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Hi David, > One other point on mixed gas diving: any deco stop on a lower % > mix than the diver was using (eg, switching from helium mixes to > nitrox, or nitrox to O2) is equivalent to a higher deco stop on the > original mix. That adds a rule to your schedule: if any Pyle Rules > stop is a mix change, make the change at the end of the stop. I'm not sure I understand - I would make the switch at the beginning of the stop, not the end. The deep stops have to do with bubbles (I think), and they are a function of ambient pressure, not inspired gas fractions. The inspired gas fractions have to do with rates of gas "offloading", not bubbles. Could you elaborate more on why you think the gas switch should be made at the end of the stop? (This > won't usually apply to caves, where "ascents" are more horizontal > than vertical, but also, since cave diving ascents ARE mostly gradual, > cavers are already following a nice substiture for your rules a lot of > the time. Cavers are pretty smart, except for the going into caves > part.) Agreed - on all points. > BTW part of the exhaustion that follows deep dives with minimal > stops might be that the lungs take a hit anytime there are bubbles in the > blood, because that's where they are trapped. Lungs don't have > nerves, but the damage leaks chemicals into the blood that shift > the brain into exhaustion and repair mode. Interesting stuff - I hadn't heard any of that before - can anyone else on the list confirm or deny? > Just thoughts. I'm an innocent in the woods (demographer), and > didn't give a thought to deco schedules not getting it quite right > until the nonsense about racing to deco stops on here awhile back > reminded me that the purpose of stopping is to keep partial gas > pressures in the tissues from getting too much above the gas > pressure in the blood. I think most people would say that the purpose of stopping is the keep the partial pressures in the tissues from getting to much above **AMBIENT** pressure, not partial pressures in the blood. No? > Your technique has to be right: coddle the > slowest tissue all the way up, fix the deco stop times to take care > of the rest. I look at it more as coddling the *fastest* tissues all the way up - but it may not even be about fast or slow tissues - it may be about bubble growth. > For the models, I haven't looked at VPM, but the *fix* to compartment > models is simple. The models need to lower the allowable difference > between the (inert gas) tissue pressure and lung-blood (ambient) > pressure more than they do for slow tissue. O.K., if you mean blood partial pressures as being equivalent to ambient pressure, I think I understand where you are coming from. But bubbles are kep small by the *ambient pressure* per se, not the partial pressures in the blood. You want to REDUCE the blood partial pressures as much as possible to maximize the gradient across the bubble surface (i.e., cause a net movement of gas out of the bubble and into the blood, where it can be purged from the body at the lungs). Thanks for the comments. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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