Newsgroup: it.hobby.scuba
Titolo: Nuova tecnica non-invasiva di indagine del FOP

Ciao gente...
si e' parlato spesso di PFO, o FOP, o Forame Ovale Pervio. Senza stare a
ripetere quanto gia' detto su cos'e e sul perche' e' utile fare questo esame,
vorrei segnalarvi una nuova tecnica di indagine, che ho trovato sul sito del
DAN.
Tale tecnica sembra essere piuttosto efficace, senza essere invasiva come
l'ecocardiografia trans-esofagea.
Si tratta in pratica di inserire in una vena del braccio una soluzione
fisiologica con delle bolle, cosi' come nella transesofagea; pero' il passaggio
nel circuito arterioso delle eventuali bolle a causa del FOP, viene monitorato
da una piccola sonda doppler esterna, sulla vena carotidea a livello del collo.
Quindi e' un esame molto meno traumatica (in pratica, solo una flebo), ma il DAN
lo promuove come efficace ed adatto ad uno screening di massa.
Mi sembra un'ottima notizia... cosa ne pensate? Soprattutto i nostri medici del
NG...
megaMAX
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 ten 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 (picture). 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 ap琨ruptly, 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: Firstly, DCS is caused by nitrogen bubbles, not
by 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 (symptoms of) 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 on Dec 8th, 2000. 
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 will encourage individual diving doctors to perform the tests. They
will receive instruction by means of a video tape and detailed written
instructions, and will engage to follow these strictly. We will publish a list
of these "investigators" on this webpage. 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. 
 
http://web.tiscali.it/megaMAX

 drops apµbruptly, causing the valve between right and left side to close.


 L'unica metodica rimane senz'altro la Transesofagea.
..... non immune da falsi positivi ;-)
Max max

 ..... non immune da falsi positivi ;-)
credo che non esista nessuna metdica in grado di essere "immune" da falsi
negativi o falsi positivi!
c'č da valutare se sia meglio avere dei falsi positivi o falsi negativi!
é il dilemma dell'epidemiologia, credo che non si possa certo risolvere!
ciao
Alga

 ..... non immune da falsi positivi ;-)
Questa cosa era gia' saltata fuori e gia' allora non mi e' stata chiara: mi
spiegate come il transesofageo puo' dare un "falso positivo"?
Cioe': se il foro non c'e', come puo' esserci shunt, o cosa puo' far
sembrare che ci sia?
Ciao,
                Paolo

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 a meno di un errore dell'operatore.....
Ovviamente.
Grazie per i chiarimenti,
                                Paolo

 non era rivolta a te la risposta ma a max max.
Ti ha già risposto Andrea. Un esame non può essere ritenuto perfetto a
prescindere dall'operatore e soprattutto a prescindere dalla media
degli operatori stessi (vale a dire senza colpa grave di questi
ultimi).
A ritenere che l'ecocardiografia trans-esofagea sia perfetta (e
comunque non è così data la "facilità" di "sbagliarsi") può capitare
sia di tenersi il proprio foramen (sul rischio effettivo comunque non
ci sono pareri concordi) sia accorgersi che l'operatore ha "sbagliato"
solo in sala operatoria per la chiusura del foramen come in almeno un
caso in Italia è effettivamente avvenuto.
Non è sicuramente chirurgia a cuore aperto, ma prima di sottoporre il
malcapito all'operazione non sarebbe meglio ripetere l'esame ?
Max max