Can divers with a PFO, still dive on O2 CCR?

RonMicjan

Doc's correct me here, but wouldnt a person with a PFO still be able to dive a pure O2 rebreather? If one is not taking on any nitrogen load, then there are no bubbles to blow past the PFO. Opinions please?

I have a friend with a PFO he and cannot afford the procedure, but would jump at the chance to dive a rig on pure O2. Shallow diving is better than no diving. He could get a used dolphin and run the O2 jet.

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chunter

I'm not a doctor, so don't do anything that I say. My feeling is that he would likely be okay as there is no nitrogen uptake, however, there isn't that much known about the effects of pressure on an existing PFO. For example, when you get checked for a PFO, they have you "bear down" when they inject the bubble-saline solution so as to open the hole wider and force the blood to shunt through the opening. Who's to say that the effects of pressure don't have the same effect. Then again, running, or going to the bathroom may also. I don't know how detrimental the "shunting" is when there is no excess nitrogen. I suppose it depends on the size of the PFO.

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Janos

I'm not a doctor so can't really answer your question, but I've always considered that diving to 11m or less on a set point of 1.3 is off-gassing (ie 11m= 2.1 bar, less 1.3 bar O2, gives ppN2 of 0.8, which is the same as on the surface).

But physiology is tricksy stuff so it might not be as rational as you might think.

Janos

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Genesis

I would expect that diving on a pure O2 rig would be the least hazardous option with a known PFO in terms of a shunt possibility and the outcome if he does shunt.

However, whether that constitutes it being "safe", I can't answer......

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nigelh

Haldane recorded bending Goats on pure O2 so bubbles are quite possible.
However I think the depth restriction of an Oxygen rebreather would protect you.

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dteubner

Remember what a PFO actually means in terms of diving.

It means that you have (roughly) a four fold increase in the risk of serious neurological DCI.

If you do dives that carry an inherently high risk of serious neurological DCI then this increase in risk is probably significant - hence the concern in technical diving circles. If you do dives which have a very low risk of serious neurological DCI then the increase in risk is probably not significant (4 times bugger all is still bugger all).

Diving an O2 rebreather has a very very very low risk of serious neurological DCI (of course O2 toxicity is another thing).

Remember though - in anything to do with medicine - it's never never and it's never always.

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tibby

Ron, as one who has gone through this PFO nightmare (as patient, NOT a doctor) I would suggest to evaluate the size of the shunt. This doesn't necessarily mean the size of the hole which I understand is hard to evaluate short of an invasive test.
There is a non-invasive test called Trans Cranial Doppler (across temples) which measures the amount of saline bubbles (entered in venous blood via IV) which pass through the shunt (PFO) into arterial blood. The saline bubbles that do not go through the shunt are filtered by the lungs so they don't get counted. The test is done at rest and while bearing down and it spits out a score like 0 out of 5 to 5 out of 5. According to my doctor a person who shows less than 100 saline bubbles in arterial blood is considered normal or 0/5 (they are assuming the lungs don't filter every single bubble). In my case, with a PFO combined with ASD I had a 2/5 at rest and a 5/5 while bearing down. This is considered a very significant shunt and I only got skin and shoulder bends after 2 consecutive dives on 18/25 trimix with 80% for deco. BTW, after the closure my TCD counted a total of 6 bubbles while bearing down, none at rest.

I think the size of the shunt would be important in evaluating the risk of diving with a PFO on pure O2 or not. A small shunt, say 2/5 while bearing down may not be significant for any diving (ask a doctor of course).
In my mind, and I may be off track here, a more significant concern would be AGE rather than DCS if diving on O2 Rebreather if the size of the shunt is significant. However, thinking of how this would work it would have to be a very unfortunate chain of events, something like: ascending a little fast, OPV is a little slow to open, while sneezing or coughing then keep ascending to the surface at the same fast rate...while fighting off a great white ?... This may allow significant size O2 bubbles to embolize in arterial blood before they could get metbolized???...Don't know! I would like to hear a doctor's opinion about this theory if possible.

I don't know exactly how much they charged for the TCD alone but I would expect something around $300-$400 including the visit. I understand how choosing to close it would burden someone since a PFO occlusion price tag could be upwards $25K. I was lucky to have had good health insurance.

All, please keep in mind this is my personal experience/opinion and I do not have medical training.

Hope this helps more than it adds to the riddle.
Tibby

babar

Once again, most studies report that about 1/3rd of the population has a PFO.
I don't think I would deny a prospective diver the right to take an intro open circuit course, or even a closed circuit course, as long as I could get some idea that they understand risks/benefits and would take be extra conservative in their tables, gas mixes, ect

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Simon TW

HI Ron

I've just recently been given the all clear to resume diving after the successfull closure of my PFO. I'm not a Doctor so i can only tell you what I was advised.

I was advised by Dr Wilmshurst that I had three choices, I won't go into detail but one of the choices was to dive within recreational limits to a max EAD of 15 metres. I did this from finding the hole to closing it without a problem. I was travelling a lot and the dives that I did were mostly on air and only on Nitrox where i could get it.

I had a 10 mil hole and was shunting at rest. What Dr Wilmshurst did say was that it would be very unlikely to suffer a bend if you keep to 15 metres EAD and keep to the normal rules re fitness and hydration.

I do know of a diver who has been diving like this every weekend for a few years now with no ill effect.

I should think that on CCR at 6 metres with pure O2 this guy should be fine.

Simon

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tibby

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Rethinking my ramblings here, it's probably better to ignore this theory since it doesn't make much sense. I think O2 CCRs don't even have OPVs since the diver is expected to metabolize the expanding O2. This means O2 gets metabolized very fast so how can it bubble out of solution and embolize?
Tibby