Deep Stops

[ric morte]

Just saw this on DAN:

<a href="http://www.divernet.com/news/stories/bends261003.shtml" >http://www.divernet.com/news/stories/bends261003.shtml</a>

Interesting that the 10m/min ascent rate with deep stops produced fewer bubbles than an ascent rate of 3m/min. Doesn't say how long the stops were though.

[neil richmond]

Ric

I have read an over view of the study and it would appear that in diver terms the continual ascent at 3m/min leads to a continually changing presure gradient that encourages bubble formation and growth. The apparently faster ascent at 10m/min allows bubbles to form but they are more effectively filtered out by the lungs by doing the deeper stops. during the stops the entire blood volume has time to pass through teh lungs, ansuring that any bubbles or seed bubbles have a chance to be filtered out,

This also allows the entire bloood volume to get closer to equilibrium in terms of gas pressure with the ambient pressure at stop depth, rather than having blood in different part of the body at differnmt relative pressure gradients depending on when it last went through the lungs and hence gas exchange process during the continual ascent

It is generaly accepted that it takes about 2 minutes for a complete cycle of the blood round the body so it would make sense that a 2 minute stop would be effective at getting as close to equilibrium as possible in as short a period as possible

Regards

Neil

[Nick McV]

I find it interesting that no one seems to talk about breathing rate at a deco stop.

If you are really relaxed at a 1min/6m stop, you might flush your lungs 4 or 5 times, at a moderate breathing rate this may be around 18 cycles. Moderating your breathing to help achieve neutral buoyancy will also affect this rate.

This must affect the pressure gradient in the lungs and therefore the rate at which N2 is passed out of the bloodstream.

I tend to try to take deep breaths to increase the tidal volume in the hope that this will improve off-gassing. I have no backup to this theory, it just seems like a good idea to me. If I've got gas left - I might as well use it, the dive shop doesn't charge any less if there's 90bar left in your tank instead of 50bar!!!!

Anyone got any opinions or info relating to this???

Nick

[Nigel Hewitt]

I find it interesting that no one seems to talk about breathing rate at a deco stop.

Anyone got any opinions or info relating to this???

I would say breathing rate would have little effect.

I am reasoning that the gas transfer depends only on the difference between the individual inert gas pp in the lungs and its tension in the blood. The volume rate of transfer of inerts isn't going to be fast enough to change the pp significantly during one breath so the inert won't build up in the avioli to decrease the transfer rate.

I'm very interested in the DAN findings as I had progressively reduced my ascent rate over the years and switching back up to 10m/min with 2min breaks actually seems a more convenient way to do things.

nigelH