Quote:
Originally Posted by getawayFK
Anyway, within your lung, there is a residual volume and within your whole respiratory system there is also whats called "dead space". You can't use whatever volume is in there as the residual volume is simply the amount of air left after a forceful expiration so that your lung doesn't collapse and the dead volume is the volume that air will occupy at any time in your respiratory system. Residual volume can greatly varie (e.g: in asthma or COPD it can occupies up to 60% of your functional volume) etc...
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I think you misunderstood my comment, GetawayFK. I did not speak about the residual lung volume. I was speaking about the gas exchange in lungs during a prolonged apnea and about O2 remaining in the air held by lungs (and not just in the residual volume). Quite oppositely I referred to the state when you have your lungs filled to the maximum or even over it (by packing / glossopharyngeal insufflation).
I meant the late state of apnea when the level of O2 in the air in lungs drops to low level. In this state the ability of Hb to bind the remaining O2 drops too because the difference of PaO2 in blood and in the gas contained in lungs is insufficient for efficient gas exchange. The effect is further amplified by the lower binding of Hb due to high acidity (high CO2), which on one hand facilitates unloading of O2 for consumption in tissue, but on the other hand it makes it difficult to bind any O2 from the air in lungs if the PaO2 gradient is not sufficient for efficient recharging. I repeat that I do not speak about the well studied and documented cases of altitude adoption - there, due to the continual ventilation, the level of O2 in lungs remains the same, so 2,3-DPG indeed has positive effect, because it facilitates O2 unloading, without significantly impacting the recharging.
However, in the moment there is no ventilation (as it is the case in a long apnea), the PaO2 in lungs permanently drops (and PaCO2 raises), making it more and more difficult for Hb to use the remaining O2 gas in lungs. And I assume that due to the 2,3-DPG's property of stabilizing the de-oxygenated state of Hb, this situation comes earlier (at higher O2 levels in air of the lungs) than it would be the case with just normal/low 2,3-DPG level.
So in fact, although 2,3-DPG is quite beneficial for altitude or hypoxic adoption with continual ventilation, I suspect it is not the case for breath holding. Fortunately, the increased 2,3-DPG is not the only part of altitude adoption - I believe that for breath-holding the increase of hemoglobin is much more important, since it increases the O2 binding capacity without increasing the minimal O2 level for efficient gas exchange.
