Dear Don:
The amount or volume of gas dissolved is quite variable. A good rule of thumb, known since the 1940s, is that about one quart of dissolved nitrogen is contained in the human body (adult) for every atmosphere of pressure when the body is saturated (sat requires about 24 hours).
Thus if one were to breathe oxygen on the surface and collect all of the expired gas and analyze it for nitrogen, you would find that you have about one quart. If you went to a habitat at 33 FSW, returned to the surface after a stay of 24 hours, and breathed oxygen, you would now find that you exhaled (that is, originally contained) about two quarts of dissolved nitrogen. That is, one for each atmosphere (33 FSW) of pressure --when saturated.
If you are down for less than this time, as recreational divers always are, the amount of dissolved nitrogen is quite small. You can see that very little of the nitrogen in your scuba tank is actually dissolved in the tissues of your body. A diver might say that he or she breathes very little gas from the tank (i.e., a large residual pressure at the end of the dive). They believe that this indicates that a small amount of nitrogen has been taken into the body. Not really. Most gas is blown off as exhaled air bubbles. What you are actually taking in is the oxygen. A large volume of residual gas in the scuba tank is not an indication of low nitrogen uptake and low risk of DCS.
Considerable gas is contained in a carbonated beverage because carbon dioxide is very soluble. There is actually a chemical reaction and carbonic acid is formed.
Dr Deco
