interesting...

[Dr Deco]

Hi SCUBA:

Early Diving Bells

In the 1920s, the bell invented by Sir Robert Davis came into use. The diver would ascend to the first Haldane stop and complete the decompression inside a protected environment. For some of this period he might be standing, especially when he removed his gear.

Later, decompression was often accomplished in deck decompression chambers to allow for a safe, dry environment for the diver and tender. These environments (I believe) allow lower body stress to be added to the decompressed individuals and bubble nuclei to be formed and grow. All decompression tests in the laboratory are performed with moving subjects in a dry chamber (although bottom exposure might sometimes be in a wet pot).

US Navy tests are not performed with subjects suspended in water and tech diver decos are not performed by divers in a chamber. We would thus have a difficulty in comparing the efficiency of these two procedures since they are not the same with respect to the possibility of nuclei formation.

WKPP and Deco

I suspect that the time period that the divers are suspended in the water (and stress free with respect to nuclei formation) is what gives them a real edge. This adynamia is also true of deep tech divers and can reduce the DCS incidence considerable. In tests of altitude decompression at NASA, the incidence was reduced by sometimes a factor of ten fold (not 10% but ten times).

It is for this reason that I have said that the WKPP (and tech diver) decos work but possibly not completely for the reasons stated.

Anesthetized verse Non-anesthetized Animals

Anesthetized animals always produce fewer bubbles; “the bends” cannot be told since the animals are asleep. Among animals, slow decompressions (e.g., taking two minutes) are always better than those that are fast and require but a fraction of a minute.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Saturation]

There are several skills and dispositions that technical divers use to reduce workload and thus, reduce gas consumption and increase range. These techniques reduce exertion in the dive, and thus, also serve to reduce the likelihood of nucleation from many phenomena such as cavitation, tribunucleation etc., These skills are nearly universally considered in cave diving, as opposed to general technical diving per se.

Streamlining gear: Reduced profile cuts the water easier. A cave rig makes swimming easier in a current or high flow caves even when carrying stage bottles. Note a single tank in a streamlined rig is still more streamlined than streamlined doubles optimized for caving

The prone position and frog kicking is part of streamlining

Bring only the gear needed for a dive, reduces the dangling and drag of these items

A GUE emphasis is also on pockets to house gear, and also reduce their drag profile

The emphasis on scooters in the GUE curricula suggest, a further extension of the no-exertion approach to diving

Cave diving includes a recommended rest period on the surface after decompression before alighting from the cave area.

 

[Saturation]

Dr Deco once bubbled...
Hello Saturation:

Activity and Nucleation

There are considerable data linking musculoskeletal activity and DCS. What is not demonstrable is that nucleation is the root cause. That is my extension of ideas of early researchers such as Harvey and Dean. The difference is that these individuals proposed nuclei stabilization in, e.g., cell wall junctions. These were not really thought to be stable. It is my opinion that we are dealing with a constantly renewing distribution of nuclei, generated by musculoskeletal activity. This makes sense based on work in physical systems but the direct sampling of micronuclei from intracellular fluids is not possible. Thus we simply demonstrate the presence of nuclei by depressurization, but this is conjectural (but logical).

I believe that we are dealing with what hydrodynamic engineers refer to as free stream nuclei as contrasted with wall nuclei (Harvey’s idea).

Dear Dr. Deco:

Many thanks for this academic reply with detailed referencing. It forced me to hit the books again, Bennett and Elliott's Physiology and Medicine of Diving, 2003 and indeed, the section I did not detail in depth was decompression theory. It did mention the issues of nucleation with exertion and referred to some of your work. It also touched on various theories whether the nuclei were always present, created de novo, by tribonucleation etc.,

 

[Saturation]

Dr Deco once bubbled...

Anesthetized verse Non-anesthetized Animals

Anesthetized animals always produce fewer bubbles; “the bends” cannot be told since the animals are asleep. Among animals, slow decompressions (e.g., taking two minutes) are always better than those that are fast and require but a fraction of a minute.

[/font] Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm [/B]

In some studies were proxies for DCI used, i.e., venous bubbles assayed by doppler?

I'd imagine if an inert gas load that would invariable be fatal without decompression were selected on purpose and used on anesthetized animals without fatal outcome, the results would be without question.

 

[Dr Deco]

Dear Saturation:

Proxy DCS

The animals, usually rats, would be dived on profiles that might produce death in, e.g., 80% of the animals. Another group on the same profile, but this time anesthetized, would have an incidence of death of, say, 20%. The death of these animals results from a massive formation of gas bubbles in [muscle and fat] tissue and a release of that into the venous return. Death comes from a right heart air lock and a loss of cardiac output. Often there is also arterialization of venous gas bubbles.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Saturation]

Dr Deco once bubbled...
Dear Saturation:

Proxy DCS

The animals, usually rats, would be dived on profiles that might produce death in, e.g., 80% of the animals. Another group on the same profile, but this time anesthetized, would have an incidence of death of, say, 20%. The death of these animals results from a massive formation of gas bubbles in [muscle and fat] tissue and a release of that into the venous return. Death comes from a right heart air lock and a loss of cardiac output. Often there is also arterialization of venous gas bubbles.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

Hi Dr. Deco:

In animal testing for products and drugs, there still is an LD50 dose, lethal dose enough to kill 50% of test subjects. In product testing [e.g. cosmetics], I'm not sure what it serves these days.

An LD80 would be startling indeed. In the test you mention, it would be unquestionable that motion and activity contribute to morbidity and mortality.

 

[Dr Deco]

What happens during the motion in the rats, is that a large number of gas bubbles are formed and released, and the rats die. When they are motionless, the bubble formation is considerably reduced.

That would imply some factor in musculoskeletal activity is involved. Proposed has been bubble formation, bubble release from capilaries, and production of carbon dioxide adding to the inert gas load. [This last is an old concept from WW II.]

Dr D.

 

[ffelix]

So--if I understand your arguments--suppression of nuclei formation &, therefore, bubbles is facilitated through slow ascent & reduced exertion. And oxygen decompression at depth exploits partial pressure differences to dump nitrogen early in the decompression process.

Since (by some counts) 50% of DCI patients were bent while "diving the tables", it seems that the use of a deep (80%), short oxygen safety stop would be useful even for relatively shallow dives by no-decompression recreational divers.

Has this been studied or advocated? Technical use of stage bottles apparently starts much deeper and well past no-deco limits.

This would seem a better potential use of a pony than as a redundant air supply :mean:. It's not as though you could overdo it with so little capacity.

 

[Saturation]

Yes, F, I would say your viewpoint sums it up.

A majority of DCS 2 that happen with bends within table limits are likely from divers with PFOs, rapid ascents, or barotrauma rather than true bends.

Since all dives are deco dives, recreational dives being simply no-stop dives with 'deco' on the surface, any procedure to reduce inert gas loads before surfacing will reduce bubbling. So a pp02 raised to 1.6 during the ascent phase would help any dive.

Which brings up the issue of technical diving. A technically trained diver need not dive technical all the time, but the added skills and knowledge provided during this training provides a huge margin of extra skills, especially when said diver simply dives recreationally.

I known of no formal studies using 02 in no-stop dives, but the use of 02 in stop dives is well established. An issues is how much trouble less trained individuals would get themselves into given a formal recommendation to use 02 in no-stop dives. The risk/benefit ratio is a bit skewed. A worse case scenario is drowning from oxygen toxicity over exceedingly rare instance DCS 2 in recreational diving has had a fatal outcome.

 

[Dr Deco]

Hello ffelix:

Oxygen at Depth

It probably would be of value but I am not really sure if it would be worth the effort. There are various ways to maximize the efficiency and, if you were to add all of them together, you would probably be constantly worrying and not enjoy the dive.

When commercial and military divers use oxygen in the water, which they do, they have a team of individuals to watch over the whole process and to assist the diver. In addition, the oxygen used is applied in sufficient amounts (from the surface) to make a truly meaningful difference in the decompression.

Neurological DCS

I suppose I would have to take issue with the statement that a “majority of DCS 2 that happen with bends within table limits are likely from divers with PFOs, rapid ascents, or barotrauma rather than true bends.” I am definitely of the persuasion that bending and flexing of the spinal cord during reboarding with gear, etc, can be a nucleating activity. This is not an "arterialization mechanism." This can only be determined by watchfulness on the part of divers in the field, and the reports that they deliver. It will never be possible to get a laboratory test with humans of spinal neurological DCS by autochthonous (= bubbles formed in place) bubbles because of the danger of this direct provocation. We have covered this before on this FORUM.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm