PFO Project
The risk for Decompression Sickness (DCS) in sports divers is low – diving is to be considered a safe sport. However, decompressing from any depth does give the diver a certain risk. Every year, hundreds of divers suffer from decompression sickness, and almost half of those divers have not committed any mistake, and have been diving according to the profiles imposed by the currently accepted decompression tables or computers.

Since almost fifteen years now, the possible role that a Patent Foramen Ovale can play in this, has been suggested. Patent Foramen Ovale is not a disease, but only a remains of the anatomy of the heart before birth. Before being born, the lungs have no function in oxygenating the blood (because the fetus is immersed in water), and all the oxygen is transported via the umbilical blood vessels, from the placenta. These blood vessels, that are part of the venous blood system, lead the oxygenated blood to the right atrium of the heart.

The “normal” path of the blood flow is by-passed by a valve-like opening between the right and the left atrium, so that 90% or more of the blood passes through this valve immediately to the left (arterial) side of the blood system. Only 10% passes through the lungs. At birth, as the child takes his/her first breath, the lungs are suddenly expanded and aspirate air. As a result, they also aspirate blood from the right side of the heart, and the pressure in the right atrium drops abruptly, causing the valve between right and left side to close. This valve subsequently fuses permanently, in the days or weeks following birth.

In approximately 30% of all people, a very small valve-like opening remains, only 2 to 5 mm wide. While this has absolutely no consequences in normal life, this opening may permit nitrogen bubbles to pass from the right to the left side of the heart, leading to decompression sickness. In this way, patency of the foramen ovale (PFO) can be considered a risk factor for unexpected (“undeserved”) DCS.

Should all divers be screened for PFO ?
This seems to make sense, but – as always – it is not so clear-cut as one might think.
If 30% of divers have a PFO, why do not 30% of all divers have DCS ? The reason for this is twofold: first, DCS is caused by nitrogen bubbles, not the PFO by itself. If divers do not produce nitrogen bubbles after their dive, they will not suffer from PFO-related DCS. Secondly, there may be bubbles passing through the PFO that do not produce DCS, because they somehow disappear in the arterial circulation. The overall risk for DCS in sports divers has been estimated by DAN Europe at 1 DCS in 42.000 dives when the diver does not dive deeper than 30m, and 1 in 7.000 dives when diving deeper than 30m. Most divers will never suffer DCS in their whole diving “career” !
From previous studies, it seems that the risk of developing DCS when diving with a PFO is between 2 and 5 times higher than if no PFO is present. These estimates have been derived from “retrospective” studies, this means that divers that have already had DCS have been tested and then compared to a “standard” diver population. Although interesting, this is no scientific proof that the DCS risk is indeed 2- 5 times higher. In fact, it may be much higher or even lower !

The only direct way to find out the real DCS risk with and without PFO, is by means of a “prospective” study. In short, this means: screening a large group (of about 4.000 divers), recording the presence or not of PFO, and then following them up for about 5 years or 1.000 dives. Only then a difference in the number of DCS in divers with and without PFO can be proven.

DAN Europe has undertaken this huge task, and needs your support in making it a success!
Participation is easy: after giving your consent, you will be tested for PFO. You need not know the result of this test, but you will be given advice about how to dive safely – every dive.

You will receive a plastic card, indicating your research number and a telephone number. Then – nothing ! You continue your “diving career” and we hope are careful and that you have fun doing so ! In the case that you should suffer DCS however, you have to report this to the telephone number indicated on your card. This has to be done only after being treated, as the numbers on the card are not emergency numbers.

All over Europe, and even outside Europe, divers will be asked to participate in this study. All that is asked from them is their engagement, to report all DCS episodes. This reporting is especially important, as the study will be constantly monitored. In case there appears to be too great a risk for divers with PFO, the study may be terminated before the 5 year period and appropriate warnings will be distributed through DAN. At the end of the 5 year period, you will be contacted again by telephone or mail and will be asked how many dives you have made and if you had any DCS. This study protocol has been fully approved by the Ethics Committee of the Belgian Armed Forces, by the Ethics Committee of the Scotland NHS Trust and in South-Africa.

How will participating divers be tested for PFO ?
Testing for PFO is not so simple. Several techniques have been used, but either they are rather unpleasant and costly (such as trans-oesophageal echocardiography), have a low sensitivity (such as trans-thoracic echocardiography), or are non-specific and costly (such as transcranial doppler, that cannot make the difference between pulmonary shunts and PFO). In any of these techniques, there is a very large variability in results, dependent on the examiner and the way the technique is performed. Therefore, neither of these techniques is suited for large-scale screening.
Recently, DAN Europe Research developed and tested a new technique, that is ideally suited for this purpose. Instead of using echocardiography, a doppler signal at the left carotid artery in the neck will be monitored. This involves the placement of an infusion catheter in a forearm vein, and the injection of an “shaken” standard physiologic saline solution by means of a syringe. This saline “contrast medium” will be monitored at the level of the carotid artery, by the examiners assistant, using a vascular ultrasound device. The whole procedure takes about 20 minutes, and is without any danger to you. In fact, thousands of cardiac patients undergo this same procedure during echocardiography every day.

How can I participate ?
DAN Europe has trained diving doctors in many European countries to perform the tests. They have received instruction by means of a personal training workshop, and engage to follow the procedures strictly. A list of these “investigators” is published on this webpage (see below). They will also present this study to groups of divers using a specially developed Powerpoint presentation.
They will organise the testing at their own convenience and report the results to a central database. In this database, your name and address will be recorded only for study purposes ! They will not be given to any other organisation, nor will DAN use this database for sending you anything else but your participation card and final questionnaire ! Also, your name and address will not be linked to the result of your screening test. This result will be recorded in a separate database, using only your participation number.
For the purpose of the study, it is important that you continue to dive (in a safe way – of course) just as you do now. The result of the test will therefore only be given to you after the 5 year study period – when a DAN Europe collaborator will contact you to fill in a questionnaire.

If you want to participate, locate a PFO Investigator near you by following the link below. If no investigator can be found in your neighbourhood, you can send a mail to research@daneurope.org with your question – we might be able to help you out !