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Does respiration rate effect off-gassing?

Discussion in 'Ask Dr. Decompression' started by burna, Feb 5, 2010.

  1. burna

    burna Manta Ray

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    I hope this hasn't been asked before, I can't seem to find it.

    Title says it all really, does someone who breathes faster on a deco stop off-gas faster?

    And, if someone was bent (or suspected) and on O2, is there a benefit of having an increased breathing rate?

    I'm not talking about unnaturally high breathing rates, where someone might be at risk of ending up with low CO2 levels, just increasing the number of breaths per minute slightly.

    Thanks in advance.
     
  2. Garth

    Garth Manta Ray

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    your body is set up to breath in and out. when CO2 levels rise, your respiratory center in your brain tells you to breath faster.

    answer: not exactly.
    Minute volume is calculated by your tidal volume (the amount of air you breath in in one breath) times the amount of breaths per minute. If you are planning on shallow breaths more times per minute you won't change anything if your minute volume remains the same.

    this is IMO...
    i'm a nurse that deals with ABG's, ventilators, Swan Ganz catheters and so on in a Trauma/surgical ICU.
    I have no decompression experience. this will be interesting to see if I'm correct here.

    sorry if this does not help

    i would continue to breath normally. :)
     
  3. TSandM

    TSandM Missed and loved by many.

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    Increasing your true minute ventilation (gas actually passing through the small air sacs) will accelerate offgassing, assuming that the gas you are breathing has a lower concentration of nitrogen than what is in your blood. This is because there is a constant process of diffusion from the blood to the alveoli (air sacs) which occurs because of the concentration difference in the two places. The longer the gas sits in the alveoli, the more nitrogen it picks up, and the slower the diffusion becomes. If you are constantly refreshing the alveoli with gas with a lower nitrogen content, diffusion doesn't slow down. This is why true hyperventilation results in lower CO2 levels in the blood.

    However, increasing your alveolar ventilation markedly increases your work of breathing, and changes your blood pH. This can cause facial tingling or cramps in the hands and feet (as anyone who has ever had a panic attack and hyperventilated knows). So it is not recommended. Just take your time and make a controlled ascent with some type of stops, and if you haven't pushed your limits, you should be fine.
     
  4. burna

    burna Manta Ray

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    Thanks.

    I wasn't thinking of modifying my breathing, it was just out of curiosity.

    I tend to have a relatively low SAC of about 12-15 Litres/min, some of my buddies are a bit higher up around the 18lpm mark so was just wondering whether they would off gas faster than me.
     
  5. TSandM

    TSandM Missed and loved by many.

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    Probably not, because you are all ventilating at a rate that will keep your CO2 at approximately 40, so the effective washout is the same.
     
  6. dumpsterDiver

    dumpsterDiver Banned

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    I often try to periodically exercise gently on a deco stop which slightly increasing the heart rate, but my primariy goal is to ncreasing blood flow to the extremities. This results in an increase in respiration. I suspect that gentle exercise and movement of the shoulders, hips, elbows, knees and fingers probably helps with the process, especially if you are cold and blood flow is being shunted.
     
  7. Dr Deco

    Dr Deco Loggerhead Turtle

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    Hello burna :

    Yes, your question has been asked before, but that is of no consequence. We all ask something for the first time – and at sometime first receive an answer.

    Lungs and Gas Exchange

    Absolutely, there is exchange in the lungs, but this is a very rapid process. The lungs have developed to allow effective exchange even when the demand is very high, e.g., when we are running. Healthy lungs always allow for normal arterial oxygen levels and low carbon dioxide tensions. If arterial CO[SUB]2 [/SUB]increases, we will breathe very rapidly to restore the proper balance.

    Incresed breathing rate will not increase blood flow in tissues and will not help treat DCS.

    Where is the Bottleneck in Dissolved Nitrogen Exchange?

    The point in the body where you wish nitrogen to exchange is that place where DCS can occur. This would be in tissues, and here exchange occurs in the capillaries. Exchange between blood in the capillaries and the tissues through which they run is slow by comparison. Exchange is promoted by increasing the perfusion [blood flow] and that can be brought about by mild exercise. [Exercise increases the production of carbon dioxide and that in turn increases local blood flow.]

    Mild exercise during the off gassing portion of the dive will increase the level of CO[SUB]2[/SUB] in the muscles [and connective tissue] and cause an increase in local blood flow. This is of value in eliminating dissolved nitrogen. Resting very still will not promote blood flow or off gassing – and sleeping is very bad.


    Dr Deco :doctor:
     
  8. burna

    burna Manta Ray

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    Thanks Dr Deco,

    I think I understood that. :D

    DCS is not a problem of getting the nitrogen out of the blood through the lungs per se, but is getting the nitrogen out of the tissue into the blood. Now that I think about it, that seems obvious and my question silly!

    So that must be the reason why decompression profiles are calculated using different tissue compartments, because different tissues give up the nitrogen at different rates/pressures?? Am I kind of in the ballpark??

    I think I have some reading to do!!
     
  9. Dr Deco

    Dr Deco Loggerhead Turtle

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    Hello burna:

    Is “Gas exchange at the Lungs” Really a Silly Question?

    Well, judging from the number of times this question has been asked, it cannot be concluded that it is “silly.” It certainly is not unique.

    We are fortunate that exchange in the lungs is rapid. We looked at this during altitude decompressions at NASA and found that, even when the venous system has many gas bubbles [Spencer-Johanson Grade IV], gas exchange was not measurably hindered. [Norfleet W, M Davis, and MR Powell. Absence of pulmonary dead space changes during hypobaric decompressions with high Spencer precordial Doppler grades. Undersea Biomed. Res. (Suppl.) 1992]

    It is a very rare incident when a diver experiences shortness of breath during a decompression – and a bad sign too, I might add. When the lungs are blocked by bubbles, a problem known as “the chokes” arises. [It is believed than bubbles are the cause although not proved.] Cigarette smoke makes a person cough uncontrollably, even in smokers. This is called Behnke’s Sign.

    Are Tissue Halftimes Real?

    They certainly are, but possible not for the reasons given in diving. All molecules enter and leave tissues of the body at varying rates. These rates are measured by pharmacologists and are of value in designing medicines for a given purpose.

    A problem arises in diving since different halftimes are ascribed to different blood flows in the tissues. As pointed out decades ago, a short deep dive [fast tissue] with inadequate decompression will give you DCS pain, e.g., in the knee. Likewise, a moderately long dive would give you pain in the knees. A saturation dive that loads only very long halftimes can again result in pain in the knee. The different halftime tissues cannot be in the same place.

    We have a situation where the “bookkeeping” algorithm has difficulty translating into physical reality. Halftimes are of value in the decompression algorithm, but less so in explanations of decompression Pathophysiology. Followers of Ask Dr Deco over the past decade will note that an explanation such as, “we can ascribe the problem to exceeding the limit in the 40-minute tissue” is never given. The explanations are given in terms of gas phase dynamics.

    Respiration

    Your original question asked, “Does respiration rate effect off-gassing? “ Actually it does. However, the physiological definition of “respiration” concerns the lungs and the circulatory system. The biochemical definition is one of cellular respiration – oxygen utilization by the living cell. The latter will affect the flow of blood to the tissue.

    We wish to minimize blood flow during the tissue nitrogen uptake portion of a dive. [Hibernation is good, but maybe not practical.] We wish to maximize the nitrogen elimination during the decompression part of the dive. Running very fast would do this, but it would generate too many tissue gas nuclei and leave us in a very bad position.

    So, different blood flows give different halftimes and this leads to table calculations using different, multiple halftimes.

    Dr Deco :doctor:
     

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