Decompression sickness
Hi,
Fred Bove published an article (I don't remember where) about it.
This word comes from symptoms that natives from Tuamotu archipielago in polynesia, suffer after freedives. They used to descent assisted by a weight and ascend pulling them selves in a rope thetered to their collection basket. The depths were from 30-40 meters and dive time around 1 and a half minute. The surface interval around 5 mins. The symptoms of Taravana are similar to that of decompression sickness (paralysis, visual changes, hearing loss, and even dead).
Dr. Paulev and Dr. Lanphier studied the nitrogen in tissues of freedivers, and the most important factors to avoid DCS is the ratio of surface interval to dive time and the rate of ascense.
The firts means that if you make freedives to some depth with low surface interval, is like you keep at a shallower depth but for all the time. For example a freedive to 30 meters of 90 seconds with a surface interval of 90 sec, is like a 15 meters continuous inmersion.
Of course all of this is theoretical and mathematical calculation, but there is many cases of DCS in freedivers. To my knowledge there is no well designed studies to document it