Gas density guidelines

[fsardone]

Just got done with reading the papers. Very interesting stuff.

I seem to recall a discussion around some videos of guys doing deep CCR diving with the little "cough" at the end of each breath indicating they were pretty close to the edge for gas density without realising. Watching the Shaw footage after that, knowing what I was listening to, was very sobering.

And the deep stop comment was firmly tongue in cheek, I have had enough of that conversation for a lifetime honestly. Seems the mods have too.

The cough was due to dynamic air way collapse and the diver was Dave Shaw during his last dive. You can find the whole video on you tube.
The coughing fragment was used by Dr Mitchell in one of his presentations on why in hyperbaric condition we are limited in the amount of gas we can ventilate no matter how hard we try. Hence bound to retain carbon dyoxide we produce with methabolism aand unable to ventilate out.

Cheers

 

[huwporter]

Simon, I realise the decompression stress paper wasn't yours, but do you know any way I could find more information on the correlation between blood cholesterol and being bubble prone? (As a technical diver with Familial Hypercholesterolaemia (under treatment) this is highly relevant to me...)

 

[RainPilot]

The cough was due to dynamic air way collapse and the diver was Dave Shaw during his last dive. You can find the whole video on you tube.
The coughing fragment was used by Dr Mitchell in one of his presentations on why in hyperbaric condition we are limited in the amount of gas we can ventilate no matter how hard we try. Hence bound to retain carbon dyoxide we produce with methabolism aand unable to ventilate out.

Cheers

Thanks fsardone. The footage I was referring to was some footage of (IIRC) guys exploring a spring system in New Zealand. We had all seen the Shaw footage, what caught me was hearing the same thing on several other videos of dives where everyone thought they were fine. Again, if memory serves, Dr Mitchell pointed out several examples of this on YouTube from "uneventful" dives as an example of how many divers were on the edge of serious issues without even knowing it.

 

[RainPilot]

Because I was bored I threw together a little XLS file to do some gas calcs , you can find it here:


Looks like this, fairly self explanatory:

Screen Shot 2016-08-25 At 14.07.22

• RainPilot
• Aug 25, 2016

Edit: Added END and PPO2 because why not. O2 considered narcotic.
Also, uploaded file instead of dropbox

 

[RainPilot]

Uploading file here instead of Dropbox, updated screenshot.

 

[dreamdive]

Simon, I realise the decompression stress paper wasn't yours, but do you know any way I could find more information on the correlation between blood cholesterol and being bubble prone? (As a technical diver with Familial Hypercholesterolaemia (under treatment) this is highly relevant to me...)

Schellart NAM, Nico AM – Free Fatty Acids Do Not Influence Venous Gas Embolism in Divers

Aviat Space Environ Med 2014; 85 (11): 1086-91


I don't remember seeing one on blood cholesterol - maybe Simon has.

 

[Dr Simon Mitchell]

Thanks a lot for that clarification.

Hello Storker,

I have heard back from Gavin.

He has virtually identical data for open circuit. Same risk inflection.

Simon

 

[Dr Simon Mitchell]

Simon, I realise the decompression stress paper wasn't yours, but do you know any way I could find more information on the correlation between blood cholesterol and being bubble prone? (As a technical diver with Familial Hypercholesterolaemia (under treatment) this is highly relevant to me...)

Hello,

The paper cited by Neil can be found here:

Blood factors and venous gas emboli: surface to 429 mmHg (8.3 psi)

This paper looked for potential associations between divers who developed high bubble grades after a standard dry chamber exposure and a variety of physiological parameters. High cholesterol was one of the parameters that had an association with high VGE. Having said that, the paper does not establish a direct causal relationship between cholesterol and VGE. Indeed, it is somewhat implausible that such a relationship exists. It is more likely that cholesterol is associated with something else that is the causal factor, such as being overweight, or some particular genetic profile, or lack of regular exercise or ????? That, of course, may not be of much comfort to you because you may "suffer" from whatever one of these causal factors is indeed linked to high cholesterol (but you might not too). I would not get overly concerned about this. The way to view it is that you should try to manage any other potentially negative things potentially associated with high cholesterol (such as excess weight and lack of regular exercise) and see the paper, if anything, as an indicator that conservative approaches to decompression are a good idea for you.

The paper may not be the final answer on this issue either. I am not being dismissive, but it is one publication. As Claudia says, the paper she pointed out is not about cholesterol, but is also interesting.

Simon M

 

[huwporter]

Thanks Simon and Claudia, lots of reading material there.

An immediate observation (...relevant to the distinction between causality and correlation), the most consistent strongly significant difference between the bubble prone and resistant groups (- the only factor significant at >p0.01 for all of the male, female and combined groups -) is age, and as cholesterol levels rise with age I'd wonder if the observed differences in total and HDL cholesterol could be an effect of this and not an independent factor.

Taken in conjunction with Claudia's paper I'd agree that this doesn't appear to be something to go overboard about at this point, and that other factors (such as overall fitness) would be much more important.

(Also, as a statistician, I have to say that is an interesting scattergun approach to experimental design - with that many factors evaluated you would expect to see significant differences at at least p0.05 for a couple of factors purely by chance... )

 

[fsardone]

Because I was bored I threw together a little XLS file to do some gas calcs , you can find it here:

Hello RainPilot,
I was rereading through this thread (I find re-reading things useful to better understanding, Thanks Simon for posting here), and I thought using as a basis your exel file to develop a spreadsheet that ,given diluent and setpoint, would calculate breathing gas density at depth for CCR.

Keep in mind that this does not take into account effect of water vapour, which can be easily ignored in OC breathing but I believe not in CCR breathing since we are at 100% RH condensing. On the other end humid air is less dense than dry.

Just for fun I filled in the data showing that a good diluent might lead to a marginal breathing mix.

Cheers
Fabio