DCS from O2 decompression

[Mr Carcharodon]

Deepmaxim,

Yes there will be all the gasses in the bubbles present but not much oxygen because oxygen never rises much over ambient pressure due to metabolic use. That is certainly true for venous blood which is inherently undersaturated. So there will always be a gradient there driving oxygen from inside bubbles out. The hemoglobin is critical because once it becomes unsaturated it will pickup excess oxygen from solution which will prevent bubbles from forming. But yes the rate of decay will be less for poorly perfused tissues like ligaments and tendons which is where you reported your pain. Still I suspect inert gas elimination drives DCS and the occurrence of symptoms after the gas switch to oxygen was a coincidence.

Thank you for reporting the details of your dive. What depths did you do the gas switches at? And why no “S” curve?

 

[deepmaxim]

2Carcharodon
I talk over possibility to have a counterdiffusion on 6m with oxygen pure.
Metabolistic you need on this depth (normal condition) not over 0,1 - 0,11 FO2 (0,16 -0,17 PPO2), but you have 100 O2 (1,6 PPO2).
You have about 10x more oxygen, as you need (talk about metabolistic o2 use). Cells take not more oxygen for metabl. as they need (or littlebit more)
Your blood (art. and ven.) begin to have (satturating) much more o2 as need for you buddy. This is normal condition (physical)

One side, we have PPO2 in tissue (we take fast tissue for example) from last deco gas (EAN50 my dive) with 0,8 PPo2 or little bit smaller and other side you change on oxygen pure (PPo2 go x 2). We know, that o2 can better go solved as nitrogen, so you can have oversaturation with helps from o2
Over ICD you can read Steve Burton as example

Isobaric Counter Diffusion - What is it?
http://www.oceanwreckdivers.com/ima...fety_using_a_combined_decompression_model.pdf

How can you becomes haemoglobin unsaturated with breathing with pure oxygen? And our cells take first oxygen not from haemoglobin, but from solved in blood (plasma)

we dont wont a S-curve, that will be maybe not work for dives like this.
We have changed with rules 1.4 PPo2 for deep decogases and 1.6 for shallow decos
Regards and Happy New Year!

 

[Mr Carcharodon]

Deepmaxim,

Passing out of the lungs on the arterial side there is something like 20.57 ml of oxygen per deciliter (ml/dl) of blood at 0.21 ATA of oxygen. The 20.57 ml/dl of oxygen is comprised of 20.28 ml/dl bound to hemoglobin and 0.29 ml/dl in solution. If the inspired ppO2 is increased to 1.6 ATA the amount of oxygen in solution goes up to about 2.2 ml/dl but that is still only 10% of the total oxygen present. There is no increase in oxygen carried by the hemoglobin because the hemoglobin is already nearly saturated at 0.21 ATA. So it is a mistake to think that switching from 50% to 100% oxygen doubles the amount of oxygen available to your tissues.

Then after passing through your tissues, and on return to the lungs, about half of the oxygen present is consumed and converted into carbon dioxide. So the venous blood returning to the lungs is unsaturated. And if it is it will pickup oxygen from solution preventing oxygen bubble formation on the venous side.

But more importantly after switching to 100% oxygen the partial pressure of inspired inert gases falls to zero. So for the reasons noted above the concentration of oxygen only increases slightly on the arterial side. But on the venous side the total pressure of all gasses drops (about 5x for air to O2) because the inert gasses have been removed and because the oxygen that has been converted to carbon dioxide exerts a lower pressure due to its higher solubility.

So the switch to oxygen lowers the total pressure of all gases in solution returning to the lungs. And the pressure gradient from solution to the inside of bubbles present is the force that drives their growth. So by switching to a higher ppO2 you should be able to get the bubbles present shrink. Or to consider it in Haldanian way the pressure drops relative to the m-value. Of course this all assumes that fast tissues were driving your decompression. If they are not this will not work.

I do not know much about ICD but I think to get it you need to switch from a less helium rich mixture to a more helium rich mixture. And based on what you said about your dive it does not appear you did that.

Happy new year.

 

[deepmaxim]

Carchadaron

I think, you dont understand me....
I talk not over O2 Window (what you try me to explain, i have enought read about it ) i talk over possibility to have IDC from O2!
It is a mistake to see a O2 only as gas without physical rules. You have a gas, (He,N2,Ar, O2 whatever), all gases can go solved and come back as in a gas form, if tissue pressure (all gases) go over 100%.
Its means, that O2 can go inside a bubble (gas form) and make the bubble biger, if you have a IDC.
Take o2 out and play with other gases (without metabolistic effect). We take a gas with 50% N2 and 50%He (sure, its not for brezhing) on the "normal" deco stops 21m, 18m, 15m, 12m, 9m and 6m. Your tissue have a solved gases, right? Now you change on 100%N2 and what happend now?
N2 go better in tissue becouse nitrogen can better solved as Helium. Your max. tissue pressure can go over 100% and you can have DCS. That it.
Now just change gases and you have the same picture. Take some O2 for metabolismus, but other part from o2 can make us problem.
PS mlO2 in blood is not interesing for IDC, but partial pressurre from o2 is interesing.
Read the links that i have posted her, you can see, why you can have IDC if you change from Helium (trimix)to N2 (air or EAN).
Regards

 

[boulderjohn]

I found the following from a chapter by Richard Vann of DAN in "Inert gas exchange and bubbles." In Bove and Davis’ Diving Medicine, 4th edition. Chapter 4, Bove AA, ed, WB Saunders, Philadelphia. 53-76, 2004.

Oxygen Bends
Increased tissue oxygen tension contributes to supersaturation, limits the oxygen window, and might raise DCS risk. Weathersby and colleagues tested this hypothesis with oxygen partial pressures of .21 atm and 1.3 atm after human dives with the same nitrogen partial pressures but found not significant difference in DCS. In experiements with goats, Donald compared oxygen partial pressures of 0.53 atm and 3.53 atm in similar experiments and saw no DCS at 0.53 but serious symptoms in six of the seven animals at 3.53 atm. Donald called this effect oxygen bends to indicate that oxygen can cause bends at 3.53 atm. (p. 65)

 

[deepmaxim]

I found the following from a chapter by Richard Vann of DAN in "Inert gas exchange and bubbles." In Bove and Davis’ Diving Medicine, 4th edition. Chapter 4, Bove AA, ed, WB Saunders, Philadelphia. 53-76, 2004.

boulderjohn

Thank you!

 

[Dr Deco]

hello Readers:

The oxygen bends observed in goats was actually a right heart embolism problem. So many bubbles were present in the vena cava, and flowed to the heart that it interfered with circulation. The goats collapsed. In a few minutes, the oxygen in the bubbles was metabolized, the circulation was restored and the goats were again DCS free. That is not the same as problems from gas bubbles in tissue - especially nerve tissue.

Oxygen does not contribute to tissue bubbles because of metabolism. If nitrogen was metabolized, you would have little to worry about from this gas for diving. Likewise, if oxygen were not toxic, you could dive to 1,000 fsw and surface with out any DCS worries.

Tissues such are nerve tissue are big utilizers of oxygen. Tissues such as bone and teeth do not have a metabolic requirement like that and we do not get bone bends. [Aseptic bone necrosis is a different issue.]

 

[Thalassamania]

Oxygen does not contribute to tissue bubbles because of metabolism.

That's what I thought. NOw to the second question, what about (under the odd circumstance that it might be possible, counter current diffusion of inerts into an oxygen bubble?

 

[Dr Deco]

Diffusion. Good question. I suspect that the in the time diffusion occurred, the oxygen would be metabolized and no longer a part of the program.

It is interesting to speculate that a bubble could be first formed primarily of oxygen and then continue its existence with nitrogen that diffused it. Quite possible..... Yes, that is what you said.

 

[Thalassamania]

Yes, that is what I said and was wondering about ... I'm guessing that's part of the reason for three hours of oxygen breathing prior to EVAs?