While "on-gassing" and "off-gassing" are generally viewed as a direct function of pressure differentials this is not entirely correct. Inert gasses are dissolved in the blood (or other liquids) as a result of diffusion rather than pressure "forcing" the gas into the liquid. Diffusion is the process of gasses or liquids moving from an area of higher concentration to an area of lower concentration. From an "on-gassing" standpoint, increasing the number of molecules in a given volume of gas will increase the number of times those molecules will collide with with surface of the liquid and thus increase the number of molecules that will dissolve in the liquid.
For "off-gassing" it is just the opposite and while it's outside of the scope of the op, this is how decompression is accelerated. Simply put we can increase the partial pressure gradient between our blood and tissues relative to our inspired gas by reducing the partial pressures of the inert gasses in our inspired gas that we are trying to expel.
_________
Since the only way to increase the concentration of molecules in a given volume of gas at a constant temperature is to increase the pressure (ie. adding more molecules of gas) then the partial pressure of that gas controls the number of potential collisions that gas will have with the liquid.
I think this is why "on-gassing" and "off-gassing" it is most often explained as gas moving from an area of greater pressure to an area of lower pressure. It's mostly correct and likely easier to explain.
BTW, Bob's sink analogy is my favorite and one of the best I have ever heard to help visualize half-times of different compartments.
Hunter
For "off-gassing" it is just the opposite and while it's outside of the scope of the op, this is how decompression is accelerated. Simply put we can increase the partial pressure gradient between our blood and tissues relative to our inspired gas by reducing the partial pressures of the inert gasses in our inspired gas that we are trying to expel.
_________
Since the only way to increase the concentration of molecules in a given volume of gas at a constant temperature is to increase the pressure (ie. adding more molecules of gas) then the partial pressure of that gas controls the number of potential collisions that gas will have with the liquid.
I think this is why "on-gassing" and "off-gassing" it is most often explained as gas moving from an area of greater pressure to an area of lower pressure. It's mostly correct and likely easier to explain.
BTW, Bob's sink analogy is my favorite and one of the best I have ever heard to help visualize half-times of different compartments.
Hunter
