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Dive Tables vs. Dive Computers

Discussion in 'Ask Dr. Decompression' started by King_Neptune, Sep 28, 2000.

  1. King_Neptune

    King_Neptune Founder

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    Dr Deco,

    You have discussed problems of tissue microbubbles (micronuclei) and diving.

    Are any of these questions or problems addressed by dive computers that make them different from printed dive tables?

    =-)

     
  2. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
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    Currently the concept of micronuclei control or modification is not addressed by dive computers or models. [It is a portion of the model that is used to develop some NASA decompression procedures.]

    In the algorithm (= calculation method) originally developed by J.S. Haldane at the turn of the century, it was thought that all inert gas in the body was dissolved and remained so during a safe, DCS-free decompression. At the time Doppler ultrasound flow meters were introduced as research tools into diving by M.P. Spencer and S. Campbell (Bulletin of the Mason Clinic, 22, 26-32, 1968), it was believed that gas bubbles never formed during ascent on, e.g., the US Navy dive Tables. It was reasoned that, if you monitored a diver and detected bubbles during the ascent, DCS would develop shortly thereafter. Doppler was thought to aid safe decompression, because you could simple stop the ascent and hold until the bubbles vanished. The results were otherwise, and when animals and humans were monitored on Navy schedules, many subjects display evidence of bubble formation. Obviously “bubbles = bends” was not a correct relationship. Bubble-free decompressions turned out to require an inordinate and excessive amount of time and were not cost effective.

    In time, it was realized that many decompressions could be accompanied by the presence of bubble formation but were in fact DCS free. Later studies indicated that these Doppler bubbles were from the circulatory system (probably originating in or near the capillaries) of muscle and fat tissue and not the ones responsible for joint-pain DCS, i.e., “the bends.” The idea began to take hold that all, real decompressions could be bubble-forming ones, to a more or less degree. Furthermore, these bubbles were not being considered by the dive tables with respect to the transport of dissolved gas.

    In general, gas bubbles are not particularly numerous during decompression and do not appear to interfere with the Haldanian calculation algorithm, the basis of virtually all commonly-employed dive tables and computer programs. If bubble formation is not excessive, table calculations are valid and even repetitive decompressions are possible and safe. These concepts were checked in the laboratory during the development of the Recreational Dive Planner [Hamilton, Rodgers, Powell, and Vann. Development And Validation Of No-stop Decompression Procedures For Recreational Diving. Diving Science and Technology. February 28, 1994, (pp. 78 + appendix)]. If for some reason, gas phase formation is excessive, real problems can develop and DCS result. Nucleation is one local effect, but this cannot be measured nor can nuclei concentration be inserted into the table or computer calculation.

    You can apparently give yourself the protective edge by avoiding straining (e.g., climbing ladders with full gear, both pre- and post dive) and promoting blood circulation (e.g., remain moderately active post dive).
    As far as printed tables or dive computers go, the underlying algorithm is the same. Several decades ago, it was thought that you could have a phone line to the laboratory that printed the tables and have an on-the-spot table made for you. The calculation method would be the same for the printed version in the book as for the custom-made version. Both methods are the same. With today’s small computers, we can dispense with the phone line to the computation lab - - but the algorithm is still the same. Dive computers, however, do not round up the time/depth combinations; they tell you exactly where you are in “time-pressure space”.

    But, it is a road map – not a license….

     
  3. King_Neptune

    King_Neptune Founder

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    Dr Deco,

    ah ok, gotcha ... Thanks for the explanation.


    =-)

     
  4. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
    2,384
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    All of this just shows that there is still a way to go. Someday, DCs may be adjustable for different divers and different dive situations.
     
  5. bullshark

    bullshark Nassau Grouper

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    Dr. Deco,

    Some dive computers are very different from dive tables in terms of the methods they use to arrive at recommendations. RGBM comes to mind, as well as ZH-L8ADT, though it is a hybrid.

    King Neptune didn't say which tables, but if he was referring to USN or PADI RDP, or the like, then I'd have to disagree with your assertion that the algorithms are the same, at least for some computers.
     
  6. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
    2,384
    89
    48
    Dear bullshark:

    Yes, your comment is correct, although the only DC that I found with a different algorithm was the VYPER. The manufacturer does indicate that it is based on the RGBM (Reduced Gradient Bubble Model) developed by Dr. Bruce Weinke. This is in turn based on the VPM (Varying Permeability Model) developed originally by Dr. David Yount, a physicist at the University of Hawaii. These concepts do not assume that all of the nitrogen is in the dissolved state, but rather that some is in the free or gaseous state. This initial gaseous state is present in the form of microbubbles or micronuclei that grow during decompression. This is contrasted with forming new bubbles as in the Haldane model. Because the microbubbles or nuclei are already present in the tissues before the dive, this model is different and the results will be different. For most recreational divers, this will manifest itself in small reductions in bottom time when performing a series of repetitive dives.

    In this FORUM, I have often discussed the concept of tissue micronuclei and ways to modify their concentration. The idea of tissue nuclei started with the physicist Edmund Newton Harvey in the late 1920s and arose from his work with the effects of high intensity ultrasound, a new methodology at that time. These concepts of micronuclei were imported by Harvey into his research into decompression sickness during WW II. Later work by Yount and Strauss (Bubble formation in gelatin: a model for decompression sickness. J. Appl. Physics, 47, 5081-5089) indicated that preformed nuclei could best account for the decompression characteristics of their gels. In time, these were elaborated by Yount and became the varying permeability model , a concept whereby micronuclei were stabilized by surface layers that can modify their ability to grow under conditions of supersaturation.

    The Buhlmann ZH-L8ADT (Zurich Limits 8 compartment adaptive) model does not start with preformed nuclei but modifies the algorithm in slightly different fashion to vary gas uptake and elimination as a function of half time compartment and depth and also adapts for environmental factors.

    In the answer that I gave, I was thinking in a large measure about the growth of nuclei under conditions of musculoskeletal stress and the modifications of blood flow with activity and rest. These later concepts are not yet in tables of computers - - - although you can introduce them yourself by maintaining conservatism in your diving habits.


     
  7. King_Neptune

    King_Neptune Founder

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    Dr Deco,

    Didn't you personally play a role in the making of the PADI dive tables? I heard a rumor and thought I would ask.

    =-)

     
  8. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
    2,384
    89
    48
    Yes, the PADI Recreational Dive Planner was one of the projects on which I was involved from1985 to 1989 while at the Institute of Applied Physiology and Medicine in Seattle. The testing of these, the most extensive program for recreational tables, involved both laboratory chamber “dives” and open water dives in the Puget Sound. It was a very large-scale endeavor involving laboratory technicians, dive masters, and volunteer divers from the Pacific Northwest.

    The program is explained in detail in a large report whose first author was Robert Hamilton, Jr, PhD. [Hamilton, Rodgers, Powell, and Vann. Development And Validation Of No-stop Decompression Procedures For Recreational Diving. Diving Science and Technology. February 28, 1994, (pp. 78 + appendix)]. It was once available from PADI, but I do not know if copies remain at this moment. It makes very fascinating reading and describes both the underlying concepts as well as the methodology of the test program.

    One of the interesting aspects of this was the considerable use made of Doppler ultrasound bubble detection for the evaluation of the tables. This was particularly valuable in the evaluation of the mutiple dives performed over the six-day series.



     

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