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Trimix gas switching
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a) they are not my remarks, I was very open about the source
but more importantly they seem to match a lot of anecdotal evidence coming from the RB foruns where we are seeing a lot of vestibular bends when swapping off of helium mixes to denser N2 containing mixes. But we also see a few of them on air dill all the way and on He based dil all the way
We just dont understand what is going on here.
In the meantime I'm staying on the helium and taking the extra 5 mins stops. Having suffered minor vertigo on several dives due to ear temperature differentials (I hate wearing thick hoods, so I wear thin neoprene which sometimes lets water to the ears if you move wrong), I'd hate to have a major attack. Its quite fun surfacing when the surface is at 45 degs:upset:
but more importantly they seem to match a lot of anecdotal evidence coming from the RB foruns where we are seeing a lot of vestibular bends when swapping off of helium mixes to denser N2 containing mixes. But we also see a few of them on air dill all the way and on He based dil all the way
We just dont understand what is going on here.
In the meantime I'm staying on the helium and taking the extra 5 mins stops. Having suffered minor vertigo on several dives due to ear temperature differentials (I hate wearing thick hoods, so I wear thin neoprene which sometimes lets water to the ears if you move wrong), I'd hate to have a major attack. Its quite fun surfacing when the surface is at 45 degs:upset:
This is an area of particular concern to me, since I am working my way toward the 500+ fsw mark with my Extended Range Inspiration.
It is unclear what is occurring here, but I would be the last to ignore reports of trouble from the field. It is perplexing that these events are happening on straight air diluent, and helium dil surface to surface as well. Fortunately, we have some extremely good sources to contact, such as Doc Deco on this board, O'Leary of NAUI, Wienke, Savatsky, et al. I will post this report to them via private e-mail and see what information they can offer.
As for the rest, let's see now...ice cold water pouring into my ears...air temp 45 degrees Farenheit on the surface...God, how I envy you!
Cheers, and happy no-bubbles diving!
Eh, dove il Dottore Deco? Over to you, Doc!
I meant an angle of 45 degs, Youd be in trouble here if the water was 45 degs temp wise (we use C!!)
is 45 F hot or cold?
Heres a fun suggestion
a) hang on deco line at 3m
b) Watch surface
c) lift hood off one ear
d) Watch surface move
is 45 F hot or cold?
Heres a fun suggestion
a) hang on deco line at 3m
b) Watch surface
c) lift hood off one ear
d) Watch surface move
madmole once bubbled...
I meant an angle of 45 degs, Youd be in trouble here if the water was 45 degs temp wise (we use C!!)
is 45 F hot or cold?
Heres a fun suggestion
a) hang on deco line at 3m
b) Watch surface
c) lift hood off one ear
d) Watch surface move
Hey, that sounds like stacks of fun! A really exciting alternative to playing "Octo" on your VR3!
Ta muchly!
Dr Deco
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Dear Readers:
I did not see this thread and it was pointed out to me that there were some questions with which I might be of assistance. The replies are not in any particular order.
Switches
Switching from a less soluble to a more soluble gas is a decades-old method. It was instigated by the Swiss mathematician and diver Hans Keller in the late 1950s. It has been found that the gas switches (e.g., helium to nitrogen mixes) must be performed slowly to prevent vestibular problems. This is more easily done breathing the gases in a decompression chamber than with a mouthpiece.
Helium and Nitrogen Solubility
Nitrogen is more soluble than helium in both aqueous and lipid tissues (and any combination of the two components).
Goats ?
The reason goats were used in the early research by Haldane was that their body mass was large and they had decompression characteristics somewhat similar to human divers. The goats would also lift their sore leg if they had a joint pain (the bends).
Goats were easy to work with, and their only problem was eating anything they could reach. [Once a goat remarked to Haldane, I liked your report, but I thought your book was better.=-) ]
Two Gases and Diffusion
When a material diffuses, the motive power is heat. Molecules jostle around at any temperature above absolute zero and will randomly change their position (e.g., Brownian motion). They do this independently of the other molecules around them.
One molecule (e.g., nitrogen) is not hindered (or blocked) in its motion when another molecule (e.g., helium) is present in a solution (or in a mixture of gases). Thus, the out flux of helium is not changed by the in flux of nitrogen in a solution. {The distance that the molecules travel, however, is modified by the fact that they hit water molecules, but that is a different question (the mean free path) .} There is no coupling this diffusion process, that is, the molecules move independently. This might not be true if the molecules possessed an electrical charge, for example.
Steady State Counter Diffusion
This is one of two general types. It was the first found in barophysiology during deep dive experiments with neon as a breathing gas. It involved the diffusion of a lighter gas through the skin and into tissue perfused with a less diffusible gas. [In this example, the diver was surrounded by helium and breathing neon.] This is termed steady state or superficial countertransport. { Lambertsen CJ, Idicula J. A new gas lesion syndrome in man, induced by "isobaric gas counter diffusion". J Appl Physiol. 1975; 39(3):434-43.} This case produced lesions (sores) on the skin of divers in hyperbaric chambers. This occurred without decompression, thus the term isobaric (= same pressure). Tissue nuclei present can grow in this situation even in the absence of decompression.
Transient Counter Diffusion
The other type appears with the switching of breathing gases where a less soluble gas (helium) is transported to a tissue containing a more soluble one (e.g. nitrogen). Apparently, one gas will dissolve faster than the other can exsolve and the sum of the partial pressures exceed the ambient pressure. Nuclei present can grow in this situation even if there is not a decompression.
Vestibular DCS
This malady is hypothesized to result fro the inward flux of helium from the space in the middle ear into the vestibular apparatus. Slow gas switches seem to alleviate this problem.
Attachment?
Its has to do with the larger nitrogen molecules attaching to the He bubble seeds. A small He bubble is mobile and diffuses quickly, once the N attaches it alters the physical properties of the bubble. A sort of RGBM plus.
Tissue helium bubbles are not mobile and neither are nitrogen ones. They will move with muscle motion, but this displacement is fluid driven. Extravascular bubbles basically stay in one place until they dissolve. Nitrogen replacing helium will not alter the chemical characteristics of the bubble to any significant degree with respect to DCS.
Surface Tension
Interaction of a He and N bubble isn't as simple as one inert gas meets another, there are surface tension issues and they are both in an active and dynamic medium which they do interact with.
There are indeed questions concerning surface tension and the changes thereof on the surface of gas bubbles. The adsorption of biomacromolecules (surfactants) to the gas/liquid interface would not be appreciable changed by the content of these gases in a bubble. There might be time-dependend changes in surfactants dependent on what is dissolved in the tissue fluid; this is the well-known Vroman effect.
I doubt I hit every topic under consideration.
Dr Deco :doctor:
Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm
I did not see this thread and it was pointed out to me that there were some questions with which I might be of assistance. The replies are not in any particular order.
Switches
Switching from a less soluble to a more soluble gas is a decades-old method. It was instigated by the Swiss mathematician and diver Hans Keller in the late 1950s. It has been found that the gas switches (e.g., helium to nitrogen mixes) must be performed slowly to prevent vestibular problems. This is more easily done breathing the gases in a decompression chamber than with a mouthpiece.
Helium and Nitrogen Solubility
Nitrogen is more soluble than helium in both aqueous and lipid tissues (and any combination of the two components).
Goats ?
The reason goats were used in the early research by Haldane was that their body mass was large and they had decompression characteristics somewhat similar to human divers. The goats would also lift their sore leg if they had a joint pain (the bends).
Goats were easy to work with, and their only problem was eating anything they could reach. [Once a goat remarked to Haldane, I liked your report, but I thought your book was better.=-) ]
Two Gases and Diffusion
When a material diffuses, the motive power is heat. Molecules jostle around at any temperature above absolute zero and will randomly change their position (e.g., Brownian motion). They do this independently of the other molecules around them.
One molecule (e.g., nitrogen) is not hindered (or blocked) in its motion when another molecule (e.g., helium) is present in a solution (or in a mixture of gases). Thus, the out flux of helium is not changed by the in flux of nitrogen in a solution. {The distance that the molecules travel, however, is modified by the fact that they hit water molecules, but that is a different question (the mean free path) .} There is no coupling this diffusion process, that is, the molecules move independently. This might not be true if the molecules possessed an electrical charge, for example.
Steady State Counter Diffusion
This is one of two general types. It was the first found in barophysiology during deep dive experiments with neon as a breathing gas. It involved the diffusion of a lighter gas through the skin and into tissue perfused with a less diffusible gas. [In this example, the diver was surrounded by helium and breathing neon.] This is termed steady state or superficial countertransport. { Lambertsen CJ, Idicula J. A new gas lesion syndrome in man, induced by "isobaric gas counter diffusion". J Appl Physiol. 1975; 39(3):434-43.} This case produced lesions (sores) on the skin of divers in hyperbaric chambers. This occurred without decompression, thus the term isobaric (= same pressure). Tissue nuclei present can grow in this situation even in the absence of decompression.
Transient Counter Diffusion
The other type appears with the switching of breathing gases where a less soluble gas (helium) is transported to a tissue containing a more soluble one (e.g. nitrogen). Apparently, one gas will dissolve faster than the other can exsolve and the sum of the partial pressures exceed the ambient pressure. Nuclei present can grow in this situation even if there is not a decompression.
Vestibular DCS
This malady is hypothesized to result fro the inward flux of helium from the space in the middle ear into the vestibular apparatus. Slow gas switches seem to alleviate this problem.
Attachment?
Its has to do with the larger nitrogen molecules attaching to the He bubble seeds. A small He bubble is mobile and diffuses quickly, once the N attaches it alters the physical properties of the bubble. A sort of RGBM plus.
Tissue helium bubbles are not mobile and neither are nitrogen ones. They will move with muscle motion, but this displacement is fluid driven. Extravascular bubbles basically stay in one place until they dissolve. Nitrogen replacing helium will not alter the chemical characteristics of the bubble to any significant degree with respect to DCS.
Surface Tension
Interaction of a He and N bubble isn't as simple as one inert gas meets another, there are surface tension issues and they are both in an active and dynamic medium which they do interact with.
There are indeed questions concerning surface tension and the changes thereof on the surface of gas bubbles. The adsorption of biomacromolecules (surfactants) to the gas/liquid interface would not be appreciable changed by the content of these gases in a bubble. There might be time-dependend changes in surfactants dependent on what is dissolved in the tissue fluid; this is the well-known Vroman effect.
I doubt I hit every topic under consideration.
Dr Deco :doctor:
Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm
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