Flying and Diving, bring me up to speed

[BigJetDriver]

Estimable readers, Charlie, James, et al,

It cannot be said that I, for one, do not like to be as accurate as possible, sometimes pedantically so. In that vein, I will post the exact e-mail conversation that Charlie99 refers to. He also has posted the link to same.

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From: MHK (mhkane@prodigy.net)
Subject: Re: To fly or not to fly?


View this article only
Newsgroups: rec.scuba
Date: 2001-08-27 14:49:04 PST


"Treehorn" <DELETEabutterworth@home.com> wrote in message
news:i8ji7.24738$f01.6592211@news3.rdc1.on.home.com...
> I was recently told by a dive shop in Tobago that I am ok to do a couple of
> dives in the morning, when I am flying to Trinidad at 10 pm that night.


Treehorn,

DAN recommends 12 hours, down from their previous recommendation of 24
hours. On almost any given weekend I can be found getting out of the water
and rushing to an airport, often times with my hair and my gear still
dripping wet and that is often times after very deep and lengthy
decompression dives, so I wouldn't worry too much about doing a few
recreational dives and jumping on a puddle jumper...

Later

-----------------------------------------------------------------------

Charlie99 is EXACTLY CORRECT in his comments as anyone can see. Also, while DAN is, in fact, working on the "Flying After Diving Study", and has been for a long time, their current recommendation stands until the study can produce the results which may (or may not) change it.

Further, I do know Dr. Richard Vann personally, and talk to him from time to time. He has NEVER indicated to me that DAN has some kind of "secret knowledge" that they just "refuse to publish"!!! :wacko: Perhaps I just don't know the "secret handshake"!!!

 

[fins wake]

Further, I do know Dr. Richard Vann personally, and talk to him from time to time. He has NEVER indicated to me that DAN has some kind of "secret knowledge" that they just "refuse to publish"!!!

I've never heard of a public body, university or research institute having any such secret knowledge which for some obscure reason is kept from the general public. In general terms, a diver should be careful when such claims are made, as Charlie and BigJetDriver have indicated.

Sometimes researchers have material which clearly points in a certain direction but which hasn't yet been formally presented for peer-review in a journal of physiology or similar. This in a sense doesn't make the findings 'official' from that researcher yet but it's a different matter from being secret.

The peer-review process takes a lot of time and effort. It is my understanding that our own esteemed Dr Deco's findings on stress-assisted nucleation belongs in this category for now - I'm sure he'll correct me if I'm wrong - but fortunately he shares these very recent findings through this forum. I, for one, certainly find that very useful from a practical dive-planning point-of-view and look forward to the coming publication.

In a similar vein, I understand Dr Vann also has some very recent findings on helium and DCI (a US Navy study) which hasn't yet been formally presented in a journal, but which I think has been presented to other hyperbaric researchers in some way. To be honest, though, I'm not sure those results are entirely consistent with MHK:s musings either ...

What I'm trying to say is that one should pay very careful heed to DAN and to a broad consensus of hyperbaric researchers, who have the scientific training, mindset, laboratory and field tests to back up some often very broad recommendations.

Others - even if they are divers with remarkable individual and team accomplishments - will only ever be able to offer anecdotal evidence for some very specific diving practices.

If in doubt, go with the DAN recommendations and it will never hurt you to be more conservative ...

 

[Dr Deco]

Dear SCUBA SOURCE Readers:

Differences in Divers

The differences in divers with respect to decompression have rarely been quantified. It was not long ago that 100 dives with one diver or one dive with 100 different divers was thought to be equivalent. The old wisdom was it made little difference whether one discussed multiple dives with the same guy or a bunch of individuals performing the same dive. It was rated as equal.

I doubt that many of my scientific colleagues would agree with that today. In the ATTACHMENT is a graph from the study of Dervay et al. (JP Dervay, MR Powell, B Butler, and CE Fife. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviat Space Environ Med, 2002; 73(1): 22-7.] It illustrates that individuals who are depressurized are quite regular in their response with respect to bubble formation (i.e., form bubbles or do not form bubbles). In addition they are quite regular in their response to exercise prior to depress. (The RED bar is exercsie and immediate depress, YELLOW is exercise and wait 60 minutes, the GREEN bar is bubbles detected after exercise and a waing period of 120 minutes.) Last it should be noted that, for this nitrogen gas load, the formation of bubbles was not equal for all test subjects. Roughly one half did not form any at all, even with exercise immediately prior to depressurization. Since these tests were made by depressurization to altitude, a difference in gas load in the tissues could not have been the reason for the response. :lifter:

Why some individuals respond differently to depress and the formation of gas bubbles is speculative. It might be a difference in the ability to form and retain micronuclei, and this might be traceable to the concentrations of different biomacromolecules leading to the varying lifetimes of either “free stream” and/or “wall” micronuclei.

I strongly suspect that some individuals with remarkable decompression techniques are in the "never form bubbles" catagory. It is physiological and has nothing to do with their "remarkable" technique(s). If you are not in the "no bubbles" category, beware!:boom:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[fins wake]

Hi Dr Deco, just a quick question regarding the interesting study you quoted. I assume the exercise was done at atmospheric pressure.

Could there theoretically be any difference in the number of "no bubbles formed" if the exercise was done at greater pressure (e.g. underwater/in a chamber) and the test subjects then further depressurized rapidly, i.e. could this conceivably limit further the number of possible 'survivors' ("never form bubbles" divers)?

I realize the physiological and physical factors at work probably will be very similar in any case, of course.

Oh, and is this study available for download somewhere? It really is interesting to us divers as well. Hopefully the Duke people are looking at this as well. Most of us lift tanks after diving, some of us even walk up hills with heavy gear right after the dive ... :nono:

Also, I surmise from the above that your study has been published and subjected to peer-review, apologies if I got this wrong.

Dang it, I'd really love to be at Wrigley in September ... ;-0

 

[Dr Deco]

If the study were performed at pressure with the subjects being pressurized and immediately exercised, I suspect that the micronuclei load would be larger when they tehn immedaitely returned to the surface. If they extended the duration at pressure, the nuceli load wiould be less as the bubbles dacayed away. If the exercise at surface, pressurized, and returned to surface, the nuclei load would also be less.

Yes, Dr Vann is aware of this study.

- - - - -

Dervay JP, Powell MR, Butler B, Fife CE. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviat Space Environ Med. 2002 Jan; 73(1): 22-7. [Medical Operations Branch, NASA-Johnson Space Center, Houston, TX 77058, USA.]

BACKGROUND: Decompression, as occurs with aviators and astronauts undergoing high altitude operations or with deep-sea divers returning to surface, can cause gas bubbles to form within the organism. Pressure changes to evoke bubble formation in vivo during depressurization are several orders of magnitude less than those required for gas phase formation in vitro in quiescent liquids. Preformed micronuclei acting as "seeds" have been proposed, dating back to the 1940's. These tissue gas micronuclei have been attributed to a minute gas phase located in hydrophobic cavities, surfactant-stabilized microbubbles, or arising from musculoskeletal activity. The lifetimes of these micronuclei have been presumed to be from a few minutes to several weeks.
HYPOTHESIS: The greatest incidence of venous gas emboli (VGE) will be detected by precordial Doppler ultrasound with depressurization immediately following lower extremity exercise, with progressively reduced levels of VGE observed as the interval from exerciseto depressurization lengthens.
METHODS: In a blinded cross-over design, 20 individuals (15 men, 5 women) at sea level exercised by performing knee-bend squats (150 knee flexes over 10 min, 235-kcal x h(-1)) either at the beginning, middle, or end of a 2-h chair-rest period without an oxygen prebreathe. Seatedsubjects were then depressurized to 6.2 psia (6,706 m or 22,000 ft altitude equivalent) for 120 min with no exercise performed at altitude.
RESULTS: Of the 20 subjects with VGE in the pulmonary artery, 10 demonstrated a greater
incidence of bubbles with exercise performed just prior to depressurization, compared with decreasing bubble grades and incidence as the interval of rest increased prior to depressurization. No decompression illness was reported.
CONCLUSIONS: There is a significant increase in decompression-induced bubble formation at 6.2 psia when lower extremity exercise is performed just prior to depressurization as compared with longer rest intervals. Analysis indicated that micronuclei half-life is on the order of an hour under these hypobaric conditions.

 

[HammerNoMore]

Charlie99 once bubbled...
No need to post the entire thread. I posted a link.

You originally posted that MHK was teaching students that they can fly immediatly after diving which we both know is not the case.

You pointed to a post where MHK indicates that HE flies right after diving, but left out all of the posts where he justified this action.

Let's look at the original post he made to the thread:

We believe in properly doing your decompression before you get out of the
water. I'm out of the water and go directly to the airport almost every
weekend..

Before this thread get's out of hand, let me state very clearly that if you
want to wait 12 hours or 24 hours by all means please do so, we just don't
believe that it is necessary assuming you deco properly in water.

The dive and fly thing is based upon conservation and not really any actual
evidence. See the following:


By government regulation, the cabin pressure cannot be less, at maximum
cruise altitude, than the equivalent of outside air pressure at 8,000 feet.

Using atmospheric scale height of 7km (23000ft), one gets a minimum of 10psi
(14.7psi/e^(8kft/23kft)), a percentage change of -29%. This is an equivalent
change to ascending from 13ft to the surface.

Use your own judgment, make your own decision, and if you believe that you
need 12 or 24 hours by all means wait, but we just don't feel that it is
necessary.

MHK is basicly presenting the information and allowing the reader to come to his own conclusions about when they think it is safe to fly after diving.

Your qotes are out of context because you are using pieces of a coversation to support a statement that is clearly not true. What's worse is that you have our pilot friend beliveing the statment.

In the case of flying after diving in Tobago, I posted MHK's ENTIRE response. His ONLY post in the thread. How is that out of context?

Because it in no ways supports your theory. Saying it is ok to take a puddle jumper (where the concern of rapid decompression due to a cabin pressure failure doesn't exist) 10 hours after a couple of shallow dives is a far cry from advising students to jump on a plane right after diving.

Go do a couple of shallow "newbie" dives as described in the original post and let me know what your computer says your deco time is. Or better yet, check the PADI tables: 6 hours from a Z diver to clean.

99% of the people are going to tell you to stick to a number from 12 to 24 pulled out of thin air because sufficient data does not exist to come up with a real number. Why is that 1% out there giving the alternative point of view such a threat?

OK, so lets look at the context of the 2nd link. Hmmmm. There's seems to be a pattern here. Here's another post by MHK:"Then you missed what I said.. I said there is very little, if any,
"credible" evidence that dispositively proves that flying post diving causes problems... "

While you don't come out and say it you clearly seem to be indicating that such evidence exits. Here is DAN's take in it's entirety: http://www.diversalertnetwork.org/medical/faq/faq.asp?faqid=54.

They clearly state that all current recomendations are based on a "best guess" and that they are currently studying it but as of yet the research is incomplete.

You can interpret "dispositively" as you wish.

dis·pos·i·tive ( P ) Pronunciation Key (ds-pz-tv)
adj.
Relating to or having an effect on disposition or settlement, especially of a legal case or will.

Different views of decompression interest me. The MHK/GUE view of various deco issues are rather different and interesting.

One should read the material and make up your own mind as to whether or not there is credible evidence that "dispostively" shows that flying post diving causes problems.

Exactly my point. Now you are on target. People should think for themselves and make up their own mind. However they cannot do so when they are only presented with half the facts. MHK never tells anyone they should fly immediatly after diving but rather to make up their own minds.

My personal opinion is that the 12-24 hour recomendation is conservitave at best. I does not hurt to be conservative in this case and I always wait 24 hours to fly. However in knowing more than the "thou must wait" propiganda, such that if an emergency ever made an early departure necissary, I would be comfortable that it would be safe to do so.

James

 

[BigJetDriver]

Lord love a duck, as the Brits are won't to say!!!!!:wacko: Here we go again. We've got men with Doctorates in Physics, Medicine, Nuclear Physics, for God's sake, who research this stuff for a living who say that there are VERY GOOD REASONS to use the tables as listed. There are VERY GOOD REASONS to be conservative and be kind to your own body and your own health.

Then we've got guys with nowhere near the education, background, and training who say: "Hey! I get away with it! It's okay!!" Lord save us all! Lord save the new diver who might be tempted to listen to this tommy-rot!!!:fury:

If you want to jump out of the water from deco dives and leap into the air, have at it, brother! But when you are lying in the aisle, frothing at the mouth, and the nearest chamber is two hours flying time away, don't be expecting any sympathy! :whack:

P.S.---The NOAA FAD table shows the wait time for an "M" group diver, fairly average for a series of dives, to be 5:35 to go to 1,000 feet! =-)

 

[fins wake]

You originally posted that MHK was teaching students that they can fly immediatly after diving which we both know is not the case.

James, the original quote was:
On almost any given weekend I can be found getting out of the water and rushing to an airport, often times with my hair and my gear still dripping wet and that is often times after very deep and lengthy decompression dives, so I wouldn't worry too much about doing a few recreational dives and jumping on a puddle jumper...

Personally, I go with Charlie's and BigJetDriver's interpretation. That's the problem. How do you know newbie recreational divers won't do the same?

You pointed to a post where MHK indicates that HE flies right after diving, but left out all of the posts where he justified this action.

He justified it by repeatedly stating, in several threads, we just don't believe that it is necessary assuming you deco properly in water and if you believe that you need 12 or 24 hours by all means wait, but we just don't feel that it is necessary.

Saying it is ok to take a puddle jumper (where the concern of rapid decompression due to a cabin pressure failure doesn't exist) 10 hours after a couple of shallow dives is a far cry from advising students to jump on a plane right after diving.

The 'puddle jumper' is still an aircraft, and you will still be depressurized. Just like you would be going up a mountain or even hill. I personally find the term 'shallow dives' as used by many DIR proponents very disconcerting. In the real world, some people still get DCI in what the WKPP may well argue are 'shallow' dives ... Horses for courses.

Or better yet, check the PADI tables: 6 hours from a Z diver to clean.

PADI RDP lists 12 hours of minimum surface interval before flying, longer if repetitive multi-day dives or decompression dives. This is clearly stated on all RDP:s and this - if I remember correctly - in fact constitutes one of the OW exam questions ... PADI does not teach or propose a six-hour surface interval before flying.

Here is DAN's take in it's entirety:

Let's quote the actual text: A minimum surface interval of 12 hours is required before ascent to altitude in a commercial jet airliner (altitude up to 8,000 feet). Divers who plan to make daily, multiple dives for several days or make dives that require decompression stops should take special precautions and wait for an extended surface interval beyond 12 hours before flight. The greater the duration before flight the less likely decompression sickness is to occur.

In fact, this is almost verbatim the text on the PADI RDP!

Now you are on target. People should think for themselves and make up their own mind.

Agreed.

My personal opinion is that the 12-24 hour recomendation is conservitave at best.

Now that is more like what MHK actually said.

I does not hurt to be conservative in this case and I always wait 24 hours to fly.

Excellent.

However in knowing more than the "thou must wait" propiganda, such that if an emergency ever made an early departure necissary, I would be comfortable that it would be safe to do so.

Propaganda? It's medical advice by hyperbaric specialists, echoed by several large dive training organizations, in order to prevent injury and illness to divers. Propaganda? For what purpose? Does somebody earn money by purposefully having divers wait before flying? (Actually, I'm sure someone will jump on that bandwagon ... )

Me, I'm not comfortable it's safe at all. It would really have to be a major emergency to get me on a plane precipitiously. A terrific hurricane, a violent revolution, civil war or the like. And I don't usually plan on diving in Afghanistan ...

James, why not just admit that some people have different views on dive safety as relates to flying-after-diving? And that they're either right. Or very wrong. Me, I don't want to find out. I'm a FAD weenie ...

 

[Charlie99]

James Goddard once bubbled...
Go do a couple of shallow "newbie" dives as described in the original post and let me know what your computer says your deco time is. Or better yet, check the PADI tables: 6 hours from a Z diver to clean.

Ummmm, James, are you saying that PADI says 6 hours to fly is OK? I think you need to look at your table again. In particular, the section that says "Flying after Diving Recommendations".

I've skipped a couple other items where it is clear you have a reading comprehension problem. The posts are there for others to read.

Clearing of the 60 minute HT compartment and clear to fly are two different things.

Here's another post by MHK:"Then you missed what I said.. I said there is very little, if any, "credible" evidence that dispositively proves that flying post diving causes problems... "

While you don't come out and say it you clearly seem to be indicating that such evidence exits. Here is DAN's take in it's entirety: They clearly state that all current recomendations are based on a "best guess" and that they are currently studying it but as of yet the research is incomplete.
[/B]

That reading comprehension problem again.

MHK is saying that he doesn't think that anyone has proven a connection between flying and DCS.

DAN is saying that they don't know the precise relationship.

Of course, I could be misinterpreting his statement, since his statement could be interpreted as saying that he doesn't see any relationship between flying fenceposts and DCS. I chose the other interpretation, which is consistent his many other statements discounting the relationship between flying and DCS.

 

[HammerNoMore]

fins wake once bubbled...
James, the original quote was:

You posted MHK's quote. I was refering to Charlie's statment of:

Ask MHK about his "hair still wet" fly-after-dive rule.

At least one GUE instructor's teaching is that, if you have properly done your decompression, then you can fly immediately.

Personally, I go with Charlie's and BigJetDriver's interpretation. That's the problem. How do you know newbie recreational divers won't do the same?

I don't. But then again I'm a Darwinist. If someone reads a statement on usenet after being taught otherwise and accepts it without doing any other personal research, then evolution is just helping the rest of us out.

He justified it by repeatedly stating, in several threads, we just don't believe that it is necessary assuming you deco properly in water and if you believe that you need 12 or 24 hours by all means wait, but we just don't feel that it is necessary.

Err, no. He justified it by stating that the GUE diving proceedures are far different than other agencies. That they treat every dive as a deco dive and do them using modified tables. That they have strict physical guidlines for divers, while the DAN estimates are based on more of a worst case scenario of physical health. And with his little post about the pressure difference about going to FL24 is equivalent to 13 feet in water.

The 'puddle jumper' is still an aircraft, and you will still be depressurized. Just like you would be going up a mountain or even hill.

No arguement. All I said was that you don't have to worry about having a sudden cabin depressurisation.

I personally find the term 'shallow dives' as used by many DIR proponents very disconcerting. In the real world, some people still get DCI in what the WKPP may well argue are 'shallow' dives ... Horses for courses.

I'm not saying I agree with MHK's assement on that. Just that the post really had nothing to do with FIAD.

PADI RDP lists 12 hours of minimum surface interval before flying, longer if repetitive multi-day dives or decompression dives. This is clearly stated on all RDP:s and this - if I remember correctly - in fact constitutes one of the OW exam questions ... PADI does not teach or propose a six-hour surface interval before flying.

Right. But their tables give 6 hours as the deco time for a Z diver. The other 6 hours is either an admission that you are not fully offgassed when the table says you are or a "lets be conservitive add on." Nothing wrong with it. But a post that takes a couple of hours off the add on is not the horrible sin it is being made out to be.

Let's quote the actual text.

Well your part of the actual text was DAN's recomendation, which I don't think anyone is arguing. Was refering to the fact that they fully admit they do not have enough information and that the 12 hours is a best guess.

Propaganda? It's medical advice by hyperbaric specialists, echoed by several large dive training organizations, in order to prevent injury and illness to divers.

Perhaps not the best choice of words.

Me, I'm not comfortable it's safe at all.

Excellent. You have weighed the evidence and opinions and made up your own mind, without bashing others who did the same but with different results.

James, why not just admit that some people have different views on dive safety as relates to flying-after-diving? And that they're either right. Or very wrong. Me, I don't want to find out. I'm a FAD weenie ...

Well that's kind of my point....obviously Charlie is so worked up about a statement MHK made 6 years ago that he is till ready to bash him for it at any opportunity. As I said, I wait 24 hours. That's my choice. MHK doesn't and that is his choice.

James