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Thread: PFO's and CC diving?

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    New Member scubasavage is an unknown quantity at this point scubasavage's Avatar
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    Question PFO's and CC diving?

    hi,

    I'm currently diving oc and am now looking into goin to cc this winter. Just wonding whats the story about PFO's (Hold in Hearth) and diving on cc?

    Would it be a good idea to go and get it checked out if a diver has a PFO or not before they invest all there €€€ in a rebreather?

    Thanks
    Barry

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    Hi There Barry,

    Testing for a PFO is a reasonably contentious area and I'm sure if you search this or maybe some of the other tech diving forums you'll get a number of discussion hits.

    I recently had the test done myself and discussed it on another list. Have a read of the thread here to get you started on some of the issues to consider.

    Best regards,
    Andrew

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    Barry,

    There is almost constant argument in medical circles about the "correct" figure to use as the percentage of humans who wind up with a PFO. Of course we all posess it before we are born, by design.

    I have seen the estimates as high as 27%, and as low as 5%. Whatever the actual case may be, a certain percentage of individuals have a hole between the chambers of the heart that is incompletely protected by a flap of tissue which normally closes at birth or shortly thereafter. The opening (foramen) is oval-shaped (ovale) and remains open (patent), thus Patent Foramen Ovale or PFO.

    In most cases, it causes little or no problems to the individual, but in the diver, it can be problematic. Note I said diver, not specifically RB diver.

    A serious problem can occur if the diver's system is off-gassing and creating a certain amount of bubbles in the venous circulation. We all have these after any dive. If they are not causing any symptoms, we say they are "silent".

    Since the lungs are such efficient filters, a fair amount of these bubbles will simply circulate into the lung filter bed and be dissipated.

    If, however, there is a PFO that is forced open by unusual effort, such as heavy coughing, or climbing a boat ladder with heavy equipment, those bubbles can pass through the opening into the arterial side, and be circulated to the brain, causing all sorts of havoc.

    As has been noted, there are invasive and non-invasive methods for detecting the presence of a PFO. Unfortunately, the non-invasive method is not as successful, and the invasive method carries with it a certain amount of risk which physicians are, understandably, unwilling to accept without good reason.

    If, for example, you were doing decompression diving and suddenly experienced an unexpected case of DCS, even though you were well within conservative limits, the presence of a PFO might well be something you would wish to rule out.

    Hope this has helped.

    Rob Davie
    DMT

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    Quote Originally Posted by Underwaterbear
    Hi There Barry,

    Testing for a PFO is a reasonably contentious area and I'm sure if you search this or maybe some of the other tech diving forums you'll get a number of discussion hits.

    I recently had the test done myself and discussed it on another list. Have a read of the thread here to get you started on some of the issues to consider.

    Best regards,
    Andrew
    I've had a bend from a very easy profile.

    I was sent for a PFO test with Dr Peter Wilmshurst. He found one.

    I then had the PFO closed. Phrases like "Intra venous trans catheter closure of a left right atrial shunt" just trip off the tongue....

    It was really good to have found a reason for the bend, and to have that "cause" eliminated. Dr W told me that the "normal" background to divers he had found PFO's in were divers that had dived for many years with no trouble, then they start doing deeper, longer dives, and then they get a hit that seems irrational.

    You may also like to know that there seems to be a link between Migraine and PFO.

  5. #5
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    Very contraversial subject that can be read extensively on any diving forum, but I think the state of play is summed up nicely here by Fred Bove (American Diving Physician):

    Bove, AA: Risk of Decompression Sickness with Patent Foramen Ovale. Undersea and Hyperbaric Research Sept, 1998

    Abstract

    Several reports have described populations of divers with decompression sickness (DCS) who have a patent foramen ovale (PFO). The presence of a PFO is known to occur in about 30% of the normal population, hence, 30% of divers are likely to have a PFO. Although observations have been made on the presence of a PFO in divers with and without DCS, the risk of developing DCS when a diver has a PFO has not been determined. In this study, we used Logistic Regression and Bayes' theorem to calculate the risk of DCS from data of three studies which reported on echocardiographic analysis of PFO in a diving population, some of whom developed decompression sickness. Overall incidence of decompression sickness was obtained from the sport diving population, from the U.S. Navy diving population, and from a commercial population. The analysis indicates that the presence of a PFO produces a 2.5 times increase in the odds ratio for developing serious (type II) DCS in all three types of divers. Since the incidence of type II DCS in these three populations averages 2.28/10,000 dives, the risk of developing DCS in the presence of a PFO remains small, and does not warrant routine screening of sport, military or commercial divers by echocardiography.

    In fact I think from memory it is Fred (happy to be corrected) who is also an interventional cardiologist (so would have a vested interest in pushing repair of PFOs), and he has currently moved away from recommending repair of the lesions, given the risks (small) of the repair vs the benefits in terms of prevention of PFO.

    With the risk of DCI in recreational divers of about 1:10 000, and of serious neurological DCI maybe 10 times less than that, it is very hard to justify routine screening of a problem that occurs in 11, 19 or 27% of the population at post mortem (the 3 studies I recall). I accept that tech divers have a higher risk of DCI than recreational divers, and that I would feel nervous about doing big dives if I knew I had PFO that shunted under modest provocation. I have no plans to be screened however. I'd feel pretty silly if I had a stroke whilst undergoing a procedure to fix an asymptomatic problem, that had yet to cause me problems with my diving. My personal opinion only.

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    Hi Harry,
    How's the water temp? Its a balmy 10degC here atm...anyway - to the point...

    Quote Originally Posted by Richard Harris
    [snip]..... Overall incidence of decompression sickness was obtained from the sport diving population, from the U.S. Navy diving population, and from a commercial population. The analysis indicates that the presence of a PFO produces a 2.5 times increase in the odds ratio for developing serious (type II) DCS in all three types of divers. Since the incidence of type II DCS in these three populations averages 2.28/10,000 dives, the risk of developing DCS in the presence of a PFO remains small, and does not warrant routine screening of sport, military or commercial divers by echocardiography.

    In fact I think from memory it is Fred (happy to be corrected) who is also an interventional cardiologist (so would have a vested interest in pushing repair of PFOs), and he has currently moved away from recommending repair of the lesions, given the risks (small) of the repair vs the benefits in terms of prevention of PFO.
    Sounds like a case of excellent scientific objectivity to me.
    With the risk of DCI in recreational divers of about 1:10 000, and of serious neurological DCI maybe 10 times less than that, it is very hard to justify routine screening of a problem that occurs in 11, 19 or 27% of the population at post mortem (the 3 studies I recall).
    I was told by my specialist that the discrepency in these figures reflects specificity of tests and the absolute rate of occurence. ie average detection rate is about 50% and the true rate of occurence is around 27%.
    I accept that tech divers have a higher risk of DCI than recreational divers, and that I would feel nervous about doing big dives if I knew I had PFO that shunted under modest provocation. I have no plans to be screened however. I'd feel pretty silly if I had a stroke whilst undergoing a procedure to fix an asymptomatic problem, that had yet to cause me problems with my diving. My personal opinion only.
    How will a positive result feel after that "undeserved hit"?

    I certainly agree that routine screening is unwarranted due to cost and the adverse side effect rate. But it's my opinion that quoting 1:10 000 is misleading given that it is an average of all three of those groups mentioned above. It is up to the individual to decide if they fall into the same "dive demographic" as used in the sample to come up with the figure.

    Lets look at the groups: Recreational divers: mostly non deco - expect a low DCI incidence rate. Military and commercial: highly controlled and professional, typically very fit - expect a low incidence rate. Amateur technical divers with variable fitness and an interest in deep trimix diving....1:10 000?
    In my book it will always come back to the individual to choose and I certainly don't advocate everyone running out an getting the test. But remember guys, life is not a game, you are risking becoming the left side of that ratio.

    Beware of advice from health professionals on statistics, and health advice from statisticians!

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    Quote Originally Posted by Richard Harris
    Bove, AA: Risk of Decompression Sickness with Patent Foramen Ovale. Undersea and Hyperbaric Research Sept, 1998

    (stuff snipped)

    With the risk of DCI in recreational divers of about 1:10 000, and of serious neurological DCI maybe 10 times less than that, it is very hard to justify routine screening of a problem that occurs in 11, 19 or 27% of the population at post mortem (the 3 studies I recall). I accept that tech divers have a higher risk of DCI than recreational divers, and that I would feel nervous about doing big dives if I knew I had PFO that shunted under modest provocation. I have no plans to be screened however. I'd feel pretty silly if I had a stroke whilst undergoing a procedure to fix an asymptomatic problem, that had yet to cause me problems with my diving. My personal opinion only.
    If you don't have a problem, then no problem. But if you've had a neurological hit (I couldn't speak properly and my balance was screwed) then the PFO has just moved out of the category of "asymptomatic".

    Your chances of a stroke after? Not big, but do remember to take the anticlotting medicine they gave you!! And the antibiotics. The benefits definately outweigh the risks.

    If you get a neuro bend after a deep trimix dive, get checked. If you have a PFO, get it fixed. Then go diving again with a "normal" risk of DCS.
    Whatever normal might mean.....

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    Quote Originally Posted by PeteS
    But if you've had a neurological hit (I couldn't speak properly and my balance was screwed) then the PFO has just moved out of the category of "asymptomatic".
    >
    If you get a neuro bend after a deep trimix dive, get checked. If you have a PFO, get it fixed. Then go diving again with a "normal" risk of DCS.
    Whatever normal might mean.....
    But was the neuro bend related to the presence of the PFO? Your PFO might still be asymptomatic? As UW Bear has clearly pointed out I'm no statistician, but as he also says, deep trimix diving is almost certain to put you at higher risk of DCS than the 1:10 000 for NDL sport divers. That doesn't mean that PFOs feature more prominently in the causation of tech divers' DCI. We get more DCI because we load ourselves with more inert gas, we are using untested algorithms and it's a long way to the surface if you have a problem.

    I worry more about the likley role of a PFO in a diver who has Type 2 DCS after a no-deco dive. If they have a PFO....I would be more inclined to get that fixed before they dive again.

    BTW I am not judging anyone who has been screened, diagnosed or fixed....just trying to keep it all in perspective. I still don't know for sure what I would do if I am the one with this diagnostic dilemma.

  9. #9
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    Quote Originally Posted by Underwaterbear
    I was told by my specialist that the discrepency in these figures reflects specificity of tests and the absolute rate of occurence. ie average detection rate is about 50% and the true rate of occurence is around 27%.
    bugga just lost my big fat post

    Thought you might like some more detail on those figures mate.

    The best IMO come from Hagen who based on 965 autopsies (supposedly normal hearts) found between 25-34% PFO rate (more in young, less but bigger in elderly) based on pushing a probe through. This gives an average of 27.3% which is the figure most often quoted. It gives no clue to the haemodynamic significance of those lesions though.

    Penther 500 autopsies (must have been bored!) 14.6% (no age difference)

    Moon (?echo) 5%

    Lechat 10-40%

    Fisher 9.2%

    Berkompas (echos) about 15%

    So about 25% seems a good figure. Now if tech divers have a DCI rate of 1:1000 or even 1:100 for dives over say 80m, would a stats link this to something that occurs in 25% of us? I suspect not.

    If we were all PFO free would the DCI rate fall? I suspect so, at least the Type 2 stuff would. So the trick seems to be to pick the PFO that will cause trouble, and the circumstances that will make a "bad" PFO misbehave. For any individual we seem to be miles away froman answer. Too many questions, not enough solutions yet.

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    Quote Originally Posted by Richard Harris
    bugga just lost my big fat post

    For any individual we seem to be miles away froman answer. Too many questions, not enough solutions yet.
    Does a PFO increase the risk of serious DCI? ........................................Yes
    Does having the PFO fixed return this risk to normal?.............................God only knows
    Does transoesophageal echocardiography to detect a PFO have risks?.....Yes, some
    Does repair of a PFO have risks............................................. ...............Yes, lots

    Does the (presumed) benefit of a reduced risk of serious DCI justify the risks involved in having an asymptomatic PFO detected and closed? I guess at the end of the day if you think it does that's fair enough for you. You absolutely cannot answer this question for me or anyone else.

    Dave T

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