No announcement yet.


Bu konu sabit bir konudur.
  • Filtrele
  • Zaman
  • Göster
Hepsini Sil
new posts


    Diving to Great Depths by Paul C. Focazio

    If you're interested in how the body reacts to severe stress, whether it be encountered at great depths, high altitude or heavy exercise, researcher Claes Lundgren says, "It is useful to push the body to its limits. These conditions allow you to look at how the body reacts as if it were under a magnifying glass." Lundgren is Director of the Center for Research and Education in Special Environments (CRESE) at SUNY Buffalo, which is set up to determine how humans cope with extreme conditions.

    Under the magnifying glass in Lundgren's studies is "the diving response," a universal reaction shared by all mammals, including humans, seals, dolphins and whales, to going underwater. And Lundgren's studies - including seven New York Sea Grant-funded projects since the mid-1980s - provide new data to better understand how humans and other mammals sharing this deep diving mechanism cope with underwater conditions.

    Caution Down Below

    According to Lundgren, a professor of physiology and biophysics, "the diving response" kicks in when the diver starts to breath-hold and water cools the face as he or she glides further down into the depths of the ocean. Exposure to excessive depths, though, can cause a collapse of the lungs, cardiac arrest, blackouts, decompression sickness and, at worst, death.

    Shallow water blackout can occur when, upon return to the surface, there is both a drop in water pressure and gas pressure in the lungs, making it so that enough oxygen is not delivered to the blood and therefore to the brain. This may result in unconsciousness and drowning. This is why Lundgren cautions that it's crucial to undergo proper training and make sure that one or more safety divers are present during record attempt dives.

    Divers of all types - SCUBA and breath-hold, recreational and commercial - risk decompression sickness (DS) that may severely disable them or cause death. DS occurs when inert gas bubbles, usually nitrogen, accumulate in the body as a result of improper decompression during ascent. Utilizing a state-of-the art hyperbaric chamber, where pressure can be increased to simulate great depths, Lundgren and his investigators conducted three NYSG-funded DS research projects. The team examined methods of reducing the potential for decompression sickness by examining modifications of its effects on the human circulation.

    Says Lundgren, "When scuba diving, ascending slowly enough to allow the timely elimination of excess inert gas from the tissues by circulating blood and respiration is essential for safe and effective decompression." Among the findings, breathing pure oxygen during decompression at the lowest possible ambient pressure was shown to reduce sickness-related symptoms. Also, the pharmacological agents, Terbutalin and Isoproterenol, were identified as possibly allowing faster decompression.

    But if free-diver Mehgan Heaney-Grier let all the "what ifs" intimidate her, she may not have made it to such great depths with her diving. On October 21, 1996, before boatloads of press, family and friends, Mehgan dove to 155 feet (47.2 m). Ten months later, she swam past her own record, reaching 165 feet (50.3 m) below the surface. Once at 165 feet, Mehgan grabs a depth marker and turns around to face the most difficult part of her journey. Kicking against the heavy water column pressing down on her, she has to be careful not to swim too fast and burn up what little oxygen she has left.

    These weren't speed races, though. She set her second record in 1 minute 58 seconds, although she has accomplished this dive in as long as 2 minutes 7 seconds. "The time can vary," says Mehgan, "because everything plays a factor - fatigue, dehydration, the current."

    During her tests of human endurance, Mehgan holds her breath for minutes at a time underwater. So how is she able to stay below the surface for over four and a half minutes? As Lundgren explains, when trained divers such as Mehgan hold their breath, their oxygen consumption goes down, allowing them to be submerged for longer periods of time.

    Practice or a Pre-determined Power?

    The skill behind deep diving has more to do with training and technique than it does genetics. Lundgren cites that there are a number of factors that may make the diving response more effective, including underwater laps, actual free diving, and apnea training -activities done in a state of breath-hold, such as immersion of the face in cold water. "What happens in the training period is that the defensive protective mechanisms develop and become increasingly better," he says.

    Whether breath-hold diving is performed as a profession or a sport, Lundgren says productivity or success depends on two intimately coupled aspects - the diver's tolerance to the stresses of the depth's high ambient pressure and his or her breath-holding endurance.

    "The challenges to the respiratory function of the breath-hold diver are formidable," explains Lundgren. "One has to marvel at the ability of the human body to cope with stresses that far exceed what normal terrestrial life requires."

    Before each dive into the depths, Mehgan engages in a period of reflection and breathing. "Before you go, everything you do should be carried out in a very relaxed state," she says. Then, she's ready to take the plunge. At 30 feet below, Mehgan's body loses its natural buoyancy. She stops kicking and begins to plummet through the sea. "You're sinking like a stone, but you still feel that weightless feeling, like you're free-falling," she says. As she goes deeper, pressure begins to build on her head and body. Her internal organs contract, and her eardrums bend inward.

    If Mehgan chooses the wrong spot to turn around, she'll be faced with dangers such as shallow water blackout. And if she does run out of oxygen before surfacing and passes out, it can be deadly. "There's no room for hesitation and panic, though" she says. "Fear and hesitation are natural feelings, but there is no room for that with free-diving so you have to just set those feelings aside."

    Are you a Free-Diver?

    Free-diving started as a way to make a living. "The history of breath-hold diving is probably as old as the history of our species," says Lundgren. "Men and women have been diving for thousands of years to gather a variety of products, including food, sponges, and mother-of-pearl, to conduct salvage and military operations, and to explore."

    Lundgren says current diving record holders are practicing in what he considers "depth ranges that are at the very limits of what is safe." By contrast, thousands of mostly female Japanese and Korean breath-hold divers are still using the relatively safe techniques developed over 2,000 years. They dive down to a maximum of about 20 meters, typically for no more than a minute at a time, with an excellent safety record. Professional breath-hold divers are also active in other parts of the world, such as in Indonesia and, at least until recently, in the South Pacific, where pearl divers have been known to operate down to 50 meters of depth, but not without accidents. But it's free-divers such as Mehgan who have popularized the sport in the United States.

    Lundgren defines a breath-hold diver as anyone who is submerged for a given time while swimming at a beach, in a pool or snorkeling. In addition, a commercial or recreational diver instantly becomes a breath-hold diver if his or her SCUBA gear fails. His research in this area is based on the idea that a person's ability to breath-hold until resurfacing in any involuntary submersion may make the difference between survival and drowning.

    Says Lundgren, "It's important to have a scientifically grounded understanding of the physiology of breath-hold diving. This knowledge is vital for recommending safe swimming and diving practices, training of both breathing and breath-hold divers, and the diagnosis and treatment of diving and near-drowning accident cases."

    In the early 1990s, Lundgren's team collaborated with the National Undersea Research Program and the Italian National Research Council on an NYSG-funded investigation on the physiology of the diving response in male and female expert divers. Utilizing a hyperbaric chamber, the team examined the slowing of the heart, blood distribution, and gas uptake and exchange dynamics. Findings supported the idea that, especially in cold water, people with cardiovascular ailments have a greater risk of potentially serious circulatory disturbances if engaged in diving.

    Information from this study, as well as Lundgren's work related to decompression sickness, is applicable for updating diver-training manuals and in the treatment of diving-related accidents. It is also extendable to diving organizations such as the National Association of Underwater Instructors, the Divers Alert Network, and international organizations such as Professional Association of Diving Instructors.

    In 1990, the practical results from Lundgren's breath-hold diving project peaked the interest of PBS's "Scientific American Frontiers" series. His appearance on "Frontiers" was followed by one in 2000 on "Ripley's Believe it or Not!," which airs on the Turner Broadcasting System's Superstation cable channel. In the "Ripley's" segment, which also featured the free-diver Heaney-Grier, Lundgren offered his expertise on the topic of deep sea diving.

    So now that Mehgan has gone to such great depths, what's next? She does have her sites set on another dive, but she's currently trying to catch her breath and keep up with all the other offers that are washing ashore. Mehgan's other recent opportunities - including executive producing duties for "Deep Diver," a one-hour special for the USA network - are currently keeping her busy. Her hope of reaching a depth of 200 feet, equivalent to diving off a 20-story building, is on the horizion, though. "I like the challenge that variety can bring, but the free diving brings me back to a simpler state, even though it's quite complex. I'm drawn to the idea of challenging both my physical and mental ability."

    "This is my high," she continues. "It's adventurous and it makes me feel alive to push myself to my limits." Unless you're highly trained like Mehgan, though, free-diving is not a sport that you should just plunge into. "It's an inherently dangerous sport, but I train really hard and take all the necessary safety precautions. Anything beyond that is out of my hands, so I've got to be willing to take the risks beyond the bounds of safety. For me, it's a good obsession."