Nitrogen and Red Blood Cell Rigidity

[BillP]

Hi Dr. Deco:

George Irvine, III and Bill Mee of cave diving and DIR fame have promoted the theory on the techdiver mailing list that nitrogen in a diver's breathing mix somehow causes red blood cells' membranes to become (?irreversibly?) rigid. This red blood cell rigidity decreases the deformability of red blood cells causing them to sludge in the circulation, reducing tissue perfusion, and damaging blood vessel walls. I get the idea from reading their writings that this damage presumably leads to an increased risk of DCS. From what I can tell from reading their writings, they go on to say that adding ANY helium to the breathing mix will alleviate the deleterious effects of nitrogen on red blood cell membranes.

Followers of GI-3's and BM's writings have been known to use their theories about nitrogen and cell rigidity to make statements like, "The long term cell rigidity effects of prolonged exposure to N2 are not to be underestimated" to support their position that trimix should routinely be used for recreational diving. As recreational divers typically breathe air or nitrox on their dives, they are supposedly risking long term damage to their cells from their exposure to nitrogen, so they should add some protective helium to their breathing mix.

I have been unable to find anything in the diving or medical literature that supports the view that nitrogen causes the membranes of red blood cells (or any other cells) to become rigid. I have found no "long term cell rigidity effects of prolonged exposure to N2", nor have I found any evidence to show that helium is protective against the effect- other than in the writings of GI-3 and BM. (The journal articles BM cited in the link below discuss the effects of pressure on red cell aggregation, not the effects of nitrogen or helium on the flexibilty of the red cell membrane.) Are you aware of the results of any research in the area? Are recreational divers risking cell injury due to this "cell rigidity" effect of nitrogen and should they add helium to their mix to protect themselves?

For some reason I haven't been able to directly log onto the techdiver mailing list archive to get more of GI-3's and BM's writings for you, but I did find another archive with a couple of GI-3's and BM's notes. You can find them at:

http://www.nwls.com/list-archive/reademail.asp?id=5573
http://www.nwls.com/list-archive/reademail.asp?id=5609
and
http://www.nwls.com/list-archive/reademail.asp?id=24174

to get an idea of what they're talking about if you haven't seen it before. This is just an example of their writings on the subject. They go into more detail and explain their theory more thoroughly elsewhere. I'll be interested to read your thoughts.

TIA,

Bill


[Edited by BillP on 09-23-2000 at 07:21 PM]

 

[Dr Deco]

[sp]NASA’s charter in barophysiology deals with depressurization of saturation (1 atmosphere) and we are seldom involved in work at increased pressure. Therefor I am not a close follower of this concept of nitrogen and red cell rigidity. I have not actually heard of it from Mee and Irvine, two well respected explorers of the Wakulla Springs system. I could speculate from a theoretical perspective, however.

1. In general, known pressure effects to date are limited to the nervous system, i.e., the high pressure nervous syndrome. This has been attributed to a change in nerve cell membranes by the pressure per se, and nitrogen is added to the breathing mix to counteract the increased tremors. The result is the well-known trimix.

2. The effect of nitrogen in the literature on red blood cells (RBC) is with regard to the clumping (aggregation) of the cells. This is a demonstrable event in vitro (in a test tube). I am not aware of it occurring in vivo (in the living system). This aggregation of RBCs is not the same as a stiffening of the membranes, however.

3. When RBC aggregation does occur in vivo in the dive setting, it was associated with decompression, intravascular gas bubbles, and was referred to a "disseminated intravascular coagulation (DIC)." DIC is a serious condition that occurs in, among other diseases, severe decompression sickness. Drugs against this (e.g. heparin) have been employed with some success in severe cases.

4. The addition of helium might or might not reverse the rigidity, but there is neither data on rigidity or its reversal by helium, at least as far as I know.

5. Certainly, the increase of rigidity would be bad in low flow situations (low shear) since it would further retard gas elimination. Again, I do not know that this RBC rigidity actually occurs.

Thanks for the question, Bill.

 

[BillP]

Re: Your point #2- "The effect of nitrogen in the literature on red blood cells (RBC) is with regard to the clumping (aggregation) of the cells."

Looking at the abstracts of the articles that Bill Mee cited to support his views on nitrogen and red cells, they seem to discuss the effect of PRESSURE on red blood cell aggregation and not specifically the effect of nitrogen on red cells. I have searched the medical literature for the effect of nitrogen on red cell aggregation, but came up empty handed. There are articles on nitrogen _microbubbles_ and _platelet_ aggregation, but I didn't find anything on nitrogen gas and red cell aggregation. Did I miss the articles? Are they in the aerospace literature?

TIA,

Bill

 

[Dr Deco]

These are the articles I found in the MEDLINE search. The first shows the effect of pressure per se [Chen S; Gavish B; Barshtein G; Mahler Y; Yedgar S Red blood cell aggregability is enhanced by physiological levels of hydrostatic pressure. Biochim Biophys Acta 1994 Jun 22;1192(2):247-52 ].

Another shows the effect of in vivo nitrogen in humans [Taylor WF; Chen S; Barshtein G; Hyde DE; Yedgar S Enhanced aggregability of human red blood cells by diving. Undersea Hyperb Med 1998 Fall;25(3):167-70 ]. In my last reply, I mistakenly referred to it as an in vitro study; it is in human subjects. The nature of the bottom gas was not listed in the abstract.

I still doubt that this has a big role in recreational SCUBA diving under the conditions normally encountered.

 

[old_mike]

if i am not mistaken, RBC's typically have a lifespan of roughly 3 to 4 months. In addition, we tend to produce on average, 2,500,000 of the little buggers per second. even if they are damaged at pressure by N, there shouldn't be too much long term damage, unless one is diving deep day after day month in month out? and the mechanics of clotting as caused by bubble formation are interesting. What could it be about either the N-pressure or the bubbles that would initiate agglutination? sorry to be a pest but this stuff really is interesting!

 

[BillP]

Thanks Dr. Deco. I noticed those studies, and Bill Mee did use them to support his views on nitrogen and red cell rigidity. Again, the first study looked at the effect of *hydrostatic pressure* (up to 15 bar for up to 2 hours) on the aggregability of red blood cells in vitro and found that the aggregability increases up to three-fold.

The second study was indeed an in-vivo study with volunteer divers in chambers diving up to 300ft. They again looked at the effect of *pressure* on RBC aggregability and found increases in red cell aggregability at 66' and 300'.

But again, neither study specifically looked at the effect of *nitrogen* on RBC aggregability and neither looked at rigidity of RBC membranes, so I frankly don't see how either study supports GI-3's or BM's views. If I were to propose the hypothesis that second hand tobacco smoke in bars causes an increase in car accidents, quoted a study that showed an increased incidence in car accidents in people who had been drinking in bars, and then said, "See! It was that awful tobacco smoke that cause the accidents!" I would be considered a scientific stroke. ("Stroke" is a cave diving term for someone who, er, doesn't know what they're doing.) I might still be right in my conclusions about second hand smoke and car accidents, but it would be, shall we say premature, for me to publish my findings without further study, and improper for me to use an unrelated study to support my views. Apparently GI-3 and BM have tried to do some studies on the subject, or have at least talked about it. I would like to see them publish their findings in a peer review journal rather than the techdiver list.

Now, mike, the life span of a red blood cell is about 180 days, but if RBC aggregability is increase by diving it could lead to clot formation in small vessels. The clot could obstruct blood flow leading to tissue damage or even cell death. The effects of that tissue injury *could* be long term and additive over multiple dives. Dunno what it is about pressure that seems to increase aggregability but Dr Chen et al's studies seem to indicate that it does. I just don't see data that show that it's the nitrogen in the pressure that causes the problem or that helium prevents the problem as GI-3 and BM propose. It's an interesting idea, but I think that I'd like to see a little more data before I start promoting trimix to reduce the risk of dangerous cell rigidity in recreational diving.

Bill

[Edited by BillP on 09-25-2000 at 06:27 AM]

 

[Dr Deco]

Thanks to Mike and Bill for their recent remarks. I have now been able to review the article on RBC aggregation as performed at the US Navy facility [Taylor WF; Chen S et al. Enhanced aggregability of human red blood cells by diving]. Curiously, the authors report that the greatest change in aggregability was between the surface and the 66-fsw level. This pressure was achieved using air as the compression gas. The increase in aggregation was little changed from there to the 300-fsw level where the compression gas was helium (added to the air from the 66 fsw level). If helium is purported to prevent or REVERSE this aggregation, these data do not at all to demonstrate that.

The authors state that the effect appears to be one of hydrostatic pressure and that helium has no effect and does not reverse this. (“In the pressure chamber, fractions of gases were adjusted to maintain the same partial pressure of oxygen and nitrogen at all depths below 66 fsw…. Therefore, as the depth increases below 66fsw, the helium partial pressure increases. If an increase in RBC aggregation is in part caused by an increase in partial pressure of inert gas, one would expect a proportional increase in RBC aggregation at 300 fsw. That was not observed.”]

I therefore do not see that the data support the concept that helium will reverse this pressure-induced aggregation, nor is it obvious (from the in vitro study) that nitrogen itself is responsible for the increased aggregability of RBCs.

 

[BillP]

Thanks Dr. Deco. I pulled the studies too. The studies do leave some questions unanswered, but your analysis of their findings seems right on the money. Interesting that BM and GI-3 would quote studies that don't support and even contradict their views to promote their theory.

It might help to use a 1 ATA diving suit for recreational diving to avoid red cell aggregation (hmmm, maybe that's overkill), but I don't see the need to recommend adding helium to the breathing mix to avoid "long term cell rigidity effects of prolonged exposure to N2" just yet.

Bill

 

[Dr Deco]

They do indeed seem to have used the references in a reversed way. In the end, the best thing that a diver can do for his blood is to keep well hydrated to insure proper perfusion and not allow surface tension to drop to a lower level.

Thanks again for the fine questions......

 

[roakey]

Dr Deco once bubbled...
Thanks to Mike and Bill for their recent remarks. I have now been able to review the article on RBC aggregation as performed at the US Navy facility [Taylor WF; Chen S et al. Enhanced aggregability of human red blood cells by diving]. Curiously, the authors report that the greatest change in aggregability was between the surface and the 66-fsw level. This pressure was achieved using air as the compression gas. The increase in aggregation was little changed from there to the 300-fsw level where the compression gas was helium (added to the air from the 66 fsw level). If helium is purported to prevent or REVERSE this aggregation, these data do not at all to demonstrate that.

The authors state that the effect appears to be one of hydrostatic pressure and that helium has no effect and does not reverse this. (“In the pressure chamber, fractions of gases were adjusted to maintain the same partial pressure of oxygen and nitrogen at all depths below 66 fsw…. Therefore, as the depth increases below 66fsw, the helium partial pressure increases. If an increase in RBC aggregation is in part caused by an increase in partial pressure of inert gas, one would expect a proportional increase in RBC aggregation at 300 fsw. That was not observed.”]

I therefore do not see that the data support the concept that helium will reverse this pressure-induced aggregation, nor is it obvious (from the in vitro study) that nitrogen itself is responsible for the increased aggregability of RBCs.

This study just popped up on the DIR/Quest list, and an interesting point was made. The authors noted that blood cell aggregation did not increase beyond the 66 fsw level, but they didn’t appear to see the correlation to the fact that they kept the PPN2 constant beyond that point with the addition of He (as your quote states).

I realize that we don’t have a control, but it could be postulated that the addition of He, which kept the PPN2 constant beyond 66 fsw, was what kept the aggregation from increasing, supporting the theory that, as George likes to say, “‘He’ is your friend.”

Roak