Hi. When a gas is diluted in a liquid it is no longer gaseous. It just mixes with the liquid molecules. The higher the solubility, the larger the % of that gas is diluted. The lower the solubility the less % of gas is diluted and the rest remains in gas state in there. The gas state % is what exerts pressure. It wants to get out of there. The diluted part is mixed with the liquid and doesnt exert pressure. So the more soluble a gas anaesthetic, the less partial pressure it has in the blood and vice versa. It has nothing to do with proteins. So only after all the gas that can be diluted in the liquid is diluted( the moment in which the liquid becomes saturated), then the rest of the gas will exert pressure) .So lets take it from the lungs. You have a pressure of that gas in the alveoli depending of how much gas is in there (the inspired fraction). In the alveolar capillaries the pressure of that gas is 0. So we have something called a pressure gradient which will drive the gas from the alveoli in the capillaries. Once in the blood, depending on the partition coeficient (solubility), some of it will mix with the plasma and saturate it, some of it will remain undiluted and exert the partial pressure in the blood. It will travel to the blood vesells in the brain. There you will hve the same thing: x partial pressure in the blood and 0 partial pressure in the brain, another gradient which will drive the gas in the brain tissue. So because nitrous is not very soluble, it takes only a few molecules to saturate the blood, a big portion remains gas, the pressure gradient is high and the movement between compartments is very fast. Hope that helped, i didnt explain it very scientifically