Old topic.....

[canuckton]

>"At shallow depths, more and more time is needed to achieve a >good gas load. If you are a deep-sea diver with a surface >supply (hose), you could stay at a shallow depth for quite a few >hours since the gas supply is unlimited. You endurance is not, >however. For long exposures, it necessary that one be in an >underwater habitat or a hyperbaric chamber in a laboratory."

Could that be construed as "controlled environment?"

>"It appears that the shallowest depth from which one can >ascend and still get the bends is about 25 feet. That is after an >exposure of 48 hours. "

Why? Is there a minimum amount of pressure that needs to be exerted on human tissues before there is significant solubility of inert gases?

>[sp]Ikeda T, Okamoto Y, Hashimoto A. Bubble formation and >decompression sickness on direct ascent from shallow air >saturation diving. Aviat Space Environ Med 1993 Feb;64(2):121->5) Doppler bubble have been found from shallower exposures.

I couldn't find this one...how can I get a copy?

>"The problem is true that as DCS becomes milder and milder, it >passes completely into the “subclinical” range. This is then the >realm of Doppler Bubbles. The minimum is probably determined >by the largest microbubbles (“seeds” or micronuclei) that are >present in large numbers."

Is it still DCS if it is "subclinical?" Is that to say as you pass into the "subclinical" range of DCS testing that the Doppler bubbles will remain asymptomatic?

Dr Deco, I am wondering if your research delves into this realm of small pressure differentials?

In my area, some commercial divers do marathon bottom times on "hookah" systems while harvesting Red Urchins or Geoducks. I would like to understand the physiologies and physics of these long bottom times at shallow depths.

Thanks ,
Canuckton

 

[Dr Deco]

Dear Readers:

This is a very interesting letter as far as I am concerned. There are certain conditions that must be met for decompression sickness to occur.

• a sufficient “chemical potential” (= great enough partial pressure of dissolved inert gas,
• a sufficient number of nuclei whose diameter is greater than the “Laplace cutoff” ( and this is determined by the surface tension and the degree of supersaturation = “chemical potential”),
• bubble formation in those tissues that respond negatively to the presence of a growing free gas phase.

For DCS, all of these conditions must be met.

There is not a minimum depth for the solubility of inert gas. Inert gas is dissolved in your tissues at one atmosphere of pressure. If you ascent to altitude to a sufficient degree, you will get altitude DCS from that gas that is dissolve when on the surface. Going deeper simply adds more inert gas in a predictable and linear fashion. This is Henry’s law.

You are correct (in my cosmology) in stating that DCS will not occur if one does not have a sufficient number of gas nuclei whose radius is larger than the critical nucleus (the Laplace cutoff).
I believe that the physical basis for the MINIMUM DEPTH is that a sufficient number of large nuclei simply do not exist in the tissues. This concept is contrasted with the Haldane idea of CRITICAL SUPERSATURATION LIMITS. The two are essential interchangeable in that radius and “chemical potential” (= supersaturation) are related.

There is not any indication that “subclinical decompression sickness” results in any problems. However, many individuals believe that the feelings of lethargy and fatigue that accompany some dives are directly the result of minor gas bubble growth in some tissues (such as muscle). The hypoxia that results from the blockage of capillaries in muscles might produce effects that are similar to heavy exercise.
Dr Deco :doctor: