Freediving and O2 toxicity

[Mullins]

I've mentioned before on here that some of the symptoms I get on deep dives sounded more consistent with 02 toxicity than with nitrogen/CO2 narcosis. I've just been on the phone with one of NZ's most experienced dive doctors, and what he had to say about it is quite worrying.

The symptoms I get include visual distortion (bright lights), a metallic taste, numb lips and tongue, and shaking that is mild through to moderate. I also feel depressed and emotional, as opposed to the euphoria that most divers report.

The doctor I spoke to thought that rather than being the result of nitrogen/CO2 narcosis these were classic symptoms of oxygen toxicity and that it sounded like I wasn't too far away from having a seizure. This is a very bad thing, as a seizure at depth would almost certainly be fatal. At 110m my pp02 would be around 2.5 assuming no oxygen consumption on the way down. Not a great deal of oxygen would be used on the descent, so it is possible my pp02 would still be close to 2 even when consumption is allowed for.

Now, I know several divers have gone deeper on sleds. However they were not exercising during their dives. Also, the problems nolimits divers encounter often don't seem to be made public so who knows.

Anyway, based on this advice I'm taking a look at how I can reduce the risk when doing deep CW dives. The first thing is probably to minimise my time at depth. This is easier said than done, because I do things pretty slowly when narked. I could also dive lighter and consume more oxygen on the way down, but that would mean a slower glide and more time spent at depth... so there is potentially a tradeoff there.

I don't mind getting narked and I can live with the risk of hypoxic blackout because we have safety divers. DCS we can manage with oxygen and a limited ascent rate. Lung squeeze you can avoid, or at least survive. Fine. But 02 toxicity is a lot more scary because it is unpredictable and if it occurs, you're not likely to come up alive. Unconscious and inhaling water at 110m does not make for a good prognosis even with a counterweight in place.

 

[efattah]

I also had many symptoms of O2 toxicity including the metallic taste and so on.

From research I did on 'deep air' scuba divers, it appeared as though the nitrogen offered a protective effect, such that a seizure seemed extremely unlikely. In particular, no deep air scuba diver has ever reported a seizure, even at 160m+ on regular air.

That doesn't mean it couldn't happen to a freediver, of course.

I'm uncertain if CO2 level has an effect on O2 seizure. I do remember a navy study that found that fasting provided a protective effect against O2 seizures.

One problem with O2 at high concentrations is that it creates a massive increase in superoxide anions, which are toxic. Your body uses superoxide dismutase (SOD) to neutralize the superoxide ions. One approach to increase protection would be to taken sublingual SOD, or some other particular antioxidant known to neutralize superoxide ions. The concentration of superoxide ions is thought to be linked to seizures.

It is likely that an FRC dive would produce a less toxic O2 level, though it could still be quite high. That's another approach.

 

[Mullins]

I was hoping you might say something like that Eric. Looking forward to meeting you and Pete in the Bahamas.

1. who was the crazy bastard who went to 160m on air??

2. an FRC dive involves very little 02 consumption on the descent, which might mean the pp02 still gets high?

3. if you don't mind saying, are you using FRC for all your deep dives these days?

 

[efattah]

There are many scuba divers who have done 140-162m on air, though not all dives were considered 'official' (sound familiar?) The infamous Mark Ellyatt was one of them.

An FRC dive is closer to the analogy of dynamic apnea, where even with low consumption, O2 levels drop linearly with time. The constant weight version is a bit different, since there is clearly some degree of hyperoxia.

As an example, when I did that 30.5m full exhale dive a few years ago, I was already slightly hypoxic when I reached the bottom and I could feel it, even despite the high partial pressure.

All my dives these days are FRC, and that's how I will dive in the bahamas, but I'm still playing catch-up against the classic style/packing divers. The 'catch-up' process could take years and years, but it is my firm belief that packing divers are going to run into some sort of insurmountable hazard around 120-130m, and that taking less air down maybe the only solution -- although it provides a painful penalty.

 

[jome]

I guess the coke bottle Herbert uses is helping a lot in this regard. Not much consolation to CW divers though. I don't think there's much we can do except reduce the amount of air and thus hopefully the probelms? Huge mouthfills and big but flexible masks might relieve a little? Let's say you put 0.5l in both at -30 - that would equal 4L NTP air. Especially if you did wet equalization, you'd simply use your mouth and mask as an "air sack", soft of like penguins do.

I must say that on my deepest dives, I've felt things very similar to what you're describing. The most obvious is the metallic taste and numb tonugue/lips.

I do also think that divers are "asking for it", as Eric put it, the limit is approaching, where toxicity/narcosis problems will start putting a limit on dives. Yeah, someone will say "but remember Enzo, all the doctors were wrong!", but I'm still afraid that it will happen if there isn't a radical change of paradigm in deep dives. We'll see...I don't mean to say world records cannot surpass this, merely that it is likely to be the next big hurdle to overcome.

It would be nice to have more information and experiences from the deep No-Limits divers. What I've heard are mostly rumors, but some of them really disturbing - for example complete loss of vision.

When will we see safety equipment that inhibits involuntary inhalation? Think of Hannibal Lecter type of mask that diver wear and the locks are opened only after they surface. Would make for a nice surface protocol as well

 

[Billextreme]

What I know, The WR on air-scuba is 156,4 meters by Mark Andrews, an English diver. He said there was big red elephants running around down there...

 

[..Sam..]

Also don't mean to worry anyone that has had these symptoms but a few of the other things that can happen with O2 toxicity or central nervous system toxicity as I think is its other name, is convulsions, visions, euphoria, nausea, tinnitus, irritability, dizziness. I got this out of a TDI (technical divers international) nitrox manual for scuba. The max pp02 for divers is 1.6 and only for 45minutes, with a max 150 minute over 24 hours. The reason you may be getting these symptoms if you are doing repetitive deep dives to say a pp02 of 2.5 or even 2 over 24 hours even if you don't have a long loading time. Dave I was watching your video from Dahab and you said something about doing 90 then 95 then 100 over three days now that may lead to a high CNS loading which works the same as nitrogen loading (just the build up of nitrogen) which gives us no deco limits and so one. You may have simply over done your o2 limit.

Just for anyone that doesn't scuba dive or doesn't know about nitrogen loading and so on i'll just explain what i know. Ok here goes.
When we dive and breath at 30m (4ATA) for say 20mins (the no deco limit) we would gain a certain amount of nitrogen into out systems. Now if I wanted to do a second dive to 30m after say an hour I would only have 10minutes on the bottom due to the already accumulated nitrogen.

Same with oxygen, you can only have so much over so long at pressure.

Hope this has helped in some way Dave, just ask if you want to know more. Or if i made a mistake....

Cheers,
Sam:friday

 

[sheepeck]

Oh my ...
Oxygen toxicity while freedive!! I guess I'll use that as excuse for not going deeper then 35m.

BTW - here is article about deep-air dive:

http://www.cisatlantic.com/trimix/text/wahwah.txt

 

[dave]

From research I did on 'deep air' scuba divers, it appeared as though the nitrogen offered a protective effect, such that a seizure seemed extremely unlikely. In particular, no deep air scuba diver has ever reported a seizure, even at 160m+ on regular air.

One of the probable reasons for no deep air scuba diver reporting an o2 seizure is that most deep air scuba dives are carried out solo with no safety divers. Anyone having a seizure in those circumstances is not going to be able to report it as they will be dead.
There are plenty of cases of air divers "disappearing" on 100m + dives, and lots of records from the 70s of mysterious "depth blackouts" on deep air cave dives in Florida and the Bahamas.

cheers
dave
Spearguns by Spearo uk ltd finest supplier of speargun, monofins, speargun and freediving equipment

 

[Erik]

A side note, but I believe the usual reaction to O2 poisoning (initially) is to not inhale. Once the PO2 drops to a safe level or CO2 gets high enough, then respiration returns. Correct me if I've forgotten something.
It wouldn't matter much if there was nobody to bring you up, but if you were on a counterweight system, you'd probably make it back as nobody would let you rest on the bottom.

 

[..Sam..]

I think CNS toxicity sort of sneaks up on you....before you know it your convulsing and your airways close. Not so bad when your freediving....you can just be swam up same as a black out but you really need good safety divers. You can't be swam up by a guy on scuba from 100m. Unless you have a recompression chamber handy....

 

[Mullins]

Erik, that's very much on the topic. If the response to a seizure is not to inhale, then yes a counterweight system would probably work fine. Ideally you'd be triggering it shortly after the diver is scheduled to leave the bottom so it follows them up.

Interesting article Sheepeck, at least I haven't heard the 'wah-wah' sound yet!

Sam - I wasn't aware that you could carry 02 loading over multiple days. In Egypt I did 90m then 95m on consecutive days, then had a rest day before the 100m dive because I got sick. I also spent ages at depth on that dive, which would have made the symptoms worse. I did get most of the symptoms I listed on my 110m dive, minus the shaking (I think) but I'd had 2 days off beforehand. My 106m dive was the cleanest I'd ever done, I just got the 'normal' dizziness without the metallic taste, shaking etc. It was a fast dive, and I'm thinking this is the way to go. Unless I join Eric in FRC-land of course.

The initial conversation I had on this topic was probably one you're all familiar with. I rang a local dive shop that runs trimix courses and told one of their instructors what I was experiencing, asking him whether he thought that sounded like N2/CO2 narcosis or elevated 02 pressure. The conversation that followed included statements like: "Yes, I am snorkelling to a hundred metres. Now can you tell me what you think about the symptoms please?" Despite clearly not believing a word I said he was nevertheless quite helpful and gave me the number of the local Naval Hyperbaric unit. Good bloke - if I was called by somebody I thought was a nutcase I'd have been much shorter with them.

I am going to get back in touch and find out if there are people in the medical/diving world who might be interested in testing this somehow. I have no idea how realistic this is, but I'll chase it up anyway to find out. I'm sure the risk of seizure is rather low at the depths we are currently diving to, otherwise it would have reared its head long ago in VW or Nolimits dives, or other CW divers. However if it ever does happen it will be pretty nasty, so it's one knowledge gap I'd like to see filled.

 

[trux]

... If the response to a seizure is not to inhale, then yes a counterweight system would probably work fine...

Well, starting to pull in the same time the diver starts ascending is exactly what Seb Murat does with his DRUMS safety system, but I did not know common countreweights are routinely triggered shortly after the scheduled bottom departure at every dive.

 

[Mullins]

Yeah Seb's system sounds like a good one and I know a few people have mentioned pre-emptive counterweight triggering in the past, although I don't think it's been put into practice often, if at all. Pain in the ass resetting it each time but excellent from a safety perspective. I expect it will become a necessity as CW gets deeper.

p.s. our local freedive training company NoBubbles is going to invest in an electric winch for the counterweight platform (which is a converted catamaran), which might make it less hassle to drop and reset the counterweight.

 

[fpernett]

My readings on this subject were few, but after a short query found 2 papers from Israel Navy about the subject, and there is a equation to predict toxicity (it works better on rats than humans). I also think that symptoms are not specific for O2 toxicity and can be a mix of things: N2 narcosis, high pressure, low temperature and O2 toxicity. At low metabolic rates there is less risk of CNS O2 toxicity, and that can be the explanation for not having a lot of seizures in deep divers. As the approach to deep dives is to have a long glide to bottom, in CWF the freediver starts the exercise at maximal depth, but the PpO2 starts to fall from there.
I had the 2 papers for the interested ones.

 

[Mullins]

Thanks Frank - without going into too much detail, what were the main variables in their equation?

 

[fabrice]

Yeah Seb's system sounds like a good one and I know a few people have mentioned pre-emptive counterweight triggering in the past, although I don't think it's been put into practice often, if at all.

Loic Leferme's team was using such a pre-emptive counterweight on deep dives. No reset issue since this was not serial diving.

 

[trux]

Loic Leferme's team was using such a pre-emptive counterweight on deep dives. No reset issue since this was not serial diving.

Now the question is if it was not what killed him in fact. At Seb's DRUMS, it is the operator of the device that watches the tension of the line and starts pulling when the diver turns, but if the initiation of the counterweight is triggered on a calculated schedule, it may cause more troubles: imagine the diver is slower than estimated (i.e. due to longer than usual equalization), blacks out on the descent (or the ascent), or gets stuck somewhere on the way. When the counterweight is initiated and he is not at the bottom plate, the rapidly ascending base will likely hit him, possibly injuring or knocking him out, ripping off the lanyard, or tangling and blocking (that's what may have happened in Loïc's tragic attempt).

The problem with current counterweight systems is that they are usually tested only with the freediver at the bottom plate, where they indeed work fine, but on my mind they are not really well suited for saving a diver anywhere above the base. From this point of view, Seb's DRUMS is much safer, on my mind.

 

[TRITON]

It would be interesting to hear Herbert's experiences with o2 toxicity as he has done many dives over 90-95m.

 

[bubbleless]

I had the 2 papers for the interested ones.

Frank, I would be keen to see these papers