Could this be DCS?

[charlesml3]

Highly improbable under the parameters set forth, but not entirely impossible without compressed air. There has been reported cases of free divers suffering DCS

Please explain the physiology behind this. I'm not arguing with you, but I cannot understand how a freediver could possibly get DCS without breathing compressed air. He takes a big breath and goes down. The amount of nitrogen in his bloodstream is going to be same going down as it is coming up.

-Charles

 

[Atticus]

Please explain the physiology behind this. I'm not arguing with you, but I cannot understand how a freediver could possibly get DCS without breathing compressed air. He takes a big breath and goes down. The amount of nitrogen in his bloodstream is going to be same going down as it is coming up.

-Charles

As the free diver descends water pressure compresses the lungs and thus the air inside. You are correct that there are the same number of nitrogen molecules in the free divers lungs but they are now at a higher pressure and can elevate tissue pressures and potentially cause dcs. Not so much at 15 ft such as in this case but on deeper free dives this can and does happen.

 

[charlesml3]

That still doesn't make sense though. A diver accumulates an abnormal amount of Nitrogen dissolved into their bloodstream due to breathing compressed air at depth.

A freediver is under the same pressure, but without the compressed air. Yes the air in his lungs does become compressed during the descent, but that just squeezes his lungs down to a smaller volume. The existing Nitrogen molecules in his bloodstream squeeze down during the descent and expand during the ascent. But since his bloodstream isn't carrying the additional Nitrogen load they don't "boil out" into the bubbles that cause DCS.

I really need a cite here for a reference. This notion that a freediver can get DCS simply by holding his breath, descending and ascending back goes against everything I've ever been taught about how the human body behaves in a high-pressure environment.

-Charles

 

[Atticus]

When the lungs squeeze down, compressing the nitrogen you have the same pressure of gas as a person who inhaled at that depth from a scuba cylinder. The exposure times are short, but the ascent rates are quite fast.


From the United States Apnea Association FAQ:
United States Apnea Association (USAA)


Q: Can you get decompression sickness, a.k.a. the bends, from freediving?

A: Yes, but only rarely and only in extreme breath-hold diving situations. Advanced freedivers conducting repetitive deep dives for long periods underwater, with little recovery time at the surface have developed decompression sickness from an accumulation of nitrogen in the body. History has revealed commercial freedivers (those making a living harvesting pearls, sponges, lobster, fish, etc.) doing breath-hold dives for several hours in a day, to depths of 60 to 90+ feet, for periods of two minutes or more per dive, have displayed signs and symptoms of decompression sickness. However, most recreational freedivers do not come close to this phenomenon. Others have become “bent” (decompression sickness) from conducting repetitive breath-hold dives using a diving scooter. Also, never freedive after scuba diving. The high rate of ascents and descents in a freedive cause saturated nitrogen from the previous scuba dive to expand and contract in the bloodstream and tissues. This can easily lead to decompression sickness. See Freediving Safety for more information.