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Another piece of information dealing with one of the studies I posted regarding PFO and DCS. One of the studies citing an increased rate of cerebral DCS in divers with PFO (Germonpre et al 1998) was actually carried out using funds from a grant from Divers Alert Network Europe. Strange that such an organization supports such important work but doesn't follow through when the results suggest that a substantial number of divers could avoid serious injuries by simply being aware of a PFO. Perhaps someone from DAN is reading this and can explain why. As George strongly points out they still could have told divers of the risks involved. I should also point out that in most patients during the normal cardiac cycle, no significant shunt or blood flow occurs from the right to left atria (even if a PFO is present as the right atrial pressure is normally lower than the left). However in some patients, reversal of the pressure gradient between the atria may occur-if you have a PFO then a signficant shunt or flow occurs. Clinically if a left-to-right shunt occurs at rest then the term PFO is not used but instead it is referred to as a "atrial septal defect" (ASD). While ASD is mostly asymptomatic, it is an accepted contraindication for sports diving. Yes thats right they bar you from diving. Why they don't see PFOs as a problem eludes me given that the type of PFOs we are talking about are really minor versions of a ASD coupled with the fact that a significant proportion of divers may experience an increase in right atrial pressure and open the PFO. Given the consequences of paradoxcial embolism of nitrogen (or any other gas) bubbles flowing through the PFO and into the cerbral vasculature has disasterous effects it is bizzare no one seems to take this seriously. Perhaps people are uncomfortable with the fact that a condition they have no control over creates a situation where the sport they love so much may seriously maim them. Sticking your head in a bucket is not the answer. As George has pointed out valve defects aren't the same thing as a inefficient valve doesn't allow blood to flow from the right to the left atria except by allowing it to travel through the lungs which are a natural bubble trap. For those interested we all start out with a PFO. This is because the foetus during development is not breathing hence its lungs are collapsed and therefore circulation through the pumonary circulation has a high resistance. So flow will occur thru the PFO into the left atria. On birth, the first breath of air inflates the lungs causing a reduction in pulmonary resistance and the PFO closes. Functional closure occurs within hours and complete fusion usually takes some months. In some people this fusion of the PFO is incomplete and a small opening between the left and right atria remains throughout life. Anyway I think I've exhaustied this subject and will go back to lurking again. Hope this information helps the list understand a subject that the agencies seem to ignore despite its lethal implications. Phil Davies -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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