Short exposure tolerance to very high PPO2s.

[DrMike]

Advice is sought from those who have knowledge on short exposure tolerance to very high PPO2s.

The situation that I am seaking advice about is as follows:

A rebreather diver at depth has a loss of all on-board oxygen but has access to an off board Oxygen in a stage tank. The stage tank has a 2nd stage fitted but no way to plug the O2 into the rebreather.

I am trying to ascertain the level of O2 Tox risk to the diver if he adds oxygen into the loop via the off boards second stage ie by breathing a lung full (or part full) of 100% O2 from the stages regulator and then blowing that O2 into the rebreather loop.


The diver will be breathing in very high PPO2 for a single breath and holding it for a fraction of a second before blowing it into the loop.


I understand that O2 tolerance is in part a function of the exposure time as well as the exposure level. Does anyone have any data or actual experience on this subject?

For this example I would be considering 3 second exposures of PPO2 of up to 11bar, repeated at a frequency of once every 7 mins.


Note: Please no comments on using whips and QCs etc, obviously thats preffered - please limit discussion if possible to the question asked.

Thanks.

 

[Rick Murchison]

Advice is sought from those who have knowledge on short exposure tolerance to very high PPO2s.

The situation that I am seaking advice about is as follows:

A rebreather diver at depth has a loss of all on-board oxygen but has access to an off board Oxygen in a stage tank. The stage tank has a 2nd stage fitted but no way to plug the O2 into the rebreather.

I am trying to ascertain the level of O2 Tox risk to the diver if he adds oxygen into the loop via the off boards second stage ie by breathing a lung full (or part full) of 100% O2 from the stages regulator and then blowing that O2 into the rebreather loop.


The diver will be breathing in very high PPO2 for a single breath and holding it for a fraction of a second before blowing it into the loop.


I understand that O2 tolerance is in part a function of the exposure time as well as the exposure level. Does anyone have any data or actual experience on this subject?

For this example I would be considering 3 second exposures of PPO2 of up to 11bar, repeated at a frequency of once every 7 mins.


Note: Please no comments on using whips and QCs etc, obviously thats preffered - please limit discussion if possible to the question asked.

Thanks.

Human experimentation in very high PPO2 exposure is, as you can imagine, limited. But there is enough out there to suggest that a single breath isn't likely (but there is no certainty) to cause any CNS problems at pretty high exposures (3 or 4 ATA - 11? haven't seen any data that high).
Results in the few experiments that have been done are highly variable. In one actual experiment CNS problems occured as soon as 5 minutes and as late as 50 minutes (If memory serves that was at about 5 ATA but I'll have to check and get back to y'all on that one).
Rick

 

[Dr Deco]

Hello Dr Mike :

Background

The scientific, academic answer to this question is “Yes you can do this.” We are talking about short exposures more appropriate to a Hollywood movie script.

There does not exist a large amount of data on high oxygen exposures, but so experiments by the English scientists Kenneth Donald (Oxygen and the Diver) and JBS Haldane (the son of John Scot Haldane of dive table fame) indicated that there is a time dependence and exposures up to 10 atmospheres were tested with humans. They found a limit of about 25 seconds.

It should also be remembered that CNS oxygen toxicity is highly variable as far as duration to a “hit.” High partial pressures have not been used because of this wide variability. In addition, the CNS effect is accentuated by carbon dioxide in the arterial circulation; this is because of autoregulation, I suspect.

Dive Practice

The above was a direct scientific answer to the question posed. It is NOT a medical recommendation. Attempting this underwater is another matter. Carbon dioxide retention is an issue and so is the hoped-for quick reduction of the oxygen partial pressure in the lungs.

I certainly would hope that this is not an operational consideration. I probably beats drowning, however. Let us all trust that it never needs to be employed, and that it was asked solely out of academic interest.


Dr Deco :doctor:
On vacation this week.

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[DrMike]

Hello Dr Mike :

Background

The scientific, academic answer to this question is “Yes you can do this.” We are talking about short exposures more appropriate to a Hollywood movie script.

There does not exist a large amount of data on high oxygen exposures, but so experiments by the English scientists Kenneth Donald (Oxygen and the Diver) and JBS Haldane (the son of John Scot Haldane of dive table fame) indicated that there is a time dependence and exposures up to 10 atmospheres were tested with humans. They found a limit of about 25 seconds.

It should also be remembered that CNS oxygen toxicity is highly variable as far as duration to a “hit.” High partial pressures have not been used because of this wide variability. In addition, the CNS effect is accentuated by carbon dioxide in the arterial circulation; this is because of autoregulation, I suspect.

Dive Practice

The above was a direct scientific answer to the question posed. It is NOT a medical recommendation. Attempting this underwater is another matter. Carbon dioxide retention is an issue and so is the hoped-for quick reduction of the oxygen partial pressure in the lungs.

I certainly would hope that this is not an operational consideration. I probably beats drowning, however. Let us all trust that it never needs to be employed, and that it was asked solely out of academic interest.


Dr Deco :doctor:
On vacation this week.

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

Thanks,

Yes the question was asked largely out of academic interest. Do you have any details on those referances so that I can get myself a copy?

 

[wedivebc]

Thanks,

Yes the question was asked largely out of academic interest. Do you have any details on those referances so that I can get myself a copy?

Let's hope you try it in a chamber first right?

 

[ChrisA]

The diver will be breathing in very high PPO2 for a single breath and holding it for a fraction of a second before blowing it into the loop.
Thanks.

What is the PPO2 in the lungs after "blowing it into the loop" Does ALL the O2 leave the lungs or are you left with (say) 5 ATM PP O2 after the first exhale? I'd bet the PPo2 in the lungs would go down by some fraction with each breath untill it reached steady state. So the exposure time would be longer than just a few seconds. Using the same resoning I'd doubt after just one breath from an 100% O2 cylinder there would be 100% O2 in the lungs. Someone who knows the total volume of the lungs and the typical volume of a breath could figure this out. Anyone know the ratio of those two volumes?

 

[wedivebc]

What is the PPO2 in the lungs after "blowing it into the loop" Does ALL the O2 leave the lungs or are you left with (say) 5 ATM PP O2 after the first exhale? I'd bet the PPo2 in the lungs would go down by some fraction with each breath untill it reached steady state. So the exposure time would be longer than just a few seconds. Using the same resoning I'd doubt after just one breath from an 100% O2 cylinder there would be 100% O2 in the lungs. Someone who knows the total volume of the lungs and the typical volume of a breath could figure this out. Anyone know the ratio of those two volumes?

Depends on the breather. It would take me 3 good breaths to fill an inspiration CL yet my modified Dolphin is set so I can completely exchange cl volume in one full breath.
Dr Mike's scenario is very unlikely since the loss of O2 would not be a huge problem as long as you still had diluent so I think the question is just academic

 

[Rick Murchison]

Here are a couple of interesting charts from some experimentation for your information/extrapolation... The first chart seems to show a strong inverse logarithmic correlation between exposure time and exposure pressure WRT O2 toxicity; the second chart shows the high variability among the same subjects over multiple exposures at 3.1 ATA PPO2.
My impression is that your question's answer is in very iffy territory.
Rick

 

[Dr Deco]

Hello readers:

I am happy to hear that this is really just an academic exercise. The graph post by Rick in the above post is from my class in Decompression Physiology and posted on an earlyier thread. The one added is a bit clearer. Note that the CNS incidence is 10% for this case – too high.

One must really stay away from these levels.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[cerich]

same question same guy in another tech forum. Same advice but there he wanted to know "just in case" not just knowledge