Um yeah, if you're asking about different tissue loading/off-gassing, then you are asking about decompression.
Fast tissues? Long tissues? What is this?
- Thread starter NAUI Wowie
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Nice of you to say "integrated" because the tissue compartments are basically the "slices" of the integral.
An integral is the way to compute an area under an unknown curve. You cut it into rectangular slices -- we know how to compute the area of a rectangle -- and add up their areas. The idea is that the "midpoint sum" below will be over the mark by the sum of the triangles above the curve, and under the mark by the sum of triangles below the curve, and those two will largely cancel each other out and get you close enough to the real thing.
And that's pretty much what "tissue compartments" are: we don't know how the gas kinetics work whole-body-wise, just like we cant figure out the area under unknown curve. But we can approximate it by "slices" that we know how to handle, and hope to get close enough.
In math, the definition of "close enough" goes into the infinite number of infinitely thin slices that are infinitely close to the real answer, but in diving "close enough" is getting the diver out of the water not bent. So 4 slices was good enough for Haldane, and we're up to (whooping) 16 now, mainly because our computers are powerful enough to handle that many in a watch-sized device.
But they are still purely abstract mathematical construct for estimating things we can't directly compute, and really have nothing to do with biology.
Sooner or later, a new diver or rec diver who, just like you, believes they have no interest in "decompression theory" will do a search using the same question you asked, and the search results might just reveal this thread, regardless of what forum it's categorized under. You asked a great question, and you were not the first diver to ask it and will not be the last. Consider yourself to have done a good service for those who come after you.
That is a pretty ignorant comment to make.I disagree. I am not looking to discuss decompression. Ive got my two dive computers for that. Im wondering what fast tissues are? and what long tissues are? Are long tissues like kidneys liver etc?
are fast tissues your bloodstream?
I can give a rats backside about algorithyms
Have you ever wondered what restricts your NDL (no decompression limits) or the depth/time tables that you learned in your Open Water course?
Should you ever move beyond NDL (aka ‘recreational’) diving, you will need an understanding of decompression theory.
Bro, I think you need more Wowie in your NAUI.
Within the context of neo-Haldane decompression theories, the "fast" and "slow" tissues don't necessarily correspond to specific fluids, organs, or body parts. Inert gas loading is modeled using a fixed number of discrete compartments, each of which have different constant coefficients representing how quickly or slowly the gas transfers in and out. Imagine you're pouring water into a bucket covered by a mesh screen: if the screen has a lot of large holes then water can flow in quickly and if there are only a few small holes then water can only flow in slowly, but in either case if you keep pouring long enough then eventually the bucket will fill up. From a physiology perspective, those fast compartments correspond most close closely to blood and the slowest compartments correspond to poorly-perfused adipose tissue — but don't take that too literally.
In a real human body there are a virtually infinite number of different tissues, with complex and poorly understood gas exchange mechanics between them. So any model such as Bühlmann ZHL-16c in common use today necessarily has to oversimplify in order to make computation practical. In that particular model, the slowest compartment has a nitrogen off-gassing half-life of about 10 hours. So hypothetically in extreme cases of near saturation exposures there could still be a significant amount of nitrogen left in certain tissues even after 24 hours. But as a practical matter this isn't really possible for recreational divers because they would run out of gas long before reaching that point.
In a real human body there are a virtually infinite number of different tissues, with complex and poorly understood gas exchange mechanics between them. So any model such as Bühlmann ZHL-16c in common use today necessarily has to oversimplify in order to make computation practical. In that particular model, the slowest compartment has a nitrogen off-gassing half-life of about 10 hours. So hypothetically in extreme cases of near saturation exposures there could still be a significant amount of nitrogen left in certain tissues even after 24 hours. But as a practical matter this isn't really possible for recreational divers because they would run out of gas long before reaching that point.
What follows is a simplified explanation of it all that I hope will help.
Nitrogen molecules enter and leave the tissues continually. Before a dive, presumably we have been at the same altitude long enough that things have averaged out--we have on average just as many nitrogen molecules entering our tissues as leaving them.
When we dive to 99 FSW, we now have 4 times as many molecules entering our lungs, and so 4 times as many molecules are entering our body as are leaving it. Let's compare a fast (5 minute) tissue to a slower (20 minute) tissue to see what is happening.
Nitrogen molecules enter and leave the tissues continually. Before a dive, presumably we have been at the same altitude long enough that things have averaged out--we have on average just as many nitrogen molecules entering our tissues as leaving them.
When we dive to 99 FSW, we now have 4 times as many molecules entering our lungs, and so 4 times as many molecules are entering our body as are leaving it. Let's compare a fast (5 minute) tissue to a slower (20 minute) tissue to see what is happening.
- The fast tissue is rapidly gaining nitrogen. As the amount of nitrogen in the tissue increases, so does the amount of nitrogen leaving the tissue increase. After about 5 minutes, the amount of nitrogen entering that tissue is only twice as much as the amount leaving it, so the rate of increase slows to half. It has reached its half time. The process repeats, with the next half (75%) reached in another 5 minutes. This continues a total of about 6 times until the tissue is saturated. It has reached equilibrium at that depth.
- At the same time, the slower tissue is also absorbing more nitrogen, but it takes 20 minutes to reach its half time.
- At some point the fast tissue will have reached equilibrium, meaning as much is going out as coming in. As the diver ascends from that point, there is more coming out than going in. The diver is off-gassing.
- When the faster tissue has started off-gassing, the slower tissue has still not reached equilibrium, and so it is still on-gassing--taking on more nitrogen. It will not start off-gassing until it has reached its own point of equilibrium.
All diving involves compression and decompression. All that varies is the amount and whether mandatory stops are required. If you don't understand that, then regardless of how long you've been diving, you are behind on your dive theory. It would be best to do some more advanced reading on decompression theory. It applies to recreational diving as much as it applies to technical diving.
TrimixToo
Contributor
O
One day, if you live long enough, you may come to realize that just because two people happen to disagree it does not mean that if you're one of them that the other person is wrong.
Similar threads
