Compartments and Deco

[261311]

I'm reading Deco for Divers and I'm having trouble understanding compartments in relation to tissues. Is anybody here able to clarify it a bit for me?

What I currently understand them to be are areas/ organs or groups/ spaces within your body but given the book, at present vaguely presents the history as low as 5, and then up to 14 with no clear definition of what they actually are. The rest of the book seems to be good reading so far but I'm unable to find a definition in the book or even through internet searching, oddly enough. Half times as well seem to be a bit dodgy because these, for some reason aren't actually represented by halving anything (from what I can tell) so it's also throwing me off.

 

[chrpai]

Here's a good read for you: PADI IDC Course & Exam Dive Theory - RDP The Recreational Dive Planner

 

[261311]

Thanks for the read. Would I be correct in believing that the more compartments you break tissues down into (if the research was behind it), the safer and more beneficial it would be to look at deco and half times at such a level? Trying to figure out the benefits of more or less compartments just to understand their place even more. That article looks to give off that gist but double checking what I'm interpreting isn't ever a bad thing here.

Also, half times by the looks of it without doing any serious math relate to surface intervals heavily, yes?

 

[TSandM]

"Compartments" are a mathematical construct. In attempting to model the movement of gas in the three phase system that is the body (alveolar air, blood, and tissues) the modelers posit different half-lives for nitrogen, and different maximum tolerated overpressure gradients for different parts of the body. Nobody knows if those half-lives and M values actually correspond precisely to anything -- as you can imagine, it's rather difficult to MEASURE nitrogen tensions in various tissues in the human body during compression and decompression. I have heard that the Navy did some experiments along this line some time ago, but I'm not aware of anyplace that we can access that information.

People have theorized that different structures in the body, or tissues, correlate to different compartments . . . For example, it has been said that the central nervous system behaves much like a "fast" compartment (short half-life, tolerates significant overpressure) because of its rich blood supply, and that bone, with a lesser blood supply and a structure which makes diffusion to cells comparatively difficult, correlates to long half-life compartments. This does go along with the observation that Type II DCS (neurologic) seems to occur frequently as a result of deep dives and poorly controlled ascents or inadequate decompression, whereas Type I DCS (bone and joint) seems to occur frequently with repeated dives and accumulated nitrogen loads. But the correlation is far from perfect.

I think, if you just hold the idea that nitrogen loads into various parts of the body at different speeds, and that the compartments are our best effort to try to model that without really completely understanding it, you'll have a pretty good grasp on what's known.

 

[261311]

I guess that's the first important lesson to understand is the reason it feels so unclear is because it is, hah. It seems like the more we break down the theory of compartments, we can do repetitive dives and have deeper bottom times (probably from the expansion of the half times theory over a wider range of tissues) but if we lump it all together, for conservatism we seem to do one/ limited dives with short bottom times and long intervals. It does make sense in a vague way. I just wish there were more behind it all in order to provide a better interpretation.

 

[chrpai]

AFAIK, you could have 6 compartments or 60 compartments but at any given moment there would be 1 controlling compartment. When that one saturates, you've reached an NDL.

 

[j2s]

"Compartments" are a mathematical construct. In attempting to model the movement of gas in the three phase system that is the body (alveolar air, blood, and tissues) the modelers posit different half-lives for nitrogen, and different maximum tolerated overpressure gradients for different parts of the body. Nobody knows if those half-lives and M values actually correspond precisely to anything -- as you can imagine, it's rather difficult to MEASURE nitrogen tensions in various tissues in the human body during compression and decompression. I have heard that the Navy did some experiments along this line some time ago, but I'm not aware of anyplace that we can access that information.

People have theorized that different structures in the body, or tissues, correlate to different compartments . . . For example, it has been said that the central nervous system behaves much like a "fast" compartment (short half-life, tolerates significant overpressure) because of its rich blood supply, and that bone, with a lesser blood supply and a structure which makes diffusion to cells comparatively difficult, correlates to long half-life compartments. This does go along with the observation that Type II DCS (neurologic) seems to occur frequently as a result of deep dives and poorly controlled ascents or inadequate decompression, whereas Type I DCS (bone and joint) seems to occur frequently with repeated dives and accumulated nitrogen loads. But the correlation is far from perfect.

I think, if you just hold the idea that nitrogen loads into various parts of the body at different speeds, and that the compartments are our best effort to try to model that without really completely understanding it, you'll have a pretty good grasp on what's known.

Thanks TSandM.....One of the best simplified and most honest explanations of 'compartments' I've yet to hear........

 

[eponym]

To add a bit to the previous good replies . . .

Would I be correct in believing that the more compartments you break tissues down into (if the research was behind it), the safer and more beneficial it would be to look at deco and half times at such a level? Trying to figure out the benefits of more or less compartments just to understand their place even more.

The selection of numbers of compartments, and their times, is not a rigorous science, to put it mildly.

In some sense, all divers are guinea pigs in an ongoing attempt to accumulate enough data to compare the predictive ability of differing deco models. By predictive ability, I mean the correlation between a deco model and observed incidences of dives which resulted in DCS.

If you use a dive computer, consider uploading your dive history annually to Dive Alert Network's ongoing analysis, project PDE - see more at Diving Medical Research Projects ? DAN | Divers Alert Network

And don't overlook pages 209-213, on DCIEM. I think it could have much to contribute.

 

[261311]

AFAIK, you could have 6 compartments or 60 compartments but at any given moment there would be 1 controlling compartment. When that one saturates, you've reached an NDL.

Ah, see that isn't clarified- simple enough to grasp though. What would happen if you've saturated more than one? Medical emergency or just a longer SI? Does the recognition of more compartments add to conservatism (ie. something with high blood flow that might be classed under a larger compartment being saturated sooner and thus NDL is reached)?

 

[chrpai]

I'm not an expert in this stuff and don't want to tell you things that aren't 100% true. But in general, the longer you stay the more compartments reach their limits the greater your deco obligation would become.