Breathing a mixture of inert gases: Disproportionate diffusion into decompression bubbles

To study the consequences of diving with gas mixtures, we simulated growth of decompression bubbles using an equation system that accounts for major determinants of bubble behavior. When breathing a mixture, bubbles are smaller than expected from linear interpolation between bubbles with either of the unmixed component gases because of disproportionate diffusion effects: a) When few bubbles form, the inert gas that permeates fastest becomes over-represented, relative to the breathing gas, inside bubbles during growth; this slows further entrance of the fast gas and enhances entrance of the slower gas. b) With N₂-He mixtures and few bubbles, the over-represented gas is He in aqueous tissue, but is N₂ in lipid tissue. c) When many bubbles form, the over-represented gas is the one with higher tissue solubility. Our simulations indicate that the smallest bubbles always occur with breathing of one of the component gases, but which gas that is depends on whether the tissue is lipid or aqueous and whether few or many bubbles form.