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>Speaking of bubbles wandering around in your bloodstream, I'm curious about >the effect of a patent ovale foramen, a hole between one side of the heart and >the other, allowing some amount of blood to get back into the body without >going through the lungs. At first glance, it seems like a bad thing for >divers, since you would expect the lungs to aid a great deal in polishing >bubbles out of the bloodstream ;). With the current thread, however, it seems >like even without a patency, bubbles persist for a while, longer than it takes >for blood to run a complete cycle through the circulatory system. So, do the >lungs not remove all the bubbles coming past, or are more bubbles coming out >of solution to keep the blood carbonated? (ok, I know that's the wrong word. I >just like the image.) Are the lungs not removing bubbles because the >complement system has formed a shell around them or is the system overloaded? > So anyway, these bubbles might be running around with or without a >patency. I can imagine a scenario where a large bubble might go through the >patency to the brain or block a critical vessel instead of being removed or >reduced by the lungs, but otherwise, is the situation that different? I >suppose the degree of difference depends on the size of the hole. > >Any comments? any data on divers with patencies? Any insight on bubble flow or >removal based on this data? > The foramen ovale is a communication between the left and right atria of the heart in the fetus, which along with the ductus arteriosus largely prevent blood flowing along the pulmonary artery to the lungs. The foramen ovale closes up after birth but 25% of the adult population have a probe patent foramen ovale (PFO), which can open under pressure. In such people if right atrial pressure is sufficiently raised, as with a valsalva manoevre (not the one you learned to clear your ears with), blood can be pushed from the right atrium to the left atrium. If there are bubbles in this blood, bubbles can enter the left heart and arterial circulation which is bad. Bubbles leaving the left ventricle via the aorta will distribute in this large vessel by flow and bouyancy, if head up they may enter the carotid arteries and pass through the brain cicrulation, which is bad (perhaps Prime Rat will comment on why this is so). Bubbles normally occur in the venous circulation and are filtered out by the lungs, before entering the arterial circulation. There is a correlation between the occurance of PFO and DCI, the data was in an abstract at a UHMS meeting a few years ago, I would have too look it up. There are values for lung removal of bubbles from blood, which I would also have to look up, but I will hazard a guess of 5-10ml gas/100ml blood/minute. If the pulmonary circulation becomes overloaded as in fulminant DCI, a serious, life-threatening form of DCI, pulmonary DCI or chokes, occurs. Normally most bubbles will be filtered by the lungs, but venous bubbles will be continually formed from gas diffusion into gas nucle and growth. I resume that small stabilized bubbles and nuclei may pass through the lungs if not resolved. Stabilized bubbles (presumably coasted with surface active molecules) probably can last in the circulation for weeks. regards, David Doolette ddoolett@me*.ad*.ed*.au*
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