My DCS Hit

[emmbee]

You are quoting me out of context, in both points. Don't be a Simon. We don't need more stupid irrelevant distractions. Keep to the context please.

No. You specifically said the following:

Then you have to decide if simplistic 'pressure x time' is appropriate, given that 'pressure to risk' is not a linear relationship. example 100 mins at 0.3 ATA, is harmless while 10 mins x 3.0 ATA is a serious risk, but they have the same ISS value. Clearly the risk scale needs a factor / exponential applied to bring stress / risk assessments in line with reality. Maybe something along the lines of 'pressure squared x time' would be more accurate

VPM's critical volume algorithm computes 'pressure x time'. And absolutely not 'pressure squared x time'.

Next problem to solve - how does stress accumulated at say 5ATA depth, relate to stress on the surface? How to transpose whole dive stress into one common pressure scale? Obviously a stress and tissue bubble that started at 5ATA depth with 1 ATA supersaturation, and grew threw Boyles law, time and ascent from 5 to 1 ATA, represents a higher stress than a new 1 ATA stress recorded at the surface. This is why dive stress is far more important than surface stress.

Rereading the papers you suggested, Yount and al use a different algorithm post-surfacing because it simplifies the math and is more conservative. Their words. This is quite the opposite of what you're obviously saying.

There is no out of context on either point.

You know, I must have read hundreds of your posts by now. Well, probably not, to be honest. It gets tedious after a while. They're entirely devoid of information. You know what's not in any of them?

Any VPM argument. Any "physics".

You're quick to claim "bubble physics" to be on your side. And VPM's math to be superior. But you never, ever, develop an argument out of it. You just stick with pretty graphs and exponential compartment 101 and quotes and semantic games. I've come to the conclusion that you actually don't understand anything about bubble physics or VPM. You just pretend you do.

But you're welcome to prove me wrong.

Cheers,

Matthieu

 

[rossh]

Attention distraction attempts.... not interested in your side show.

 

[Randy Thornton]

Randy, look around you.

Do you see a trend in diving, where the active people get bent more often? Do beginner divers, clumsy divers, river divers, self propelled cave divers, and anyone else who got caught in a strong current... do these people get bent far more often than the lazy / easy going dive sites? Answer NO.

What data is this based on?

 

[rossh]

The data you can see is right in front of you..... The fact that there is no trend, or real world high occurrence of DCS is those diver types I mentioned within the case reports or long term studies. I challenged Simon to produce some data that showed how higher exercise induced perfusion is an issue for the diving community, but he was not able.

So Randy, you're asking me to prove a negative... that something does not happen. Hard to show a negative, so its up to those wanting to believe there is an elevated risk, to show a positive and its affects regular divers.


Yes, if you were part of structured test, you would be at higher risk, but we are not. This save energy concept sells a lot of scooters, but does it really avoid DCS?

.

 

[Randy Thornton]

The data you can see is right in front of you..... The fact that there is no trend, or real world high occurrence of DCS is those diver types I mentioned within the case reports or long term studies. I challenged Simon to produce some data that showed how higher exercise induced perfusion is an issue for the diving community, but he was not able.

So Randy, you're asking me to prove a negative... that something does not happen. Hard to show a negative, so its up to those wanting to believe there is an elevated risk, to show a positive and its affects regular divers.


Yes, if you were part of structured test, you would be at higher risk, but we are not. This save energy concept sells a lot of scooters, but does it really avoid DCS?

.

OK, so you have no data to back up this statement. That's fine. I just wanted to make sure that I understood what the statement was based on.

 

[jason drake]

Hello again Ross,

I am having trouble following the chief points you are making. Could you please summarise for me?
For decompression planning:

Does surface saturation matter?
Does perfusion matter?
Does exercise matter?

Just a yes or no would clarify things hugely, as I am out of my depth with the arguments lately.
Thanks for your time,

Jason Drake

 

[Simon Mitchell]

The data you can see is right in front of you..... The fact that there is no trend, or real world high occurrence of DCS is those diver types I mentioned within the case reports or long term studies.

You a manufacturing a non-existent narrative. You can't answer a question like this based on case reports. There are plenty of cases of DCS in "regular divers" (whatever you mean by that) who worked hard underwater, and plenty in "regular divers" who did not work hard. So what? That demonstrates nothing. You need a carefully constructed study to compare the effect of a variable like exericse at depth on outcome. You demonstrate a profoundly naive perspective in believing anything else.

I challenged Simon to produce some data that showed how higher exercise induced perfusion is an issue for the diving community, but he was not able.

This is a flat out lie. I cited multiple studies that have demonstrated either higher risk of DCS arising from harder work during a dive or undisputable evidence that exercise influences tissue inert gas kinetics. You just refused to acknowledge this. We have known since the earliest days of decompression research that exercise at depth increases the risk of DCS. Try:

van der Aue OE, Kellar RJ, Brinton ES. Surface decompression: derivation and testing of decompression tables with safety limits for certin depths and exposures. NEDU Report 5-45. Panama City, Florida, US Navy Experimental Diving Unit: 1945.

That study showed a doubling of the rate of DCS for work dives compared to rest dives. There are others I could cite. If you go to our pathophysiology chapter in Bennett and Elliott they are listed there.

Then there is copious evidence that exercise affects inert gas kinetics from very carefully controlled denitrogenation studies in aviators and astronauts. For example, exercise enhanced denitrogenation has been studied U2 pilots. Reduces DCS by 35 - 40 % according to Andy Pilmanis.

Pilmanis A. Altitude DCS risk mitigation - U2 practice. In: Bennett PB, Michaelson R, Butler F (eds). Best practice guidelines for prevention and effective treatment of decompression illness proceedings: Part 1. Durham NC; Undersea and Hyperbaric Medical Society. pp87-122. 2010.

There there are the studies cited by David.

Doolette DJ, Gerth WA, Gault KA. Addition of work rate and temperature information to the augmented NMRI Standard (ANS) data files in the "NMRI98" subset of the USN N2-O2 primary data set. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2011 Jan. 92 p. Report No.: NEDU TR 11-02.

Doolette DJ. Addition of work rate and temperature information to the augmented NMRI standard (ANS) data files in the "he8n25" subset of the U.S.N. primary data set. Panama City (FL): Navy Experimental Diving Unit; 2017 Sep. Report No.: NEDU TR 17-10.

Doolette DJ, Gerth WA, Gault KA. Probabilistic decompression models with work-induced changes in compartment gas kinetic time constants [abstract]. Undersea Hyperb Med 2010;37:294.

Notice how in those titles he refers to adjustments of decompression algorithms for temperature and work rate.

You have been caught both contradicting yourself and exhibiting a very poor understanding of decompression physiology. You want to claim that reductions in tissue perfusion in response to cold explain the results of the NEDU study, but at the same time you have argued vehemently that increases in tissue perfusion during exercise don't matter. Put simply, it is not physiologically plausible, and totally at odds with all the existing evidence that you could have it both ways like this. And now you are spouting some sort of Ross-speak by implying that these comments apply to "regular divers". What is a "regular diver"? What other sort of diver is there?

Given that you constantly cite the "science formula" for gas kinetics, and given that formula contains a term for perfusion when calculating both uptake and elimination of inert gases, can you explain the physiological basis for your belief that "increased perfusion doesn't matter to the outcome in regular divers".

Simon M

 

[Simon Mitchell]

What data is this based on?

Great question Randy, but I think you know the answer.

Simon

 

[Simon Mitchell]

Do you see a trend in diving, where the active people get bent more often? Do beginner divers, clumsy divers, river divers, self propelled cave divers, and anyone else who got caught in a strong current... do these people get bent far more often than the lazy / easy going dive sites? Answer NO.

This is utter nonsense. How would you know this? Can you point to the source(s) of the data upon which this conclusion is based?

Simon M

 

[PeterN]

Ok after 388 posts, no harm to remind us of post 57:
"To be honest most of us on this forum and others (RBW) have witnessed Ross's contributions on this topic over the years, most of us attempted to politely show him where he erred in his analysis but we were all wrong, the leading scientists in this area e.g. Doolette and Mitchell attempted to explain to him and guess what they were wrong as well. We all were met with his confirmation bias that he was right no matter what"

The reason why I posted this reminder and as Simon alluded to in an earlier post, nobody and no evidence will persuade Ross to abandon his view point, its a text book example of cognitive dissonance. Did we learn anything new from this thread diving wise? Not really but what this thread did illuminate, was the completely isolated and bizarre position Ross has taken on this subject. To the subject matter experts who helped highlight this to the dive community in general, thank you.

While I mostly agree with this post, I must say that I have learned much from this thread and the previous mother of all threads on burger world. I am deeply appreciative of all who contributed. Many of the points made were done so in very accessible language and the visuals were for me most helpful.

Much of the “wisdom” passed along in technical diving circles has been imho as much tribal as technical. I have the strangest advice suggested to me over the years by instructors and mentors. Clearly some of us struggle to decern the difference between anacdotes and evidence. Often this doesn’t much matter if it simply a way to do some skill or procedure for getting ready. Clearly though when we are choosing an appropriate deco strategy the good ol boys need take a backseat to the scientists.

 

[silent running]

Randy, look around you.

Do you see a trend in diving, where the active people get bent more often? Do beginner divers, clumsy divers, river divers, self propelled cave divers, and anyone else who got caught in a strong current... do these people get bent far more often than the lazy / easy going dive sites? Answer NO.

It doesn't matter what theoretical math relation you have... the realistic situation is... the increased exercise and it associated increased perfusion, does not matter to the outcome of normal divers. And why is that?

The simplistic "More gas = more nitrogen = greater DCS risk." is relevant to dive size / depth.

But the point here is whether the exercise perfusion changes make a difference. Clearly there are bigger issues and influences at play.

.

Ross, what bigger issues in decompression theory are there than gas exchange, and which only happens through the respiratory cycle?

Do you really think there is only a minimal difference in inert gas uptake between a diver at rest and a USN diver pedaling away on an underwater stationary bike with a sustained high RMV like in some NEDU tests? This is clearly countered by the large difference in their volume of consumed gas during heavy exertion underwater, vs the volume of a diver at the same depth who is at rest..!

And what is a "river diver"? And by "self propelled diver", do you mean a scooter? Why wouldn't their gas consumption be lowest of all? What is your point in bringing such things into the discussion?

 

[rossh]

Do you see a trend in diving, where the active people get bent more often? Do beginner divers, clumsy divers, river divers, self propelled cave divers, and anyone else who got caught in a strong current... do these people get bent far more often than the lazy / easy going dive sites? Answer NO.

This is utter nonsense. How would you know this? Can you point to the source(s) of the data upon which this conclusion is based?

Simon M

I can't prove a negative, but I can take note of the absence of the positive. Various organizations publish yearly statistics, but they do not have a column or sub group identified as DCS by excess activity or the like. Or maybe do a quick field survey of the local boat captains, and get his take on the people he knows who got treated.

Where are these mysterious group of "DCS by excess underwater activities" divers? Did you identify many in your NZ case study report? If they exist in large numbers, then you Simon can show to us the positive existence of this cause in regular divers..

But last year you were trying to convince us that deeper stops was the culprit in many treatments, so I don't think you have any room left to now shift the blame for DCS treatments onto excess underwater activities.
.

 

[rossh]

Ross, what bigger issues in decompression theory are there than gas exchange, and which only happens through the respiratory cycle?

Do you really think there is only a minimal difference in inert gas uptake between a diver at rest and a USN diver pedaling away on an underwater stationary bike with a sustained high RMV like in some NEDU tests? This is clearly countered by the large difference in their volume of consumed gas during heavy exertion underwater, vs the volume of a diver at the same depth who is at rest..!

And what is a "river diver"? And by "self propelled diver", do you mean a scooter? Why wouldn't their gas consumption be lowest of all? What is your point in bringing such things into the discussion?

David said it in that DAN tech conf 2008 p129. report summary from 2008. The key sentence is; "However, don’t expect the substantial differences seen in the experimental trials were extreme levels of risk factors were used. " . We in the normal world, are not subjected to test conditions, so we can't incur the bigger differences seen in tests....

How much do you think you might be able to add to your deco time by heavy exercise? 10% or 20% perhaps at worst?

Imagine two divers go to the bottom, one is a photographer and he sits still most of the time, while the other one chases fish and swims everywhere. They both then ascend, but is there a real deco difference needed? No not in practice.

Think about how much you can change your perfusion... its easy to maintain a 2x increase in O2 consumption for a long time, with bursts of 4x. Does your deco obligation double? No. Not much correlation there then. A well perfused person does not appear to on gas significant extra amounts from higher activity as they don't seem to need more deco time to compensate.


Now lets go to the surface. If you feel that perfusion is the limiting feature in on/off gassing, then surface exercise should just pump the excess gas out of you - right?. Well that doesn't work because DCS increases with post dive surface exercise.

The correlation from increased perfusion through exercise, to the required deco changes in ordinary everyday divers, is invisible.

.

 

[Simon Mitchell]

Where are these mysterious group of "DCS by excess underwater activities" divers? Did you identify many in your NZ case study report? If they exist in large numbers, then you Simon can show to us the positive existence of this cause in regular divers..

Ross, millions of dives and hundreds of cases of DCS occur in the world every year. NO ONE is out there objectively measuring the work performed by these divers underwater. You can't reliably compare the exercise levels between divers who got bent, and those who didn't in community data; no one has the required information. And there are many other factors that could contribute to risk in these disparate uncontrolled dives. It is therefore impossible to draw any conclusions about the effect of underwater exercise based merely upon "looking around you" as you suggest. The mere fact that you obviously don't understand this is extremely concerning.

In contrast, there are a number of studies (cited above) of relatively standardised dives and subjects in which exercise levels have been prospectively observed. These are the sort of studies which can be used to answer this question. They all support the concept that exercise matters. There is no-where for you to go on this. You can say the sky is not blue as many times as you like, but it just makes you look more and more stupid.

But last year you were trying to convince us that deeper stops was the culprit in many treatments, so I don't think you have any room left to now shift the blame for DCS treatments onto excess underwater activities.

I know you would like to obfuscate the reason we are discussing this issue, so I will keep bringing us back to it.

You have been caught both contradicting yourself and exhibiting a very poor understanding of decompression physiology. You claim that reductions in tissue perfusion in response to cold explain the results of the NEDU study, but at the same time you have argued vehemently that increases in tissue perfusion during exercise don't matter. The fact that you portray yourself as a "decompression software developer" but don't understand the physiological dissonance in this position or acknowledge the overwhelming contrary evidence would be funny if it weren't so concerning.

Simon M

 

[Simon Mitchell]

David said it in that DAN tech conf 2008 p129. report summary from 2008. The key sentence is; "However, don’t expect the substantial differences seen in the experimental trials were extreme levels of risk factors were used. " . We in the normal world, are not subjected to test conditions, so we can't incur the bigger differences seen in tests....

This is a cynical misrepresentation of Dr Doolette who, based on his earlier post on this thread, clearly does not agree with you on this matter at all. All David was saying in the above quote is that effects of risk factors deliberately exaggerated in trials will probably not be as large in the real world, but they will still be risk factors. Moreover, he was not talking about exercise in diving specifically, but all the risk factors discussed in that paper (including your favourite - cold).

How much do you think you might be able to add to your deco time by heavy exercise? 10% or 20% perhaps at worst?

So what is this? An admission you were wrong? Are saying that exercise does affect decompression (10 or 20% more are not insignificant increases)? I'm confused because you categorically stated exercise doesn't matter earlier?

Imagine two divers go to the bottom, one is a photographer and he sits still most of the time, while the other one chases fish and swims everywhere. They both then ascend, but is there a real deco difference needed? No not in practice.

Yes, actually, if you want the risk for the divers to be the same the exercising diver will need to do more deco.

I think it is important to reflect on what is happening here. This is advice from Ross that is contrary to that given by every diver training textbook, every diving medicine textbook and every diving physiologist in the world. See Neal Pollock and DAN's official position on this here.

Amongst the things that Neal says:

"Exercise during the compression and bottom phase increases inert gas uptake, effectively increasing the subsequent decompression obligation of any exposure".

Ross, would you care to interpret that in the context of your two diver story above, and state why you disagree with it?

Now lets go to the surface. If you feel that perfusion is the limiting feature in on/off gassing, then surface exercise should just pump the excess gas out of you - right?. Well that doesn't work because DCS increases with post dive surface exercise.

A naive and incomplete interpretation. Yes, DCS can be precipitated by post-dive exercise. Exercise at the surface will wash out inert gas more quickly, but we dont recommend it because exercise in a supersaturated state at the surface promotes bubble formation, and depending on the nature of the exercise, promotes passage of venous gas emboli across right to left shunts which is associated with spinal, cerebral and inner ear DCS. But I guess you would not have thought of that because, according to you, surface supersaturation doesn't matter, and nor do venous gas emboli!!???

Actually, isn't this another example of self contradiction? If surface supersaturation doesn't matter, how would post dive exercise cause any problems?

The correlation from increased perfusion through exercise, to the required deco changes in ordinary everyday divers, is invisible.

Keep it up Ross. This is stuff everyone can understand and I suspect there are some jaws dropping as they read this.

Amongst other things:

Venous gas emboli don't matter.
Surface supersaturation doesn't matter.
Surface supersaturation doesn't matter, but if you exercise after surfacing it can cause DCS.
Gas kinetics are controlled by half times, which have nothing to do with perfusion.
Perfusion matters when it is reduced by cold, but not when it is increased by exercise.
Exercise at depth makes no difference to decompression requirements.

All from someone who portrays themselves as a decompression software developer.

Simon M

 

[HowardM]

David said it in that DAN tech conf 2008 p129. report summary from 2008. The key sentence is; "However, don’t expect the substantial differences seen in the experimental trials were extreme levels of risk factors were used. " . We in the normal world, are not subjected to test conditions, so we can't incur the bigger differences seen in tests....

How much do you think you might be able to add to your deco time by heavy exercise? 10% or 20% perhaps at worst?

Imagine two divers go to the bottom, one is a photographer and he sits still most of the time, while the other one chases fish and swims everywhere. They both then ascend, but is there a real deco difference needed? No not in practice.

Think about how much you can change your perfusion... its easy to maintain a 2x increase in O2 consumption for a long time, with bursts of 4x. Does your deco obligation double? No. Not much correlation there then. A well perfused person does not appear to on gas significant extra amounts from higher activity as they don't seem to need more deco time to compensate.


Now lets go to the surface. If you feel that perfusion is the limiting feature in on/off gassing, then surface exercise should just pump the excess gas out of you - right?. Well that doesn't work because DCS increases with post dive surface exercise.

The correlation from increased perfusion through exercise, to the required deco changes in ordinary everyday divers, is invisible.

.

Thanks for this post.
It made it possible for even the average scuba Joe to get a good insight into your amazing lack of understanding on the subject.

 

[UWSojourner]

Keep it up Ross. This is stuff everyone can understand and I suspect there are some jaws dropping as they read this.

Amongst other things:

Venous gas emboli don't matter.
Surface supersaturation doesn't matter.
Surface supersaturation doesn't matter, but if you exercise after surfacing it can cause DCS.
Gas kinetics are controlled by half times, which have nothing to do with perfusion.
Perfusion matters when it is reduced by cold, but not when it is increased by exercise.
Exercise at depth makes no difference to decompression requirements.

All from someone who portrays themselves as a decompression software developer.

Simon M

This is gold. I'll add a few.

Total supersaturation exposure doesn't matter.
The results of carefully conducted human dive trials don't matter.
The fact that nations have abandoned bubble models based on research doesn't matter.

...
Perhaps a new tagline?

When nothing matters ... dive VPM-B.

 

[silent running]

David said it in that DAN tech conf 2008 p129. report summary from 2008. The key sentence is; "However, don’t expect the substantial differences seen in the experimental trials were extreme levels of risk factors were used. " . We in the normal world, are not subjected to test conditions, so we can't incur the bigger differences seen in tests....

How much do you think you might be able to add to your deco time by heavy exercise? 10% or 20% perhaps at worst?

Imagine two divers go to the bottom, one is a photographer and he sits still most of the time, while the other one chases fish and swims everywhere. They both then ascend, but is there a real deco difference needed? No not in practice

Think about how much you can change your perfusion... its easy to maintain a 2x increase in O2 consumption for a long time, with bursts of 4x. Does your deco obligation double? No. Not much correlation there then. A well perfused person does not appear to on gas significant extra amounts from higher activity as they don't seem to need more deco time to compensate.

As Simon stated above and as I understood the quote originally, you are citing DD's statement incorrectly. The point is not the "extremity" of the fasctors, it's that KNOWN risk factors WILL produce observable differences in DCS symptoms, and that's all that is necessary from a statistical and methodological standpoint for a study to elicit observable results. The bigger point in all this is that there are mechanisms of gas exchange during decompression which are more and less understood. As I understand it, the point of these comparative studies such as the NEDU, is relatively modest, which is to further identify risk factors and quantify their mechanisms, like distribution of stop depths and times, and the weighting of the different tissue compartment saturation/offgassing thus affected by different profiles.

Your point about potentially increasing deco time by some scalable amount related to exercise further exhibits a strange and inexplicable confidence in your knowledge of decompression science. People operating within NDLs get bent! So clearly there are way too many unknowns, and as such a careful, incremental approach to designing and conducting studies is the only responsible way to gather new, reliable information. Your jumping to conclusions ahead of people who have spent vastly more time studying and working in such a new and difficult field is non sensical on all levels except a very conspicuous one.

I've said it before and now again; if you feel you have something to contribute, like some good hunch that you feel is being overlooked, make your case, and go ahead and feel free to speculate. No one will penalize you for that, on the contrary. It's the overconfidence in your own self reported "data base" of dive profiles from your product sales and your strident asserting of anecdotal info which so undermines whatever your points are and the discussion in general...

 

[Simon Mitchell]

Hello,

I would like to walk away from this thread if I can. It is taking up too much of my time and my colleagues think I'm mad. Unless Ross posts something too egregious, my plan is to get on with other things. I would like to share a couple of perspectives though.

First, to anyone who may have formed the view that I have been hard on Ross, I would remind you that I only joined this thread after he had publicly accused me of being responsible for an injury to one of my fellow tech divers. In my view, he deserves everything that has happened after that.

Second, to those who think it has dragged on too long - I fundamentally agree. BUT, based on appraisal of past behaviour, it is almost certain that this will not be the last time Ross will try the "you are to blame" line of argument. My sense has therefore been that we might as well have it out thoroughly here because this thread will serve as a permanent record that I can refer back to when Ross tries it again.

The other advantage of dragging it on is that, as often happens with Ross, cracks in his arguments turn into yawning chasms. When the discussions are around some of the arcane aspects of decompression theory it can be difficult for onlookers to appreciate what is happening. But when the discussion moves on to concepts that are more widely understood (as has happened here) Ross's lack of knowledge of the field and the unreliability of his opinions become obvious to a much wider audience. This thread has been very useful in that regard.

I will contribute if I need to, but I would like it to be a lot less.

Don, if you want to discuss anything in relation to your accident off line please feel free to PM me.

Simon M

 

[rossh]

This is a cynical misrepresentation of Dr Doolette who, based on his earlier post on this thread, clearly does not agree with you on this matter at all. All David was saying in the above quote is that effects of risk factors deliberately exaggerated in trials will probably not be as large in the real world, but they will still be risk factors. Moreover, he was not talking about exercise in diving specifically, but all the risk factors discussed in that paper (including your favourite - cold).



So what is this? An admission you were wrong? Are saying that exercise does affect decompression (10 or 20% more are not insignificant increases)? I'm confused because you categorically stated exercise doesn't matter earlier?



Yes, actually, if you want the risk for the divers to be the same the exercising diver will need to do more deco.

I think it is important to reflect on what is happening here. This is advice from Ross that is contrary to that given by every diver training textbook, every diving medicine textbook and every diving physiologist in the world. See Neal Pollock and DAN's official position on this here.

Amongst the things that Neal says:

"Exercise during the compression and bottom phase increases inert gas uptake, effectively increasing the subsequent decompression obligation of any exposure".

Ross, would you care to interpret that in the context of your two diver story above, and state why you disagree with it?



A naive and incomplete interpretation. Yes, DCS can be precipitated by post-dive exercise. Exercise at the surface will wash out inert gas more quickly, but we dont recommend it because exercise in a supersaturated state at the surface promotes bubble formation, and depending on the nature of the exercise, promotes passage of venous gas emboli across right to left shunts which is associated with spinal, cerebral and inner ear DCS. But I guess you would not have thought of that because, according to you, surface supersaturation doesn't matter, and nor do venous gas emboli!!???

Actually, isn't this another example of self contradiction? If surface supersaturation doesn't matter, how would post dive exercise cause any problems?



Keep it up Ross. This is stuff everyone can understand and I suspect there are some jaws dropping as they read this.

Amongst other things:

Venous gas emboli don't matter.
Surface supersaturation doesn't matter.
Surface supersaturation doesn't matter, but if you exercise after surfacing it can cause DCS.
Gas kinetics are controlled by half times, which have nothing to do with perfusion.
Perfusion matters when it is reduced by cold, but not when it is increased by exercise.
Exercise at depth makes no difference to decompression requirements.

All from someone who portrays themselves as a decompression software developer.

Simon M

Well done Simon, all quoted way out of context.... how typical of you.

OK I promise I will stop annoying you with the reality... for now.
.