Orientation during deco/safety stop

[DrSteve]

Hi,

I was chatting with an ex user of SB last weekend and he told me that he always does his deco and safety stops horizontal. His reasoning was the pressure differential between feet and outstretched arm was too great and could contribute to greater deco risk.

So I did a quick calculation based ona uniform body 10 feet long. At 20 feet the absolute pressue is 1.61ata, at 15ft and 25 ft it is 1.46 and 1.76 ata respectively. This gives a pressure differential of 0.31 ata (approx). So the difference in volume between a gas bubble of unit size in the upper extremity and the lower extremity is 1.21x.

As a chemist this isn't a huge difference to me (and I wonder if he lays down when he flies just in case), but I am curious as to if this makes a difference once the body chemistry and physiology is taken into account. After all, the trunk area is where the gas exchange is happening.

Any thoughts or comments? I think his idea is fine in principle, I just wonder if it is going to an extreme.

 

[gcbryan]

This doesn't really answer your question but he may not be going to an extreme because he may ascend horizontally in the first place so just maintaining that attitude during a safety/deco stop would be natural. I find it more comfortable and stable.

 

[Dr Deco]

Hello Dr Steve:

There is such a degree of safety built into decompression tables and meters that something such as body position would not make a difference in decompression incidence.

You can rest assured vertical or horizontal will produce the same result.

Dr Deco :doctor:

The next class in Decompression Physiology for 2006 is September 16 – 17. :1book: http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[bennedc]

I usually just hang on to the anchorline or rope or whatever there is and just hold on...however I orient with the current is how I hang. No sense fighting the current if there is any!

I saw a diver do something really smart once...she brought a lanyard with her and tied it to the anchorline. That way, she could hold on to her lanyard a little bit off of the line and not get in the other divers' way. Cool idea.

 

[Kevrumbo]

I was told in my DIR-F Class that the Lungs have greater vascularization in the middle to lower third of the organ as a whole. Therefore you would have slightly more efficiency in off-gassing from a Horizontal Position vs. a Vertical Position, because a greater cross-section of that Lung vascularization is exposed to the absolute pressure/gradient effects as you progress along by your Deco Schedule/Profile or Safety Stop. Put in another way, visualize it as cutting a thin slice through the entire length of the Lung, as opposed to a transverse thin slice through only the width: which would yield a greater tissue cross-section?

 

[gcbryan]

I was told in my DIR-F Class that the Lungs have greater vascularization in the middle to lower third of the organ as a whole. Therefore you would have slightly more efficiency in off-gassing from a Horizontal Position vs. a Vertical Position, because a greater cross-section of that Lung vascularization is exposed to the absolute pressure/gradient effects as you progress along by your Deco Schedule/Profile or Safety Stop. Put in another way, visualize it as cutting a thin slice through the entire length of the Lung, as opposed to a transverse thin slice through only the width: which would yield a greater tissue cross-section?

Then it must be true.

 

[DrSteve]

Put in another way, visualize it as cutting a thin slice through the entire length of the Lung, as opposed to a transverse thin slice through only the width: which would yield a greater tissue cross-section?

Clearly laying at an angle will give an even bigger cross section

 

[DA Aquamaster]

My understanding when trained with US Navy tables, way back when, is that they were designed with the idea that your chest would be at or below the stop depth.

Personally,I don't think it makes a hill of beans worth of difference whether I or my lungs are horizontal or vertical during the stop. Any increases in effectiveness in a horizontal position would probably be made up for in a vertical postion by extending the stop about 1/2 of a second. Practically speaking, at any stop, I'd prefer to err on the side of caution and be a foot or so deeper if their are waves etc. So in that vein, staying vertical would theoretically seem to put most of me at a slightly greater pressure and would keep me from fizzing quite as much.

But again it has never made any difference in my opinion, and I will stay vertical or horizontal as the current, conditions and comfort dictate.

 

[Kevrumbo]

Clearly laying at an angle will give an even bigger cross section

Yes; as it turns out, I'm slightly oblique to the horizontal anyway as the gas bubble in my drysuit migrates up and exhausts out during ascent/Deco Stops. . .

(P.S.> Congrats on the newbie Newborn !)

 

[DrSteve]

Yes; as it turns out, I'm slightly oblique to the horizontal anyway as the gas bubble in my drysuit migrates up and exhausts out during ascent/Deco Stops. . .

(P.S.> Congrats on the newbie Newborn !)

Thanks He's not quite so new now and is getting huge...14lbs 14oz last time he was weighed. If he actually took a pacifier I might be able to get him a "Junior reg", but I spose I will have to wait At 25 inches, he also wouldn't need to worry about such things as orientation during deco!