Freediving and DCI

[richhagelin]

I overheard someone talking about how free-diving after scuba can increase the probability of DCI. It seems to me that there is no relation. Am I wrong?

Rich Hagelin

 

[Simos]

Hi Rich

I'm afraid you are wrong (as far as I know at least - please correct me if I'm wrong). During freediving courses (e.g. AIDA 2*) they teach that one should allow 12 hours before freediving after scuba and 18 hours if having done multiple scuba dives. If wearing a dive computer you should wait until the 'no-fly' time has elapsed before freediving.

There's not much explanation for the reasons in the AIDA courses (or at least I don't remember it) but I'm guessing that the main danger is that by freediving, you are essentially going back to an environment of high pressure while having a high concentration of nitrogen in your body and then coming back to the surface (often rapidly ascending), which can lead to DCI. I would have thought that an additional problem is that you are exercising while freediving and as far as I remember, it's best to avoid exercise after a scuba dive (I can't remember the rationale but I think it boils down to the fact that it can cause bigger 'bubbles').

As an aside, I believe there are extreme cases where even freediving alone can lead to DCI so I guess it's not the best idea to start a freedive already carrying an excess nitrogen load from previous scuba dives...

Hope this make sense (and I hope it's correct!)

Best

Simos

 

[fdog]

I have read accounts (quite chilling, actually) from two different freedivers who were severely bent from freediving after scuba diving.

Here's the mechanism:

Even moderate profiles while scuba diving produce bubbles. These asymptomatic "silent bubbles" are typically filtered out by the lungs.

If you freedive while your body is producing these bubbles, you travel to a higher pressure area at depth. This compresses these bubbles, which then are small enough to pass through the capillary bed of the lungs.

Blood flow from the lungs is sent to the heart, then as arterial flow, to the rest of the body, where the bubbles can expand as you surface from the freedive. Worst case is in delicate places like the brain or spinal cord.

For the depths I dive to - about 30-40 meters - I wait 24 hours. Really.

As an aside, it is possible to get DCI just from freediving. It doesn't take very many bounces to 75' with a minute's bottom time to build up a decent nitrogen load.


All the best, James

 

[bleeb]

Here's the mechanism:

Even moderate profiles while scuba diving produce bubbles. These asymptomatic "silent bubbles" are typically filtered out by the lungs.

If you freedive while your body is producing these bubbles, you travel to a higher pressure area at depth. This compresses these bubbles, which then are small enough to pass through the capillary bed of the lungs.

Blood flow from the lungs is sent to the heart, then as arterial flow, to the rest of the body, where the bubbles can expand as you surface from the freedive. Worst case is in delicate places like the brain or spinal cord.

This phenomenon is sometimes also labeled "bubble pumping". You can find more information by searching in either this forum or Dive Medicine.

 

[richhagelin]

Thanks for the info.

Rich Hagelin

 

[Dr Deco]

Hi Rich:

I concure with the previous posters. Free diving, by itself, can lead to DCS. When added to dive gas loads, it could lead to bigger problems.

 

[Chuckitall]

dddddd

 

[Amazz]

Interesting. After suffering numerous bouts with skin bends, mild neurological DCS, and lung burning over the years, I had a PFO closed recently. I learned over the years to moderate my diving and manage my gas and depth to minimize these occurances. However, this topic answers why I suffered a bout of DCS in the Bahamas last year. I was on a liveaboard and had done three dives during the day. Then around 4pm, we saw a pod of spotted dolphins and jumped in to free dive with them. Over a 45 minute period, I made MANY free dives to 20-some feet and some rapid ascents (not while holding breath) while playing with the dolphins. Within an hour I felt the DCS arriving. I didn't think that free diving less than 30 ft. would bring this on after 3 fairly conservative dives during the day. Now thinking back, it had to be related to the free diving after diving. I was used to dealing with mild DCS and stayed within my limits earlier that day. I found this on a site called scuba diving planet.



2) Never Free Dive after a Scuba Dive

The Nitrogen remaining in the tissues after Scuba Diving can lead to decompression sickness when micro-bubbles are recompressed and their consequent expansion upon the rapid ascent during an ensuing freedive. Those with PFO are in a much higher risk category. Wait at least 12 hours after a Scuba Dive before you do a Free Dive.