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> After I wrote this the obvious struck me: Maybe the water pressure on > your chest (which usually raises right sided pressures) keeps > almost *everybody's* foramen ovale open while they dive! Here's a task > for you George, while you are locked in your habitat deco-ing for hours. > Take down a doppler and see if you can pick up R to L blood flow on your > buddies. These things actually work just like a video camera, so you > could have the unit on the surface with an umbilical. All you need is the > jelly to spread on your buddies chests. Hmm. > > -ph I wouldn't expect either of these to be the case since the lungs are at ambient pressure, the blood is at ambient pressure, and the chest is at mabient pressure; i.e. all pressure differentials should be the same. Where PFOs *do* become a problem is the after dive exercises carried out. If you haul yourself back up a ladder, you are puttin moer stress on your chest than will normally be generated on any PFO test, so you are quite likely to open the FO. You comments about 'a bubble in the right place' suggest you follow the theory that single bubbles do damage; leaving aside autocthonous lesions for the moment, it has been suggested that directly after surfacing, you carry a very large number of sub-critical bubbles, aka nuclei, microbubbles whatever. These then take several minutes to either causes damage to an already stressed cardiovascular system, *or* combine with each other or dissolved gases to form serious bubbles. Normally these are scrubbed by the pulmonary beds. This is OK, but if you stress your chest, you may send several mls of 'foam' through to your arterial system, not a single bubble. These small bubbles now get a chance to hit the arterial system, after a similar delay to their venous partners. i.e. they get in *then* some of them form bubbles. To avoid, I guess, either over deco, or allow a few mins (5-15) doing zip-all on the surface before exiting. That way the worst of the nuclei get scrubbed before you open your FO. Doing extra stops under water is probably *less* helpful... Doncha love blind guesswork? Jason > Peter Heseltine wrote on 7/22/96: > > Maybe the extra pressure on > your chest from the water keeps the PFO closed 99.999% of the time, even > in people who have one. > -- > Send mail for the `techdiver' mailing list to `techdiver@terra.net'. > Send subscription/archive requests to `techdiver-request@terra.net'.
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