The air tanks that divers use are composed by 78% to 80% of nitrogen gas. As the diver descends the pressure increases, more partial pressure causes more gas dissolving in the liquid (which in the human case will be the blood ). Nitrogen in its liquid form travels through blood to the Nervous System, where in contact with the lipid membrane of the neurons dissolves in them, causing its thickening and increasing the flow of sodium and chlorine ions. It is an interference on the electrochemical processes that are necessary for the exchange of electrical potential in the synaptic buttons. Ascending to the surface will make all the symptoms that causes this disease to go away.
While in Decompression Sickens, as the diver ascends to the surface the pressure decreases, therefore the partial pressure of the nitrogen causing it to go from liquid to gas again. Nitrogen bubbles collect together forming larger bubbles in the bloodstream, this causes many problems, however it can be resolved by breathing high oxygen fraction gases at an oxygen partial pressure of between 2.8 ATA.
