original Post
    Ross and Lift bag,

    The Proceedings have only just been printed. I do not even have a copy yet, though I expect it in the next couple of days. I doubt the UHMS will make it available through Rubicon at this stage, but it will appear there sometime in the future. The UHMS office should have copies for sale very soon. I don't think it will be very expensive, and there are some excellent papers in there. The ones from the laboratories that have objectively researched deep stops in decompression diving (Gerth et al from NEDU, Brubakk / Gutvik from Norway, and Blatteau from France) are particularly relevant to the RBW group. I would watch the DAN and UHMS websites. If nothing happens in a week or two I will find out why.

    .....

    Warm regards,

    Simon M
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