PFO EAD [Archive] - BSAC Scuba Diving Forums

Helen (AKA Hellvet)

26-01-2006, 12:59

I had this for a while, while waiting for diagnosis and pre/post-surgery on my PFO and got very confused as i hadn't been taught it on my BSAC Nitrox course. After finding out what it was i actually set up a spread sheet so that i could work out my EAD at each depth, on each nitrox mix, as well as consider my ox-tox MOD.

MOD when you're diving like this has to consider the ppO2 of 1.4, plus your max EAD. EAD normally cuts you off before max ppO2 becomes a problem, unless you're qualified on some very rich mixes!

My maximum depth was similar - i was initially restricted to 10m EAD, which was then relaxed to 15m EAD later. That allowed me to get to my overall medical restricted depth of 20m on 40%.

If you are not completely clear what your restriction means (EAD, END, etc) then CHECK - either with the diving doctor who provided the medical certificate, or someone on the UKSDMC list of diving cardiologists.

PM me if u have any more questions...

John Williams

26-01-2006, 22:00

If you are given a restriction in your diving of 15metres EAD by a diving Doc, do they really mean Equivelant NITROGEN depth?

The ONLY person who can answer that is the person that wrote it!

No-one else can interpret their intention....so you MUST go back to them for clarification (and in the interim - treat it as a maximum depth on whatever you dive!)

John

johnabbott

28-01-2006, 09:14

Has anybody got any references or links to research or theoretical information upon which these depth restrictions are based?

John

David G

04-02-2006, 14:32

You could look at this article in the Medical section of the BSAC website:

http://www.bsac.org/medical/c_intra.htm

hth
David.

JohnDuncan

04-02-2006, 22:46

I was told on thursday that you can use He in the mix to decrease your EAD and the He bubbles wont matter with a PFO, it is the Nitrogen that matters

Paul Watts

04-02-2006, 23:09

I was told on thursday that you can use He in the mix to decrease your EAD and the He bubbles wont matter with a PFO, it is the Nitrogen that matters

I'd be very surprised. I would have thought a bubble of any gas going into the arterial stream and getting stuck would be a problem....

As has been said, I think you should get professional advice to be sure.

Good luck.

Mike Halligan

04-02-2006, 23:45

If you are given a restriction in your diving of 15metres EAD by a diving Doc, do they really mean Equivelant NITROGEN depth?

John,

If the referee is using the PADI/DSAT term EAD, then (s)he means Equivalent Air Depth (PADI Enriched Air Diver manual p20 et seq). It is the means by which PADI EANx Divers convert the PADI RDP (tables) when using Nitrox of various mixes up to 40% Oxygen. [An example would be the use of 36% EANx at 20 metres, where the diver has an EAD of 14.3 metres.]

However, only the referee knows where the term used on your certificate originates so I suggest, as has John Williams, you should ask.

Hope this helps,
Mike

JohnDuncan

05-02-2006, 21:23

that was told to me during my consultation with Dr Wilmshurst, and I questioned him ab out the helium bubbles. not too much of a problem was his reply, surprised me too!

MattS

06-02-2006, 12:21

The calculations for EAD and END are one and the same

EAD or END = ((FN2 * D+10)/0.79) - 10

The term EAD is used in decompression calculations. END is used to compare a gasses narcotic affects with that of air breathed at a similar depth.

Your body does not read text books so the best advice is to ask the doctor that stipulated the limit, what he actually meant.

Nigel Hewitt

06-02-2006, 15:03

The calculations for EAD and END are one and the same
EAD or END = ((FN2 * D+10)/0.79) - 10Are you sure?
I would calculate EAD on total inerts and END on nitrogen alone.

OK using EAD on 'mix is a bit naughty but up to 30% helium you can deco on air tables factored with EAD and they're OKish

Also I think you are missing a bracket...
((FN2 * (D+10))/0.79) - 10

Vic

06-02-2006, 16:03

Very true mate, but as it is the N2 that is the problem surely that is the "equivalent" bit that is important when talking about deco matters

Errr - helium is also important when it comes to deco...

And if you're not talking about mix diving, then I'm not sure I understand the distinction you're drawing[1].

Vic.

[1] I'm ignoring the "oxygen is narcotic" stuff, naturally...

Vic

06-02-2006, 16:07

I was told on thursday that you can use He in the mix to decrease your EAD and the He bubbles wont matter with a PFO, it is the Nitrogen that matters

I think someone is pulling your leg.

The problem with a PFO is that bubbles don't get trapped in the lungs (where they can be eliminated much more safely).

If a bubble ends up lodged somewhere nasty, it makes not one jot of difference whether it's made of He or N2 - it's still a bubble, and it's still going to bend you. It's a mechanical action, not a chemical one.

Swapping He for N2 in your breathing mix just means you have more inert gas dissolved in your tissues...

Vic.

JohnDuncan

06-02-2006, 17:45

I think someone is pulling your leg.

Vic.

I didnt think that Dr Wilmshurst was comedian, although he was a nice guy.

Vic

06-02-2006, 18:32

I didnt think that Dr Wilmshurst was comedian, although he was a nice guy.

Then you've misunderstood him.

It wouldn't surprise me if he was distinguishing between N2 and O2 - since O2 bubbles have almost no part to play in DCI. I'm entirely certain that he would neither have stated nor implied that He didn't matter. Because it does.

Vic.

JohnDuncan

06-02-2006, 20:30

thats what I thought, but I asked him the question twice....

Vic

07-02-2006, 10:06

thats what I thought, but I asked him the question twice....

Did you mention helium?

If you didn't, it's likely he gave you an answer suitable for a nitrox diver, where N2 is the more relevant of the gases. He doubtless wouldn't want to confuse someone who doesn't use He, and would expect someone mix-qualified to understand that both He and N2 count towards your decompression obligation without needing to be told.

Vic.

MattS

07-02-2006, 11:15

Are you sure?
I would calculate EAD on total inerts and END on nitrogen alone.Well I guess it depends how complicated you want to get. For Nitrox EAD calculation FN2 = 1 - FO2. Traditional Trimix END calculation FN2 = 1 - (FHe + FO2). You might modify END to treat O2 equally narcotic as Nitrogen, FN2 = 1 - FHe. So I think it is fair to say the calculations are one and the same, but as you point out there are different ways to arrive at the terms of the calculation.
OK using EAD on 'mix is a bit naughty but up to 30% helium you can deco on air tables factored with EAD and they're OKishIs that Ok as in it has not bent you, or Ok as in you have run a range of numbers and the profiles turn out similar. There is perhaps a point where a sufficiently low FHe leaves N2 controlling the decompression throughout. There would also seem to be a point where He can be physiologically ignored. Theoretically though I can't see how you can apply EAD to Trimix as He has significantly different decompression characteristics to N2.
Also I think you are missing a bracket...
((FN2 * (D+10))/0.79) - 10Why thankyou. Having been lambasted on my last course I cam trying to committ the EAD calculation to memory. Much easier when you get to write it on two lines ;)

Vic

07-02-2006, 12:21

Having been lambasted on my last course I cam trying to committ the EAD calculation to memory. Much easier when you get to write it on two lines ;)

That's got to be by far the hardest way to do EAD.

Far easier is :-
- What is my current ppN2?
- How deep would I be on air to get that same ppN2?

Same result, but based on recognition of equivalence, rather than attempting to memorise an equation, so less prone to error...

Vic.

MattS

07-02-2006, 13:56

Same result, but based on recognition of equivalence, rather than attempting to memorise an equation, so less prone to error...I don't have a problem with conceptual thinking, but it does not provide the solution to the closed book exam question;
What is the maximum no stop time for a CCR dive to 25m using a high setpoint of 1.3 and air as a diluent?

I suspect that you might be able to think your way from concept to equation. Personally I have to revert to writting things out as often as possible until it is memorised. Each to his own.

Vic

07-02-2006, 16:07

I don't have a problem with conceptual thinking, but it does not provide the solution to the closed book exam question;
What is the maximum no stop time for a CCR dive to 25m using a high setpoint of 1.3 and air as a diluent?

Sure it does.

Ambient pressure at 25m is 3.5bar. That's easy.

ppO2 is 1.3 - that's defined in the question.

ppN2 is what's left - 2.2 bar.

So the question boils down to "how deep would I be on air if my ppN2 was 2.2bar?". And that's a smidge under 18m.

Now we just look up the max dive time for 18m on an air table...

I suspect that you might be able to think your way from concept to equation. Personally I have to revert to writting things out as often as possible until it is memorised. Each to his own.

Yup. And by doing that, you end up with homework to do, whereas I'm in the pub because I simply fall back on what we used to teach Club Divers...

Vic.

PeteM

07-02-2006, 16:21

Yup. And by doing that, you end up with homework to do, whereas I'm in the pub because I simply fall back on what we used to teach Club Divers...

The trouble is Vic, you (and I) think in way that makes your description obvious. Others, like my DPO don't and can not think things through in what to us is a logical way and from that work out what to do, so they have to resort to learned formulae.

She however can spell without resort to the F7 button;)

Vic

07-02-2006, 17:20

Others, like my DPO don't and can not think things through in what to us is a logical way and from that work out what to do, so they have to resort to learned formulae.

I firmly believe that this reliance on formulae is a learned response.

My DPO used to do the same thing - except she was rubbish at remembering equations, so often got them wrong. At the root of the problem was that EAD didn't mean anything to her - it was just something she had to calculate to pass courses.

I walked her through what was meant by "equivalence"[1], and the light went on...

Vic.

[1] This was not a ten-minute chat :-(

PeteM

07-02-2006, 17:27

I walked her through what was meant by "equivalence"[1], and the light went on...

Sometime when you have a spare fortnight you can have a chat with t'missus

JohnDuncan

07-02-2006, 18:55

Vic

07-02-2006, 19:39

YES, that is part of the point about this post. if you are told to modify your diving to have an EAD of 15m you can do that but then you also have to contend with the helium. I am just reporting the answer that Wilmshurst gave me, and I questioned him twice.

No, the point of this is that you are deliberately trying to misunderstand what's been said to you.

If you've been given a 15m EAD, then that's that. If you manage to work out a way to calculate EAD for trimix, do share it with the rest of us - 'cos it doesn't work. By talking about EAD, you're inherently talking about a nitrox dive, and any inference you might make about getting deeper by adding helium to the mix is clearly spurious.

If you genuinely feel that the good doctor meant to tell you that it's fine to dive really deep on helium-rich mixtures, just as long as the ppN2 doesn't go beyond 2bar, then I suggest you ring him up and tell him about your misconceptions. Coming onto a public forum to make assertions that a respected figure said something as stupid as you have implied is neither helpful nor likely to impress anyone.

Now - the space below this post is for you to have the last word. I'm quite sure you want it, and I can't be bothered to respond to you any more.

Vic.

JohnDuncan

07-02-2006, 19:44

Ben Panter

07-02-2006, 19:59

Why are you being so confrontational? I am only posting this as it was told to me by a Doc. I realise that the attitudes on people on this BSAC forum hasnt changed since I last used it, and now know why it is pointless posting anything here and not expecting people with childish attitudes to reply.

Hang on there John. You asked a question, you got many replies, all saying pretty much the same thing.

If you are given a restriction in your diving of 15metres EAD by a diving Doc, do they really mean Equivelant NITROGEN depth?

Lots of people tried to stop you from doing something that may kill you. Further, several pointed out that if you wanted a definitive answer, you should contact the medical referee who you spoke to before for clarification. Just because you don't like the answers you got, all from people trying to help you, there's no need to lash out.

Ben

MattS

08-02-2006, 09:34

Why are you being so confrontational? I am only posting this as it was told to me by a Doc.I don't particulalry agree with how Vic replied to you but I understand his frustration in the lack of an explanation. The decompression characteristics of Helium would lead one to think it presents more of a problem than Nitrogen. The possibilities are that Dr Wilmshurst got it wrong, you misunderstood or he knows something we do not.
I realise that the attitudes on people on this BSAC forum hasnt changed since I last used itThat's quite a generalisation. Do you really mean to say that the several 1000 people registered to this board all respond childishly all the time? Or that one person has rattled you once and you think that justifies tarring everyone with the same brush.
and now know why it is pointless posting anything here and not expecting people with childish attitudes to reply.If you think someone has responded childishly I can only suggest that you treat them as a child and ignore them.

I am wondering why you asked the question in the first place if you were so completely happy with Dr Wilmshurst's advice. It's kind of interesting that such an eminent authority seems to be casting doubt on our understanding of Trimix decompression but fairly useless when all we are told is 'Because the Doctor said so' I am sure that should you seek clarification from the good Doctor and report back here we would all appreciate it and more importantly you would know for certain what is and is not safe for you.