Freediving and O2 toxicity

[Billextreme]

Trux,

Will the DRUM system help a freediver that got caught by fishing net that is strongly attached to the bottom somehow?

/B

 

[trux]

Trux,

Will the DRUM system help a freediver that got caught by fishing net that is strongly attached to the bottom somehow?

/B

You best ask Seb, but I guess that in such case there would not be a too great difference between DRUMS and and a counterweight system. You could also use both DRUMS for the routine safety at each dive, and the counterweight system as a backup if DRUMS fails for some reason.

EDIT: However, the disatvantage of DRUMS is that it may pose an additional risk of tangling if used together with a descent line - I believe Sebastian Murat does not use any descent lines. So if there are too many lines (descent + DRUMS + counterweight), it might cause a nasty mess easily.

 

[Fondueset]

Just subscribing. Carry on.

 

[efattah]

The NEPTUNE system offers all the advantages of the DRUMS system with no risk of tangling. Its only drawback is the cost and size/weight.

 

[trux]

The NEPTUNE system offers all the advantages of the DRUMS system with no risk of tangling. Its only drawback is the cost and size/weight.

Eric, do you have any links or other references to that system?

 

[Erik]

Here it is.

 

[trux]

Back to the topic - the oxygen toxicity:

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.

Sam - I wasn't aware that you could carry 02 loading over multiple days...

It is actually not the case Sam describes. Saturation of oxygen is not an issue - oxygen is being consumed pretty quickly even if dissolved in body liquids under higher pressure, so unlike at nitrogen, there is no concern about oxygen saturation. However, repetitive diving in the same day or over the period of several days is still an issue. Not because of the saturation, but because of the depletion of antioxidants. Eric Fattah already mentioned it earlier in this thread. Although the oxygen toxicity is not yet fully understood, it is relatively clear that it is caused by the production of free oxygen radicals. If your body antioxidants are depleted due to higher exposure to free radicals (which is the case in the depth), you may suffer oxygen intoxication even on the surface while breathing atmospheric oxygen.

You can read some information about oxygen toxicity and free radicals for example here: Pulmonary Oxygen Toxicity

Gerschman and Gilbert were the first to propose that oxygen toxicity is caused by the production of free radical intermediates in excessive concentrations during exposure to increased oxygen pressures. The initial involvement of these agents is now well established, and several excellent reviews have summarized the literature on the biochemistry of oxygen free radicals. Although exact mechanisms are not yet known, free radical intermediates including superoxide anions, hydrogen peroxide, hydroperoxy and hydroxyl radicals, and singlet oxygen are potentially toxic to cell membranes, enzymes, nucleic acids, and other cellular constituents. Along with better understanding of oxygen free radicals has come a greater awareness of the dependence of vital biologic processes on cellular antioxidant defenses such as superoxide dismutase, catalase, and the glutathione system. It is now thought that in the absence of these defenses, the same oxygen pressures required to sustain life would cause lethal oxygen poisoning.

 

[fpernett]

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

PpO2, exposure time, metabolic rate and PpCO2. They can't conclude at the end, if the equation is useful for humans, because metabolic rate and PpCO2 data were mainly from rats. The CNS toxicity in rats was the seizure threshold, which is unethical to do with humans. But in general, main determinants of oxygen toxicity were high PpO2 ( the mathematical formula to calculate risk with different PpO2 in the same dive is quite complex), at higher metabolic rate and higher PpCO2 there is more risk of CNS toxicity (at least in rats).

I don't think we can get conclusions, but lowering exposure time at maximal depth, lowering metabolic rate (which is possible) and a strong diving reflex, to keep pCO2 at lower values. FRC diving has many of this advantages, but I don't know (I don't think) that a measurement of metabolic rate had been made.

For those interested in the articles, send me a PM to send it to you.

 

[chrismar]

Perhaps the high CO2 levels you start the dive with, combined with the big lungs are a bit of a worst-case scenario for you, Dave. I guess you could start with FRC diving, but lets face it; your FRC is almost my TLC

 

[sheepeck]

Risk of oxygen toxicity is also higher if some medicines based on ephedrin and it's derivates (as Sudafed, decongestants, etc) are used. There some reported deaths of tekkies related to it. Also shortage of vitamine E could be a kind of trigger.

 

[marc25]

One stupid question,

do you think, the body can get used to oxygen toxity?
If yes, the symptoms of oxygen toxity should become less by the time.

Dave, have you thought about testing/simulating this in a pressure chamber?
I think some universities do research in pressure chambers and might be glad to do some research in this field,

kind regards,
marc

 

[trux]

The synthesis of antioxidant enzymes is reported to increase after long-term oxygen exposure, so it would help with the toxicity tolerance. See for example this articles: Oxygen toxicity and tolerance. (mentioning increase oxygen tolerance after long term oxygen exposure) or http://www.chestjournal.org/cgi/reprint/67/2/39S.pdf (discussing the influence of SOD antioxidant on the oxygen toxicity tolerance). On the other hand, regular deep freedives would be barely sufficient for stimulating such effect. The intake of antioxidant supplements mentioned by Eric Fattah may be more efficient. Also, the long term exposure to high oxygen levels may have also very negative side effects - besides others, it may have the exact opposite effect of hypoxic tents used by athletes to increase the hematocrit levels. So after taking an oxygen cure to increase your tolerance against the toxicity you could find yourself with lower capacity of hemoglobin.

 

[rogam44]

Also, the long term exposure to high oxygen levels may have also very negative side effects - besides others, it may have the exact opposite effect of hypoxic tents used by athletes to increase the hematocrit levels.

Here is a interesting document about EPO production after normobaric and hyperbaric oxygen breathing:
http://jap.physiology.org/cgi/reprint/100/2/512.pdf

High pressure oxygen is not healthy.

 

[jome]

This is an interesting paradox that comes with several questions. I guess most have assumed that breathing normobaric o2 would have the opposite effect.

So would a freediver benefit from it?
Obviously the increased EPO production could help performance, but even more importantly, EPO has a neuroprotecting effect that Dr. Balestra was more worked up about. How would all this affect oxygen toxicity? Could you indeed increase tolerance to it by breathing normobaric oxygen regularily? That could make sense if it's clear that it does NOT hurt your blood levels (but indeed the opposite). Does the increased EPO (and other changes) help in this regard? How much does having thick blood protect you from hyperbaric oxygen symptoms?

And would it be ethical? The magic letters EPO are a huge red flag - even if we talk about increasing natural EPO via "unnatural" means. That's big can of worms he's opened...

Personally I just find playing with pure oxygen too risky, no matter what the benefit there's always the side effects and too many unknowns. I appreciate the work, but I'm afraid people will read this wrong and soon we'll see beginners walking around with a can of o2 instead of doing proper training, looking for the shortcut that does not exist and hurting them selves in the process.

 

[trux]

Yes, that's indeed an interesting document! However, since the normobaric oxygen paradox is documented at short term oxygen exposures, while increased oxygen toxicity tolerance requires long term exposure, the question is how it would work together. A freediver playing with the idea of using oxygen (whether for the EPO generating effects, for improving the oxygen toxicity tolerance, or for decompression) has also take in view the negative effects of oxygen - besides the toxic effects, there are diverse hyperoxia pulmonary changes (influence of bronchiolar epithelium, secretory activity of neuro-endocrine cells, impact on the alveoli surfactant liquid, vasoconstriction of alveolar blood vessels, increased permeability of alveolar wall, increased pulmonary blood pressure - most of that with the consequence of higher risk of pulmonary edema).

As for the ethics of using oxygen for the EPO stimulation - I think it is about the same as using hypoxic tents, but I am afraid that the risks associated with the hyperoxic exposure may be more serious than at the hypoxic method. From this point of view I think the probability it will be commonly abused is not too high.

 

[unobreath]

One stupid question,

do you think, the body can get used to oxygen toxity?
If yes, the symptoms of oxygen toxity should become less by the time.

Dave, have you thought about testing/simulating this in a pressure chamber?
I think some universities do research in pressure chambers and might be glad to do some research in this field,

kind regards,
marc

The max pp02 to where CNS 02 toxicity is possible is different for a wet diver than it is a dry diver.
1.3-1.6 wet
2.6-2.8 dry (chamber)

Im kinda curious to know who was diving over 100m on standard air. This is just not possible as the partial pressure of 02 would be way to high. (depth in feet + 33 divided by 33 times percent of gas (i.e. .21 for amount of oxygen in standard air) 2.12pp02 that is extremely high.

plus the narcotic effect of nitrogen.

a lower percent of oxygen mixed with helium is used when deep diving is involved.

 

[Ulf]

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...

Apparently I have to enter at least 10 characters.

 

[ricki]

Never have come close to oxygen toxicity while free diving, haven't gone deep enough! Doing deep air SCUBA in my teens, different story. I think I suffered two bouts of it. The setup is markedly different from what happens in free diving but I thought I would toss it out just to highlight the symptoms in my cases.

The OT symptoms subtly evolved from those of intense nitrogen narcosis, starting with barely perceptible light headedness, air exhaust sounding silvery (low pass auditory filtering effect), tingling in extremities, increasing euphoria, fogged perception, lethargy, metallic taste and impaired motor control. All these symptoms would increase to very substantial degrees, I believe far more than might be obtained at the surface from alcohol consumption, thinking you would pass out first. I have long felt narcosis in my cases was more like being excessively drunk and fighting it to do something important rather than something pleasurable.

Anyway, with OT the first symptom I would notice would be tunnel vision through all that intense narcosis. Later on with continued descent perception would slowly dawn that my eyes were closed and yet I was still staring at a retinal image of the bottom. This happened twice to me about a year apart. So in my case the symptoms that I was able to pickup on were mainly optical. That is in addition to what I judged to be passing out in short order which was enough to compel me to ascend, fortunately. What motor impairment occurred was common enough with narcosis on dozens of other dives with no association to OT being identified (perception was heavily impaired of course on the OT dives).

I had no idea OT was an issue in free diving until coming across this thread. Be careful guys. I suspect this may have been an issue for deep exposure for sometime what has changed is ready communication and awareness development worldwide here. Excellent point about the solo and teams of deep air divers disappearing over the years and taking the story of what went wrong with them.

 

[unobreath]

Apparently I have to enter at least 10 characters.

That was on trimix not standard air.

 

[immerlustig]

@ unobreath:

Im kinda curious to know who was diving over 100m on standard air. This is just not possible as the partial pressure of 02 would be way to high.

i know several guys who do so on air (scuba).

also, i think you should have mentioned exposure time in your last post.

roland