Charlie99, thanks for the link to the article by Baker. It is very helpful and interesting to note the similarities among the different tables.
I understand that the faster tissue compartments have higher M-values, but I was never quite sure why this is so. My intuitive answer has been that the fast compartments can tolerate higher nitrogen loads because they can unload enough by the time one reaches the surface (assuming a safe ascent rate) to avoid excessive bubble formation.
According to Baker, Buhlmann's M-values were determined empirically using actual decompression testing. I do not know whether the testing was done and the formula derived from the results, or whether the formula was hypothesized and the data found to confirm it.
In any case, when asking why fast compartments have higher M-values, it seems one could answer that the M-values are what they are because that's what testing showed they should be. Indeed, Buhlmann tweaked his formula to lower the values when it was discovered that the original values were not conservative enough.
When one also starts considering "compartment shift" as fast compartments off-gas into slower compartments on ascent, it really gets complicated, and that is where empiric data do help. On the other hand, empiric explanations can seem a bit like when a parent tells a child who is asking why, "Because I said so."
In medicine we usually try to provide a physiologic explanation for results obtained through clinical experiments. In other words, we try to match what we think should happen with what actually happened.
So empiric testing showed that faster compartments have higher M-values, but is that what we think should be the case? Again, my explanation is yes -- because although the fast compartments load up more quickly, they can also unload more quickly. Thus they can tolerate a deeper dive with its higher nitrogen pressures.
Am I right or am I off base here?
