100% Oxygen

[Doppler]

A few years ago, several of us did some "experiements" where we cut our pure oxygen with "a squirt' of helium when decompressing from deep mix dives here in the Great Lakes.

The squirts of helium varied from about 10% to 15% and our reasons for diluting our oxygen included wanting to counter vasocontriction. We figured adding helium might offer better offgassing opportunities in those cool spots like hands and faces.

We also used helium in our 70 foot mix.

We didn't really go anywhere with the data we collected, and I still sometimes use an oxygen helium mix on the 20 foot stop, but can't say there's any proof this is beneficial.

My question is this: anyone seen any science to back up this practice.

Please refrain from telling me second or third-hand how someone else runs their deco. I have a pretty thorough understanding of bubble mechanics and a grasp of Brian and Eric's mathematical work with modern decompression algorithms. I understand the face of the algoritm and can produce decompression schedules on the fly, and have been using these methods during 10 years of "technical diving." So please no: "The only gases so and so endorse are..." postings. I'd like to hear from people actually doing the dives, rather than people reading about doing the dives... thanks


Doppler

 

[100days-a-year]

Those constraints will make this conversation short

 

[cast55]

I have been using helium in all of my deco gases except for the oxygen, for about four years now. Gases as follows:


190 fsw 20/40
120 fsw 35/33
070 fsw 50/25
020 fsw oxygen

If I had a booster, I'd probably go even higher on the helium. Feel better post dive, and on deeper gases the helium allows for a clearer head, which is not a bad idea at a gas switch. Granted, using helium in deco gases like this only makes sense if you use deep stops and accordingly aren't spending too much time in the intermediate stops.

I can't see cutting your oxygen with helium being a good idea. On the oxygen stop, you have really passed the point at which you're still trying to get rid of gas in solution, and are just pressing the gradient while maximizing the oxygen window - you need the highest possible oxygen concentration for this to be most effective, coupled of course with cycling low PPO2 breaks to maintain the effectiveness of that large oxygen window. I think that adding helium here would simply increase the intervals required between breaks, while doing little to actually get you out of the water faster. Vasoconstriction shouldn't be an issue, provided 1) you are switching to oxygen from a long enough interval on a low enough PPO2 that you are effectively coming off a break that was achieved on the previous gas, and 2) You insert back gas (or lowest breathable PPO2) breaks at frequent enough intervals, depending on exposure.

-Sean

 

[padiscubapro]

Doppler once bubbled...
A few years ago, several of us did some "experiements" where we cut our pure oxygen with "a squirt' of helium when decompressing from deep mix dives here in the Great Lakes.

The squirts of helium varied from about 10% to 15% and our reasons for diluting our oxygen included wanting to counter vasocontriction. We figured adding helium might offer better offgassing opportunities in those cool spots like hands and faces.

We also used helium in our 70 foot mix.

We didn't really go anywhere with the data we collected, and I still sometimes use an oxygen helium mix on the 20 foot stop, but can't say there's any proof this is beneficial.

My question is this: anyone seen any science to back up this practice.

Please refrain from telling me second or third-hand how someone else runs their deco. I have a pretty thorough understanding of bubble mechanics and a grasp of Brian and Eric's mathematical work with modern decompression algorithms. I understand the face of the algoritm and can produce decompression schedules on the fly, and have been using these methods during 10 years of "technical diving." So please no: "The only gases so and so endorse are..." postings. I'd like to hear from people actually doing the dives, rather than people reading about doing the dives... thanks


Doppler

There was a study done that recommended adding 4-6% helium into the oxygen mix.. I remember reading about it and it said it it had theoritical benefits.. I'll have too see if I can find it..

I can tell you something from personal experience.. I have done some quite long dives that had required extensive decompression at 20fsw.. I felt better when I stayed on my rebreather loop which was flushed to bring back the oxygen to 100% then the offgassing would drop the po2 and I would do the same over and over.. when I have used surface supplied oxygen for the same profiles (on my RB) I didn't feel as good .. It may be anecdotal but Its worth mentioning..

It probably has less strain on the lungs and allows for better gas transport.. @94% the po2 is 1.5 so you are still offgassing very efficiently and the gas marginally easier to breathe..

 

[Doppler]

cast55 once bubbled...
I have been using helium in all of my deco gases except for the oxygen, for about four years now. Gases as follows:


190 fsw 20/40
120 fsw 35/33
070 fsw 50/25
020 fsw oxygen

SNIPPED

-Sean

Thanks for the posting Sean:

I use similar mixes myself... well, actually, very similar mixes, and agree with you on the oxygen window and it's role... the genesis of our experiments really came from a desire to see if there was any change... and there didn't seem to be one way or the other. I just wonder about any cold water studies since there probably is some peripheral shut down due to bottom temperatures in the 40 degree range... and I've heard differing "science" on the effects of pure oxygen and vasoconstriction.

Frankly we were running modified Buhlmann type profiles back then and therefore were spending longer at 20 feet than we do now. With our exposures here in the frozen north now on VPM type schedules, we do not usually spend long enough on the oxygen deco to warrant more than a single break (bit of a generalisation but our bottom times are usually shorter than 35 minutes and most of the "tourist" wrecks are shallower than 250). And as I said, I rarely throw the helium in the O2 these days... still, was interested to see if there's anyone working in this area.

Thanks again.

 

[saturated]

Vasoconstriction, I do have a study that related the breathing of pure 02 at 2atm to vasoconstriction. I cannot remember the exact #'s but final abservations are as follows. While vasoconstriction does reduce blood flow, all conclusions are that because of the extra o2 in the system tissue oxygenation is not reduced. the tests were done on three High O2 mixes in a variety of age groups. The main difference in vasoconstriction occured by age group as opposed to mix(100%, 92%, 85%).

I personally would not add any HE to my 20'. For reasons as stated above and the reduced off gasing capabilities of a lower mix.

Pm me a mail address and will gladly send you a copy.(sory its in print)