Great discussion! Thanks, Debersole...
I'm a doc but not a cardiologist, so feel free to correct me if I'm wrong, but I just wanted to clarify something, terminology-wise.
Gas bubbles forming in the bloodstream (where they are not supposed to be!) is a phenomenon seen in Decompression Illness (DCI), associated with a too rapid reduction in ambient pressure. The bubbles can be either in the veins of the body (Decompression Sickness, DCS), or in the arteries of the body (Arterial Gas Embolism, AGE). So AGE and DCS are both forms of DCI.
Since the bubble mainly form in the lower-pressure venous side of the circulation, the two most common ways for AGE to occur are with some sort of leak from the venous side to the arterial side (e.g. PFO), or from lung trauma (as may be seen in expansion injuries from breath holding on ascent). Apparently, there is still some controversy about AGE and PFOs, since if it was a simple shunt issue, one would expect the AGE rate to be higher (given the fact that asymptomatic PFOs are relatively common, and that you don't need as much gas volume for a symptomatic AGE as for DCS). However, I would defer to those with more knowledge than me for this analysis!
In any case, the reason that AGE can be more dangerous for a given volume of gas is that the arteries get smaller as you go downstream, while the veins get bigger. The veins pass through the right heart and end in the lungs which can safely filter a certain amount of gas. When you get even a small bubble traveling downstream in an artery, and that artery ends, say, in the brain, you can cause a stroke by blocking bloodflow to certain areas that may not have good alternative flow arrangements.
Here's a good summary from DAN:
DAN Divers Alert Network : Decompression Illness: What Is It and What Is The Treatment?
I'm a doc but not a cardiologist, so feel free to correct me if I'm wrong, but I just wanted to clarify something, terminology-wise.
Gas bubbles forming in the bloodstream (where they are not supposed to be!) is a phenomenon seen in Decompression Illness (DCI), associated with a too rapid reduction in ambient pressure. The bubbles can be either in the veins of the body (Decompression Sickness, DCS), or in the arteries of the body (Arterial Gas Embolism, AGE). So AGE and DCS are both forms of DCI.
Since the bubble mainly form in the lower-pressure venous side of the circulation, the two most common ways for AGE to occur are with some sort of leak from the venous side to the arterial side (e.g. PFO), or from lung trauma (as may be seen in expansion injuries from breath holding on ascent). Apparently, there is still some controversy about AGE and PFOs, since if it was a simple shunt issue, one would expect the AGE rate to be higher (given the fact that asymptomatic PFOs are relatively common, and that you don't need as much gas volume for a symptomatic AGE as for DCS). However, I would defer to those with more knowledge than me for this analysis!
In any case, the reason that AGE can be more dangerous for a given volume of gas is that the arteries get smaller as you go downstream, while the veins get bigger. The veins pass through the right heart and end in the lungs which can safely filter a certain amount of gas. When you get even a small bubble traveling downstream in an artery, and that artery ends, say, in the brain, you can cause a stroke by blocking bloodflow to certain areas that may not have good alternative flow arrangements.
Here's a good summary from DAN:
DAN Divers Alert Network : Decompression Illness: What Is It and What Is The Treatment?
