Decompression Tissue Question

[NAM001]

especially where they have fat cells. A person with more adipose cells might have fat in organs that have X half-life in one person but the extra fat makes them X+ z in another

would not that hypothetical organ be covered as 2 different organs. if you had a fatty heart then it would be 3 tissues muscle fat and blood. since it has mutiple different tissue types. I would think that there would be more concern for the quantity of those tissues. for instance IF tissue 3 is representative of say fat for the most part. a diver with a 3% body fat would be effected differently than one with 33% when it comes to the time it takes to off gass from that amount of tissue. and if that is reasonable to call true. than look at avg body fat of men vs women. In the military 22% was considered obease for men but avg for women where 12 was avg for men. I guess this is where perhaps conservatism settings may come to the rescue.

 

[boulderjohn]

As pointed out earlier, the origin of theoretical tissues was John Haldane. His model had 5 such tissues, and they were purely theoretical and not based on any specific tissue.

 

[dmaziuk]

I figured it started something like, hey if you stay in this caisson for more than 4 hours you get this funny rash when you get to the surface but less than 4 hours you'll be ok, or 95% of you will anyway.

Actually it was "caisson workers coming up directly to the surface from 10 msw or shallower never had DCS symptoms no matter how long they spent in the caisson".

Compartments and half-times are needed when you can't come up directly to the surface and have to make a deco stop. Then you need to figure out for how long, and you're typically aiming to minimize overall ascent time. That's where you try to model relative contributions of real tissues in a mathematical construct back-fitted to empirical observations, optimizing for ascent time vs. statistical risk of DCS.

 

[Scuba_Nick27]

Morning all. I didn't want to hijack another thread on decompression theory so I figured I'd start a new one.

I have learned and, in a former life, taught basic decompression theory as it relates to tables. I understand that all tables/computers use a theoretical model to represent tissue groups and that different models use different numbers of these groups to determine time to on gas and off gas nitrogen (primarily). I also understand that different "tissue compartments" on gas/off gas at different rates.

My question is what tissues do those compartments represent in the body?

I have read somewhere that blood is one type of tissue compartment and that it has very fast on and off gas times. That got me to thinking that if blood is a compartment, what other tissues are compartments are represented in models?

I thought of blood, cartilage, muscle, fat, lung, various organs, and maybe brain tissue. Is this what is meant by tissue groups or is it something else?

Also, since all gas is carried into the body by blood from the lungs, and blood on gasses and off gasses quickly, are slow compartments just tissues that have less circulation than other parts, for instance cartilage? Without adequate blood flow do they just have less ability/resources to move gas from one place to another?

I can teach a 7 year old HOW to use tables but what some of the theory represents is something I don't fully understand.

Anyway, this was just something I was thinking about while reading another thread.

Thanks for your answers.

I have been studying anatomy, and on/off gassing all relates to diffusion of gas molecules through the tissues. I'm pretty sure that the tables account for all tissues, because you can't base everything off of the tissue with slowest diffusion, or the tissue with fastest diffusion. Tissues include; bone (bone is a mineralized connective tissue, don't forget that bone is porous and still goes through diffusion and changes in partial pressures; do your bones hurt when barometric pressures change? think about that), connective tissue, blood, muscle, epithelial, and nervous tissue. These are the 4 basic tissues. Things like hair and outer skin cell layers don't matter. Basically, the way dive tables were calculated, the depth and pressure and type of gas affect each type of tissue and the rates of diffusion for each tissue were calculated, and then averaged for the average person. Some tissues don't pressurize quickly, while others do. That is what dive tables account for, as well as DSAT and Z+ and other algorithms in dive computers do. If dive tables were based off of only blood for example, which has very fast on/off gassing, then decompression in itself wouldn't exist; just surfacing slower than 30 feet per minute would be sufficient to de-saturate blood. But if dive tables were based off of bone only, then you can stay under water for hours doing decompression. That is also why there is an NDL, because with increasing pressures, diffusion happens quicker, and tissues will become more saturated faster. NDL's are based off of the depth, pressure, and gas mix (some gasses also diffuse faster than other gasses, helium is a noble gas therefore it is not included in metabolic processes, and diffuses faster, nitrogen is used in some metabolic processes and diffuses slower, and oxygen diffuses the slowest through tissues that aren't blood because it is involved in metabolic processes) that you are running, and once you hit that limit, then you will have to go through decompression because all 4 tissues are becoming saturated at the specific pressure, in respect to your current depth.

I myself am learning the theory behind decompression so I do not know everything. If you see that I made a mistake please let me know, but otherwise that is pretty much it to dive tables and how they relate to tissues.

 

[PfcAJ]

I have been studying anatomy, and on/off gassing all relates to diffusion of gas molecules through the tissues. I'm pretty sure that the tables account for all tissues, because you can't base everything off of the tissue with slowest diffusion, or the tissue with fastest diffusion. Tissues include; bone (bone is a mineralized connective tissue, don't forget that bone is porous and still goes through diffusion and changes in partial pressures; do your bones hurt when barometric pressures change? think about that), connective tissue, blood, muscle, epithelial, and nervous tissue. These are the 4 basic tissues. Things like hair and outer skin cell layers don't matter. Basically, the way dive tables were calculated, the depth and pressure and type of gas affect each type of tissue and the rates of diffusion for each tissue were calculated, and then averaged for the average person. Some tissues don't pressurize quickly, while others do. That is what dive tables account for, as well as DSAT and Z+ and other algorithms in dive computers do. If dive tables were based off of only blood for example, which has very fast on/off gassing, then decompression in itself wouldn't exist; just surfacing slower than 30 feet per minute would be sufficient to de-saturate blood. But if dive tables were based off of bone only, then you can stay under water for hours doing decompression. That is also why there is an NDL, because with increasing pressures, diffusion happens quicker, and tissues will become more saturated faster. NDL's are based off of the depth, pressure, and gas mix (some gasses also diffuse faster than other gasses, helium is a noble gas therefore it is not included in metabolic processes, and diffuses faster, nitrogen is used in some metabolic processes and diffuses slower, and oxygen diffuses the slowest through tissues that aren't blood because it is involved in metabolic processes) that you are running, and once you hit that limit, then you will have to go through decompression because all 4 tissues are becoming saturated at the specific pressure, in respect to your current depth.

I myself am learning the theory behind decompression so I do not know everything. If you see that I made a mistake please let me know, but otherwise that is pretty much it to dive tables and how they relate to tissues.

“Tissues” as far as decompression modeling goes are just constructs. They have nothing to do with actual tissues like muscle, fat, etc. It can be helpful to think about gas diffusion in these terms, but it’s absolutely not “real”.

Your ascent is limited by the most saturated “tissue” (remember, that’s a construct of the model and not a physical thing). If surfacing would create an overpressure situation In a particular tissue then you’ve gotta stop on the way up.

N2 (atmospheric nitrogen) is not used in biological processes.

 

[dmaziuk]

“Tissues” as far as decompression modeling goes are just constructs. They have nothing to do with actual tissues like muscle, fat, etc. It can be helpful to think about gas diffusion in these terms, but it’s absolutely not “real”.

Furthermore one of the features of Buhlman's ZH-L16 is that you can invent your own tissue half-times and calculate allowed overpresure from those half-times. You can have 4 tissues, or 64, it's up to you.

 

[Bernie_U]

In Buhlmann's book Tauchmedizin (Diving Medicine), the author explains his way to associate human tissues with half-times in chapter 6.4 on page 77 f.
The story is pretty simple: Experiments with different dive profiles resulted in different types of injuries: Skin irritation, muscle bends, joint pain etc.
Due to the experimental set-up, the calculation of the most super-saturated mathematical tissue (i.e. half-time) was easy. The knowledge of the peak super-saturated tissue was combined with the medical diagnoses. Buhlmann discovered a pattern, e.g. dive profiles ending on peak supersaturation in tissue compartments no. 5 to no. 11 (27 - 187 minutes) led to skin irritations.
Muscles are no. 9 to no. 11, that's 109 to 187 minutes. And so on.
So, there is no one-to-one and onto relationship between half-times and human tissues, but it is not pure theory either.

@KWS: On page 78, Buhlmann also wrote that perfusion of a tissue is more important than the content of fat. A fatty heart is still one tissue and not a combination of two (muscle and fat).

 

[Scuba_Nick27]

“Tissues” as far as decompression modeling goes are just constructs. They have nothing to do with actual tissues like muscle, fat, etc. It can be helpful to think about gas diffusion in these terms, but it’s absolutely not “real”.

Your ascent is limited by the most saturated “tissue” (remember, that’s a construct of the model and not a physical thing). If surfacing would create an overpressure situation In a particular tissue then you’ve gotta stop on the way up.

N2 (atmospheric nitrogen) is not used in biological processes.

Yeah you are right. But the models are still based off of tissues and how they respond to pressure and gas changes... also nitrogen is used somewhat - in things like DNA synthesis, protein synthesis, and enzymes. But yeah, you pretty much repeated what I said, your ascent is limited by your most saturated tissue... This stuff is really interesting and confusing, I need to find a book.

 

[dmaziuk]

But the models are still based off of tissues and how they respond to pressure and gas changes...

Response to pressure changes is very simplified, all it is is partial-pressure difference that equalizes at ln(2) rate. The key parameter is time constant, specifically the time it takes delta-P to drop to half its initial value. You fine-tune the model by futzing with the number "tissue compartments" and their half-times, trying to back-fit your theoretical "compartments" to empirical observations (as @Bernie_U posted).

You would typically have extra criteria to judge when you're "close enough". DSAT report, for example, mentions that 1990s USN tables were developed for 2% predicted DCS because the Navy considered 2% acceptable at the time.

I.e. you're actually looking at optimizing for multiple parameters, and the "real tissues" aren't even on the list.

 

[PfcAJ]

Yeah you are right. But the models are still based off of tissues and how they respond to pressure and gas changes... also nitrogen is used somewhat - in things like DNA synthesis, protein synthesis, and enzymes. But yeah, you pretty much repeated what I said, your ascent is limited by your most saturated tissue... This stuff is really interesting and confusing, I need to find a book.

They really aren’t based on real tissues. “Tissue 5” in ZHL-16 isn’t an actual physical structure. It’s a model, not reality.

Nitrogen used in biological processes does not come from what you breathe in (N2). It comes from the food you eat, and it’s always in a different form than N2.