RBC's & PPN2

[Lost Yooper]

Howdy,

I have recently posted this topic on another board and thought I'd get some input from some of you docs here. I'm pretty sure I know the answers to most of my own questions, but I thought it might make a nice discussion.

I've had these questions for a few years, but haven't gotten around to asking them. As I understand it, high PPN2 (resulting from deep air diving) does something to red blood cells (RBC's) that causes them to become more rigid. This rigidity makes their passage through micro vessels difficult. As a result, this difficulty causes the body to release some chemical (nitric oxide??) that, in turn, causes an immune response. By introducing helium, and thereby lowering the PPN2, this effect is reduced.

OK here's my questions:

Is this more or less right?

What is it about the high PPN2 that causes the rigidity in RBC's?

Is the released chemical related to, or directly involved, in the lesions that are formed on the spine and brain and picked up by MRI's as the result of deep air diving? How do these lesions occur?

It makes sense that nitrogen bubbles would cause the same reaction, but how big do the bubbles have to be to cause it -- are we talking micro bubbles here?

At what PPN2 does the rigidity of RBC's become too much? Is it time related or rather instantaneous?

Is the immune response (flu like symptoms) the sub DCI that is felt after deep air dives?

There, that's enough for now.

Thanks again.

Mike


Ok docs, what say you.

 

[BillP]

Hi Mike:

I had heard the same claims on another board and decided to look into them. The idea that increased partial pressures of nitrogen causes red blood cells to become rigid seems to originate from a series of studies done by researchers at Britain's Diving Diseases Research Centre. The researchers were looking for the cause of dysbaric osteonecrosis in commercial divers and hypothesized that blood cells becoming "stiff" (or rigid) in those divers prevented the cells from passing easily through the tiny capillaries found in bone leading to loss of blood flow and bone death. (Bone has particularly small capillaries.) Some of their research is unpublished, and some of what was published is found in (non peer reviewed) proceedings of papers presented at meetings so I contacted the DDRC and got copies of their papers to review.

In their studies on saturation dives the researchers found that increased partial pressures of nitrogen did decrease blood's ability to pass through a polycarbonate filter, but not to the degree that they had hypothesized was enough to cause the damage they were looking for. It should be noted that the researchers did not look at dive profiles like a recreational diver might experience, they did not find obstruction to blood flow sufficient to cause the damage they hypothesized, and the damage they were looking for (dysbaric osteonecrosis) generally does not occur in recreational divers. While the research is interesting and IMHO merits further study, I think it premature to claim that the results of the studies are relevant to recreational divers.

To answer your specific questions:

Yes, you are "more-or-less" right. To clarify further, the effects don't have to be from "deep air diving". The effects were found in saturation dives with an equivalent PPN2 of as little as diving in 50fsw on air. The effects might not be increased substantially by diving deeper. Are you going to start recommending trimix or heliox for all dives below 50fsw based on this info? The effect the researchers were looking at was mechanical obstruction of blood vessels (polycarbonate filters really). Speculation about what that small degree of mechanical obstruction would cause in people- like immune effects- is just that, speculation, until it's specifically looked at. It might be right though. Also, the researchers assumed that the obstruction of the filters that they saw was caused by the blood cells becoming rigid. They did not actually measure the rigidity of the cells. The effect could have been caused by the blood cells becoming attracted to polycarbonate for all I know. BTW, some divers who have heard about this research (but don't really understand what it shows, IMHO) claim that adding ANY helium to the mix relieves the "problem". I have seen no research to support this claim.

As I implied above, I don't know what effect of nitrogen is to the blood cells that causes them to stick in laboratory filters.

Not sure if your next question at all relates to the "rigidity" issue. Some studies show increased MRI lesions in commercial divers, others do not. Relating any such lesions to blood cell rigidity would be speculation on my part at this time. (Until further studies are done.) I'm going to defer to Dr. Deco on your questions about inflammation, nitrogen bubble size, and DCS.

Again, the researchers found the decreased blood flow through filters with a PPN2 of 2 ATA (or 50fsw on air) in saturation dives. They did not look at short dive profiles like a recreational or even recreational "technical" diver might perform. I don't know that you can extrapolate the data from a saturation dive to a recreational dive. When does the rigidity become "too much"? Again, the researchers did indeed find the (possible) rigidity in their studies, but in none of their findings, even with saturation dives, was the obstruction caused by the cells "too much" (enough to cause the damage they were hypothesizing, that is).

If you would like to read my review of the DDRC research, it can be found at:

http://www.scubadiving.com/talk/read.php?f=1&i=293032&t=293032

HTH,

Bill

 

[Lost Yooper]

Wow! Thanks Bill. I'll have to digest this for little while.

Mike

 

[BillP]

Hey, no problem. It took me over a year from the first time I heard about the "rigidity issue" to research the literature, track down the relevant studies (they are a bit obscure and little referenced), and try to figure out the source of the claims. If you find out anything else on the subject, I'd be glad to hear it.

Bill

 

[Lost Yooper]

Hey Bill,

The only other little tid bit of info that I have is from another doctor who basically said the following:

"nitrogen would form weak ionic bonds on the convex side of the RBCs, impairing flexibility"

This whole thing was brought to my attention by George Irvine a few years ago. He said there was a British training video for North Sea Oil Operations showing what's going on.

That's all I have so far. I've e-mailed him recently to see if he has discovered anything else.

Mike

 

[BillP]

Thanks Mike. In researching the question, I've run across a lot of things that "people have said", but I have found precious little support for why they say them.

I too contacted George Irvine to ask him the source for his claims. I guess that since he didn't know me he assumed that I was challenging his authority rather than just asking a question. I had to suffer an incredible amount of invective and abuse before I was able to convince him that my intentions were genuine. Even then he was able to provide little more than vague rememberances of info he had heard about years ago. I hope you have better luck than I did.

I have also heard about the "oil company training videos". They reportedly contain autopsies and are therefore secret- only available to those with access to the inner sanctum. I can see where an autopsy video for commercial saturation divers might show injuries to their tissues from diving, but I have a hard time figuring out how that might show that the damage is due to increased PPN2 causing red blood cells to become rigid. (Remember, these were presumably commercial divers diving with helium in their mix.) I also have a hard time figuring out how it might relate to recreational divers.

I think you'll find that there are plenty of rumors, unsupported claims, idle speculations, and even informed ruminations out there on the subject. If you find any more scientific studies on the question, I would be very interested.

Good luck!

Bill

 

[Dr Deco]

Dear Yooper:

With respect to your first posting - - -

[sp] 1. The mechanism of effects caused by nonreactive gases is very often difficult to elucidate. Even something as definite as nitrogen narcosis has defied explanation for almost a century. (The mechanism of anesthesia itself has not been determined after 150 years.)

Unless there is a systematic error in the experimental measurement, it does appear that the filterability of diluted blood is reduced in the presence of increased partial pressures of nitrogen. The authors do state, however, that this is not necessarily the result of increased rigidity of RBCs but rather the result of some change of white cells. This may or may not be rigidity. Decreased filterability may be the result of
- increased adhesion of cells to the filtering material,
- rigidity of the cell membrane, or
- stiffness of the cytoskeleton (= tiny filaments within the cell itself),
but it does not necessarily mean that there is a pathological condition.

[sp]2. There is not any chemical released from the red blood cells during diving (of which I am aware). The lesions (= injuries) seen on magnetic resonance images (MRI) are more common in divers but are also found in the population as a whole but to a less degree. The etiology (= cause) of them is currently not known, but they evoked speculation as to whether they are pathologies. The may be the result of a continuous embolic (=small clots) phenomena. Individuals who have them appear to be asymptomatic for any neurological problem. They are simply medical curiosities. Remember that the group investigating this effect was looking for the cause of aseptic bone necrosis. ABN has many causes, and diving is but a minor one.

[sp]3. Since the effect was caused by dissolved nitrogen at increased pressure, bubbles were not involved.

[sp] 4. Increased rigidity, were it to occur from diving, would need to be more than found here to produce bone necrosis. The researchers did not measure the time dependence. In nitrogen narcosis, the effect of nitrogen is very rapid. Other gas effects are likewise quick in their onset times.

[sp]5. The manifestations of subclinical DCS are the topic of debate. Most frequently cited is lethargy. I could not say if this is related to this phenomenon.

Dr Deco

 

[Lost Yooper]

Bill, the reason I tend to pay attention to GI, JJ, and those guys is because they have done more in "proving" some aspects of so-called "science" wrong than vice versa. JJ, especially, frequently admits there is more to these various subjects than is currently known by science. These guys aren't scientists, but rather are the guinea pigs doing it. I've always had decent discussions with these guys, and they don't seem to mind me buggin' them.

It doesn't seem like there is much scientific data on the subject yet.

Mike

 

[Lost Yooper]

Dr. D,

On your third point:

I was wondering if the same thing might hold true if nitrogen bubbles that were too big were passing through capilaries and triggering some sort of chemical release, and thus an immune response from the body.

Does that make any sense? Nitrogen bubbles that are too big for capilaries and cause an immune response from from the body?

Assuming this might be true, what would this immune response be and how would it effect you as a diver?

On your second point:

Are these lesions found on deep sea divers who have no history of high PPN2 diving, but rather dive heliox or very "rich" trimix. I am very interested in knowing if deep air divers are more proned to get these lesions in greater numbers or severity.

Ok, that's it for now.

Mike

 

[BillP]

Hi Mike:

So long as you're talking about a technical aspect of diving or subjective observations made over time through experience I agree with you. If GI, JJ, or those guys tell me they feel better after diving with helium, I'd tend to believe them. They've sure done enough of it. But if they venture into hypothesizing on the physiolgical reasons behind why they feel better- and then go on to present their unsupported hypothesis as absolute fact that is not to be questioned despite being able to show very little to no relevant research to support it, then I frankly begin to have a problem.

It's like Dr. Deco was saying to you about Professor Buhlmann's theories and tables in another thread. He was talking about how Buhlmann's theories are based on Haldanian principles and his tables work on a practical basis. But just because his tables work in a practical setting doesn't prove Haldane's theories are true. The tables might work for completely different reasons. And whether Trey feels good or bad after a dive might have nothing to do with cell rigidity. It's an interesting hypothesis, but that's all it is. And so far it's an unsupported hypothesis IMHO, and should not be presented as fact.

Just my 2¢,

Bill