Scuba Diving

Scuba Diving
Sports Injuries: Mechanisms, Prevention, Treatment
Visit & Buy from: http://www.drugswell.com/wow/index.php

37
SCUBA DIVING
KEVIN O'TOOLE

History of Diving
The Underwater Environment
?
Definitions
?
Gases Used in Diving
?
Gas Laws
Heat and Heat Transfer
Diving Equipment
?
Open-Circuit Scuba
?
Buoyancy Compensator
?
Face Mask
?
Weight Belt and Weights
?
Swim Fins
?
Submersible Timer and Depth Gauge
?
Knife
?
Protective Clothing
Diving-Related Injury Statistics
Medical Problems
?
Nitrogen Narcosis
?
Barotrauma
?
Pulmonary Overinflation Syndrome
?
Ear Barotrauma
?
Sinus Barotrauma
?
Face Mask Squeeze
?
Ear Canal Squeeze
?
Dental Barotrauma
?
Decompression Sickness
Prevention of Injuries
?
Nitrogen Narcosis
?
Pulmonary Overpressurization Accidents
?
Middle Ear Barotrauma
?
Sinus Barotrauma
?
Face Mask Squeeze
?
Ear Canal Squeeze
?
Decompression Sickness
?
Sport-Specific Treatment
Chapter References

The sport of scuba (self-contained underwater breathing apparatus) diving has had phenomenal growth over the last 25 years. It has gone from an activity that was limited to a relatively few physically fit individuals to one that has many millions of participants, many of whom are not in peak condition. In the United States, it is estimated that there are 3 million active divers. The incident rate for injuries is surprisingly low at 0.04%, which places it at the same level as bowling. However, the types of injuries that occur in scuba diving can be serious, even fatal. In 1997, there were 82 recreational scuba diving deaths involving U.S. citizens. This number has been as low as 66 (1988) and as high as 147 (1976). The fatality rate for scuba diving has declined from 8.6 per 100,000 in 1976 to 3.7 per 100,000 in 1990 (1). This decline in death rate in the face of a large increase in the number of divers may very well be the result of rigorous standards for training recreational divers. It is a tribute to the training organizations involved that there are few deaths in a sport that can be extremely dangerous to its participants. This chapter is intended to allow the physician to recognize injuries and illnesses unique to scuba diving and to initiate treatment. It also is intended to be a guide for the practitioner as to when to refer the patient for specialty care.
HISTORY OF DIVING
Scuba diving as an entity is a relatively new activity. Diving, however, goes back many centuries. Breath-hold diving is the earliest form of diving known to humankind. It has been shown to have been practiced around 4,500 bc. These divers were diving for food and for treasures (2). In early times, the divers also were used for military purposes, as they are today. Free diving continues to be a popular method of diving today. Examples include pearl divers and recreational snorkeling.
The next innovation in diving was the diving bell. This allowed for a longer time underwater because there was an air supply for the diver. It is recorded that Alexander the Great descended in a diving bell in 330 bc. to view the recovery of a ship (2). The continued problem with a diving bell is that it limited the mobility of the diver. Until the 17th century, the diving bell was state of the art in diving.
The development of surface-supplied diving apparatus in the 17th and 18th centuries dramatically increased the mobility and capabilities of divers. Now a diver was free to move about and not have to worry about returning to the diving bell for the next breath of air. This allowed the diver to do a significantly greater amount of work. This hard-hat diving is still used today by the military and in the underwater construction fields.
The development of a self-contained breathing apparatus was the next evolutionary step in diving. From the middle 1800s, various individuals attempted to create such a device. It was not until 1943, when Emile Gagnan and Captain Jacques-Yves Cousteau unveiled their so-called aqua lung, that the development of the modern scuba gear occurred (2). It is because of the work of these two individuals that we have the sport of recreational scuba diving. It was no longer necessary to be tethered to a surface-supplied air source while wearing a heavy and cumbersome diving suit. This opened the door to ordinary citizens being able to enjoy the underwater environment. All of today's scuba gear is a refinement on this initial apparatus.
THE UNDERWATER ENVIRONMENT
The world of the scuba diver, if looked at objectively, is an extremely hostile one. The surrounding ?atmosphere? is one that cannot support a diver's oxygen needs without special equipment. This atmosphere is continually changing its ambient pressure with every change in the diver's depth. It is this change in pressure that leads to many of the medical problems that develop in divers. A diver cannot see well if he or she is not wearing a mask. Even with a mask, objects are distorted by appearing closer and larger than they truly are. The surrounding water tends to drain the heat from a diver and expose him or her to the risks of hypothermia. The diver can visit this world for only a limited time, because the air supply is finite and because of the risks of decompression sickness. As can be seen, there are many factors that work against a diver. They are not, however, insurmountable, as evidenced by the popularity of the sport. It is important for the diver, as well as his or her physician, to understand the physics of the underwater environment. A diver learns this while undergoing training. For the physician, to understand the pathophysiology of diving injuries requires a basic understanding of underwater physics. As will be shown, most of the common and serious injuries unique to scuba diving occur because of the effects of pressure on gases in the body.
Definitions
Several terms will need to be defined to understand the gas laws that are discussed below. Pressure is defined as an amount of force acting on a unit area. In diving, pressure is usually expressed as pounds per square inch (psi). Mathematically, it can be expressed as pressure=force/area, or p=F/A.
The amount of pressure that is exerted on a body by the earth's atmosphere is defined as 1 atm. When measured at sea level, it is equal to 14.7 psi. At higher elevations, it is less. Atmospheric pressure acts in all directions at any specific point equally. For this reason, its effects are usually neutralized. In diving, pressures also are expressed in atmospheres. For example, a pressure of 147 psi is 10 atm (10 ? 14.7 psi).
Hydrostatic pressure is the pressure produced by the weight of fluid acting on a body submerged in the fluid. It is equal in all directions at any particular depth. In sea water, for every 1 foot a diver descends, the hydrostatic pressure increases 0.445 psi. This number is 0.432 psi for fresh water. For sea water, the pressure at 33 feet is equivalent to 1 atm. For fresh water, every 34 feet is the same as 1 atm, or 14.7 psi.
The definition of absolute pressure is the sum of the atmospheric and hydrostatic pressures exerted on a submerged body. Its units of measure are pounds per square inch absolute (psia) or atmospheres absolute (ata). The term ambient pressure is defined as the pressure surrounding a submerged body (atmospheric + hydrostatic) and is usually stated in absolute pressure terms.
Gauge pressure is defined as the difference between the pressure being measured and the atmospheric pressure. Most gauges used in scuba diving are calibrated to read zero at normal atmospheric pressures. Gauge pressure is what is measured on a diver's depth gauge. To convert gauge pressure to absolute pressure, one needs only to add 14.7 psi to the gauge pressure.
The final pressure that needs to be defined is partial pressure. In a mixture of gases, the proportion of the total pressure contributed by a single gas in the mixture is called the partial pressure. This partial pressure is directly proportional to the percentage of the total volume of the mixture that the individual gas occupies. The partial pressure of a gas determines how much of the gas will be dissolved in the tissues and blood. The concentration of gases in tissues plays an important role in the development of specific diving illnesses such as nitrogen narcosis and decompression sickness.
Gases Used in Diving
There are a number of important gases that are encountered in recreational scuba diving. Air, in a compressed form, is the mixture of gases that are used in sport diving. It is composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and a mixture of other rare gases (0.003%).
Oxygen, as is well known, is essential to life. It is the only gas that is used metabolically by the diver. All other gases in air serve only to dilute the oxygen concentration. In high enough concentrations, oxygen is toxic to the pulmonary and central nervous systems (3). Until recently, sport diving did not include the use of oxygen-enriched gas mixtures for this reason.
Nitrogen is the most abundant gas in air. It is an inert gas and does not support life. Nitrogen is involved in a number of the illnesses associated with diving. Its anesthetic effects at high partial pressure is the cause of nitrogen narcosis, also known as the rapture of the deep (4). The formation of nitrogen bubbles in tissues and blood is the cause of decompression sickness, or the bends (5,6,7,8 and 9). Nitrogen does serve a useful purpose for the sport diver, however. It dilutes the oxygen so that the diver is not at risk for oxygen toxicity, which would develop at higher partial pressures of oxygen.
Carbon dioxide is normally found in minute amounts in air. Normally, it is not of any concern to the diver. However, if the diver would happen to get a tank of air contaminated with carbon dioxide, the results could be disastrous. Carbon dioxide in high concentrations (>10%) is toxic to humans and can lead to seizures and death (2,3,10). Having a reputable supplier of compressed air is the principal way to prevent this potential disaster.
Carbon monoxide is produced by the incomplete combustion of hydrocarbons in internal combustion engines. It is an extremely poisonous substance that must be excluded from the diver's air supply at all costs. The most common cause of carbon monoxide contamination of a diver's air supply is the intake of an air compressor being near an exhaust system of an internal combustion engine (2). Again, prevention of this disorder can be accomplished by obtaining compressed air only from reputable dealers.
Gas Laws
To understand fully how changes in pressure can lead to the common ailments that are seen in scuba diving, it is important to understand some common gas laws. The effects of change in pressure on liquids is negligible. For this reason, most of the body, which is made up of liquids, has no direct effects from the pressure. It is the air-filled body cavities?the middle ears, sinuses, lungs, and gastrointestinal tract?that are most affected by pressure changes. To understand what changes occur and why they occur, it is essential to discuss several gas laws. The behavior of all gases can be explained by three factors: the pressure, volume, and temperature of that gas. The interrelationships between these factors has been explained by the gas laws. There are four of these laws that are applicable to the diver: Boyle law; Charles law; Dalton law; and Henry law.
Boyle's law can be stated as follows: At a constant temperature, the volume of a gas varies inversely with absolute pressure, whereas the density of a gas varies directly with absolute pressure. For any gas at a constant temperature, Boyle law can be written as follows:

where p=absolute pressure, V=volume, and K=constant. This law is vital to the scuba diver in that it describes what happens to an air-filled cavity in the body if it cannot be equalized with the ambient pressure. An example would be barotrauma to the middle ear caused by eustachian tube dysfunction.
Charles law is stated as follows: At a constant pressure, the volume of a gas varies directly with absolute temperature. For any gases at a constant volume, the pressure of a gas varies directly with absolute temperature. This law can be expressed mathematically as follows:

where p=absolute pressure, V=volume, T=absolute temperature, and R=universal constant for all gases. This law comes in to play when dealing with the compressed air tanks that divers use as their air supply. If a tank is left in direct sunlight, it can be seen from the formula given earlier that either the pressure or volume must increase. Because the air tank is rigid, making the volume constant, the pressure in the tank will increase. This can lead to an overpressurization of the tank and possible tank or valve rupture.
The definition of Dalton law is as follows: The total pressure that is exerted by a mixture of gases is equal to the sum of the partial pressures of each of the gases if it alone were present in the same volume. The mathematical formula for this law is written as follows:

where ptotal=total pressure of that gas, pp1=partial pressure of gas 1, pp2=partial pressure of gas 2, ppn=partial pressure of other gas. Dalton law is important when one is discussing contaminated air supplies, nitrogen narcosis, and decompression sickness.
Henry law deals with the solubility of gases in a liquid. It can be stated as follows: The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas that is in contact with the liquid and the solubility coefficient of the gas in the particular liquid. To put it simply, in a diver, the amount of gas that will dissolve in blood and tissues will increase with increasing depth until the point of tissue saturation takes place. The formula is as follows:

where VG= volume of gas dissolved at standard temperature and pressure (STP), VL = volume of the liquid, ;Va. = Benson solubility coefficient at specified temperature, p1 = partial pressure in atmosphere of that gas above the liquid. Henry's law is the basis for the development of decompression sickness and is explained later in this chapter.
HEAT AND HEAT TRANSFER
No matter where a person is diving, be it in the tropics or the cold waters of the Great Lakes, heat loss from the diver's body occurs. Because the human body requires a relatively narrow temperature range to function normally, this loss of heat energy can have significant effects on diver performance and health. There are several mechanisms by which a diver loses body heat: radiation, convection, evaporation, and conduction.
Radiation heat loss by the diver is not significant compared with conduction and convection. Radiation heat loss from the body is in the form of infrared waves. The head, neck, and hands, if left exposed, are areas of the body where radiation heat loss can occur in cold water.
Conduction is the transfer of heat energy by direct contact. This is the most significant cause of heat loss in divers. Water conducts heat much better than air, and a diver that is unprotected loses a great deal of heat by direct contact with the water. The purpose of a diver's wet suit is to prevent the conductive heat loss.
Convection is the transmission of heat energy by the movement of currents. In a diver, even sitting perfectly still, little currents are formed by the rising of water heated by conduction and its replacement by cooler water. This leads to the loss of heat by convective currents.
Evaporation of water vapor from the lungs is another method of heat loss in a diver. The compressed air in a scuba tank has essentially no water vapor present. Each time a diver takes a breath, this air enters the lungs, where large amounts of water vapor and thus heat are transferred to it. This heat is lost with each exhalation.

Pages: 1 ? 2 ? 3 ? 4

pittsburgh pirates mariners mets shades of grey pittsburgh penguins record store day jennie garth