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Hi Ian! The problem is really complicated if you look at, from not to the best side. I will not write about the (right but not the new one) diffusion decco model, but about benefits of breathing 100% O2 at 6m (20') rather than 3m (10'). If somebody does a decompression dive (long) at the end of dive he wants to make safety but as short as possible decco. If one in procedure of decco is low on nitrogen and helium and another inert gases so that his (calculated) ceiling is 6m (20') he will accent to 6m (20')a switch to max inert offgasing of course with 100% O2. Logical? Ok, after some decco time the concentrations of inert gasses are so low that he can continue his 100% O2 decco on 3m (10') with less or more the same speed off offgasing (there are some difference connected with PPO2). BUT IF HE IS CLEVER HE WILL NOT DO THAT. HE WILL STAY ON 6m (20') TILL THE END OF DECCO. Why? Simple, is he convinced that after part of decco his ceiling is 3m (10')? So it is calculated by program, but sensitivity to decco of the same diver can be much different regardless to many factors. Does the program know how you feeling or are you dehydrated ..? NO! So if his decco is critical regardless to shape of the diver, maybe he will get bent. So if he stays at 6m (20') he lower risk of getting bent not the breaking eventual deeper ceiling and has less or more the same speed of offgasing. This meaning if you want to do the decco with the same risk you can short it with not going to 3m (10')! If you look at this explanation little wider, you can see that this philosophy is nothing that application of DEEP DECCO STOPS. Why to accent to 3m (10') to irritate possibilities of bubble growing? Because of toxity benefit of 1.3 against 1.6 PP02? What is conclusion of this email? DOING DECCO ON 100% 02 ON 6m (20') IS THE RIGHT WAY. Viktor -----Original Message----- From: Ian Puleston [mailto:DiverIan@pa*.ne*] Sent: 4. januar 2001 3:39 To: techdiver@aquanaut.com Subject: ppO2 and off-gassing N2 Reading the stuff previously posted on the Oxygen Window - especially Bill Wolk's postings which are very helpful - it almost all makes sense, except that I can't quite understand why the high ppO2 in the blood helps the Nitrogen come out of the cells. I understand the advantages of 100% O2 over 80/20, but can't fully see why breathing 100% O2 at 20' is better than breathing 100% O2 at 10'. I accept that it has proven to be better, but would like to understand the theory as to why. Bill Wolk defined the Oxygen Window as used in diving theory as "the difference between the concentration of inert gas dissolved in tissue vs. the concentration of oxygen and inert gas in arterial blood". Breathing an elevated ppO2 forces extra O2 to dissolve into the blood plasma, in addition to that normally carried bound to Hemoglobin. So far I'm with the program. But what I can't see is how this additional O2 affects the N2 coming out of the tissues. When there is no N2 in the arterial blood anyway, why does forcing additional O2 into it make a difference? According to Henry's law the amount of Nitrogen that will dissolve into the blood is affected only by the partial pressure of the Nitrogen itself, so increasing the ppO2 will have no effect on that. A previous posting (which I can't find now, but I don't think anyone argued against it) indicated that increased ppO2 will tend to block the Nitrogen molecules from coming out of the cells by osmosis. The only beneficial effect of the additional O2 that I can see is that (again from a previous Bill Wolk posting) "the additional osmotic pressure forces O2 into the surrounding tissue, which has the effect of oxygenating tissue and reducing swelling and clotting -- essentially, healing the cellular damage caused by deco diving". Is that the only benefit of the higher ppO2, or is there something other way in which it aids off-gassing N2? Anyone care to explain? Ian -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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