Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: nicksin on 21/10/2017 09:07:29
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I completed a series of diving courses and it was well explained around why you should not hold your breath and how dangerous this can be. I understand these reasons very well, however I'm looking at this from a theoretical point of view and not at all to try myself or suggest that anyone else should go and try this. Please don't, you'll die.
My question is, seeing as you are at depth you are breathing compressed air made up out of the same percentages of gasses as you would find on land, meaning the volume of air, breathed at 10 meters for instance, measured at sea-level would be larger.
My assumption here is that your body would still require the same amount of oxygen as it would at sea-level, meaning there is more oxygen available. The same assumption leads me to believe that the body would still produce the same amount of CO2 which is the dangerous part, but percentage wise in the closed system it would take longer for this to become dangerous due to the much larger total volume of air in the system.
Please help, the diving community was looking at me funny when i tried to explain my thinking ;D
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Are you referring to nitrogen narcosis? https://en.wikipedia.org/wiki/Nitrogen_narcosis (https://en.wikipedia.org/wiki/Nitrogen_narcosis)
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I'm not sure.
It's reasonable to imagine you could collect enough oxygen breathing more slowly, but I don't think you would expel the CO2 properly.
Don't try it.
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Please help, the diving community was looking at me funny when i tried to explain my thinking ;D
I’m not too surprised. Although the basics of breathing air at pressure are covered in most courses the detail is left out because of time.
This is not as simple as it seems at first sight. You are right that a breath at 10m will contain more oxygen, however, at the surface haemoglobin is 97% saturated and despite the increased partial pressure O2 it is difficult to get it above this level. Also solubility of O2 in plasma is low and only with hyperbaric O2 at high % can you get a significant increase in solution - eg at 3atm on 100% O2 you will get enough dissolved O2 to meet the body’s needs even without haemoglobin, hence why it is used in CO poisoning.
The other problem has to do with air density. At 30m the increased density and airway resistance results in maximum voluntary ventilation being half of surface level. There is also a tendency for CO2 to be retained due to increased partial pressure and so oxygenation is poorer, plus dead space effects in the lungs all means the computation is not straightforward. For these reason diving tends to be ventilation limited rather than O2 availability limited.
Ps, noticed @Bored chemist replied while I was typing. Agree, CO2 retention in haemoglobin is an issue as I mentioned plus ventilation resistance means harder to empty lungs - greater dead spaces.