. . .The allowable changes [in a deco gas to mitigate ICD] are based on the physical properties of nitrogen and helium. As we have seen, helium is a fast gas and will diffuse in and out of a tissue approximately 2.7 times faster than nitrogen, however nitrogen is approx 4.5 times more soluble in lipid tissues than helium.
. . .When switching from a high helium mix to a high nitrogen mix, the higher solubility factor of nitrogen offsets the decrease in pressure of the helium [and its faster diffusivity]. This results in an increase in the total quantity of dissolved gas. As nitrogen is approx 4.5 times more soluble than helium, Burton proposes that by increasing the nitrogen percentage by no more than 1/5th of the reduction in the helium percentage, then the total quantity of dissolved gas will not increase and hence an ICD event can be avoided. . .