Freediving on 36-40% O2

[amatsumoto]

After reading about SWB being the number one pressure related injury to snorkelers, I'm thinking about trying EAN 36 or EAN 40 to prevent SWB and maybe increase my bottom time.

As I understand it SWB is caused by a rapid drop in pO2 as the freediver ascends. Because pO2 is increased at depth, it may be possible to feel like you have enough air (low CO2 saturation) at depth but cross the critical limit as pO2 drops causing unconsciousness.

What if instead I free dived with 36 or 40% O2, instead of 21% air? I think I would feel the urge to breathe far earlier than my oxygen reserves burn out even on ascent because the accumulation of breath-reflex inducing CO2 in my tissues will still accumulate at the normal rate. I may also be able to increase my bottom time.

In any case it seems to me that freediving on enriched air will help me stay safe as long as I follow the MODs for 1.4 ata pO2.

This is what I'm thinking, but I'd really like to hear some constructive comments / criticism about what might happen freediving on enriched air.

 

[trux]

This exact topic resurfaces repetitively on DB, so make sure you have read the previous discussions before doing any attempts. Especially the comments of Eric Fattah are worth of reading. Replacing Shallow Water Blackout with Deep Water Blackout is probably not the best idea.

http://forums.deeperblue.com/freediving-training-techniques/27838-breath-holding-nitrox.html
http://forums.deeperblue.com/freediving-training-techniques/57274-freediving-nitrox-40-o2.html
http://forums.deeperblue.com/general-freediving/62175-nitrox-swb.html

 

[amatsumoto]

Thanks trux, I'll check it out

 

[Mullins]

The main risk that keeps coming up in those discussions is that of CO2 blackout. I think it would be a risk only if you dived much, much longer/deeper than you would normally (after all, CO2 production would be at the same rate). The only substantial reasons I can see to avoid nitrox freediving are:

- CO2 blackout if you push really, really hard (low probability but very dangerous if it happens)
- very difficult to judge subjectively how much time/distance you've got left

I think O2 toxicity would be a non-event with nitrox unless you go very, very deep. You use a fair bit on the way down, and the bottom time (which the dive docs tell me is a bit factor in O2 toxicity) is relatively brief.

Any other forseeable problems?

 

[trux]

Well, yes, there are other problems too - first of all the higher PaO2 has great influence on the dissociation of CO2 from blood. It means it will also increase the level of CO2 in lungs, which will be then higher than at normal dive of the same length, and have impact on the pH, hence also on the Bohr curve, and on the tolerance against hypoxia - it will act similarly as hyperventilation. It will not only mess up with the urge to breath, and with the Diving Reflex, but will also lead to a lower threshold of hypoxic blackout. Also, the higher level of CO2 in lungs can have toxic effects.

And since the freediver inhales the Nitrox on the surface prior the dive from a regulator, he would tend to make several deep breaths - that would lead to a hyperventilation much stronger than at the same level of inhales of plain air (thanks to the high PaO2). It could actually lead to a rapid blackout already during the immersion or shortly thereafter.

I would definitely avoid experimenting with it without the surveillance of medical experts. On the other hand, some deeper scientific studies on this topic would be interesting. There may be much more in play than we think.

 

[trux]

Then I also believe, although I did not see it documented anywhere in scientific studies, that at freediving, high CO2 can cause DCS similarly as Nitrogen. In scuba and tech diving, it is well known that high CO2 amplifies nitrogen narcose and DCS, but usually it is not considered itself to be the gas creating bubbles in blood. Personally, I would not exclude that possibility at all, especially at higher than usual levels of CO2. In contrary, I'd suspect CO2 plays more important role in freediving DCS accidents, than we currently recognize.

 

[Mullins]

Aside from the risk of BO at the start of the dive, the Bohr effect only really becomes a factor when the diver is fairly hypoxic. By that stage presumably the ppO2 has dropped a great deal, meaning that blood CO2 has been able to rise, bringing O2-haemoglobin affinity back to normal(ish) levels? I suppose it depends whether the decrease in O2-haem affinity stays ahead of hypoxia, if you know what I mean. Just about impossible to say without actually testing I suppose, anybody want to be the lab rat??

 

[trux]

Yes, that's correct, but I mean that everything will be messed up, and out of normal, and there are many more factors involved, so unexpected things can happen. Breathing Nitrox can perhaps work fine, but your body signals are messed up, your body behaves differently, and you do not know what your limits really are. So in the time you start pushing, an accident can happen easily. And additionally it will also mess up your habits in plain-air diving, so once you come back to standard freediving, you may get into troubles quicker too. So Nitrox freediving may be interesting and may work, but because it is more or less Terra Incognita, and we do not know exactly the limits and risks, increased safety measures and extreme vigilance would be needed.

 

[Mullins]

Absolutely - it's the messed up body signals I'd be particularly worried about. I'd give it a go in controlled conditions just to see how the theory played out, but it's probably more trouble than it's worth with regards to practical application.

 

[efattah]

I have done quite a few dives on enriched air, but I have never tried going deeper than 10m for safety reasons.

However, it is quite easy to do a 6 or 7 minute recreational dive in the 7-10m zone even with no packing. Contractions come pretty early, but you can take them forever. After several minutes of contractions, my body starts to shake from CO2 and I get a weird dizzy feeling. Eventually the shaking becomes so strong that I come up for air. Sometimes I get a CO2 headache after. The required surface interval is ENORMOUS due to the massive CO2 build up.

Please don't try this yourself! So far I was mostly doing these shallow high O2 dives as a 'fun' way to do recompression after deep dives. I figure I might as well enjoy myself during deco. Where we dive the shore is so close to deep water that we can do recompression dives on the wall.

 

[JennyWren]

I have done quite a few dives on enriched air, but I have never tried going deeper than 10m for safety reasons.

However, it is quite easy to do a 6 or 7 minute recreational dive in the 7-10m zone even with no packing. Contractions come pretty early, but you can take them forever. After several minutes of contractions, my body starts to shake from CO2 and I get a weird dizzy feeling. Eventually the shaking becomes so strong that I come up for air. Sometimes I get a CO2 headache after. The required surface interval is ENORMOUS due to the massive CO2 build up.

Please don't try this yourself! So far I was mostly doing these shallow high O2 dives as a 'fun' way to do recompression after deep dives. I figure I might as well enjoy myself during deco. Where we dive the shore is so close to deep water that we can do recompression dives on the wall.

I should come out diving with you sometime, this sounds like a good way to get some nice photos (before the shakiness sets in, of course).

 

[amatsumoto]

I'm an experienced Scuba diver, but as far as serious freediving goes I am fairly new. As of now I think I'm CO2 limited as far as how long I can hold my breath goes. I can take a little discomfort, but usually turn back soon after.

From efattah's post I assume contractions are caused by increasing CO2 concentrations. I would like to know what a contraction feels like as I'm not sure I've ever felt one. Is there significant discomfort before contractions occur? I suspect I may usually surface before feeling contractions. My typical spearfishing dives last 1-2 minutes within a depth range of 20-60 feet (~7-20m). My static record sitting in a chair is 2:30. Is that long enough to feel contractions, and are they obvious?

I'm thinking that if contractions are caused by elevated CO2, then if I surface when I feel the first contraction I should be in the green (assuming I make it to the first). Of course this is speculation... I don't typically push my limits when spearfishing because I don't need to, but would like a little more safety and tolerance.

Also are there any other signs you consciously notice when CO2 levels are elevated (but not critical)?.

Thank you all for your thoughtful and well informed opinions.

 

[trux]

It looks like you did not give up the idea. Perhaps you should reread the posts - there are far too many known risks, and likely even more of unknown ones, to be worth of taking them, just for staying little longer underwater. As we wrote, if you decide freediving on Nitrox, you should only do it in presence of a doctor with CPR equipment and experienced freediving buddies capable to rescue you even in case of a deep water blackout.

And especially you should avoid such experiments if you are not really an experienced freediver, and do not even know to read your body signals properly. Eric Fattah is an extremely experienced freediver, ex world record holder, and experimentator, who tried probably more different methods and substances than all other DB members together, so please do not base your decision just on the fact he tested oxygen enriched freediving too.

If you really want to stay long time underwater, simply switch to scuba.

 

[amatsumoto]

I'll take the advice of your great wisdom and forget about freediving on Nitrox. Would you be so kind though to answer my newbie questions about contractions?

 

[trux]

You will get a much more detailed answer than I can give you, and more complete picture if you read through a few threads, already discussing contractions in details. Just go to the advanced search and enter "contractions" into the search field, and select "search titles only" to limit too many false hits (contractions are in almost every second post here on DB). You can also check out the first sticky thread in the beginner's section - terms like contractions and many more are well explained there too.

 

[amatsumoto]

Well I read some of the posts and figured there's no better way to find out than to try it out.

I relaxed and took long, deep breaths for several minutes then hyperventilated 3 times and held my breath watching Youtube. I zoned out as much as possible, absorbing myself into what I was watching (Whale evolution 1of5, haha). I timed my start with the video timer on the minute to see how long I could go. I astoundingly beat my old time of 2:30 dry static by over a minute @ 3:40! I also felt several involuntary contractions in my lower chest/stomach. I felt the first one, felt another several seconds later and they increased in frequency until I gave up. They are more subtle than I was expecting.

Another sensation I feel when I first inhale and hold is that of slight tingling in the limbs and lightheadedness. This sensation passes after the first 10-15 seconds or so but is this normal?

EDIT: I know, use the search function...sorry... Its new and interesting and I can't help myself. Will check it out.

 

[trux]

Hyperventilation is the exact opposite of what you need to do when you want to get contractions. You have to hypoventilate, or do a series of long breath-holds with very short recovery (i.e. just one breath). And you should definitely avoid hyperventilation when diving - but you will find that in every beginner's guide, so I guess you know it already. Tingeling and lightheadedness is the signal of heavy hyperventilation.

 

[TimoP]

. Just about impossible to say without actually testing I suppose, anybody want to be the lab rat??

Here is the answer of our ever trusty and courageous freediving lab rat :blackeye

I have done quite a few dives on enriched air... ...After several minutes of contractions, my body starts to shake from CO2 and I get a weird dizzy feeling. Eventually the shaking becomes so strong that I come up for air. Sometimes I get a CO2 headache after. The required surface interval is ENORMOUS due to the massive CO2 build up.
Please don't try this yourself!

It's for lab rats and EricF only!

I've heard this is really something MUCH WORSE that a BAD low-O2 black out:

So I do not recommend to test O2 static and specially O2 dynamic due risk of CO2 black out. CO2 black out is a scary thing. I have seen one and it is pretty difficult to rescue (tap, talk, blow or similar did not work).

 

[rnsaicic]

Several aspects of CO2 blackout remain ambiguous to me. If the urge to breath is driven by high pCO2, and not (to a significant extent) by low pO2, how comes that this urge is much less pronounced when breathing pure O2, or oxygen enriched mixtures (the production of CO2 should be the same)? I can speculate on two reasons: the first one is that there is no N2 in the lungs, so as O2 is consumed there is a plenty of space for receiving CO2 from the blood; if this is correct CO2 should be present in the lungs in the amounts much superior to those normally found there (otherwise the lungs would be empty at the end of apnea). Another conclusion would be that extremely high pO2 in blood diminishes the urge to breath stimulated by high pCO2. Does someone know more about these facets of diving on O2 enriched mixtures?
Radomir

 

[apneaboy]

What works to revive somebody after a CO2 blackout?
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