Bubble pumping theory

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ballastbelly

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What's the theory behind 'bubble pumping' when breathhold diving with residual nitrogen from a scuba dive? From googling forums the common sentiment is that it is a very real danger. One way i am imagining is that breath hold diving actually helps move around nitrogen bubbles which might be stuck or be dissolved in tissue. The moving around might be to the lungs for eventual exhalation (same effect as chamber) or to some other more vital tissue. Unlike a chamber however the pressure is released very suddenly on this sort of ascent.
. Thx
 
It does move the bubbles around but you're forgetting something. You descend, your bubbles get smaller and move around. You ascend, the bubble will expand. Where does it expand? In a good place or a bad place?

If it's a bad place, you're one more statistic on the DCS list.
You're already offgassing and moving bubbles fine on the surface interval. Rapid depth changes are not going to help, slow depth changes such as safety or deco stops or chamber rides will. Because like you're getting at, slow ascents (changes in pressure) reduce the risk of bubbles expanding rapidly and overwhelming your body (DCS bends).
 
The "bubble pumping" theory has to do with the lung filter. It is felt that, under normal conditions, the lungs are capable of capturing and keeping the majority of intravascular bubbles (which are thought to originate in the venous circulation), preventing them from entering the arterial circulation. When you submerge with bubbles in your bloodstream, they compress, and may pass the pulmonary filter to the arterial side. Then, when you ascend, they will expand, potentially causing a bubble embolus, especially in the central nervous system (brain and spinal cord).

That is the theory, but it is interesting that many studies with Doppler have shown the peak of bubble presence in the bloodstream is delayed, 20 minutes to an hour after surfacing, which is just about when most divers are getting in for the next dive . . . There is a lot of theory in decompression, but very little good research.
 
Thx for the info. From this it seems bubble pumping is not limited to free diving, but also scuba, say a diver who has just surfaced after his safety stop is asked to return to 30m to look for a weight belt.
Sent from my RM-914_eu_italy_283 using Tapatalk
 
Oh, absolutely . . . and it is a topic of discussion with technical diving, where there is a camp that feels that the advice to do your deepest dive first is possibly quite wrong, because you might be better off doing the deeper one second, compressing the bubbles, and then doing the long, slow decompression from the second bottom time, to allow nitrogen to be absorbed, possibly without ever forming bubbles again. This is probably NOT relevant to recreational diving, mind you.
 

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