Commentary on viewpoint "Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law".

TO THE EDITOR: Arieli (1) draws attention to experiments showing that solubility of individual gases may be reduced when high concentrations of multiple gases are present simultaneously. Results with in vitro systems of ethanol and water may not be representative of gases in tissue; for example, metabolism of oxygen will lower the oxygen partial pressure far below the inhaled value so tissue may still behave as a one-gas system despite a high inspired partial pressure of oxygen. The underlying mechanisms of bubble formation in divers, aviators, or astronauts who suffer decompression sickness (DCS) are poorly understood. It is suspected that DCS bubbles are generated from semi-permanent gaseous micronuclei. Gas diffusing into a micronucleus to initiate a bubble may be more closely related to gas partial pressure than to dissolved gas, but the final size of a bubble, if it does form, is probably related to dissolved gas. Interaction among the gases inside a bubble effects inward diffusion, an additional complication to breathing of gas mixtures (2). There is considerable difference of opinion about what constitutes successful decompression, as evidenced by the differences between instructions used by several of the world’s navies (3). Also one must be cautious when interpreting the self-reported safety data collected by the Diver’s Alert Network. The effect of one gas on the solubility of another may ultimately be shown to be an important factor in decompression, but, at present, we regard it as just one uncertainty among a great many other uncertainties.