Hello ottercat:
Minimal Depth for DCS
It is essentially true that there is a minimal depth for DCS. This is dependent [I believe] on the maximal size of micronuclei present in the body. [The old Haldane concept would say that sufficient supersaturation does not exist for bubbles to form. ]
Micronuclei appear to be [by calculation] never bigger that about three microns. That is about one third the diameter of a red blood cell. For DCS to develop, it is necessary for these nuclei to grow to a sufficient volume. Because of surface tension effects, not all nuclei can grow with any given supersaturation. [Only those larger than the Laplace limit.] Generally, it is surmised, the microbubbles must be a sufficient number for them to grow collectively to a certain volume in a tissue.
At the same time, dissolved nitrogen is entering the blood stream and is being carried away by the blood. Thus bubble growth following a dive is a competition between diffusion into the capillaries versus diffusion into a microbubble. In general, unless there are a large number of microbubbles, the diffusion of dissolved nitrogen into the capillaries is the predominant process.
Pulmonary Barotrauma
In the above discussion, I am referring to DCS that is the result of gas phase growth. Problems from pulmonary barotrauma, that is, holding ones breath while ascending is a different matter. Lung tissue can easily expand; it is not particularly tough. A lungful of air will expand in the lungs while the diaphragm is being pushed downward. A rupture with air being injected into the circulatory system can lead to severe problems.
This is not the same DCS we speak about when we mean the growth of bubbles in tissue (the bends). For pulmonary barotrauma, the limiting depth as about three feet and it has happened!
Ascent Rate
Because of surface tension effects, ascent rate is important. Slow ascent is better than rapid ascent. The same is true with soda pop bottle. Slow release of pressure is better than rapid decrease of pressure (by quickly unscrewing the cap.) remember with soda pop, slow releasing the pressure is not the same as elimination of dissolved carbon dioxide. It is still in solution wither you open slowly or quickly. Think about it! :280:
Dr Deco :doctor: