Which one is the leading compartment?

[DiveNav]

A couple of weeks ago, a member came by our office to say hello.
We chatted a little bit about divePAL, then he asked .... "but, which one is REALLY the leading compartment"?

I tried to explain to him the intricacies of the Buhlmann algorithm and the fact that overpressure gradients and half-times made the whole algorithm not linear at all.

Afterwards it dawned on me that maybe we should do a better job at explaining this ... so, in the next release of divePAL there will be a nice indicator showing which one is the leading compartment .

Meanwhile, here a quiz for you; look at the image below and then pick one of the 3 choices:
A) The leading compartment is #3
B) The leading compartment is #6
C) It is not possible to determine the leading compartment from the image, because ....... (provide your explanation)

Alberto (aka eDiver)

 

[redacted]

Well, I believe the "controlling compartment" is that compartment which is the closest in time to reaching its NDL. Although compartment #3 has the greatest nitrogen load, it is off-gassing so it is not impacting NDL and will not unless the diver descends. None of the off-gassing compartments can be the limiting compartment until the dive incurs a deco obligation. In this case, Compartment #6 has the greatest current loading of the compartments that are on-gassing, but it also has the greatest M-value of the on-gassing compartments. So I guess I will have to go with "C". I guess you need to compute an NDL for each compartment to determine which is the controlling compartment.

But I had never really thought about it this way before. Now I think I understand why my Oceanic computer can be in the yellow on the Tissue Loading Bar Graph while it is showing very large NDL.

 

[lowviz]

...//...C) It is not possible to determine the leading compartment from the image, because ....... ...//...

-you did not provide the ascent profile.

 

[TMHeimer]

Interesting stuff. If you follow your computer (or tables in the "old days") it doesn't really matter which compartment controls. Following everything learned in OW will almost 100% keep you away from DCS.

 

[DiveNav]

.....But I had never really thought about it this way before. Now I think I understand why my Oceanic computer can be in the yellow on the Tissue Loading Bar Graph while it is showing very large NDL.

Exactly!

 

[DiveNav]

.... Leading Compartment Indicator
-
divePAL 0.12: Added indicator of the leading compartment in the Compartments section.

Alberto (aka eDiver)

 

[racerx_]

Interesting.. so why is this the leading compartment?

And is that why the bars change from green to yellow? Based on whether they are on gassing or off gassing? Never knew..


Sent from my HTC Incredible S using Tapatalk

 

[Bubbletrubble]

Alberto, you might want to consider not putting icons of various body parts below the compartments.
As you know, the compartments are theoretical, mathematically-calculated constructs which have are not correlated with specific anatomic structures in humans. The scientific evidence to make such a correlation simply doesn't exist. We have yet to develop the technology to monitor real-time on-/off-gassing in humans and localize it to anatomic structures.

Other things to consider...

• If we want to believe that the amount of blood flow in/out/through a specific anatomic structure influences on-/off-gassing, then it might be a little misleading to categorize "bone" as a "slow" compartment. Different parts of (and types of) bone have various levels of vascularization.
• Blood flow through muscles can vary with exercise. With use, muscles tend to "recruit" a greater blood supply, which may affect on-/off-gassing.

On a side note, you might want to label your axes and provide a color key. If the y-axis represents nitrogen loading, it's unclear what the yellow and red horizontal lines mean. If the red line signifies 100% inert gas "saturation" (indicated by the exclamation point triangle/deco sign), what percent saturation does the yellow line represent?
What do the green and yellow colors of the bars indicate? Off-gassing vs. on-gassing at a particular moment in time?
Perhaps all of this is "common sense knowledge" for those who own certain dive computers, I don't know.

 

[lowviz]

...//...you might want to consider not putting icons of various body parts below the compartments.
As you know, the compartments are theoretical, mathematically-calculated constructs which have are not correlated with specific anatomic structures in humans. ...//.....

BT: Technically spot-on, but I think the icons are a reasonable first approximation that offers a bit of value in quickly connecting to the n-compartment model. I like to see uncluttered graphics that immediately visualize important points. The leading compartment is a nice addition.

Nice to be able to do post-dive analysis. I would like to see a similar circle on the depth/time line that shows where significant off-gassing begins. -might be some surprises with various ascent plans...

 

[DiveNav]

Interesting.. so why is this the leading compartment? ..

Well .... in short ... it has to do with the characteristics of the compartments (PM0 and Half Time), its current loading AND what is happening during the dive (ascent vs. descent) in that specific moment :shocked2:

.....And is that why the bars change from green to yellow? Based on whether they are on gassing or off gassing? Never knew..

Here is the color coding we use in our Nitrogen Loading Meter

Alberto (aka eDiver)