Posted by Ken Kurtis on June 06, 2001 at 22:22:47:
In Reply to: What is he talking about? posted by Neil on June 06, 2001 at 17:02:39:
Neil asked: "The bubbles get compressed enough to get past the lungs WHERE?"
Hopefully this will simply it a bit (may not be exactly physiologically correct but should be illustrative of the point):
1. As you ascend, the nitrogen starts to outgas.
2. Sometimes, it forms asymptomatic or "silent" bubbles.
3. In the normal course of events, these "silent" bubbles, as they grow a bit (while ascending or while on the surface) will/should be trapped/caught/filtered by the lungs.
4. If you re-descend after completing your ascent, you may compress the bubbles enough that they slip through the lungs.
5. Now they're on the "other" (arterial) side of your body and as you come up (again), they re-expand and now lodge in places where they can potentially do greater damage.
The PFO George refers to is the "hole in the heart" (natural thing at birth but doesn't close fully in 20% [I think] of people) which allows bubbles in the venus side of your heart to go directly to the arterial side, bypassing the filtering effect of the lungs, and causing damage.
Since, in both cases, you end up having a mechansim where bubbly blood can get over to the more dangerous arterial side of the blood flow, it's not a good thing.
The difference is that you can't control (absent of surgery) a PFO. But you CAN control whether or not you do a bounce dive and if you do chose to do one, you can also control whether or not you take proper steps to slowly ascend and do a safety stop(s).
Hope that helps.
Ken Kurtis
NAUI Instr. #5936
Co-owner, Reef Seekers Dive Co.
Beverly Hills, Ca.