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In addition to previous comments of:
Low pressure area in heart -> spontaneous bubble formation
Incomplete blood transport
etc
A big worry is that a bubble may pass through the patency, thus bypas-
sing pulmonary circulation (read pulmonary *filtration*), and run out through
systemic circulation again. This would allow for the bubble to increase further
in size.
Although the pressure differential in the heart should prevent blood
flow from the right to left, I have personally seen smaff "puffs" of emboli
pass from R ->L.
Some other current knowledge:
Microemboli exist after almost all air dives ("silent bubbles")
Recent studies of those receiving chamber rides: a disproportionate
number had pfo.
Pulmonary circulation catches emboli > 5 micrometers (or is it 20...
well, at >500 dynes), lets hope they diffuse faster than they expand,
and that if they release, won't cause any more trouble. Put it this
way: bubbles formed in the body travel (hopefully) via venous return to
the heart, then on to the lungs. Stopped here, they hopefully decrease
in size due to differential gas tensions. If passed through the lungs,
this means a) they are very small and b) will hopefully dissipate in
the aorta. Aortic gas tensions very closely match PPgas in the lungs.
Gasseous microemboli are okay as long as they stay in circulation,
and a diver comes up slowly, allowing for filtration or better yet dissolving.
Dave
David Cloutier
Scripps Clinic & Research Foundation
GCRC
La Jolla, CA
e-mail cloutier@sc*.ed*
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