The Latest Research on Nitrogen Narcosis
To understand the current theory for what causes nitrogen narcosis, you must first know a bit about how the nervous system works. Electrical nerve impulses are transmitted throughout the body via nerve cells called neurons. These neurons, which are made partially of lipid (fat) tissue, transmit electrical signals to other neurons at junctions called synapses. The narcotic potency of an inert gas is a function of its solubility in fat tissue — those that dissolve more easily into fat are more narcotic. The greater the solubility, the less partial pressure is needed to induce narcosis. Sedation occurs, it's thought, because the inert gas causes the synaptic membrane to expand, which slows or stops transmission of electrical impulses.
By the 1960s an alternative to the nitrogen theory was proposed, suggesting that narcosis was caused by high levels of carbon dioxide resulting from reduced respiratory efficiency. Although researchers have refuted the carbon dioxide theory, it has been shown that high levels of carbon dioxide will enhance the onset and severity of nitrogen narcosis. More recently, scientists have been looking at neurotransmitter receptor protein mechanisms as a possible cause of narcosis.
Regardless of the mechanism involved, the result is a slowing of our mental processes and reaction time. Essentially, information cannot be processed as fast as the input is received, and our performance of tasks ranging from reason to manual dexterity suffers.
The Effects of Nitrogen Narcosis
Most divers are taught that the symptoms of narcosis usually don't occur until a depth of 100 feet. But that's really the depth at which symptoms become noticeable; subtle impairment starts in as little as half that depth. In fact, studies done by the U.S. Navy have documented that some highly susceptible individuals are affected by nitrogen narcosis at pressures as low as 2 atmospheres (33 feet). Studies also show that, in virtually every diver, by the time they reach 3 atmospheres (66 feet) there's a measurable slowing of mental processing, although at this depth you're usually unaware of any change. By 4 atmospheres (99 feet) most are aware of some impairment. In the depth range of 5-6 atmospheres (99 to 165 feet), divers can experience a variety of debilitating symptoms.
The effects of narcosis are also highly variable among individuals, and even with the same individual on different days. Some divers even believe they're virtually immune to the disorder, citing their ability to function well below 100 feet without any apparent effect. But the truth is, no one is immune. Everyone is affected; the only questions are when, how, and to what degree.