Mechanism One of the important factors leading to its occurrence seems to be the vertical speed of the diver`s descent. Pressure increases as the diver descends, but nitrogen dissolves more slowly than other gases in blood. Similar to the mechanism of alcohol`s effect, this change may cause altered permeability properties of neural cell lipid bilayers. The Meyer-Overton hypothesis states that narcosis happens when the gas penetrates the lipids of the brain`s nerve cells. Here it apparently interferes with the transmission of signals from one nerve cell to another. The relation of depth to narcosis is informally known as "Martini`s law": It`s like one martini per 10 meters below 20 meters. This is a very rough guide, which can never be a substitute for the real diving safety rules. Professional divers never suggest such calculation attempts, stressing instead that deep dives can be made only after a gradual training to increasing depths, and always with a linear vertical speed, other diving organisations such as GUE claim that a diver can never train to overcome narcosis, the same way as you can not train to not get drunk when drinking. Instead, they ban diving with gases that cause too high narcosis levels at depth, and use trimix instead. The mechanism of the narcosis is related to the solubility of nitrogen in the blood occurring at elevated atmospheric pressures. Once it leaves the tank and enters the diver`s lungs it will have the same pressure as the surrounding water, the ambient pressure. Although some experienced divers recommend a constant vertical speed, avoiding sudden changes of inclination which would cause an irregular solution of gas in blood due to a "delay" of pressures adapting, this is not supported by scientific evidence.