Portal de Periódicos da CAPES

Historical and basic perspectives of SCUBA diving

1996; Lippincott Williams & Wilkins; Volume: 28; Issue: 5 Linguagem: Inglês

10.1249/00005768-199605000-00005

1530-0315

PETER R. LYNCH,

Cardiovascular and Diving-Related Complications

Shakespeare's King Richard III; Clearence's Dream Clarence: Methought I saw a thousand fearful wracks; a thousand men that fishes gnawed upon; wedges of gold, great anchors, heaps of pearl, inestimable stones, unvalued jewels, all scattered in the bottom of the sea. Some lay in dead men's skulls; and in the holes where eyes did once inhabit there were crept, as t'were in scorn of eyes, reflecting gems, that woo'd the slimy bottom of the deep, and mocked the dead bones that lay scatter'd by. The Keeper: Had you such leisure in the time of death to gaze upon these secrets of the deep? To swim, glide, and soar weightless and free over an underwater landscape was a dream 50 years ago. Today it is a wonderful reality. SCUBA(self-contained under-water breathing apparatus) gave us that reality. In 1943, Jacques Cousteau and Emile Gagnon invented the modern SCUBA, opening a whole new world for the adventurous, creating a new sport now referred to as recreational diving. By strapping on a compressed air tank complete with a demand valve, regulator, and a mouthpiece, it is possible to explore the local pond, river, lake, or ocean. Initially, the underwater world was viewed as hostile and dangerous.“Everything will maim or kill you!” This was learned from the media or so-called local experts, who were never actually underwater but who presumably understood everything about that environment. The public's perception developed from various sources, like Jacques Cousteau movies or the Lloyd Bridges' television series Sea Hunt. Magazine and newspaper accounts of undersea events were often sensational in nature portraying SCUBA diving as an exciting but dangerous sport. A basic fear of the unknown created a macho image of the risk-taking diver, who at any moment could be eaten by a huge shark. Unfortunately, this image still exists in many minds. In trying to popularize the sport, some well-meaning divers and commercial entrepreneurs tried to paint a portrait of a fantasy world where“everything underwater loves man and nothing is harmful.” Beautiful films were made of pristine coral gardens with benign, exotic, and colorful marine life. Around every corner or on every seascape there were treasure ships with mounds of gold and heaps of pearls waiting for the underwater explorer to gather up in his arms. Today the knowledgeable, well-trained SCUBA diver knows these concepts are wrong and may, in fact, be dangerous. There are creatures with a frightening appearance that are quite harmless and creatures with a harmless appearance that can hurt or even kill the unwary diver. Hazardous marine life and dangerous diving conditions are easily avoidable, but one must be well-trained to recognize problems before they occur. Knowledge of the underwater environment can offer the modern sports diver a great level of protection. Early skin and SCUBA divers were often spearfishermen or food gatherers. There was a misplaced pride in being the one who speared the biggest fish or collected the largest number of fish in a certain time period. The individuals who caught the largest lobster, the most crabs, clams, oysters, scallops, or mussels were the local heroes. Little concern was expressed about conservation, or whether they were antagonizing the local fishermen. Only after the depletion of local species from favorite wreck or reef sites did the divers question what they were doing to the environment. Only after recognition that areas could be depleted of desired species were conservation societies, such as the American Littoral Society, organized. Spearfishing, while still practiced by a few sports divers, is no longer popular in the United States. The spearfishing phase was followed by the wreck diver's view of the undersea sphere. All sunken vessels were fair game. Treasure could be a centuries-old Spanish doubloon or a port hole from a ship that sank the week before. When wreck divers began to destroy ancient ship wrecks to retrieve the gold or amphora they ran into conflict with marine archaeologists. Today, very few sports divers are willing to invest the needed capital to become treasure hunters. However, there will always be a small number of recreational divers who will evolve into treasure seekers. The next phase to occur in sports diving was the emergence of underwater photographers. Their philosophy was “take nothing but memories(photographs) and leave everything intact.” These divers and their bulky equipment sometimes crashed into reefs, destroying the coral environment. Often, to get dramatic shots, they created dangerous situations or promoted hazardous deep diving. Feeding sharks without a shark cage produces some great photographs but is extremely risky; diving deeper than the normal limits of SCUBA diving, i.e., 130-150 fsw, should never be encouraged. Many sports divers enjoy both video- and still-photography without risking their lives or endangering the environment. Today there are recreational divers, well-trained in environmental issues, who are often recruited by marine scientists to help retrieve data from the sea. Sport diver has become a useful tool in monitoring the marine world, often supplying useful observations that serve the scientific community. They have become an extra pair of eyes on the sea bottom and have alerted fisheries about pollution not reported by standard monitoring techniques. Observations of the sport diver are expressed in such publications as the Underwater Naturalist published by the American Littoral Society. Finally, a new type of sport diver, the world traveler, has evolved. It is the goal of this diver to visit every remote diving location in the seven seas. Catering to this group are beautiful tropical resorts and live-aboard dive charter boats. For example, over 600,000 Americans visit the Caribbean islands yearly to participate in exciting fun-filled diving vacations. Throughout this developmental period, the sport of SCUBA diving has become steadily safer due to a greater awareness of the need to be physically fit and better trained. Improved training has resulted in a better understanding of the environmental challenges. The diver knows that heat is rapidly lost from the human body in water and a well-designed protective wet or dry diving suit must be worn or the diver will encounter serious trouble. The modern diver is also knowledgeable about the physical properties of breathing gases, the operation of SCUBA equipment, and the medical aspects of diving. Boyle's Law states that at a constant temperature, the volume of a given mass of gas is inversely proportional to its pressure. For instance, it a diver descends to 33 fsw, the ambient pressure doubles and the volume of gas in an enclosed air space would decrease by half. The tendency for the volume to decrease in an enclosed air space can be painful and result in barotrauma, tissue injury by pressure. Generally, barotrauma is avoided by well-trained sport divers, who learn to prevent the collapse of the body air spaces, especially around the mask, middle ear, or sinuses. The well-trained sport diver will also recognize that the demand valve regulators used in SCUBA diving deliver air at the surrounding ambient pressure, at a volume equivalent to that at the surface, and at a greater gas density. While at depth, the gas the diver is breathing has a greater density than it would on the surface. Therefore, to ascend safely, divers must never hold their breath, or their lungs could overinflate or burst. This form of pulmonary barotrauma can result in arterial air embolism or pneumothorax. Another gas law, Henry's Law, states that the amount of any gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of that gas in contact with the liquid and the solubility coefficient of the gas in the particular liquid. As the diver descends, more gas will dissolve in the body tissues. Upon ascent the dissolved gas must be released gradually or the diver may suffer from the bends, or decompression sickness. Death from a severe case of decompression sickness is a possibility, but risk of this crippling effect is minimized if safe diving practices are followed. The modern sport diver must understand the consequences of preventable medical problems and know that such problems can be avoided if safe diving practices are employed. Over the past 50 years, the diving industry has introduced many new devices that enhance the safety and comfort of sports diving. Masks are no longer made of a hard rubber compound that needed to be sandpapered to fit comfortably. The modern mask may be made of a soft silicone hypoallergenic material with safety glass ground to individual prescription. The mask may have a built-in device to pinch the nose to easily clear ears while descending. The mask may also be equipped with a purge valve to eliminate any water that might find its way into the mask. Modern fins are no longer made of a stiff, heavy, rubberized material prone to produce leg cramps. Fins are now hydrodynamically designed of light-weight material that is colorful, flexible, and can be fitted to any shoe size. With quick-release buckles they are easily pulled on and off. A good pair of swim fins will be comfortable even after a few hours of use and increase the efficiency of swimming remarkably. Original snorkels were simple hooks shaped like shepherds' crooks made of stiff narrow bore rubber tubing. These became very difficult to breath through as soon as a diver moderately exercised. Modern snorkels are lighter, with large bore tubes, and made with clear or colored silicone material. They may be equipped with a purge valve for easier clearing and are more comfortable to swim with than the original models. With a modern set of mask, fins, and snorkel, one may feel ready to skindive, often called snorkeling or free diving. However, for safety reasons, the diver should also include a snorkeling vest, which features an oral inflation device to allow the diver to float comfortably on the surface. Some vests are equipped with a CO2 cartridge for emergency inflation. Additional items are needed for SCUBA diving. First, a modern-demand valve regulator and a metal cylinder containing compressed air are needed for breathing underwater. The SCUBA regulator is an open-circuit demand regulator, since it delivers compressed air at the ambient pressure (on demand of inhaling) and releases the exhaled air into the surrounding water. Modern regulators are well-made, light, and comfortable to use underwater. The double-house regulator called the Aqua-Lung as first used by Cousteau and his crew has now been replaced by a single-hose, sophisticated breathing device with a number of built-in safety features. A balanced pressure reduction regulator tends to make breathing easier at depth and is more likely to handle the air needs of two divers breathing from the same tank in an out-of-air situation for one of the divers. The regulator attaches to a compressed air cylinder usually made of aluminum and typically contains 80 cubic feet of air. At moderate depths to 60 fsw, this tank of air would last anywhere from 30-60 min, depending on breathing rate and workload. Additional SCUBA equipment would include a brass pressure gauge to inform the diver of the air pressure remaining in the tank. A second regulator, called an octopus, is another safety feature that divers find useful if their dive buddy should run out of air. Finally, a low-pressure hose can be used to fill the diver's buoyancy control device, a vest or jacket worn to provide buoyancy while on the surface or at depth. A wrist watch and a depth gauge are also essential. In addition, many divers today carry an underwater computer to keep track of time, maximum depth, rate of ascent, decompression time, and the surface interval between dives. The computers are increasingly sophisticated and if properly maintained are a reliable adjunct to diving safety. The sports of skin and SCUBA diving are just as thrilling as they were 50 years ago but are now much safer for all who participate.