VPM vs BUHLMAN

[Dr Deco]

Hello Readers:

In the day of JS Haldane, it was certainly thought the decompression calculation was indeed based on a physiological model. Today it is generally accepted that it is NOT a physiological model and simply a calculation method (algorithm). It works because it produced dissolved gas tensions in “compartments” that are very low and avoid the growth of tissue micronuclei. That is all. There is no “fine tuning.” Divers will put in intermediate stops, but these were found by experience and not theoretical prediction.

JS Haldane was the first to introduce

[1] a relatively rapid ascent to the surface as contrasted with a long, slow pull. He also
[2] introduced the “compartment” concept coupled with
[3] exponential gas loading and unloading.

Those are currently the basics. There are assumptions in all of these. However, if you avoid much supersaturation – and excessive straining to generate nuclei – experience shows that the vast majority of times you will end up fine.

There are models and there are models, but they all depend for their success on a set of variables that are adjusted to fit past diving data, dives that were DCS free.

Dr Deco

 

[BOTTOMTIMER]

Hello Mr Deco

What is the micronuclei?

 

[Dr Deco]

Hello Bottomtimer :

Liquids and Nuclei

Liquids have a certain cohesive, “stick-together” quality. This is certainly not as strong as solids but it is difficult to “poke a hole in it.” These holes would be the cavities (nuclei) that would grow to be decompression bubbles. The gas pressures we encounter in diving are not very large, definitely not great enough to overcome the water-to-water cohesiveness that results in surface tension. Very small nuclei, much smaller than a red blood cell, have internal pressures from surface tension that is hundreds of atmospheres.

All fluids do have nuclei generated by heat, thermal motion. There is always a probability that small “holes” will be present. The smaller they are, the higher the probability of their existence. When water is heated to its boiling point, the cavities become easily visible; they are filled with water vapour.

Decompression Nuclei

Nuclei can be enlarged in the body by local reductions in pressure such as results from muscle movement. Vigorous straining activity can actually precipitate DCS in some instances. For this reason, I have suggested that such activities be minimized during off gassing.

Micro Nuclei in Nature

These are present in many situations from volcanic eruptions to bubbles forming in glass. They are controlled in many industrial processes but do not receive much attention in diving.

Dr Deco