bluebanded goby
Contributor
I'd be very interested in hearing the reaction of MD's here to a couple of different explanations I've heard about the DCS risk posed by bounce diving.
A message on another bulletin board quoted a message from yet another source that was attributed to George Irvine, the well-known proponent of the DIR philosophy. If you want to read the quoted message, you can see it at:
http://diver.net/bbs/messages/12918.shtml
The main point that I'm interested in is this assertion:
"(B)ouncing to 20 feet or whatever to pick up a bottle and immediately returning to the surface is the like giving yourself a home-made PFO: the bubbles in the venous side compress enough to get past the lungs and then will reexpand on the arterial side and lodge in the worst places, the spine and brain blood supplies."
By contrast, I noticed that Lawrence Martin MD has this to say about bounce diving in his book "Scuba Diving Explained," the text of which is visible online at:
http://www.mtsinai.org/pulmonary/books/scuba/sectiong.htm
"Bounce and sawtooth diving probably increase DCS risk because of silent bubble formation at depth. On ascent any silent bubbles that form begin to release nitrogen harmlessly. However, if the diver quickly returns to the deepest depth, more nitrogen will enter the tissues; _that_ nitrogen, on re-ascent, will then flow into the existing bubbles, which expand further. Thus, the risk of DCS increases by diving immediately after formation of any silent bubbles; bounce or sawtooth diving is one way to do this."
My question is this: Do we really know which of these scenarios is more correct? If so, which one? It seems to me that if re-descending to depth caused any currently outgassing bubbles to shrink and sneak through the lungs into the arteries, then a lot of divers would be experiencing a lot more problems on multiple dives. Thanks in advance for any reactions.
A message on another bulletin board quoted a message from yet another source that was attributed to George Irvine, the well-known proponent of the DIR philosophy. If you want to read the quoted message, you can see it at:
http://diver.net/bbs/messages/12918.shtml
The main point that I'm interested in is this assertion:
"(B)ouncing to 20 feet or whatever to pick up a bottle and immediately returning to the surface is the like giving yourself a home-made PFO: the bubbles in the venous side compress enough to get past the lungs and then will reexpand on the arterial side and lodge in the worst places, the spine and brain blood supplies."
By contrast, I noticed that Lawrence Martin MD has this to say about bounce diving in his book "Scuba Diving Explained," the text of which is visible online at:
http://www.mtsinai.org/pulmonary/books/scuba/sectiong.htm
"Bounce and sawtooth diving probably increase DCS risk because of silent bubble formation at depth. On ascent any silent bubbles that form begin to release nitrogen harmlessly. However, if the diver quickly returns to the deepest depth, more nitrogen will enter the tissues; _that_ nitrogen, on re-ascent, will then flow into the existing bubbles, which expand further. Thus, the risk of DCS increases by diving immediately after formation of any silent bubbles; bounce or sawtooth diving is one way to do this."
My question is this: Do we really know which of these scenarios is more correct? If so, which one? It seems to me that if re-descending to depth caused any currently outgassing bubbles to shrink and sneak through the lungs into the arteries, then a lot of divers would be experiencing a lot more problems on multiple dives. Thanks in advance for any reactions.