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Carlos, A sizable number of people have a hole in their heart. This does not necessarily correlate with having a hole in your head, but when coexistant, may be fatal while diving: if one doesn't get you, the other may. PFO or patent foramen ovale is supposedly a common reason for being bounced out of the US NASA astronaut program. Here, government doctors, unrestricted by managed care and laughingly squandering the tax-payers' money, put astronauts through absurd training programs that not even the dive training agencies ever thought of or were too cheap to afford, e.g, the vomit comet etc. On arrival in this world, or shortly thereafter, the pressure in the left side of your heart exceeds the pressure on the right and the toilet seat that covers the hole in your heart (foramen ovale) slams shut and hopefully rusts over never to open again. However, for about 30% of folks the cover is about as successful at preventing a backflow as your toilet seat is at preventing an overflow. Most of the time this doesn't matter. You briefly raise the pressure on the venous (right) side of your heart in a time honored manner (yelling at gmiiii, breaking wind, singing loudly or choking on pasta) and there's a little leak. Nobody even notices the extra blood stain on the left side of your heart. However, if you have just inflated your bass(?) and are a teensy bit supersaturated with N2, your veins may fill with the aloha spirit (tiny bubbles). If one of those bubbles passes onto the arterial side, (instead of being filtered by your lungs) and gets sent (because you are upright) to your brain, should you choose to survive you are an instant candidate for rehab. Cardiologists used to make a lot of money injecting CO2 (...no, no Peter NOT monoxide) into the veins of would-be divers and then checking to see if the bubbles appeared on the left (arterial) side. Occasionally they did and the lawyers were extremely happy. So now they use saline solutions and rely on the difference between the density of saline and blood as detected by Doppler. The test should not cost more than the price of a set of DiveRite wings. There are in a fact a number of reasonably safe ways to do this test. As most major advances in cardiology have originated in Brazil over the last 20 years (cardiac bypass surgery for one) you can probably get a better rate where you are than here in the US........BUT THE MEAT STARTS HERE I don't think (a) the tests are reliable (b) they test what you think they do (c) it makes a damn bit of difference. If you can demonstrate a left to right shunt, then one can exists, but the chance of a bubble being in the right place to pass through the opening just as you fart is pretty small and the chance that the bubble will go to your head (? like a glass of champagne) even less. More relevant is the reliability of a negative test. What does it mean when bubbles are not seen to pass through? You haven't tried hard enough? You weren't in the right position? You have the mother of all toilet seats covering your foramen? The fact that you can demonstrate the defect in 30% of folks doesn't mean the test is 100% sensitive and that more of the other folk don't have the same physiology. Air embolus is a pretty rare event in sport divers, but if it can occur by blowing a hole through from a vein to an artery in your lung, then I would guess you can blow that toilet seat open with even less force. Rather than waste your money on a test of dubious value, spend it on doin' it right. No bubbles, no troubles. Peter Heseltine "Safer diving through wiser physiology"
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