Oxygen Window?

[bullshark]

Dear Dr. Deco,

The subject phrase is all the rage these days.

It is used in so many ways that I'm afraid it's meaning has been lost to me. Some people say that Oxygen Windows are better than Tempered Glass, but not as good as Lexan. Others say that understanding and using them is vital for optimal decompression.

Do you have any idea what it is supposed to refer to, and if so could you explain a little about how it affects the decompression process?

 

[Dr Deco]

Dear bullshark:

[sp]When the pressures of all gases in a tissue are added together, the sum is either less than (undersaturated), equal to (saturated), or greater than (supersaturated) the ambient pressure. Depending on which, the gases either stay dissolved or can come out of solution in the form of gas bubbles. One way to increase the transport of dissolved gas and not to ever exceed ambient pressure, that is, never have the blood supersaturated, is to remove some of the gases. With gases employed in diving (nitrogen, helium, neon), this is difficult, since they were chosen because they are inert in biological conditions. That is, they cannot be chemically removed, only excreted by the lungs. Oxygen, however, can be removed by the tissues of the body, and a “space” results since the pressure of oxygen can now be subtracted from the total (sum) of all gases. If oxygen were not metabolized and removed, it would act just as any other inert gas and contribute to gas bubble formation.

[sp]Naturally, the concept here is that oxygen is metabolized and used up by the tissues of the body; this leaves a partial pressure vacancy , a term coined by C. B. Momsen, or an oxygen window , a term from Dr. Al Behnke, in the tissues and the venous system. In some decompression procedures, such as those developed in the 1970s in Germany, oxygen is used in rather high partial pressures to prevent the formation of gas bubbles [MR Powell, W Thoma, HD Fust, and P Cabarrou. Gas phase formation and Doppler monitoring during decompressions with elevated oxygen. Undersea Biomed. Res., 10 (3), 217-224 (1983)] and minimize DCS even though the decompression times were relatively short.

[sp] The maximum oxygen window will be found while breathing pure oxygen as is done in hyperbaric chambers when treating decompression sickness. Here the gradient is such that no inert gas is brought in via the blood stream. Virtually all of the oxygen is used by the tissues, and very little oxygen gas is in the venous blood. This allows the venous inert gas to be high and still be undersaturated. Currently in the world of scuba diving, the oxygen window finds its greatest utility in nitrox diving. Oxygen is added in place of some of the nitrogen and a very large partial pressure vacancy results.

[sp]The limit to oxygen in water (or even in a chamber) is its toxicity. We all have enzyme mechanisms in our bodies to control the buildup of reactive oxygen intermediates, but these protective mechanisms can be overwhelmed at pressure. If that is not a complete enough answer, please tell me what needs amplification.

 

[bullshark]

That is pretty much what I took it to mean. The attribution to Behnke is very interesting. I'll have to conclude that some the applications of the term I have read recently were not, um, quite appropriate.

Thanks for the informative reply

 

[shugar]

well the guys outside the PPD forum shouldn't find that pic... imagine all the flaming tim will get for not being "normal"...

Jag

 

[Kendall Raine]

Dear bullshark:

[sp]When the pressures of all gases in a tissue are added together, the sum is either less than (undersaturated), equal to (saturated), or greater than (supersaturated) the ambient pressure. Depending on which, the gases either stay dissolved or can come out of solution in the form of gas bubbles. One way to increase the transport of dissolved gas and not to ever exceed ambient pressure, that is, never have the blood supersaturated, is to remove some of the gases. With gases employed in diving (nitrogen, helium, neon), this is difficult, since they were chosen because they are inert in biological conditions. That is, they cannot be chemically removed, only excreted by the lungs. Oxygen, however, can be removed by the tissues of the body, and a “space” results since the pressure of oxygen can now be subtracted from the total (sum) of all gases. If oxygen were not metabolized and removed, it would act just as any other inert gas and contribute to gas bubble formation.

[sp]Naturally, the concept here is that oxygen is metabolized and used up by the tissues of the body; this leaves a partial pressure vacancy , a term coined by C. B. Momsen, or an oxygen window , a term from Dr. Al Behnke, in the tissues and the venous system. In some decompression procedures, such as those developed in the 1970s in Germany, oxygen is used in rather high partial pressures to prevent the formation of gas bubbles [MR Powell, W Thoma, HD Fust, and P Cabarrou. Gas phase formation and Doppler monitoring during decompressions with elevated oxygen. Undersea Biomed. Res., 10 (3), 217-224 (1983)] and minimize DCS even though the decompression times were relatively short.

[sp] The maximum oxygen window will be found while breathing pure oxygen as is done in hyperbaric chambers when treating decompression sickness. Here the gradient is such that no inert gas is brought in via the blood stream. Virtually all of the oxygen is used by the tissues, and very little oxygen gas is in the venous blood. This allows the venous inert gas to be high and still be undersaturated. Currently in the world of scuba diving, the oxygen window finds its greatest utility in nitrox diving. Oxygen is added in place of some of the nitrogen and a very large partial pressure vacancy results.

[sp]The limit to oxygen in water (or even in a chamber) is its toxicity. We all have enzyme mechanisms in our bodies to control the buildup of reactive oxygen intermediates, but these protective mechanisms can be overwhelmed at pressure. If that is not a complete enough answer, please tell me what needs amplification.

Mike;

Is there a physiological maximum to the window (vacancy)? I think I read somewhere such a maximum was 3.0 ATA. That is, nothing is accomplished, vacancy wise, of breathing oxygen deeper. Is it coincidence that this is slightly above the 2.8 ATA achieved breathing 100% at 60 feet as proscribed in Table 6? Is the 60 feet based on a toxicity threshold. If this is not true, why is 60 feet used as the deepest pure oxygen exposure?

Many thanks,

 

[Gene_Hobbs]

Naturally, the concept here is that oxygen is metabolized and used up by the tissues of the body; this leaves a partial pressure vacancy , a term coined by C. B. Momsen,

The Momsen work referenced is:
Report on Use of Helium Oxygen Mixtures for Diving.
Momsen, 1942
RRR ID: 3312, NEDU: AD0728758

or an oxygen window , a term from Dr. Al Behnke, in the tissues and the venous system.

So, a quick look for other terms that would have been used, include 'partial pressure vacancy' (mentioned above) and 'isobaric inert gas transport'. The first use I can find of the term 'oxygen window' is by Albert Behnke [1]. He also refers to early work by Momsen on 'partial pressure vacancy' (PPV) where he used partial pressures of O2 and He as high as 2-3 ATA to create a maximal PPV [2]. Behnke then goes on to describe 'Isobaric inert gas transport' was described by LeMessurier and Hills [3] and Hills [4] in actual diving operations [2].

1. Behnke. (1967) The isobaric (oxygen window) principle of decompression. In: The New Thrust Seaward. Trans. Third Marine Tech. Soc. Conf. 5-7 June, San Diego. Washington, DC: Marine Tech. Soc.
2. Behnke. (1969) Early Decompression Studies. In: The Physiology and Medicine of Diving and Compressed Air Work, Bennett and Elliott. First Edition. p234
3. LeMessurier and Hills. (1965) Decompression Sickness. A thermodynamic approach arising from a study on Torres Strait diving techniques. Hvalradets Skrifter, Nr. 48, 54-84.
4. Hills. (1966) A thermodynamic and kinetic approach to decompression sickness. Thesis

MR Powell, W Thoma, HD Fust, and P Cabarrou. Gas phase formation and Doppler monitoring during decompressions with elevated oxygen. Undersea Biomed. Res., 10 (3), 217-224 (1983)

RRR ID: 2966

Two others worth a read are:

Reinertsen, R. E., V. Flook, S. Koteng, and A. O. Brubakk.Effect of oxygen tension and rate of pressure reduction during decompression on central gas bubbles. J. Appl. Physiol. 84(1): 351-356, 1998.
<http://jap.physiology.org/cgi/content/full/84/1/351?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=Reinertsen+&fulltext=oxygen+tension&searchid=1100358969825_1755&stored_search=&FIRSTINDEX=0&sortspec=relevance>

The oxygen window and decompression bubbles: estimates and significance. <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8216150>

One other I found an interesting read but not 'really' on 'Oxygen Window' is:
Statistically Based Decompression Tables IX: Probabilistic Models of the Role of Oxygen in Human Decompression Sickness.
RRR ID: 3410
(there are 11 in the series RRR ID's 3402 to 3412)

If you need help getting started with the repository <http://archive.rubicon-foundation.org/>, please visit: http://rubicon-foundation.org/RRRfaq.html Also, don't forget our "Diving Medical Literature" presentation. (http://rubicon-foundation.org/download/Dive_Med_Lit.pdf)

 

[Dr Deco]

Hello Kendall:

I suspect that there is a maximum to the window. It is created by the metabolism of oxygen, and this does have a maximum. Tissue can only use so much.

When the oxygen levels rise, however, so do the oxygen-derived free radicals. These are one of the agents responsible for oxygen toxicity. Thus, there is a practical limit.

Dr Deco :doctor:

 

[Saturation]

Its almost certain that a maximum size window exists and its related to the rate of 02 metabolism by individual divers. Once reached, the excess 02 can be subject to supersaturation, and the rare 02 induced DCS ... more commonly as AGE related 02 bubbles.

 

[Kendall Raine]

Its almost certain that a maximum size window exists and its related to the rate of 02 metabolism by individual divers. Once reached, the excess 02 can be subject to supersaturation, and the rare 02 induced DCS ... more commonly as AGE related 02 bubbles.

Thanks Marv;

Do you know what this maximum is and is there a relationship between the maximum and the choice of 60 feet as the first O2 stop in recompression protocol?

Many thanks,

Kendall

 

[Saturation]

Thanks Marv;

Do you know what this maximum is and is there a relationship between the maximum and the choice of 60 feet as the first O2 stop in recompression protocol?

Many thanks,

Kendall

Hi Kendall,

Several studies suggest maximum 02 uptake at ~ 3 ATA P02; its a magic number, after that clearance of 02 from within tissue nearly plateaus.

Interestingly, it correlates well were humans will almost certainly get 02 convulsions.

Note, 02 metabolism differs for different tissues; some tissue 'saturate' quickly, and others metabolize it fast e.g. the brain. Different metabolic rates also explains why whole body oxygen toxicity occurs to different tissues are different times, suprisingly those that sustain higher tissue concentrations longer get tox sooner and except until you reach 3 ATA, the brain can sustain high P02 very well, especially with 'air' breaks.