Sorry to be such a pain, but what's a tissue halftime and how does it work? Does stable supersaturation exist? Are the tables we use still based on Haldane's work?
In regards to Haldane, What's a half time?
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Dr Deco
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Hello sushidiver:
[1] What is a tissue halftime?
A tissue halftime was the point where the tissues exchange the ball and switch goals not really. It is a concept that nitrogen is dissolved and released in such a way that, e.g., a saturated tissue will lose one half of the nitrogen in a given period. In the next period of equal time, it will lose half of that which remains. This continues to a point wherel no tissue nitrogen remains. Theoretically, it would last forever, but there are not an infinite number of nitrogen molecules.
[2] how does it work?
The tissues are now called compartments ,since they are more mathematical entities than anatomical entities, The halftimes allow one to calculate [estimate] the dissolved gas loads in the body. Should the nitrogen come out of solution and form bubbles, then the scheme no longer works. The calculated gas loads for your dive are compared to calculated compartment loads for clean [successful, DCS free] dives. If the loads are equal or less, all should be fine.
[3] Does stable supersaturation exist?
In the form envisioned by Haldane, it does not. But for practical purposes it does, since surface tension will prevent small bubbles from growing. From the outside, it all looks the same.
[4] Are the tables we use still based on Haldane's work?
Yes, most are to a more or less extent degree. The bubble models, e.g., RGBM, have the component of surface tension in them. Thus, in some cases, they will suggest deep stops.
In the end, all models rely on comparing a table's calculated gas loads to actual 'clean' dives. Parameters are then adjusted to 'force' the model to work.
[1] What is a tissue halftime?
A tissue halftime was the point where the tissues exchange the ball and switch goals not really. It is a concept that nitrogen is dissolved and released in such a way that, e.g., a saturated tissue will lose one half of the nitrogen in a given period. In the next period of equal time, it will lose half of that which remains. This continues to a point wherel no tissue nitrogen remains. Theoretically, it would last forever, but there are not an infinite number of nitrogen molecules.
[2] how does it work?
The tissues are now called compartments ,since they are more mathematical entities than anatomical entities, The halftimes allow one to calculate [estimate] the dissolved gas loads in the body. Should the nitrogen come out of solution and form bubbles, then the scheme no longer works. The calculated gas loads for your dive are compared to calculated compartment loads for clean [successful, DCS free] dives. If the loads are equal or less, all should be fine.
[3] Does stable supersaturation exist?
In the form envisioned by Haldane, it does not. But for practical purposes it does, since surface tension will prevent small bubbles from growing. From the outside, it all looks the same.
[4] Are the tables we use still based on Haldane's work?
Yes, most are to a more or less extent degree. The bubble models, e.g., RGBM, have the component of surface tension in them. Thus, in some cases, they will suggest deep stops.
In the end, all models rely on comparing a table's calculated gas loads to actual 'clean' dives. Parameters are then adjusted to 'force' the model to work.
I would also suggest Dick Vann's online seminar if this area is of interest.
DAN Inert Gas Exchange, Bubbles, and Decompression Theory Seminar
DAN Inert Gas Exchange, Bubbles, and Decompression Theory Seminar
