Interpreting Suunto Tissue Saturation Graph

[Yeoh Chee Weng]

I would be most grateful if someone can explain what are the tissue groups that the Suunto Dive Manager software are referring to?

This is the Help info which I found:
"Tissue Saturation % Each bar on this graph represents one tissue group in your dive computer's decompression math model.

The bar graph shows the math model for one sample at a time.

The bar graph approximates the result of the math model as calculated by the dive computer during the actual dive. Dive Manager's bar graph sometimes shows small errors.

The vertical height of a bar shows the amount of dissolved gas represented in one tissue group of the decompression math model. A decompression ceiling appears if any bar reaches above 100%."

At the bottom of the graph is labelled "Fast" on the right side and "Slow" on the left.

1. What are the "fast" and "slow" tissue groups?
2. Does it mean that if any bar reaches above 100% the dive becomes a decompression dive?

Thank you for any help rendered. :11:

 

[Kim]

Different tissues in your body will ongass or offgas (take up nitrogen or release it) at different speeds. As the fast and slow suggests - fast tissue (often referred to as compartments) will take up gas much quicker than slow tissue. However, fast tissue will also release nitrogen a lot quicker as well - while the slow compartments need a lot longer to return to normal levels.
If you rise above 100% then yes, you are beginning to incur a decompression obligation and depending on how much of an obligation you have will dictate your maximum ceiling that you should stay or just under and how long you should stay there. If you cross the 100% threshold with a fast compartment then generally the time that you have to stay at the decompressing depth will be a bit shorter than for the slower compartments. The Suuntos work out the times according to which compartment/s has/have been violated.
As far as becoming a decompression dive you should also realize that ALL dives are decompression dives. The different between a recreational dive and a more formal deco dive is that the decompressing in a rec dive happens during your slow ascent and safety stop. In a formal deco dive you have what becomes a soft overhead where you can't return immediately to the surface without the high chance/certainty of a DCS hit - so you have to make planned decompression stops which are different to recreational diving in that they often start much deeper and there are often more of them so that your body can offgas enough nitrogen before you reach the surface to be safe.
Decompression theory is NOT completely understood and depending on many other factors different people can react differently diving the same profiles. To stay as safe as you can it's better NOT to push the NDL's and plan dives with a bit of conservatism built in to the plan. It's often at the limits of the tables or your computer that people can run into trouble. Even the same person doing the same dive a few times could get a problem where they didn't have one before.

 

[Otter]

(1) The short answer is that these are theoretical tissue groups / compartments. They don't represent actual physiological body parts, but rather attempt to model the fact that some parts of our body seem to load/unload nitrogen faster than others. I haven't researched it, but I assume that the maximum values and compartment loading/unloading times are proprietary.

(2) If you define a 'decompression dive' as not being able to directly ascend to the surface, then yes it appears that once you are over 100% on any tissue, the 'ceiling' indicator is displayed indicating a mandatory stop. As soon as the tissue drops to/below the 100% level, the 'ceiling' indicator is removed.

EDIT: I was answering your post while Kim was composing his.

 

[Yeoh Chee Weng]

Thanks Kim & Otter,

Wow, your replies were quick. Now I understand.

 

[cmalinowski]

while oceanic and suunto use different algorithms, oceanics manual does a good job at describing their representation of the tissue loadin bar graph (TLBG). The way they explain it is that if you imagine that there are 12 separate tissue graphs, the one that is in charge currently is the one that is shown. So, knowing what Kim said in the message above, if the tissue compartment that represents a theoretically slow tissue compartment is in charge because you are deep, it may switch to a faster theoretical tissue compartment as you ascend and then that graph is "in control". Additionally, one compartment may be on-gassing while another is off-gassing.

They explain it a little better than me, but hopefully you get the picture.

If you want, oceanic sends this with the atom (and I would imagine other dive computers). It may help explain how they come up with their TLBG which will help explain how Suunto comes up with theirs. Different algorithms, and different number of tissue loading compartments, but essentially the same principals apply.

Copy of oceanics safety and reference manual

 

[Geezer]

I've found the graphs to be helpful, both in analyzing dives, and improving my understanding of nitrogen loading/decompression theory. It's also been impressive to see the difference (graphically) that using nitrox makes for a series of dives.

 

[Yeoh Chee Weng]

Thank you Cmalinowski for the copy of the Oceanic manual.

It makes interesting reading and helps me to understand how algorithms work.