Lung irritation - PO2 vs. FO2

[Kendall Raine]

Atticus

Aside from the issue of whether the presence of an inert gas has an effect on lung irritation, there are benefits to using 100% at 20 rather than 80/20 at 33 which are not necessarily reflected in decompression models. These benefits are heavily dependent upon gas selection during the whole dive, not just the last deco gas, as well as deco technique. The evidence is found in the field, not the text book.

 

[dlegros]

Dr Deco once bubbled...
Mechanism - - -

It is independent of the type of inert gas, and the effect is probably physical.

It has been proposed that it delays what is known as absortion atelectasis. This is the collapse of an alveolus because the oxygen is utilized by metabolism.

Dr Deco
:doctor:

Hmmm. Food for though there - I can certainly see the logic that presence of an inert could prevent such a phenomenon. Not sure about the link between atelectasis and super-oxide formation, but this is getting into territory to deep for my nursey feet

Thanks for all the info.

Dom

 

[Atticus]

Hi Kendall,

Thanks for your reply.

It is precisely because of this that I brought the subject of 100% up to my NAUI trained trimix dive buddy.

As I understand it (from reading a couple of papers) the benefit of 100% at 20' has to do with the oxygen window, or, more precisely, with reduced venous blood gas pressure. The real trick of the oxygen window is the flat spot in the plot of ppO2 vs. CO2 production.

This effect is often used by switching to 50% at 70' for a few minutes, then ascending with stops to 20' where the diver switches to 100%.

The benefit of an approach like this as opposed to, say, a constant ppO2 rebreather is that between 70' and 20' the ppO2 drops which gives the lungs a chance to recover from any vasoconstriction due to high ppO2 at the 70' stop.

Additional backgas breaks may be needed at the 20' stop, depending on duration for the same reason.

I'm in no way trying to create a debate between 80% and 100% - there are some very good arguments on both sides and this has been beat to death.

I am trying to get the facts and resolve a few things I didn't understand (such as the benefits of inert gas in 80% that my buddy brought up).

If any of the above doesn't sound right, please feel free to correct me. I'd much prefer to have good information.

Best Regards,
Atticus

 

[Kendall Raine]

Agreed, Atticus.

Oxygen window is one benefit, but an important one. With 100%, I know the inert gas elimination is as rapid as I can get it for any given pressure. With toggling (as you point out) and movement (as Dr. Deco has said many times), I can improve on this further.

Also, to the extent I'm suffering sub-clinical DCS issues during the hang, I'm already conducting HBO therapy. I'm pretty sure I've "unbent" myself from a number of dives without ever knowing for sure.

If I subsequently need O2 treatment on the surface, I've got it.

The list goes on, as you know.

At the end of the day, the issue to me is what works better. The real world case for 100% has been made pretty convincingly.