Hyperbaric Chamber visit report

[Liquid]

Doc-can you post the sketch of your lecture with computers?
I'd really like to read it (and about 20000km between us makes it impossible to attend.

Ari-when I go dive in meduza area I'll post you a mess. right now I'm stuck in beer-sheva where tests are starting in two weeks (well, actualy I just returned from Eilat, but that's a different issue and it will be at least a month untill I can even think of going diving)

 

[Dr Deco]

Dear Liquid:

While explained in pictures for a new audience, the “Computer” talk is basically what has been said here on the Scuba Source board for a couple of years. That is, decompression sickness is the result of two factors:

[a.] Inert gas supersaturation, and
[b.] The presence of suitably large tissue micronuclei.

You must have both present for DCS to occur.

Gas supersaturation during and dive and the rate of off gassing during the surface interval are a function of blood flow. This flow can change with activity level. It is at its lowest when a person sleeps during the surface interval, and this “activity” is to be avoided. Dive computers do not adjust for large changes in blood flow in you body. The “compartments” reflect blood flow situations, but they are not “adaptive.”

Micronuclei result from physical activity, and thus strenuous activity before, during, and after a dive should be avoided for safety. The concentration (and size/number distribution) of micronuclei is not incorporated into the computer algorithms.

That is it in a nutshell - - but without the background material.

Dr Deco :doctor:

 

[Liquid]

Thx Doc, as you said, it is more or less things that were discussed here. Tell me doc- do you have any idea/suggestion how these factors may be incorporated into decompresion algorithms?
I mean, besides just another conservatism factor, but in a more thorough way. Maibe how it affects M-Values?

 

[Dr Deco]

Dear Liquid:

No, I do not have any real idea. I do have some suspicions, however. (Scientists are always fully of hypotheses, many of which are pure flights of fancy.) :book:

• There is no doubt some factor(s) that influences the sensitivity of individuals to decompression. For a group of individuals, some are resistant and some are prone to DCS. { Dervay, J, MR Powell, B Butler and CE Fife. Effective lifetimes of tissue micronuclei generated by musculoskeletal stress. Aviation, Space and Environmental Medicine 73:22-27, (2002)}. What accounts for this difference? I suspect that it involves the number of tissue micronuclei, their lifetimes, and their size. This is governed, in part, by surface tension of the tissue fluids.
  
  We do not yet know how to incorporate an individual’s surface tension into decompression algorithms.
  
• Exercise levels are controlled carefully in NASA studies and on orbit during EVA. This type of control is probably impossible in SCUBA situations because it is such a varied activity. The divers themselves must really monitor this.
  
• When you have such a low incidence of DCS as is encountered in recreational diving, the individual risk factors are difficult to determine. In altitude decompression, with its attendant risk of 5 - 20% DCS (during testing procedures), the risk factors are relatively prominent. In diving, with one “hit” per 10,000 dives (estimate), it is difficult to identify these factors.
  
• It is possible that some decompression test might be performed in a chamber to assay the sensitivity of a diver. I do not know the day-to-day variability of this, however. It is without doubt dependent of the activity level of the subject, before and after the test. It is also dependent of the hydration state (which determines the surfactant concentration of the individuals).

This is something for a fictional story; possible I will write one someday……:book2:

Dr Deco
:doctor:

 

[Liquid]

Fictional or not-
THERE MUST BE a way to put it into formulae!!!!!!!!!!!
MUST MUST MUST!!!!!!!!!

ok, I'm relaxed now.

How can you study tissue micronuclei?
Can they be seen in microscope?

Gone have to check some studies about it.

 

[Dr Deco]

Dear Liquid:

[1.] Tissue micronuclei are elusive. I have never seen them in a microscope, only the larger bubbles that grow from them (supposedly) during depressurization.

[2.]Given the time and money (for testing), some of these fators probably could be put into a formula. However, that time and money does not exist for recreational purposes. PADI/DSAT were the only ones willing to put some money into considerable table testing (although the EDGE was also tested in 1982) for the recreational diver. That program was based on concepts in the mid 1980’s.

NASA and the US Navy are will to invest in a test program, but here we are talking about a narrowly defined decompression scenario and considerable economic importance. The RGBM schedules have been developed from the use of field data, so they also have a traceable pedigree. Other computers basically incorporate the standard data and models. These are fine but will not do what I alluded to above.

In the absence of specific data on in vivo bubble formation and the individual’s susceptibility on that day (or dive), I do not see how an “adaptive computer” could be designed.

Is it true that decompression could be faster? Certainly. A table with a one percent incidence of DCS means that ninety nine percent of the divers completed it without any problem. Could they have ascended faster? Most definitely, the data indicates.

The future will tell how this story unfolds.

Dr Deco:doctor:

 

[Liquid]

10x doc.

I guess that for the time being RGBM and the likes will have to do