> Tom Mount posted a while back about a study that was done where deco on
> air for 100 ft dives > 60 mins caused symptomatic bubbling.  Better deco
> gases solved the problems, but I still wonder what's wrong with model
> that we didn't predict the bubbles better.

The general problem with all the models is that none of them are based on 
a solid understanding of what's actually going on in our bodies during 
comprerssion and decompression.  The tissue-compartment-based models are 
the most popular, but are probably farther from reality than the 
bubble-based models (which, by comparison to the tissue-compartment 
models, are largely untested).  The compartment models assume no gas 
phase in the blood, and bubbles start to *form* if the difference between 
the dissolved gas tension and the ambient pressure gets too great. The 
bubble models assume the gas-phase bubbles are already there 
("micronuclei"), and these bubbles grow or shrink depending on the ratio 
of gas partial pressure inside the bubble, and the dissolved partial 
pressure in the surrounding blood and tissues.  The partial pressure in 
the blood & tissues is a function of what we are breathing, what the 
profile was, diffusion characteristics of the particular gas, perfusion 
characteristics of the particular diver's circulatory system, etc.  
Partial pressure inside the bubble depends on a variety of things, 
including ambient pressure, the diver's blood pressure (over ambient 
pressure), the size of the bubble (smaller bubbles have higher internal 
pressures due to proportionally larger effects of skin tension), etc. We 
get "bent" when the bubbles grow to a sufficient size or cause sufficient 
secondary effects that symptoms occur.

From all I know, the real-world data (e.g., doppler studies, my personal 
dive history, dive histories of other experienced divers, etc.) tend to 
suggest the bubble models are a more accurate reflection of what is 
really going on.

Aloha,
Rich

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