Offgassing

[RikRaeder]

I was wondering about some facets of offgassing, in a rather hypothetical way. I do that sometimes, wonder...
I was hoping that someone could explain, or direct me to an explaination (fit for a layman, but not a laim-man: I can deal with small amounts of clearly presented scientific-type information) of the process of offloading nitrogen. Specifically, considering the following hypothetical case:
A diver with some non-major bubble formation who does not take recompression treatment. Would the bubbles never re-enter solution without the pressurization? Would this diver carry the bubbles around (provided they didn't render said diver immobile with pain or jump up into his cartoid artery or something) forever/until his next dive, or would he eventually, somehow, release the nitrogen? Related: how about sub-clinical DCS? Perhaps that's what I was referring to in the above example, or does sub-clinical DCS only refer to lack of bubbles or bubbles of a certain size?

[ianr33]

I'm no expert but the bubbles will slowly shrink as the gas dissolves in the blood.Might take a while though (days?)

[fisheater]

As the gas dissolved in the diver's tissues migrates to areas of lower concentrations of that gas, it will form microscopic bubbles that will do no harm, assuming that the pressure gradient is low, i.e., proper dive procedures have been followed and nothing "funny" happened that would lead to an undeserved hit.

It's when the pressure gradient is large that big, nasty, dangerous bubbles form.

[emcbride81]

Originally Posted by fisheater

As the gas dissolved in the diver's tissues migrates to areas of lower concentrations of that gas, it will form microscopic bubbles that will do no harm, assuming that the pressure gradient is low, i.e., proper dive procedures have been followed and nothing "funny" happened that would lead to an undeserved hit.

It's when the pressure gradient is large that big, nasty, dangerous bubbles form.

This is good, from what I have read. If you push limits or are dehydrated, etc but follow otherwise normal and safe procedures such as a slow ascent, the pressure gradient increase slowly forming small bubbles...versus ascending quickly which forms larger ones. I read that someone who was giving CPR to a diver that shot up from 200 feet related the formation of bubbles to shaking a soda bottle...which isn't a pleasant thought...he stopped chest compressions when the chest felt "squishy" as he called it.

As for resaturation without pressure, I dont think it can happen. The body has no use for nitrogen, so there would be no uptake into the cells. If all goes well it is exhaled.

Subclinical DCS, from what I have read, seems to mean DCS that does not require medical attention. Fatigue and headache are the usual symptoms, and I think skin rash and itchiness are some others. I am to believe that these symptoms are created by the amount of N2 in the blood stream and the effect is has on the body.

In my reading, I have seen where it is believed that all divers that dive below 2 ATM will have SC DCS wether they feel it or not, others have said 3 ATM. Both parties suggest a 50 percent of max depth safety stop for at least one minute. As to wether these reports hold any validity or not I am not sure. Hopefully some of the smart people on this board will answer.

[navyhmc]

The not-so-short answer to the OP is: Yes, a small bubble or microbubbles will eventually be reabsorbed in to the system. "Bib bubbles" will also eventually reabsorb as well. The problem comes from the amount of inury and insult all these bubbles will do prior to reabsorption.

Essentially, these bubbles act just like a thrombus (blood clot that breaks free and travels through the body). If the bubble forms on the arterial side of the blood flow, you will have a problem with the organ or tissue that it eventually blocks. The amount of damage is depending on the size of the bubble and the amount of blood flow it blocks. As most know, the original "Bends" came from the formation of these bubbles in the joints where the circulation is a little more complex than a normal artery.

Micro bubble can form in the organ or tissue as well and can wreck havoc on the function of the tissue or organ-the good news is that these bubbles reabsorb the fastest.

If the bubbles form on the venouse side of the circulation, the flow will eventually wind up in the lungs and act as a pulmonary embolism. This will interupt the exchange of gasses in the lungs and can have very rapid and serious life threatening concsequences. This in only one reason why oxygen shold be adminitered to DCS victims.

The rate of re-absorption is depending on so many variables that it would be difficult to explain outside of postdoctorate papers.

Long and complicated answer to the OP's question, so to sum up:

Yes, the bubbles will reabsorb over time but until they do, they will cause ongoing life altering conditions. Recompression is indeed the fastest way to minimize the damage. The best course of action is to think "DCS is some really, really, REALLY BAD(!) Ju-Ju and I will make every effort to avoid it and plan safety factors into my dive planning and diving."

[DivingCRNA]

I saw a post abut "offgassing" and I thought it was about that thing that makes my wife so mad when I do it in the bed and pull the covers over her head!!!

[cummings66]

Originally Posted by emcbride81

As for resaturation without pressure, I dont think it can happen. The body has no use for nitrogen, so there would be no uptake into the cells. If all goes well it is exhaled.

What about Henry's Law, 14.7 psi all the time ya know. Wouldn't that be enough over time? Might be why some hits that go untreated take 6 months or longer to go away.

[navyhmc]

Originally Posted by cummings66

What about Henry's Law, 14.7 psi all the time ya know. Wouldn't that be enough over time? Might be why some hits that go untreated take 6 months or longer to go away.

The blood does have the ability to absorb gasses via the aveolar membrane, so the gasses will absorb directly in the blood. Non-red blood cells don't have this ability-well, they might, but it's drastially less. Which is a big reason why bubbles are so damaging. And it does take a lot of bubble to cause problems. As for organs themselves, the solid organs take more of a hit.

Think about this: Put a deflated balloon in a jar of marbles and slowly inflate the balloon. Eventually, the ballon is going to put more force on the marbles and if enough pressure is put in the balloon, the jar will burst. The jar is a functioning area of an organ, the marbles are cells and the balloon is the expanding bubble. You survive the DCS episode, but have tissue/organ injury or damage. How life altering it is depends on the size and location of the bubbles.

[emcbride81]

Originally Posted by cummings66

What about Henry's Law, 14.7 psi all the time ya know. Wouldn't that be enough over time? Might be why some hits that go untreated take 6 months or longer to go away.

I didn't think that one all the way through...good call...hence why I said "smarter people than me will post".

[hydro]

Since you asked specifically for the hypothetical explanation, we have to refer to the most accurate hypothetical model we have to explain bubble diffusion/perfusion: dive tables.

Since dive tables are all designed around M-values of compartments that are based on half-times, hypothetically (which is what you asked), the nitrogen bubbles that form in our blood stream once we compress are never completely eliminated. Rather, they just continue to decrease in size (or quantity) by compartment half-time ad infinitum. Of course, dive tables say once this happens ~6 times, the bubbles are effectively eliminated in reality (because they're negligible in size and quantity at this point). However, if you strictly followed the hypothetical table math, the bubbles would just continue to decrease by 50% each go-round of the half-time, and this would never really reach nothing again. Whoa man, that's deep <takes a hit off the m-value pipe and passes it around>.

Ok, but really that doesn't happen as far as we can tell qualitatively through doppler or by reason of common sense inference from bubble behavior in other applications.

Neato!

Originally Posted by RikRaeder

I was wondering about some facets of offgassing, in a rather hypothetical way. I do that sometimes, wonder...
I was hoping that someone could explain, or direct me to an explaination (fit for a layman, but not a laim-man: I can deal with small amounts of clearly presented scientific-type information) of the process of offloading nitrogen. Specifically, considering the following hypothetical case:
A diver with some non-major bubble formation who does not take recompression treatment. Would the bubbles never re-enter solution without the pressurization? Would this diver carry the bubbles around (provided they didn't render said diver immobile with pain or jump up into his cartoid artery or something) forever/until his next dive, or would he eventually, somehow, release the nitrogen? Related: how about sub-clinical DCS? Perhaps that's what I was referring to in the above example, or does sub-clinical DCS only refer to lack of bubbles or bubbles of a certain size?