Where When How Summer 2012 : Page 110While these are certainly the highlights, this is far from an adequate explanation given that the consequences of being “narked” can be life-threatening. Additionally, the current popularity of technical diving has made recre-ational divers more aware and curious about diving to much greater depths than our own limit of 130 feet (39 m). But whether you’re interested in learning more about the chal-lenges of deep diving as a bridge to technical diving, or just want a better understanding of what goes on inside your body at any depth, all divers should possess a more thorough in-sight into narcosis than they’re given in most open water, or even advanced, certification courses. While we call it nitrogen narcosis, many gases, including oxygen, can have a nar-cotic effect when breathed under enough pressure. The condition produces a state sim-ilar to alcohol intoxication or breathing nitrous oxide (“laughing gas”) at surface pressure. The good news is that, unlike decompression sick-ness, the effects of narcosis are completely re-solved by ascending to a shallower depth, and resulted from high-pressure gas causing in-creased blood f low, therefore stimulating nerve centers. A bit later, in 1881, a physician named Walter Moxon proposed that pressure forced blood to inaccessible parts of the body and the stagnant blood somehow caused emotional changes. Others believed it was a result of psychological factors, such as latent claustrophobia. It wasn’t until 1935 that a diving physiolo-gist named Albert Behnke — the father figure of the U.S. Navy’s diving program — sug-gested that it was the nitrogen component of air responsible for the narcotic symptoms. In 1939, Behnke and his colleagues were also the first to demonstrate that gases other than ni-trogen, such as helium, could cause narcosis. That year was auspicious for yet an-other reason. On May 23, 1939, the U.S. Navy submarine, Squalus , suffered a cat-astrophic valve failure during a test dive off New Hampshire’s Isle of Shoals. For-tunately it came to rest in just 240 feet { In his hallmark book, “The Silent World,” Jacques-Yves Cousteau recounted personal experiences involving a mysterious diver’s disease, which he termed l’ivresse des grandes profondeurs (“rapture of the deep”). He wrote, “The chief symptom of this phe-nomenon is, to put it bluntly, the sensation of becoming as drunk as a hoot owl.” (73 m) of water, rather than the crushing depths just offshore. Only a quick salvage and rescue operation would save the lives aboard, but the depth made air diving op-erations less than ideal due to the effects of narcosis. The rescue operation gave the Navy its first oppor tunity to try the then-experimental gas mixture heliox (helium-oxygen); and the recovery of the Squalus crew went down as one of the most fa-mous and successful in U.S. Naval history. 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 par-tially of lipid (fat) tissue, transmit electrical sig-nals 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 needed to induce nar-cosis. 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 nitro-gen 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 en-hance the onset and severity of nitrogen nar-cosis. 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 down of our mental processes and reaction time. Essentially, infor-mation cannot be processed as fast as the input is received; and our performance of tasks ranging from reasoning to manual dex-terity suffers. A portion of the brain called the reticular center, which is responsible for receiving and distributing nerve impulses throughout the body, is particularly susceptible to this anes-thetic effect. It’s interesting to note, however, that although this theory is based on solid ev-idence, to this day no one is absolutely cer-tain about what causes nitrogen narcosis. WHAT ARE THE EFFECTS? Most divers are taught that the symptoms of narcosis usually don’t occur until a depth of around 100 feet (30 m). But that’s really the depth at which symptoms become notice-EARLY INSIGHTS able in most divers; subtle impairment starts We’ve known about nitrogen narcosis for in as little as half that depth. In fact, studies about as long as technology has enabled peo-done by the U.S. Navy have documented that ple to breathe air under pressure. In 1834 a some highly susceptible individuals are af-French researcher, Victor Junod, was the first fected by nitrogen narcosis at pressures as to describe it, noting “the functions of the low as 2 atmospheres (33 feet [10 m]). Stud-brain are activated, imagination is lively, ies also show that, in virtually every diver, by thoughts have a peculiar charm and, in some WHAT’S UP WITH THAT? the time they reach 3 atmospheres persons, symptoms of intoxication are pres-To understand the current theory for what (66 feet [20 m]) there’s a measurable slowing ent.” As a cause, he proposed that narcosis causes nitrogen narcosis, you must first know of mental processing, although at this depth 110 • • • • • SUMMER 2012 “Where When How -Turks & Caicos Islands” with no long-term consequences. Therefore, provided a diver is aware of its symptoms and ascends to manage it, narcosis rarely develops into a serious problem. Publication List Using a screen reader? Click Here |
