DiveGolfSki:
Now that is a more civilized way of correcting or, to be more precise, clarifying someone's knowledge rather than simply saying "consider yourself corrected - as usual you're wrong."
Thanks Mac for that info. I should point out that after the 1912 program to test Haldane, the Navy's Experimental Diving Unit developed the Air Decompression Tables during the years after 1927 but I'm not sure if these are tables used today.
It seems that all models are eventually tested (a theorem is developed and is then tested ... basic scientific method 101). How are the tests conducted? On humans or goats? I would think the latter would have PETA consequences
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That would mean that computers and tables are developed theoritically (models) and through practical methods (human testing). Either way, you're right about the accuracy of any of these models as they relate to individual human physiology.
I made the original comment about the model underlying tables and computers many posts ago. Others have essentially said the same thing, but let me clarify just a little. And I am summarizing.
The orginal experiments were done based on Navy divers, but the data went farther back to include caisson workers. Based on this data and based on Haldane's work with goats, the tissue half-life model of nitrogen absorption/release was proposed. And for the life of me, I don't remember who first proposed it. But this is the model that is followed today by everyone. There are variations of this model, but they all ultimately are similar.
No one knows if this model is correct or reflects reality. Without going into the complexity of proving theoretical models in living organisms (especially when some of those organisms are people), let's just say that it is unprovable. But, the predictions of this model has been shown to be pretty darn accurate.
Though I remember having a discussion with a PH.D. physiologist at the Air Force's High Altitude decompression program in Brooke Institute of Research concerning his belief that DCS is ultimately a chaotic, unpredictable event and that following tables or computers ultimately won't prevent it. But he wasn't a diver. But his point was that no one really knows what is actually happening.
So today, we have this theoretical model that attempts to predict what is safe and what is not. And that it is all based on statistical analysis of dives. And remember how statistics work. I can predict that no one reading this will ever win a lottery (and probably be right), but every day, someone somewhere does win one.
Based on this theoretical model (or a variation of it) tables were developed to attempt to predict the safe limits. But tables can only take into consideration one tissue half life, so the original tables were developed based on a 60 minute half life compartment (I think; I could be wrong here as to which tissue compartment was used). But the bottom line was that the original experimental data was used to develop the model. But that the model was used to create the original tables.
It turns out that according to the model, different tissue compartments load and unload nitrogen at different rates depending on depth. (note: these are all theoretical compartments that do not correspond to any particular type of tissue) One of the real advantages of computers, and one of the reasons that I started using one back in 1984, was because computers can actually track multiple tissue compartments at the same time. Something the tables can not. For those who remember the EDGE, it actually showed twelve tissue compartments on its display and how they were increasing or decreasing nitrogen absorption.
One of the unanswered questions is whether multiple tissue compartments are necessary. In other words, does tracking a 5 minute or 480 minute tissue compartment really make a difference in safety. I don't know. But I would rather track more compartments that fewer.
I hope this explains some of the underlying theory behind our tables and computers.
Steve
