Surface interval and snorkeling

[tc]

The problem is that while "off-gassing" there are two possible issues with snorkeling.

1.) The possibility of pushing any "bubbles" from the venous to the arterial side exists during a breath hold dive. Divers have gotten bent going down to quickly retrieve an object during their surface interval (but I believe this occured after a heavy exposure, i.e. a quick bounce during the surface interval following a deco dive).

2.) Heavy exercise after diving is thought to increase the chance of DCS.

So, easy snorkeling on the surface is no biggie, but diving down is a possible risk.

Best wishes.

Hmmmm....... not exactly.

The bubbles only go from the venous to the arterial side if there is a transport path for them- a PFO (opening between the two sides of the heart) or a lung over expansion injury. (Or possibly with a volume of bubbles that simply overwhelms the system) Since folks free diving are not breathing compressed air there really isn't a chance for a overexpansion injury- the gas volume in the lungs, if they hold their breath throughout the free dive, would be exactly the same when the returned to the surface.

Heavy exercise can induce bubbles to come out into circulation (It's amazing to hear it on a doppler if you ever get the chance) but absent a PFO that would be very unlikely to get bubbles to the arterial side.

Minor nag- you never get DCS from going down too quickly, you get it from coming up too quickly, as an AGE if it results in a lung over expansion or in DCS if there was not sufficient time to decompress fully.

If the bubbles do get to the arterial side you have an embolism rather than DCS.

 

[LeadTurn_SD]

Hmmmm....... not exactly.

The bubbles only go from the venous to the arterial side if there is a transport path for them- a PFO (opening between the two sides of the heart) or a lung over expansion injury. (Or possibly with a volume of bubbles that simply overwhelms the system) Since folks free diving are not breathing compressed air there really isn't a chance for a overexpansion injury- the gas volume in the lungs, if they hold their breath throughout the free dive, would be exactly the same when the returned to the surface.

Heavy exercise can induce bubbles to come out into circulation (It's amazing to hear it on a doppler if you ever get the chance) but absent a PFO that would be very unlikely to get bubbles to the arterial side.

Minor nag- you never get DCS from going down too quickly, you get it from coming up too quickly, as an AGE if it results in a lung over expansion or in DCS if there was not sufficient time to decompress fully.

If the bubbles do get to the arterial side you have an embolism rather than DCS.

Hi TC,

I get what you are saying, but I'm not talking about classic AGE or PFO. I really did mean transport from venous to arterial via lung capillary beds. I'll see if I can find the references for what I mentioned above. But I think similar topics have been posted in the Deco section of this board.

1.) The theory (at least as I understand it, and I could certainly be confused! ) is that any post-dive micro-bubbling on the venous side could, during a free-dive, be pushed across to the arterial side because the bubbles would compress at depth and could go back into solution, pass through the lungs and heart, then out into the arterial blood, and re-enlarge in the distal arteries as the diver surfaced, and then become trapped and lodged in the arterioles. Not necessarily PFO related as I understood it, although I suppose a PFO would make it more likely? I don't know.

2.) I didn't say it was caused by a diver going down too quickly, I said TO quickly , as in the diver went down to quickly retrieve the deco bottles before anyone noticed he was gone.... I should have worded it differently

3.) I should have said DCI rather than DCS or "bent". My bad, but for what I'm trying to describe, the presenting symptoms would be pretty much the same I'd think.

Feel free to beat my about the head and shoulders with any convenient blunt object if I've totally got this backwards or mistaken.

One final tidbit that I only recently read about that surprised me: Rare cases of DCS in free divers doing repetitive deep dives. Go figure. No compressed air = No DCS is what I had always believed. Apparently, that is not always the case.

Best wishes.

 

[tc]

I'd be interested is reading that if you find the reference. (Gene- you reading this?) The concept seems plausible.

My bad on #2- I figured to was a typo for too.

I've also heard about (rare) cases of free divers and DCS- You do still on gas at depth but most folks just can't spend enough time deep enough for it to be a problem. I've run across a few that commonly hunt in the 100 to 130 fsw range though. If you do it enough times you could have a problem.

 

[tc]

And for Rank66- simpler answer to your question, paddling around at the surface without a lot of exertion would pose no problem.

Free diving to fairly shallow depths if you don't have a big nitrogen load should also be OK. (Again- less heavy exertion= less bubbles)

The problem scenario would be doing a deep, long dive followed by heavy exertion and a bunch of deeper, longer free dives. And then diving again.

 

[LeadTurn_SD]

I'd be interested is reading that if you find the reference. (Gene- you reading this?) The concept seems plausible.

My bad on #2- I figured to was a typo for too.

I've also heard about (rare) cases of free divers and DCS- You do still on gas at depth but most folks just can't spend enough time deep enough for it to be a problem. I've run across a few that commonly hunt in the 100 to 130 fsw range though. If you do it enough times you could have a problem.

Hi TC,

This was not what I was looking for, but a very good read, some by Dr. Powell, and a couple of other good posters:

http://www.scubaboard.com/forums/ask-dr-decompression/159-freediving-after-scuba-long.html

This is actually arguing against, or somewhat against the point I was trying to make, but do read down to post #6 by Dr. Powell. The main risk may be (as I understand it) the rapid ascent that is typically made by a free diver.

The other references I've found don't list sources (but I consider Dr. Powell a prime source so linked that post ); the ones I saw basically repeated the same explanation I described, but did not offer proof.

I'm still looking for the original reference that I saw. Sigh. It was a couple years ago. I thought it was an original source, but could just have been a second-hand description I read on some board or in an article regarding the risk of microbubbles moving across the lung capillary beds.

Gene might be the best bet.

I'll see if I can dig anything up tomorrow.

To the OP (Rank66): Sorry for the hijack! But barring any new information, I'd still recommend not freediving after scuba (but surface snorkeling by all accounts should be just fine).

Best wishes.

 

[SkipperJohn]

what I meant was it was not going to increase the nitrogen levels.
the other stuf is quite interesting, I didn't know this.. Thanks.

 

[blue steal]

Really interesting replies. I remember when I dove down to retrieve the mask, I returned to the surface very slowly, no finning up.

 

[AzAtty]

I'm still looking for the original reference that I saw. Sigh. It was a couple years ago. I thought it was an original source, but could just have been a second-hand description I read on some board or in an article regarding the risk of microbubbles moving across the lung capillary beds.

You might be thinking about a little blurb entitled "Why We Don't Do Bounce Dives in the WKPP," or something similarly titled by GI3. It essentially sets out the theory that: (a) during surface intervals bubbles tend to increase in size while offgassing, (b) a bounce dive during a surface interval could cause a larger bubble to be compressed on descent to the point it could transit from the venous side to arterial side by passing through the lungs unfiltered, which (c) could result in a homemade AGE on the ascent. WKPP implemented a "no bounce" rule after multiple divers surfaced with DCI symptoms after bounces to retrieve deco or stage bottles.

 

[LeadTurn_SD]

You might be thinking about a little blurb entitled "Why We Don't Do Bounce Dives in the WKPP," or something similarly titled by GI3. It essentially sets out the theory that: (a) during surface intervals bubbles tend to increase in size while offgassing, (b) a bounce dive during a surface interval could cause a larger bubble to be compressed on descent to the point it could transit from the venous side to arterial side by passing through the lungs unfiltered, which (c) could result in a homemade AGE on the ascent. WKPP implemented a "no bounce" rule after multiple divers surfaced with DCI symptoms after bounces to retrieve deco or stage bottles.

Thanks AzAtty.

I actually remembered the GI3 WKPP reference, and sort of hinted at it with the stage bottle reference in my post, but had thought there was another "primary" research source I had read... but maybe it was just the WKPP policy I remembered.

Best wishes.

 

[dumpsterDiver]

what I meant was it was not going to increase the nitrogen levels.
the other stuf is quite interesting, I didn't know this.. Thanks.

Again, this is NOT true. Diving down will increase nitrogen load in blood and then tissues, even without breathing compressed gas.