Isomeric Counterdiffusion
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but do you mean "isobaric counterdiffusion?"
Steven
Steven
Dr Deco
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Dear Readers:
Isobaric Counter diffusion
This was a phenomenon discovered by Idicula and Lambertsen in 1973. The test subjects were immersed in an atmosphere of helium and were breathing neon gas. The object was to study the effects of a dense gas on breathing mechanics. While the neon duplicated the density of helium at a much deeper depth, the test subjects also displayed red patches on their skin.
This was reasoned to arise from the rapid ingress of helium through the skin by diffusion and the partial pressure of this gas added to the partial pressure of the neon in the tissues (from the lungs through the blood stream). The sum of the partial pressures was such that bubble growth could occur.
I recall seeing a demonstration of this in Dr Lambertsens laboratory with a small pig as the subject. Because of the experimental arrangement, it was possible to hear a large number of Doppler bubbles from this preparation while the anesthetized pig breathed neon in a helium-filled chamber.
What Happens?
One gas can enter tissues faster than another can leave in some particular circumstances. One case is when you are immersed in a very rapidly diffusing gas and breathing a slowly diffusing one. Blood carries in one gas and the diffuses through the skin; numerous gas bubbles grow.
Curiously enough, this is one of the best demonstrations of tissue micronuclei. Although the supersaturations are small, the supply of gas is endless. The nuclei of a sufficiently large radius will expand and visible gas bubbles form.
It appears to be possible to have some problems (e.g., in the inner ear) with gas switches, especially when the middle ear contains helium and the diver is breathing nitrogen (air).
References
D'Aoust, B.G., and C.J. Lambertsen. Isobaric gas exchange and supersaturation by counter diffusion. In: The Physiology and Medicine of Diving and Compressed Air Work. 3rd ed. Bennett, P.B. and D.H. Elliott. London: Balliere-Tindall: 383-403, 1983.
Lambertsen, C.J., and J. Idicula. A new gas lesion syndrome in man induced by "isobaric gas counter diffusion". J. Appl. Physiol. 39: 434-443, 1975.
Dr Deco :doctor:
Isobaric Counter diffusion
This was a phenomenon discovered by Idicula and Lambertsen in 1973. The test subjects were immersed in an atmosphere of helium and were breathing neon gas. The object was to study the effects of a dense gas on breathing mechanics. While the neon duplicated the density of helium at a much deeper depth, the test subjects also displayed red patches on their skin.
This was reasoned to arise from the rapid ingress of helium through the skin by diffusion and the partial pressure of this gas added to the partial pressure of the neon in the tissues (from the lungs through the blood stream). The sum of the partial pressures was such that bubble growth could occur.
I recall seeing a demonstration of this in Dr Lambertsens laboratory with a small pig as the subject. Because of the experimental arrangement, it was possible to hear a large number of Doppler bubbles from this preparation while the anesthetized pig breathed neon in a helium-filled chamber.
What Happens?
One gas can enter tissues faster than another can leave in some particular circumstances. One case is when you are immersed in a very rapidly diffusing gas and breathing a slowly diffusing one. Blood carries in one gas and the diffuses through the skin; numerous gas bubbles grow.
Curiously enough, this is one of the best demonstrations of tissue micronuclei. Although the supersaturations are small, the supply of gas is endless. The nuclei of a sufficiently large radius will expand and visible gas bubbles form.
It appears to be possible to have some problems (e.g., in the inner ear) with gas switches, especially when the middle ear contains helium and the diver is breathing nitrogen (air).
References
D'Aoust, B.G., and C.J. Lambertsen. Isobaric gas exchange and supersaturation by counter diffusion. In: The Physiology and Medicine of Diving and Compressed Air Work. 3rd ed. Bennett, P.B. and D.H. Elliott. London: Balliere-Tindall: 383-403, 1983.
Lambertsen, C.J., and J. Idicula. A new gas lesion syndrome in man induced by "isobaric gas counter diffusion". J. Appl. Physiol. 39: 434-443, 1975.
Dr Deco :doctor:
Ok every one and Dr. Deco your explanation was perfect and in any diving book in the world what ever it was u have some thing like what u said and of course we study these books to learn more about these things.
And after years I heard from some one every important in the tek diving world that this is not 100% true or not true and they are still doing some studies to make sure from these things. Maybe what I said was stupid to post but why not , but I am just telling u what I heard.
One more thing, I was talking with some one else in an other occation last year who did a dive deeper that 220msw
And we were talking about tek diving in general and he told me, we dont have a lot of information about what we are doing yet, and we are working with the information we have and maybe after few years we will discover that all of this was wrong and we could have new rules specially in deco diving if it was on air or more than a 3 mixes.
Anyway ..
And after years I heard from some one every important in the tek diving world that this is not 100% true or not true and they are still doing some studies to make sure from these things. Maybe what I said was stupid to post but why not , but I am just telling u what I heard.
One more thing, I was talking with some one else in an other occation last year who did a dive deeper that 220msw
And we were talking about tek diving in general and he told me, we dont have a lot of information about what we are doing yet, and we are working with the information we have and maybe after few years we will discover that all of this was wrong and we could have new rules specially in deco diving if it was on air or more than a 3 mixes.
Anyway ..
Thanks for the explanation. Let me put in my own words to see if I understand. If you breathe something dense (like neon) while immersed in something light (like helium), then the helium will enter your body directly through the skin and cause bubbles in the skin because the Neon can't evacuate fast enough. This much I can follow (I think). It would require the presence of tissue micronuclei and would depend upon the amount of super-saturation a tissue could take the difference of the molecular weights of the gasses. Right? And Dalton and Henry would seem explain the mechanics......right?
As applied to diving, it seems to be limited to ear-bends (to give it a word) precipitated by gas changes but might also cause a skin bend if you put He in your dry-suit. right?
I have two questions:
1) In practice do people have much trouble with this?
2) is the effect independent of ambient pressure?
R..
Dr Deco
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Dear Diver0001:
The explanation, in your words is pretty much it. Basically we have situation where one gas accumulates on top of another gas. One must enter the tissue faster than the other can exit it.
Vestibular DCS
This is what you called ear bends. What is thought to occur is the formation of a gas bubble(s) in the semicircular cannels of the ear. This causes a sensation of dizziness and is very unsettling for the diver. It occurs in commercial and military divers when performing a gas switch from helium to air while in the deck decompression chamber.
Recreational Diving
This problem would not occur ion recreational diving as practiced today since diving bells and deck decompression chambers are not used. I understand that some cave divers use a small tent underwater for a portion of the decompression, but I have not heard of any untoward difficulties.
Depth Dependent
The deleterious effects of isobaric countertransport are depth dependent. The simple buildup of partial pressure is not depth dependent, but it would be trivially small at the surface, for example. Bubble growth will be governed by the Laplace equation and there is a dependency on the initial micronuclei radius. Because the supersaturations are very small, the nuclei that are capable of growing are initially also very small.
Dr Deco :doctor:
The explanation, in your words is pretty much it. Basically we have situation where one gas accumulates on top of another gas. One must enter the tissue faster than the other can exit it.
Vestibular DCS
This is what you called ear bends. What is thought to occur is the formation of a gas bubble(s) in the semicircular cannels of the ear. This causes a sensation of dizziness and is very unsettling for the diver. It occurs in commercial and military divers when performing a gas switch from helium to air while in the deck decompression chamber.
Recreational Diving
This problem would not occur ion recreational diving as practiced today since diving bells and deck decompression chambers are not used. I understand that some cave divers use a small tent underwater for a portion of the decompression, but I have not heard of any untoward difficulties.
Depth Dependent
The deleterious effects of isobaric countertransport are depth dependent. The simple buildup of partial pressure is not depth dependent, but it would be trivially small at the surface, for example. Bubble growth will be governed by the Laplace equation and there is a dependency on the initial micronuclei radius. Because the supersaturations are very small, the nuclei that are capable of growing are initially also very small.
Dr Deco :doctor:
BRW
Contributor
Guys,
Problems with isobaric countertransport
are easliy ameliorated by two simple rules:
1) -- employ only light-to-heavy gas mix
switches when ascending (standard apps
in military, commercial, and scientific
sectors), thus helium rich to nitrogen
breathing mixes on way up;
2) -- use heavier gases inside diving suits
than breathing mixtures (common again),
thus nitrogen in suits when on helium.
Coupled to 1) above is an advantageous feature
of isobaric countertransport, called isobaric
desaturation, whereby lighter helium outgasses
faster than nitrogen ingasses (in both bubbles
and tissues) and supports efficient staging
strategies for mixed gas, deco diving. Simply
stated, that strategy is ride helium as close
to the surface as possible, then switch to a
nitrogen mix in the intermediate zone, and then
to pure O2 in the 20 fsw range.
Coupled to 2) is the use of air (or nitrox)
or other heavier than helium breathing mix
for suit insulation.
All this applies to both OC and RB diving,
underscoring both safe and efficient diving.
Check Technical Diving In Depth (pps 75 - 85)
if you want to catch more detail.
Regards,
Bruce Wienke
C&C Dive Team Ldr
Problems with isobaric countertransport
are easliy ameliorated by two simple rules:
1) -- employ only light-to-heavy gas mix
switches when ascending (standard apps
in military, commercial, and scientific
sectors), thus helium rich to nitrogen
breathing mixes on way up;
2) -- use heavier gases inside diving suits
than breathing mixtures (common again),
thus nitrogen in suits when on helium.
Coupled to 1) above is an advantageous feature
of isobaric countertransport, called isobaric
desaturation, whereby lighter helium outgasses
faster than nitrogen ingasses (in both bubbles
and tissues) and supports efficient staging
strategies for mixed gas, deco diving. Simply
stated, that strategy is ride helium as close
to the surface as possible, then switch to a
nitrogen mix in the intermediate zone, and then
to pure O2 in the 20 fsw range.
Coupled to 2) is the use of air (or nitrox)
or other heavier than helium breathing mix
for suit insulation.
All this applies to both OC and RB diving,
underscoring both safe and efficient diving.
Check Technical Diving In Depth (pps 75 - 85)
if you want to catch more detail.
Regards,
Bruce Wienke
C&C Dive Team Ldr
Is there then a danger of a vestibular hit if EAN deco gas is lost and one has to revert to Helium rich backgas?
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