Why Aren't Dive Tables/Computers Customizable?

[Selachimorpha]

Speaking of "inexact science" what you also need to consider is a number of things with regard to the acctual pressure on your body during a dive. You need to be completely horizontal during your entire dive for your whole body to experience the same amount of pressure. A lot of divers spend some of their time vertical, some horizontal. The different parts of your body are now experiencing different pressures. The pressure on your dive computer or depth gauge is not necessarily the same as the pressure on your body. Further to that, I challenge you to take 10 dive computers and gauges diving and get them all to read the same depth (pressure). Depending on your position and the accuracy of the instruments you are using, maybe parts of your body are experiencing completely different pressures than other parts.

Measuring pressure is only the beginning, we are not even getting into physiological factors in unthinkable numbers, all different, day after day, always changing.

Someone on this board has a great quote, something along the lines of "Decompression Theory is like measuring with a micrometer, marking with chalk and cutting with an axe".

I think that really sums it up, its like all physics, you can develop as many theories as you want, but when you come to apply those theories in the real world, there are simply too many variables, too many factors that change, and you can measure as often as you want and collect as much data as you want, but in the end it just becomes statistics, along with all the limitations of statistics.

You have to think in terms of the real world, with so many factors you can never include in your calculations, like what you had for breakfast in the morning, if the left sleeve of your wetsuit is cutting of the circulation to your hand, if you see your favourite fish underwater and get excited etc etc.
I dive at least 6 days a week and see hundreds of divers, some of them doing crazy things and coming away unscathed, others with perfect conservative profiles getting bent.

What I do know from personal experience is that I can "feel" a good dive and a bad dive for my body. But maybe I am mistaken, and what I am feeling has no relation to nitrogen and is only to do with everything else that has happened during the day.

We just don't know.

 

[WetCell]

wetcell, you COULD take a pound of human fat and expose it to ambient nitrogen and measure absorption -- but the results would have nothing whatever to do with what happens while diving, because nitrogen in that setting is delivered by perfusion. To know how to adjust models, you'd have to have a perfusion-based delivery system and vary both nitrogen tension in the perfusate and amount of perfusion -- and then you'd have to know how perfusion in fat in various portions of the body is affected by the temperature, activity and pressure changes while diving.

It might be possible to design and carry out such experiments for each kind of tissue you'd be likely to run into, and then try to amend the models using those data, but it would be a huge project and the math involved daunts me. And there is very little reason to carry out such studies, except for knowledge, because the existing models keep people pretty safe and allow as much bottom time as the majority of people can have on their gas supplies.

In actuality I found a great paper, CONCERNING THE AMOUNT OF NITROGEN GAS IN THE TISSUES AND ITS REMOVAL BY BREATHING ALMOST PURE OXYGEN by J. A. Campbell AND Leonard Hill (J Physiol. 1931 March 23; 71(3): 309–322). They did exactly what I suggested (tested tissue absorption of gaseous Nitrogen) and they did it back in 1931. Needless to say, I am now impressed and have a different view of dive science in general. That brings me to my second item, the Undersea and Hyperbaric Medical Society (UHMS). These people are doing some serious research and have made available a significant number of publications on it.

The trouble with science is that the scientist is so busy with discovery that they have little time, or interest for that matter, in doing things with it. That takes an engineer. I guarantee you that the math is not rocket science, the dive computer has instant access to the changes in gas consumption, water depth and temperature as well as pre-stored biometrics on the diver. Worst case a few PDE's to solve, no big deal.

My time here is over, got work to do.

 

[WetCell]

Speaking of "inexact science" what you also need to consider is a number of things with regard to the acctual pressure on your body during a dive. You need to be completely horizontal during your entire dive for your whole body to experience the same amount of pressure. A lot of divers spend some of their time vertical, some horizontal. The different parts of your body are now experiencing different pressures. The pressure on your dive computer or depth gauge is not necessarily the same as the pressure on your body. Further to that, I challenge you to take 10 dive computers and gauges diving and get them all to read the same depth (pressure). Depending on your position and the accuracy of the instruments you are using, maybe parts of your body are experiencing completely different pressures than other parts.

The pressure effects during vertical vs horizontal aspects is important, however, the data estimate would be fairly easy using just an inclinometer. Keep in mind that the biometric enhanced computer knows the height of the diver, his basic shape, whether or not he's in saltwater or fresh, etc.

Measuring pressure is only the beginning, we are not even getting into physiological factors in unthinkable numbers, all different, day after day, always changing.

Well, in the system I am describing, the diver steps on a scale and it sends his biometric data to his dive computer. Take a look at the Tanita BC-1000 for a glimpse into this future. His height and shape will not change that dramatically from day to day, as well as his skinfold and age data.

Someone on this board has a great quote, something along the lines of "Decompression Theory is like measuring with a micrometer, marking with chalk and cutting with an axe".

Exactly!! I am working to make it more exact by giving the computational process more data.

I think that really sums it up, its like all physics, you can develop as many theories as you want, but when you come to apply those theories in the real world, there are simply too many variables, too many factors that change, and you can measure as often as you want and collect as much data as you want, but in the end it just becomes statistics, along with all the limitations of statistics.

Yawn! We know all of that, been there, done that. They said there were too many variables to automate wave soldering machines and cement kilns.

You have to think in terms of the real world, with so many factors you can never include in your calculations, like what you had for breakfast in the morning, if the left sleeve of your wetsuit is cutting of the circulation to your hand, if you see your favourite fish underwater and get excited etc etc.
I dive at least 6 days a week and see hundreds of divers, some of them doing crazy things and coming away unscathed, others with perfect conservative profiles getting bent.

I would say that is anecdotal, but we shall see, won't we?

What I do know from personal experience is that I can "feel" a good dive and a bad dive for my body. But maybe I am mistaken, and what I am feeling has no relation to nitrogen and is only to do with everything else that has happened during the day.

We just don't know.

We will. A lot of science and engineering is attitude. The Wright Bros were told men couldn't fly, Fulton was told you could not have a steam powered ship, the list is endless. I venture Cousteau was told that self-contained underwater breathing apparatuses weren't practical and would never work

 

[gcbryan]

The problem as I see it with what you're talking about is that although it could be done...it's too simple. It still wouldn't explain anything. I think you'd agree that we don't really know all the things going on in decompression/DCS, etc.

If all that was needed to completely understand all this was the height/weight/body fat of an individual then we would have understood this long ago. This isn't the Rosetta Stone of decompression theory.

 

[Gene_Hobbs]

In actuality I found a great paper, CONCERNING THE AMOUNT OF NITROGEN GAS IN THE TISSUES AND ITS REMOVAL BY BREATHING ALMOST PURE OXYGEN by J. A. Campbell AND Leonard Hill (J Physiol. 1931 March 23; 71(3): 309–322).

This was the start of some very interesting research. The modern "state of the art" in body fat measurement is hydrostatic weighting. The cool history behind this technique is why it was developed by Al Behnke for quantifying inert gas loads in the body. The connection to diving research is lost in most text books.

That brings me to my second item, the Undersea and Hyperbaric Medical Society (UHMS). These people are doing some serious research and have made available a significant number of publications on it.

It's nice to see their work recognized. It is important to also remember that hyperbaric research is in trouble. In 2002, The Office of Naval Research tasked UHMS with performing a comprehensive analysis of the Navy's research and development program in Undersea Medicine (1). The panel found that 60% of the young researchers in the field left within less than ten years. Additionally, it was discovered that many of the senior scientists in this arena would retire in the near future (52% retiring in less than 10 years and 96% retiring in less than twenty years). Further, the Navy had not trained any investigators in the previous ten years. This turnover in researchers and the loss of senior scientists potentially signifies a great loss in human knowledge that can be transitioned to new researchers.

(1) Undersea and Hyperbaric Medical Society. An Assessment Of A National Naval Need For Undersea Research. Office of Naval Research, report in response to 5000 Ser 341/270 20 Feb 02.

 

[WetCell]

The problem as I see it with what you're talking about is that although it could be done...it's too simple. It still wouldn't explain anything. I think you'd agree that we don't really know all the things going on in decompression/DCS, etc.

If all that was needed to completely understand all this was the height/weight/body fat of an individual then we would have understood this long ago. This isn't the Rosetta Stone of decompression theory.

Spoken like a scientist--are you one? The goal is not to explain but to fine tune. We already know how to prevent, within an excellent margin of error, DCS in the recreational diver. The problem is, as I see it, and I am not alone as I did not start this thread, is that the current methods are based on conservative statistics rather than individualized data. There is absolutely no reason that a dive computer should not be able to include biometrics into the dive profile and no-decompression analysis.

I will be the first to admit that the gain may not be worth the effort, but that is always a possibility when engineering seeks to push the envelope. I have not yet heard a powerful enough argument not to proceed.

If this is not the Rosetta Stone, what research can you cite that showed that biometrics knowledge has little or no effect on time to decompress?

My bet is on the fact that for a long time we only had the "gold standard" of hydrostatic weighing to give us the requisite biometric data. As such, a customized table or computer capable of taking that data into account was not practical.

 

[WetCell]

This was the start of some very interesting research. The modern "state of the art" in body fat measurement is hydrostatic weighting.

I think you are confusing "gold standard", which is what hydrostatic weighing is referred to in physiological circles, with "state of the art", which is what bio-impedance measuring is in the big picture of body composition measurement. Of course, get a couple of physiologists in a room and toss this nugget in and they will come to blows.