Rise and Fall of the Bubble (Model) ?

[rsingler]

dissolved gas models originally aimed to prevent bubble formation. And then doppler ultrasound came along and showed that bubbles are always present

This!

Why much DCS occurs is still unknown. Yes, there are pieces we understand clearly -
-- You have a Patent Foramen Ovale, bubble from a rapid ascent, shunt a bubble over to the arterial side and have a stroke or get paralyzed. That makes sense.
-- You are a caisson worker, get filled with nitrogen, ascend too rapidly and dissolved gas bubbles out in your joints. That makes sense.

So you develop a model that creates an ascent strategy that minimizes bubble formation! That makes sense.

But along comes echocadiography and we see bubbles in almost everybody. Everybody! No matter their ascent strategy. Huh?

Along comes NEDU with an ascent strategy experiment that compared deeper stops with a similar length decompression profile with shallower stops, pushing some divers deliberately into DCS!! And despite theoretically minimizing bubble formation, the deeper stops fared worse. Huh?
So we argue passionately about fast tissues and slow tissues and gradients and bubbles, and try to make a modestly complex model fit a really complex system.

So we're wrestling with this. Minimizing bubble formation makes intuitive sense, but that system by itself doesn't work!!! Something else is going on...
Creating a society where we all share stuff and get along makes intuitive sense, but Communism by itself doesn't work. Other factors come into play.

Does that mean we can't get along? No.
Does that mean minimizing bubbles is unimportant? No.

We're diving a blended system that seems to work okay, while we try to figure it out.
We're living a blended system that seems to work, while we try to figure it out.

Like politics, arguing bubbles vs. gradients is futile. There is too much we don't know. Some things are obvious, in both arenas! But that doesn't mean that that's all there is to it.

For me, the analogy to failed political systems really helps me. As a college student, I wanted sharing and communes and joint effort to work. It made sense in my heart. But some people were lazy and some people stole stuff.
As a diver and scientist, I wanted the bubble model to work. It made sense in my mind. But facts are stubborn things.

This is a cool time to be alive. In politics and in diving. Let the experiments continue. Folks will suffer, no doubt. I don't know of another way to find the answer. In the meantime, I just try to keep my head down, and dive...safely?

 

[doctormike]

Excellent analogy. And just like politics, there are some people who pick a team and then try to find evidence to support the conclusion that they have already drawn. Which is the opposite of the way science works.

Our understanding of complex systems like human physiology evolves over time. Non-scientist will make a joke out of this, or use it as an excuse to believe whatever they want ("Are eggs good for you this week or bad? LOL"). Yeah, scientists are human and get attached to pet theories like the rest of us, but as a whole they are by definition open minded. I know that you can find counterexamples throughout history, but that's the point. They are the exception, not the rule.

Seriously, I saw a number of episodes of the Simon and Ross show here and elsewhere. And the thing that really bothered me was when people (well, mainly one person!) would criticize Simon for "pushing a theory", as if he wanted his side to win. Like most real scientists, I never heard him say anything like that. If anything, he goes to great pains to not only explain decompression to the rest of us, but also to explain the scientific method. Of the importance of not reading beyond the data. Of looking for weaknesses and holes in your current knowledge, and of testing it again and again under different conditions. And of understanding that the search for truth isn't a race with a finish line and a prize in most cases, but a journey that never ends. The only thing that happens when you figure something out, is that you get a bunch of new questions.

 

[rsingler]

I find some poetic justice in the fact that the guy who has taken a fair amount of bashing for his passionate defense of a deco system that has some problems, is the same guy that had the best system currently available for planning deco, and offers it in BOTH models.
Since he's not here to defend himself, I feel like it's worth pointing that out. And since he's not here to defend himself, I don't think the Moderators will allow much Ross bashing. It's water under the bridge.

 

[doctormike]

I find some poetic justice in the fact that the guy who has taken a fair amount of bashing for his passionate defense of a deco system that has some problems, is the same guy that had the best system currently available for planning deco, and offers it in BOTH models.
Since he's not here to defend himself, I feel like it's worth pointing that out. And since he's not here to defend himself, I don't think the Moderators will allow much Ross bashing. It's water under the bridge.

Yup. I also once read a post by Simon saying that HE used MultiDeco as well! Hey, I use it too...

I guess the takehome message is that the person who wrote the code for Microsoft Word doesn't necessarily have their own column in the New Yorker...

 

[dmaziuk]

But my point is, if I were to choose who should implement that model into real world software, I'd really, really prefer a programmer who at least had an inkling of understanding of what the model is trying to represent rather than someone who doesn't understand crap about the real world system the model tries to represent.

You're talking 2 simple equations and a 16x5 table of numbers, that's all there is to ZHL-16. And when you run into someone who understands the real system, the result may be the opposite of what you want: didn't we recently have a physicist point out that helium kinetics in the model make no physical sense. I've a pet peeve about oxygen, myself: the model simply subtracts it from "inert gas", all the way to 100%. I'm reasonably certain I can't metabolize 100% of it, the model says it doesn't dissolve and bubble out later, so it just goes *poof*. So, you know... be careful with what you wish for.

 

[TrimixToo]

I don't think so. Buhlmann ZHL-16 is a model. Abstracted, sure, but still based on real life physiology. And sure, GFs is an ad hoc hack to introduce additional conservancy into that model.

But my point is, if I were to choose who should implement that model into real world software, I'd really, really prefer a programmer who at least had an inkling of understanding of what the model is trying to represent rather than someone who doesn't understand crap about the real world system the model tries to represent.

It is not necessary to understand an algorithm at all to be able to code it correctly. For most programmers working on cryptography these days, that's a really good thing!

 

[Trace Malinowski]

Our understanding of complex systems like human physiology evolves over time. Non-scientist will make a joke out of this, or use it as an excuse to believe whatever they want ("Are eggs good for you this week or bad? LOL").

I'm open-minded, though, Mike. I dove a GF of 40/85 today on the Roy A. Jodrey. I think too many eggs and too many bubbles are bad.

 

[doctormike]

I'm open-minded, though, Mike. I dove a GF of 40/85 today on the Roy A. Jodrey. I think too many eggs and too many bubbles are bad.

If you get bent, the FIRST question I'm going to ask you is "what did you have for breakfast?"

 

[Trace Malinowski]

If you get bent, the FIRST question I'm going to ask you is "what did you have for breakfast?"

If eggs are bad that week they could be a factor.

 

[GJC]

You're talking 2 simple equations and a 16x5 table of numbers, that's all there is to ZHL-16. And when you run into someone who understands the real system, the result may be the opposite of what you want: didn't we recently have a physicist point out that helium kinetics in the model make no physical sense. I've a pet peeve about oxygen, myself: the model simply subtracts it from "inert gas", all the way to 100%. I'm reasonably certain I can't metabolize 100% of it, the model says it doesn't dissolve and bubble out later, so it just goes *poof*. So, you know... be careful with what you wish for.

Doesn't you body use oxygen faster than it can bubble out of solution?

Are there deco tables for oxygen?