Breath-Hold Diving and Barotrauma/DCS
By Dr. Sawatzky
In the February/March/April 1997 issues of DIVER Magazine, I wrote a series of columns on lung squeeze, shallow water blackout and pulmonary barotrauma. I did not really discuss the topic of DCS/pulmonary barotrauma and breath-hold diving as I did not think it would interest the readers of DIVER Magazine. However, in June 1999 I attended the Undersea and Hyperbaric Medical Society (UHMS) conference in Boston and the first day focused on Decompression Illness: Mechanisms of Disease. During the presentations, a new (to me) form of pulmonary barotrauma was discussed and soon after I received a request for advice from the physician who runs one of the recompression chambers in the Caribbean. He was managing an unusual case of decompression illness that perfectly fit what I had just learned! Therefore, in this column we will explore the possibility of DCS while breath-hold diving and look at a newly understood form of lung damage that can occur while breath-hold diving.
Decompression sickness results when inert gas (nitrogen in air) has been absorbed by the tissues of the body and the pressure on the body is subsequently reduced so that the amount of inert gas dissolved in the tissues is greater than the body can tolerate. In diving, we start at the surface with the partial pressure of nitrogen in the tissues equal to the partial pressure of nitrogen in the air we are breathing. When we dive breathing air, nitrogen is taken up by the tissues according to the depth (partial pressure of nitrogen in the inspired air), the time of exposure and the blood flow through the lungs and tissues. In general, tissues with the highest blood flow take up nitrogen the fastest. Therefore, when we return to the surface at the end of the dive (no decompression stops), the tissues with the highest blood flow will have the highest partial pressure of nitrogen. The ratio between the partial pressure of nitrogen in the tissues and the ambient pressure is called the "supersaturation ratio". Different tissues can tolerate different supersaturation ratios. In general, when any tissue in the body has a supersaturation ratio higher than it can tolerate (the ëcriticalí supersaturation ration for that tissue), the person has a significant chance of developing decompression sickness.
In diving, when we dive within the limits of our dive tables or decompression computers, we ensure that no tissue ever exceeds its critical supersaturation ratio, as calculated by the mathematical model. What is "actually" happening inside the body is unknown and therefore it is possible to get DCS even when doing dives that are "safe" according to tables or computers. We know that it is possible to dive to 60 feet (18 meters) for approximately 50 minutes (varies with different tables and computers) without significant risk of developing DCS. In breath-hold diving no one can dive to 60 feet for 50 minutes so there should be no risk of DCS, right? Not necessarily.
For more on Breath-hold diving and DCS pick up a copy of the November issue of DIVER Magazine.