Decompression terminology and mechanics

[AzAtty]

Now you know why it's called decompression THEORY.

Haldanean models assume that all gas is dissolved. In that sense, a Haldanean model is a "single phase" model. Bubble models attempt to explain not only elimination of dissolved inert gas, but also the elimination of the "free phase" (undissolved inert gas bubbles). Bubble mathematics are significantly more complicated.

[gcbryan]

Now you know why it's called decompression THEORY.

Haldanean models assume that all gas is dissolved. In that sense, a Haldanean model is a "single phase" model. Bubble models attempt to explain not only elimination of dissolved inert gas, but also the elimination of the "free phase" (undissolved inert gas bubbles). Bubble mathematics are significantly more complicated.

I understand that (or rather I understand that the math is much more complicated...not that I completely understand it) but am I correct in thinking that bubble models still consider ongassing and offgassing rates as being the same?

[Sloth]

I heard someone say the other day that the problem with decompression models is they are looking for a digital solutions to an analog problem. Probably not accurate at all but thought it sounded good

[AzAtty]

I understand that (or rather I understand that the math is much more complicated...not that I completely understand it) but am I correct in thinking that bubble models still consider ongassing and offgassing rates as being the same?

Not necessarily.

Tissue ongassing and offgassing of the dissolved gas phase is modeled as an exponential equation in the bubble models such as VPM and RGBM. So to that extent, yes, ongassing and offgassing "rates" are modeled by the same type of equation (differences in halftimes and other variables in each equation will, of course, affect the result).

However, bubble models assume that an exponential distribution of bubble "seeds" is excited to growth by compression and decompression. As I understand it, the goal of a bubble model is to control the volume of the bubbles ("phase volume limit point")--if they get too big, we have problems.

It has been suggested that once the free phase (bubbles) exists in the circulatory system, the uptake and elimination process for the dissolved phase becomes asymmetric. The halftime for elmination may need to be lengthened (relative to the uptake halftime) or the equation changed, e.g. an exponential formula for uptake, and a linear formula for elimination. The idea is that the presence of the free phase gradient during elimination "competes" with the dissolved gradient, so elimination would have to be weighted in proportion to the amount of separated gas.

EDIT: I neglected to insert my standard disclaimer that my doctorate isn't in hyperbaric medicine, so I welcome corrections to any inaccuracies.

[gcbryan]

Not necessarily.

Tissue ongassing and offgassing of the dissolved gas phase is modeled as an exponential equation in the bubble models such as VPM and RGBM. So to that extent, yes, ongassing and offgassing "rates" are modeled by the same type of equation (differences in halftimes and other variables in each equation will, of course, affect the result).

However, bubble models assume that an exponential distribution of bubble "seeds" is excited to growth by compression and decompression. As I understand it, the goal of a bubble model is to control the volume of the bubbles ("phase volume limit point")--if they get too big, we have problems.

It has been suggested that once the free phase (bubbles) exists in the circulatory system, the uptake and elimination process for the dissolved phase becomes asymmetric. The halftime for elmination may need to be lengthened (relative to the uptake halftime) or the equation changed, e.g. an exponential formula for uptake, and a linear formula for elimination. The idea is that the presence of the free phase gradient during elimination "competes" with the dissolved gradient, so elimination would have to be weighted in proportion to the amount of separated gas.

EDIT: I neglected to insert my standard disclaimer that my doctorate isn't in hyperbaric medicine, so I welcome corrections to any inaccuracies.

So the answer is actually yes.

[AzAtty]

I think the answer is actually yes...and maybe no.

In the bubble models that treat dissolved and free phase gas: for dissolved inert gas, the answer is "yes"; for bubbles, I think the answer is "maybe no."