on gassing vs off gassing

[AquaTec]

Dr Paul Thomas once bubbled...


= less micronuclei NOT more ongassing. The offgassing at the stop will be the same if the diver is doing the same, whereas the ongassing at depth is greater when the diver is active AT DEPTH. Thus the relative differences in half times and the theory of asymmetrical diffusion, which is a completely separate issue from micronuclei formation.

lets discuss this idea.

on and off gassing should not only be relative to the partial pressure of that gas but it seems that it would also be effected by how much of that gas is flowing through the blood stream.

I don't know how to measure blood flow other that a pulse rate, I am sure BP somehow factors in.

but for now lets say just the pulse is the determining factor.

so lets say at rest at the surface your pulse is 60. now you do a dive, weather by exersice or other factors you pulse increases. [purposly leaving exertion out of this] lets just say a mermaid swims by at 300 ft and your pulse shoots up to say 120

so if you pulse has doubled then it would seem that the blood flow rate has doubled [again using my laymans understanding of flow rate] if that is the case then your blood is carring with it inert gasses that saturate your system faster.

now you are in deco and your pulse is back to 60 but lets say that the gradiant is maxed, say 100% at 20 feet.

so you should be maximizing your ability to decompress, however i am guessing that algorithams are based on a constant blood flow. so it would make since that you would either need to keep that pulse at the same level or extend the deco time [or a little of both]


now after reading this don;t get caught up with the term pulse, if i am mistaken in how it relates to blood flow through the body.
i am thinging of blood flow through the body, while swimming vr non swimming, etc

 

[The Iceni]

AquaTec once bubbled...
on and off gassing is not only be relative to the partial pressure of that gas but is affected by how much of that gas is flowing through the blood stream.

Thus more activity at depth leads to a greater than "normal" nitrogen load at the level of the tissues, say 30% more.

now you are in deco and your pulse is back to 60 but lets say that the gradiant is maxed, say 100% at 20 feet.

so you should be maximizing your ability to decompress, however i am guessing that algorithms are based on a constant blood flow. so it would make sence that you would either need to keep that pulse at the same level or extend the deco time [or a little of both]

That is exactly how I understand it, Aquatec! The standard algorithm assumes a "normal" blood flow at all times but in this case since there is a 30% greater gas load caused by the increased activity and blood flow at depth this increased tissue gas load will take 30% longer to offgas. Thus the normal unadpative algorith underestimates the "Haldane" deco requirement by 30%. The adaptive algorithm employed by the Explorer allows the diver to select for such an increased deco requirement of 15% or 30%, the settings being 100%, 115% or 130%.

If ongassing is greater than "normal" offgassing it is "assymetrical".

Micronuclei

It would indeed seem sensible to decompress at the same level of activity. Swimming against a current during decompression or on the surface should increase offgassing for the same reason as an equivalent increase in activity increases ongassing at depth. However, as Dr Deco repeatedly states DCI is dependent on both an excessive offgassing gradient AND the formation of micronuclei into which that inert gas diffuses to form bubbles. Excessive muscular activity during a stop or post-dive predisposes to micronuclei formation - hanging on like grim death to a shot or anchor line or swiiming against a current are now thought to predispose to the formation of excessive micronuclei.

As I understand it, any expected increase in offgassing due to musclular activity with an associated increase in blood flow is more than offset by the inevitable formation of micronuclei, which grow to form bubbles which reduce the circulation at the level of the capilliaries. Thus violent exercise during stops or in the immediate post-dive period actually does the opposite and reduces offgassing;- thus predisposing to DCI!

There is also of course RGBM, a factor which I admit I do not yet fully understand.

 

[Dr Deco]

Dear Readers:

Off Gassing vs. Micronuclei Formation

The portion of the "Synoptic Model" (as I call my decompression model) that is always found to be the most difficult is the relationship between nuclei formation and off gassing. This is viewed by most as a “zero sum game.” That is, if you increase blood flow to promote off gassing, you will, at the same time, offset the advantage by forming tissue microbubbles. The beauty of this is that it appears not to be true. God was in a good mood the day He made diving.

Blood flow

Blood flow is increased at the tissue level to a considerable degree with but little activity. In fact, heat rate will increase in response to thoughts about moving (how about that for benefit without cost). What we find is that improvement in off gassing over total rest is considerable. The algorithms have been calibrated using exercising individuals depressurized to altitude. (Altitude is used because, well, I am at NASA. On the serious side, all initial gas loads in test subjects are the same in altitude studies, and DCS rates can be high because subjects are immediately repressurized to site level.) Exercise will off set microbubble formation if it is not weight bearing. {Loftin KC, Conkin J, Powell MR. Modeling the effects of exercise during 100% oxygen prebreathe on the risk of hypobaric decompression sickness. Aviat Space Environ Med 1997 Mar; 68(3): 199-204}.

The salient point is to avoid weight-bearing activities. Such activities as running in place, jumping jacks, stair stepping and the like were tried during WW II and found to be of no value. They found that more problems arose than were solved. At that time, however, they hypothesized that such activity generated carbon dioxide to such excess that it functioned like an inert gas diffusing into growing bubbles.

Microbubbles

Fortunately, hydrodynamic cavitation requires considerable activity in contrast to increasing blood flow. There is a “free lunch.” Now the down side of this is that there does exist a constant “background” of micronuclei that can not be removed by anything short of high pressure. It is because these nuclei are present, that direct decompression with supersaturation is restricted. In the absence of micronuclei, one could surface from the ocean bottom without fear of DCS. This is not possible, of course.

Asymmetry

This can arise from two primary sources.

• The change in the blood flow, and hence the half times; and
• the presence of tissue microbubbles in such numbers that considerable amounts of free gas are sequestered; this gas is held in tissue bubbles and never reaches the capillaries.

This last concept is the "reduced gradient" in the RGBM.

Dr Deco :doctor:

 

[The Iceni]

Dr Deco once bubbled...
Dear Readers:

Asymmetry

This can arise from two primary sources.

• The change in the blood flow, and hence the half times; and
• the presence of tissue microbubbles in such numbers that considerable amounts of free gas are sequestered; this gas is held in tissue bubbles and never reaches the capillaries.

This last concept is the "reduced gradient" in the RGBM.

Dr Deco :doctor:

Ah! We learn something every day. Now I understand precisely what RGBM means.

Without the benefit of your considerable background knowledge I had assumed, wrongly it seems, that any form of aggressive exercise could cause micronuclei formation.

So, I take this to mean that as micronuclei sequester a certain amount of inert gas in any case on the ascent from any dive, all such gas diffusion (ongassing and offgassing) is assymetrical to a certain extent. Does this mean that the "symmetrical" starting point has been "calibrated" for this in the basic RGBM algorithm.

 

[Dr Deco]

Dear Paul:

The effect of asymmetry in uptake and elimination, the effects of micronuclei formation from standing in 1-g, etc, are determined from the NDLs. These are starting points for all models, even the RGBM. They are “calibrated” into the model from the initial data. There can be additional factors, also, known only to the table designer.

It is important to recognize that heavy exercise at the end of the decompression is not a part of the test program. So if you partake in big time post-dive activity, you are generating data for the next modeler.

The factors in the algorithm may be caused by some effect other than they really are, e.g., stable supersaturation limits probably are the Laplace limits (= “critical nuclei radii”). However, once the constants are determined, the algorithm will work. It does not mean, however, that useful extrapolations will result if the underlying concept(s) is incorrect. Haldanian models are notoriously difficult to extrapolate; modifications to the model must always be made.

Table designers and barophysiologists will always have their particular reasons why something will not work. For each scientist, there is at least one model. As Dr Richard Vann (Duke University) says, “Models are like feet, everyone has a couple, and they all smell.”

Dr Deco :doctor:

 

[The Iceni]

Thanks, Dr Deco.

 

[Alban]

Dr Deco

Does the rgbm model try to elliminate the number of micronuclei at the deep stops to reduce the gradient at the shallower stops between free and dissolved gas , so reducing overall tissue tension ?

Many thanks Alban