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Hi Scott, I didn't mean to be cryptic in my previous question, but I'm really having a tough time grasping on to this concept that a high PP(O2) in a deco gas helps with the off gassing of nitrogen. I of course understand how a low PP(N2) helps. But I don't understand why a higher PP(O2), say for the same PP(N2), would aid in accelerating decompression. Am I incorrect in thinking that this is what is being inferred with the concept of the "oxygen window"? Or maybe I've just got the whole thing screwed up simply because of the name "oxygen window". If this name means the same thing as "maximum differential PP(N2) between tissue PP(N2) and deco gas PP(N2)", then I have no problem. But I get the impression that there is more to it than that, and this is where I get stuck. In your explanation of the oxygen window to KRussellTX@ao*.co* you said <<The oxygen window refers to a variation between the partial pressures of oxygen on the arterial and venous sides. >> That's why I assumed you meant the difference between the PP(O2) in the blood in the left atrium and the blood in the right atrium of the heart. I guess that assumption was not too good. So I'm still in a quandry as to what exactly is the definition of the "oxygen window". You also mentioned << It comes into play when we have saturated the hemoglobin with O2 and are forcing O2 to dissolve into plasma, which is also used. >> Now I have no training in internal medicine other than first aid, and I really don't understand about O2 dissolving into blood plasma. Is this just a simple example of Henry's law at work? (Henry's law I understand.) You then followed with the statement << Assuming a resting workload and continued cardiac output, O2 demands should stay the same which will allow the dissolved levels to climb, to a point that is dependent on pressure, as long as O2 is being breathed. >> From this I would definately infer that you are referring to a Henry's law phenominon. You then continue with << The O2 window should become set at pressures higher than we should see during safe decompression PO2's. >> Now I believe I am following your reasoning. I think you are saying that it would be better to have even more oxygen dissolved into the plasma, but the PP(O2) that would be required in the deco gas needed to accomplish this, would need to be too high (unsafe). And then you finish the explanation with << The goal is to come as close to this "window", as well as the "curve", as possible to maximize the physiological benefits of decompression. >> And unfortunately I am completely lost again. Does this "window" refer to the amount of oxygen dissolved in the plasma? Or is it the PP(O2) in the breathing gas that gives rise to this level of oxygen dissolved in the plasma? It is not clear to me. And unfortunately also, the definition of the "curve" you refer to is not clear to me either. And finally my basic question, the one I tried clumsily to ask previously, remains exactly what is the relationship between this level of dissolved oxygen in blood plasma (if that's what the "window" is), or the PP(O2) in the deco gas that gives rise to it (if that's what the "window" is), and the rate of off gassing of nitrogen. I'm just having a lot of difficulty following the concept. Let me try to ask my question in a slightly different way. If I weren't worried about oxygen toxicity (this is just a fictious example here), then I get the impression that the theory is that deco'ing on 100% O2 at 30 feet or forty feet would be more efficient at offgassing nitrogen than deco'ing on 100% O2 at 20 feet. Is this correct, or am I all screwed up again? I know I've asked a lot of questions, but I've been really trying to get a hold of this "oxygen window" thing for quite a while. And I'd appreciate any help you might be able to provide. Take care and safe diving, Scott In a message dated 8/27/00 10:44:10PM, swhac@pc*.gu*.ne* writes: Karl, >I have been reading in this group how 80/20 is not the gas to use for deco. >I have also been reading that Decoplanner is great and EAN50 @ 70 ft. and 100 >% oxygen at 20 ft. is the DIR way to go. The merits of DIR have been, and are being discussed, by many people and these lists and therefore will not be part of this discussion. I will only say that these principles work in the most extreme diving conditions you can imagine, they make dives possible that only a short time ago were thought impossible. If these principles, and all that go with them,far beyond what you read about on the net, work here, imagine what they can do for simpler dives. > In truth I haven't got the >slightest idea what the "oxygen window" means unless it simply refers to >using the closest PO2 that is below 1.6 that you can get to. The oxygen window refers to a variation between the partial pressures of oxygen on the arterial and venous sides. It comes into play when we have saturated the hemoglobin with O2 and are forcing O2 to dissolve into plasma, which is also used. Assuming a resting workload and continued cardiac output, O2 demands should stay the same which will allow the dissolved levels to climb, to a point that is dependent on pressure, as long as O2 is being breathed. The O2 window should become set at pressures higher than we should see during safe decompression PO2's. The goal is to come as close to this "window", as well as the "curve", as possible to maximize the physiological benefits of decompression. >Now the question I have to ask is that if 80/20 is only used by strokes, why >is it that on a dive to 200 ft. on 18/35 for 30 minutes, doing a deco using >EAN 36 @ 110 ft. and EAN 80 @ 30 ft. actually results in a shorter deco than >EAN50 @ 70 ft. and 100% oxygen @ 20 ft.? I have run the same dive mentioned above and do not get the same results that you have obtained. I also ran several other dives along the same line and with different, but still appropriate gases, and saw an average of four minutes saved by using 50 and 100. Remember that deco programs are nothing more than an easy way to do the mathematical computations that should provide us with a safe time needed to avoid DCS. The reality behind the physiology, which varies from day to day, is often different than what we obtain from such calculations. Four minutes are neither here nor there and are truly inconsequential. The most appropriate approach is to understand the mechanics and the physiology of what is happening to us on a cellular level, and to use that knowledge to achieve the best outcome down to the cellular level. >Any explanations why the stroke mix seems to get you out of the water sooner? As was mentioned before, albeit in slightly different terms, the goal is not necessarily to get out of the water sooner (when we are only talking minutes) but to do the correct amount of deco as well as to simultaneously reap all of the physiological benefits while subsequently reducing the physiological damage. One must consider the damage that this activity can reap on cells and think in a long term fashion in order to reduce damage and hopefully be problem free when we are all chasing each other in wheelchairs and screaming over the hum of our hearing aids. Sincerely, Scott Hunsucker BTW the N2 comment in your last post did not take into consideration that once we stop breathing from a reg we are no longer under pressure and therefore N2 is no longer a concern. There is a small amount of N2 that is dissolved in our tissues all of the time, but breathing N2 at the surface will not get you bent. In a message dated 8/27/2000 11:33:35 PM Scott Bonis@ao*.co* writes: In a message dated 8/27/2000 10:44:41 PM US Mountain Standard Time, swhac@pc*.gu*.ne* writes: << ...The oxygen window refers to a variation between the partial pressures of oxygen on the arterial and venous sides. It comes into play when we have saturated the hemoglobin with O2 and are forcing O2 to dissolve into plasma, which is also used. Assuming a resting workload and continued cardiac output, O2 demands should stay the same which will allow the dissolved levels to climb, to a point that is dependent on pressure, as long as O2 is being breathed. The O2 window should become set at pressures higher than we should see during safe decompression PO2's. The goal is to come as close to this "window", as well as the "curve", as possible to maximize the physiological benefits of decompression. >> Hi Scott, Thanks for the discussion of the oxygen window. But there is still one piece of the puzzle that I'm having trouble understanding, and perhaps you might be able to help. Exactly what is the relationship of this condition of forcing excess oxygen into the blood in the left atrium, and the off gassing of nitrogen from the body? It is not clear to me how this works and moreover how to quantify the increase in gas exchange rates. I'd really appreciate any light you can shed on this situation. Thanks a lot. Take care and dive safe, Scott In a message dated 8/28/00 6:29:15 PM, swhac@pc*.gu*.ne* writes: << >Hi Scott, > >Thanks for the discussion of the oxygen window. But there is still one piece >of the puzzle that I'm having trouble understanding, and perhaps you might be >able to help. Hopefully. I will be short at this point, there is a lot to do tonight. Perhaps more later if needed. > Exactly what is the relationship of this condition of forcing excess > oxygen >into the blood in the left atrium, and the off gassing of nitrogen from the >body? There is not more oxygen in the blood in just the left atrium. (The phrasing of your question was a little confusing so if I am off let me know). The hemoglobin is totally saturated with O2, normally the amount is around 97%, but rises to 100% with increased PO2. If we continue to breath O2 it has to go somewhere so it dissolves into the "liquid" part of blood mainly plasma. Once this process has started it will continue to dissolve until a point that it to can take no more (we should not see this and live though it in the water). The body will use the O2 that is dissolved in the plasma first then use what is in the hemoglobin. You should have learned in a basic nitrox class about O2 helping to off gas N2, the higher the concentration of O2, and subsequently the lower the N2, the better the off gas. >It is not clear to me how this works and moreover how to quantify the >increase in gas exchange rates. Not clear how what works? The off gassing itself? Or the increase because of the higher O2? If you understand the first just amplify the effect and you will have the basics of the second. >I'd really appreciate any light you can shed on this situation. I hope that I have at least helped. I would be happy to provide a little more if this as not done it, but it will take me several days to get to it. Sincerely, Scott Hunsucker >> -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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