Reverse profiles--pro's & con's

[rcohn]

I attributed an original thought to UP. After checking the Techdiver archive of course we see the concept of shallow first comes from (or at least through) George Irvine.

http://www.aquanaut.com/bin/mlist/aquanaut/techdiver/display?52239,subject
.

I think you can see where I am going to tell you that you need to do
your shallowest dives first, do your drills before yo do your dives, and why
you can basically ignore repetitive dives using the correct deco. You can
NOT ignore them with respect to oxygen exposure.

From GI3, comments on bubbles compressing and passing through the lung filter, http://www.aquanaut.com/bin/mlist/aquanaut/techdiver/display?48622,subject

Now here is the important part. If you understand everything I have said
above, then you know that bouncing to 20 feet or whatever to pick up a
bottle and immediately returning to the surface is the like giving yourself
a home-made PFO: the bubbles in the venous side compress enough to get past
the lungs and then will reexpand on the arterial side and lodge in the
worst places , the spine and brain blood supplies. You do not want this.

Also from http://www.aquanaut.com/bin/mlist/aquanaut/techdiver/display?52239,subject
.

You do not bubble into the arteries. If bubbles get into the arteries
it is because they passed the filter or were "shunted" over through a PFO in
the arterial walls, or because they were momentarily compressed enough
momentarily to get past the lungs and then reexpanded as the pressure
dropped prior to reaching the capillaries, in which case they lodge in the
smaller and smaller vessels and block them. This occurs in bounce diving, as
in doing a dive and then bouncing back down to retrieve something, like a
deco bottle.

I don't see words like "maybe" or "theory" in here.

Ralph

 

[pipedope]

You also won't see any attribution of controlled studies or use of air as a diving gas in those articles by G.I..

Having read the GI stuff on deco I think you can only apply it to *his* diving including the dive profiles and gasses used.
Do NOT attempt to apply what he is doing directly to air diving. Remember that He is a very fast gas. It goes into you fast and comes out fast. That is why his deco system works for him.

I think that diving anything even remotely like that on air would be dangerous in the extreem.

 

[Waterlover]

2. It is then taught that the reason (not just a theory) is bubbles compressing and bypassing the lung filter. Not good, the evidence weighs against this theory and the empirical experience of the tech divers offers no insights into the underlying causes of DCS. I still wonder why they feel the need to pretend they know all the answers?

Ralph,
with regard to your statement I see evidence that it does occur:

" Arterialization of Venous Bubbles...The bubble-trapping quality of the lung is degraded by pulmonary hypertension and may be overwhelmed where there is considerable volume or rapid delivery of venous gas. The transpulmonary passage of bubbles is also promoted by oxygen toxicity, the use of bronchodilators and bubble recompression during the recompression of divers." ( Butler & Katz 1988)( Butler & Hills 1981;1985)

IMO,I think what we may be seeing is a large volume of bubbles which in fact do get by the lungs, possibly aided by the compression on that bounce dive back to 20 ft.
Ken

 

[Uncle Pug]

Originally posted by rcohn
I attributed an original thought to UP. After checking the Techdiver archive of course we see the concept of shallow first comes from (or at least through) George Irvine.

Shoot, no problem Ralph... you've been wrong before and you'll be wrong again but we love you anyway....

You just missed the end of my second post in this thread where I wrote:
~~~~~~~~~~~~~~~~~~~~~
But I don't know for sure...
Just repeating what I was taught...
No personal experience...
I haven't been hit myself...
~~~~~~~~~~~~~~~~~~~~~
Keep reading George though... great stuff... and he has the experience to back up what he says... unlike you and me and the guy with the theoree!

 

[rcohn]

Waterlover,

That is an old quote and I'm not sure what research backs it up. The theory that bubbles get past the lung has been around for a long time, this statement may be based on the theory alone.

I do know that in 1995 the idea that bronchodilators allow the lung filter to be bypassed was considered to be unproven. This is one of the four reasons generally given to support the concept that asthmatic divers are unfit to dive and was discussed in the Undersea and Hyperbaric Medical Society Workshop Are asthmatics fit to dive?. No information was presented to support this theory and the statistics showing no increased risk of DCS in asthmatic divers would tend to refute it. I've heard nothing in any asthma and diving discussion since 1995 to support the idea that bronchodilators increase the risk of DCS.

As to the rest of the quote, I have no information, you should ask Dr. Deco when he returns.

IMO (the following is my speculation) if large volumes of bubbles were bypassing the lungs they would easily be detected in dry chamber experiments which has not been the case according to Dr. Deco. This means that only small bubbles in low volumes (if any) could be passing and are unlikely to be the cause of the increased hit rate.

Ralph

 

[Alban]

There is some info http://www.ssiusa.com/articles/reverseprofiles.htm

Alban

 

[Lost Yooper]

Hey Mike:


I'm not too up on the detailed physiology of persistent bubbles, but there are a number of mechanisms that are well-documented that can allow bubbles to be observed in arterial circulation :

1) "The Chokes" rapid and severe onset of DCS from excessive missed deco. It's hard to say just what part of this trauma leads to death, but bubbles overload the filters and pass into arterial circulation.

2) Rupture of the capillaries. Blood itself will almost certainly not bubble --even under the most extreme diving decompressions. Contrary to popular belief, bubbles are probably not formed in the circulation, but break into capillaries and then flow through. It is thought by some researchers that the body's immune system reacts to these microscopic injuries in ways that we perceive as feeling sick, tired, or not-right --even if we aren't overtly bent.

3) Patent Foramen Ovale (PFO), where the heart's chambers have a venous/arterial shunt that should have sealed shut soon after birth. Something like 10% of the population has this congenital defect, while 40% of dcs incidents are in divers with pfo.

4) As you point out: Recompression of a diver with bubbles in circulation may allow bubbles to sneak through to the arterial side. On decompression, these bubbles would likely be trapped at the capillaries or in the lung's filters. Hopefully not in the brain, where they could cause a stroke.

The Winter issue of GUE's "Quest" magazine has a good article on PFO, with lots of references.


Eric