The kingdom of the seas and its multitude of life forms are without question, fascinating but no more so than the world within the diver himself. A realm that measures no more than a few cubic feet. Here the currents flow through a myriad of tiny tubes and vessels. Water laps not upon shores but rather on the walls of trillions of our cells. Yet despite the similarities, certain adaptations need to take place when man enters the ocean as a diver. Every diver realizes that at the close of the dive he must ascend slowly and avoid exceeding the no decompression limits. In all of diving there probably exists no more enigmatic a puzzle than the mysteries of decompression. It is a physiological puzzle the pieces of which have been played for almost 150 years and for which the picture is not yet complete. Triger in 1841 was the first to describe the pain in the joints of workers exposed to compressed air in mines that were pressurized to prevent flooding. Pol and Watelle in 1854 coined the phrase," you pay when you leave," to describe this unusual disease that sometimes afflicted compressed air workers. At that time, decompression sickness was attributed to many different factors such as the compression of blood from the extremiti es into the trunk of the body, or rheumatism brought on by the cold damp working conditions. To Pol and Watelle it was almost as if a person living in a town ravaged by the plague did not contract the disease until he left the city limits, and more curiously, the symptoms would then vanish when the person entered the city once again. Thus from its beginnings, decompression sickness has always been a disease enshrouded in mystery. The first to notice the bubbles following decompression was Robert Boyle who in 1650 while performing research with the newly invented vacuum pump, noted a gas bubble that formed in the eye of a snake following an ascent to high altitude. But not until the research of Paul Bert in the late 1800s was the cause of the malady traceable to the formation of these gas bubbles in the body. A TINY TEMPEST Human divers have an unfortunate proclivity to gas phase or bubble formation that is not found in pure liquids. In the laboratory, pure water can be compressed with nitrogen or helium and then decompressed directly from almost 200 atmospheres without the formation of a gas phase. Theoretically, in pure water, the tensile strength or the tendency to resist tearing or cracking, is on the order of 1,000 atmospheres. Were a deep sea diver composed only of the purest water, he could surface with consummate ease directly from six miles without the need for decompression. A core problem in hyperbaric or high pressu re physiology is attempting to explain the difference between the six miles and the actual depth of about 33 feet from which a diver can usually ascend free of the signs and symptoms of decompression sickness. To explain this considerable deviance, to say the least, between theory and experiment, scientists have evoked the concept of heterogeneous nucleation. In simple terms this means that something exists prior to decompression upon which the gas phase can grow. A concept that has been gaining wider acceptance in the last several years is that there exists preformed gas micronucleus or small gas seeds within the cells or in the circulatory system. Upon decompression gas that is dissolved, diffuses into these pre-existing seeds, causing them to expand. This expansion when taking place in tendons and ligaments causes the joint pain commonly referred to as the bends. This micronuclei viewpoint, while extremely useful for explaining many facets of decompression, is at variance with the concept first ascribed to J.B.S. Haldane, the progenitor of the Haldane method of decompression. He postulated that gas dissolved in the tissue of the divers body, remained in this dissolved state or condition, even during decompression; provided that the depth from which the diver was ascending was kept within specific boundaries. He described this as a ratio between the bottom depth and the decompression stops. He was therefore a proponent of homogeneous nucleation in which a gas phase would spontaneously form if a definite super saturation limit was exceeded. The argument went that during the limited ascent, the divers tissues were super saturated with nitrogen, but the gas could remain in this dissolved state without ever forming bubbles, for essentially an infinite period of time. This highly controverted, though often employed concept, has been called the metastable state, meaning that it is a condition stable for long periods of time, if not disturbed. The fixed upper boundary of super saturation is referred to as metastable limit. Because they are below this supposed limit, gently opened bottles of carbonated beverages will not fizz if allowed to stand quietly in an unagitated state. WE DO NOT HAVE A CLEAR UNDERSTANDING NOR FIRM THEORETICAL GRASP OF THE MECHANISM BY WHICH THE GAS MICRONUCLEI ARISE. They may be generated by tribonucleation, that is, the rubbing together of two surfaces, such as joints, or they may be produced by negative pressures, the result of muscle motion. Wherever their origin may lie, we have not yet learned to quantify their numbers and even a simple question such as, "Do they vary in numbers from day to day?" is not answerable. These pre-existing nuclei may account for some of the variability seen between divers. The relationship between gas phase formation, gas micronuclei and super saturation is easily observable in this simple experiment. After pou ring some carbonated beverage into a glass, one notices a considerable evolution of gas that accompanies the agitation. However after a period of time, the gas evolution ceases and the liquid becomes still and quiescent once again. If one now drops in a few crystals of salt, sugar or sand, there results an immediate evolution of gas on the surfaces of the small particles that have been added. The effervescence continues for a short period of time and then the liquid again becomes still. Even at this point, more dissolved carbon dioxide can be coaxed out of the solution by dropping in another pinch of salt, sugar or sand. This can be repeated several times until the liquid is reduced to a condition where it is no longer saturated with carbon dioxide. Hence, if super saturation were the only factor controlling gas phase evolution, any carbonated beverage should bubble up and become flat in a short period of time. The fact that it can remain super saturated and be caused to effervesce repeatedly by the addition of surfaces with their micro gas nuclei is evidence that there is more involved in gas phase formation than simply the total quantity, or more accurately the pressure of gas that is dissolved in the liquid. This applies to some degree to gas phase evolution in the tissues of the diver, and, with respect to the design and calculation of decompression tables, the question of gas nuclei is not taken into account except in a very gener al manner. Dive table designers manage the problem by allowing only a minimal level of over saturation that appears to be repeatedly tolerated by the vast majority of divers. The critical question in decompression table design is accurately determining this low level of over saturation. This does not mean to imply however, that there is a truly precise limit, metastable or otherwise, that is always tolerated by 100% of the divers in every instance. It is incumbent upon the diver to realize that there is always a theoretical possibility that things can go awry. The diver must be cognizant that there is a risk involved every time he begins his ascent even if the table has calculated that risk to be, on average, practically non existent. A TUG OF WAR The concepts of gas micronuclei in tissues and the metastable state are at variance with one another. Both cannot simultaneously coexist for any length of time. Super saturation decreases as the dissolved inert gas slowly diffuses into the pre existing gas nuclei. The rate of the whole process will depend in part upon the degree of super saturation and the number of preformed gas nuclei. When super saturation is excessive, and the gas seeds grow to a relatively large size, overt signs and symptoms of decompression sickness will most likely occur. If gas phase formation is too great, circulatory disturbances can occur that interfere with tissue gas washout. This can lead to a snowball effect with catastrophic consequences. If this growth is kept minimal, then decompression sickness will most likely not occur. The body is able to handle the minor physiological consequences of the gas phase without any noticeable damage, and the disease remains sub clinical or silent. The proposition of silent decompression sickness and silent bubbles was first advanced in 1943 by Doctor Albert Benke, then in the U.S. Navy. It was not until the advent of the Dopplar ultrasound flow meter and its use in hyperbaric physiology in the late 1960s that the idea was given firm experimental under pinning. Using sheep and pigs as experimental diving subjects, several researchers found, quite to their amazement, that gas bubbles were detectable when the subjects were decompressed in accordance with the U.S. Navy diving tables. Since that time when the Dopplar flow meter has given a voice to silent bubbles, our viewpoint has not been the same. Dive tables, for one, are now looked upon with a more cautious eye, and decompression sickness is no longer considered to be the all or nothing phenomenon as once thought. WHERE IS THE BOTTLENECK? In a calculation of a dive table, there arises the question of the amount or partial pressure of inert gas that is dissolved in the tissues of the diver just prior to ascent. This uptake is calculated on the basis of bottom time and depth. In actual practice, these are only two quantities that are found in a decompressio n table. It is known however, that other factors, in addition to time and bottom depth, influence the amount of gas that dissolves in diver's tissues. These include the temperature of the extremities, heart rate, and the level of exercise performed while the diver is under water. These modify the local blood flow or perfusion rate that partially governs the transport of inert gas from the lungs to the capillaries in the diver's tissues. At the cellular level, the distribution of this inert gas is highly dependent upon both the regional blood flow and the actual geometric arrangement of the capillaries. Even between identical twins, this arrangement is not exactly the same. However this micro architecture of the capillaries does not enter into the calculations of contemporary decompression schedules. At least theoretically, it should account for some of the variability in gas uptake and elimination among divers. To further compound the problem. After the inert gas leaves the capillaries it must diffuse its way into the cells. These cells are not homogonous boxes filled with a jelly like medium, but rather they are irregular in their shape and filled with solid organelles that modify the diffusion pathway. It cannot even be said that the diffusion rate of gas in an up and down direction in the cell is the same as that from right to left. This diffusion rate, furthermore, depends upon the individual body characteristics of the diver. Curre ntly we do not know the relative degree to which perfusion or diffusion limits gas uptake and elimination in any given tissue. A good argument can be made for either as the bottleneck, or rate limiting step. These two distribution modes may actually alternate in importance as capillaries open and close. Within minutes perfusion rates and diffusion distance will vary. In diffusion as well as perfusion, the concept of uniformity from diver to diver must be accepted irrespective of whether this uniformity actually exists in practice. Only by staying within certain boundaries, where a minimal amount of tissue gas super saturation will exist, can one begin to minimize individual characteristics. Research involved in the discovery, treatment and avoidance of decompression sickness has a long and varied history. From the mine workers struck with an unknown ailment to today's sophisticated Dopplar ultrasound flow meter. As this research continues and our knowledge increases, the sport of diving will become safer and more enjoyable for more people than ever before. SO WHAT DOES THIS MEAN IN TERMS OF OUR DIVING FROM DAY TO DAY? Quite simply this is a warning that dive tables are based on the theory and knowledge we have accumulated to date. They are by no means a guarantee that you will not suffer from decompression sickness just because you followed them. They are the only guidelines we have to go on at present, and they should be used sensibly . Never dive to the limits of the Recreational Dive Planner. Always allow a margin of error and avoid going deep for the sake of going deep, or staying underwater that extra ten minutes just because you have sufficient air to do so. When diving with a computer remember that this is meant to be a back up to the Recreational Dive Planner and should not replace it. Plan your dives with the RDP then dive the plan. In relation to maximum bottom times allow for an increased margin of safety by reducing that bottom time. That extra ten metres or ten minutes for the sake of going deeper or using up air could make a big difference in the decompression stakes. Dive conservatively and there is always another day. Dive recklessly and there may not be. The Editor

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Our Last topic is: - Education is the Key to Reducing Diving Accidents. Have a read and feedback your comments to our expert.

The Divers Alert Network (DAN) has recently released its 2004 report on diving accidents. The data and conclusions contained therein point to the role of quality diver education. As you read this, reflect as I have on your own responsibility and commitment toward continually improving the safety of scuba diving. A major key is education. Through guidance, students not only learn the skills and academics of diving, but more importantly, they develop a responsible attitude. Your attitude often makes the difference in making good judgments when diving. As I went through DAN's report, I found many interesting statistics that are worth sharing with you. The contributing factors to accidents identified by DAN are the same as those identified and currently presented to students in the Open Water Diver course. However, that these factors still play a role in diving accidents reinforces the need for careful explanation of the risks diving presents, combined with elaboration on key health information. By identifying the causes of accidents we are able to focus on the areas to elaborate on in the teaching methods used. DAN reports that many varied factors contribute to diving accidents. Alcohol use is often reported; approximately 50% of div ing accidents involve alcohol. DAN considers this a factor for 2 reasons: Dehydrating effects on the cardiovascular system and its potential alteration of a diver's mental and physical performance. Either of these effects can contribute to a diving injury. 4% of accidents involved recreational drug use. 10% of accidents involve divers without depth gauges. 15% did not use a watch. Ignorance is not tolerable when you are playing with your life or someone else's. Health is another issue, if a diver is experiencing symptoms of an illness; the safest thing to do is wait out the illness before diving again. Do people underestimate the possible effects of diving while ill? It is the duty of the instructor to emphasize to his student the importance of this issue. DAN analysed 218 cases of diagnosed decompression sickness (DCS), revealing some styles of diving that might have increased individual susceptibility to the occurrence of decompression sickness. In their findings, DAN identified certain factors that may contribute to decompression accidents. Factors such as: - Decompression Diving, Rapid Ascents, Multi-Day Diving, Diving while ill, Diving beyond 130ft of sea water, Diving with Risk Factors and Flying after Diving. These issues are presented to the students in the PADI Open Water Diver Manual. DAN reiterates that oxygen and body positioning can clear many symptoms prior to arrival at hospital. Paralysis, pain, ting ling and the other major neurological symptoms may be completely resolved by rapid administration of oxygen and/or the Trendelenberg position. DAN strongly recommends that divers who have had any symptoms cleared by oxygen be treated with recompression therapy. Long term complications, such as aseptic bone necrosis, short term memory loss and arthritis syndromes, may occur. Whenever the possibility of DCS or air embolism exists, oxygen should be administered; nearly all diving professionals see it as a generally accepted standard of practice. To further reduce the number of diving accidents, we both students and instructors must continue emphasizing key safety information to the diving public. These are: - 1) Fitness and continued training to develop skills and health habits conducive to safe diving. 2) Proper equipment for safe dive planning and execution. 3) Information elaboration, because instructors are the key element to delivering live information from the AV or textbook. 4) Attitude development, that is, the ability to appreciate limitations and the value of education and its applications toward good judgment.

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