Behaviors of Those Suffering from Nitrogen Narcosis

In divers, the effects of narcosis generally start with some form of impairment of mental function. This may include loss of memory, reasoning ability or a reduced ability to concentrate or to make sound judgments. These symptoms are especially dangerous because they often occur at times when divers need their wits about them the most; yet the individual may not even be aware that anything is wrong. As these symptoms can causes lapses in judgment, a “narked” diver can easily run out of air or overstay his allowable bottom time. It also makes a breakdown of the buddy system much more likely.

As depth increases, the symptoms can progress to impaired motor coordination, and in some divers a reduced or delayed response to sound and visual stimuli. This, combined with decreased mental capability, puts the diver at great risk. In extreme depths — beyond 165 feet — symptoms can become quite severe, and include extreme confusion, sleepiness and even hallucinations.

Most textbooks caution divers about the sudden and abrupt onset of symptoms, but many experienced technical divers disagree. They contend that the onset of narcosis, while subtle, can be detected in its very early stages. Symptoms they often point to include a reduced ability to read one's gauges, and an increased awareness and sensitivity to sound. “Perceptual narrowing,” a condition akin to tunnel vision, is also a very common early symptom. It's important to note, however, that only those who are highly experience at deep diving are likely to recognize such subtle symptoms. It's also not uncommon for victims of narcosis to have amnesia, reporting no recollection of events that took place at depth.

Both research and practical experience indicate that the effects of narcosis can be enhanced by several factors. Two such factors are the environment you dive in and your mental state. For example, some studies have shown that divers in warm, clear-water environments — conditions likely to evoke a sense of comfort and control — are more likely to experience a sense of overconfidence, well-being, and euphoria. But, in a less secure environment, such as cold, dark water, or in a less secure state of mind, symptoms of anxiety are more likely. In some cases, even terror and panic have been noted. This is a very important consideration because, as your diving environment and your mental state change, you can never assume that your susceptibility and response to nitrogen narcosis will always be the same.

There's also evidence of the importance of psychological factors, and how the onset of nitrogen narcosis could be influenced by what's termed “negative modeling,” a form of self-fulfilling prophecy. One such study of anticipatory behavior modeling conducted back in 1965 resulted in some very interesting findings. The study involved three groups:

  1. The first group was taught that virtually all divers succumb to narcosis at 130 feet, and that symptoms would be severe.
  2. The second group was taught about narcosis, but was told that it was far from certain to occur and its severity downplayed.
  3. The final group was given a three-hour lecture on narcosis, including a review of all known research, and told that strong willpower could greatly reduced its effect.

Each group was then given a series of cognitive exercises in a recompression chamber at depths ranging from 100 feet to 240 feet.

The results showed an apparent correlation between how the divers were trained and their ability to deal with narcosis. For example, no members of the first group could perform past the 200-foot level, and two subjects from the second group were also unable to perform. Amazingly, however, members from the third group actually showed better performance at 200 feet than at their surface test, and all but one subject continued to function well to the final depth of 240 feet. While one single study is far too little to form solid conclusions, instructors may do well to keep these results in mind the next time they teach their students about narcosis.

Another contributing factor is alcohol consumption or taking drugs that block nerve transmission. The drugs in question include not only prescription medications, but also over-the-counter remedies for conditions such as sea sickness, diarrhea and nasal congestion. Besides drugs, high levels of carbon dioxide, exertion and fatigue can also contribute to the onset and severity of symptoms. There's even some evidence that an increase in oxygen partial pressure might influence the early onset of symptoms.

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