The underwater environment causes a diver to be at a tremendous disadvantage due to:
–the difficulty in propulsion through the surrounding water;
–through rapid heat loss to water generally colder than body temperature;
–breathing gas of compressed density;
–the diver uses an altered cardiorespiratory system from a changed environment;
–in order to prevent damage to air-containing spaces in the body, the diver has to accommodate to changes in gas volume and pressure;
–accommodation to the effects of the partial pressure of gases that can cause toxic, narcotic, stimulatory and gas solubility changes to bodily functions.
Divers have to have a reasonable level of physical and physiological fitness because of the obligatory stresses of the underwater environment. They must also be free of other limitations compromising safety in the underwater milieu. For safe diving, the millions of recreational and sport divers should maintain a reasonable level of fitness, the medical requirements for sport diving not being stringent.
Exercise is any activity that raises the resting oxygen consumption above basal levels. Most parts of the body contain a functional reserve which can be called up during exercise–this applies particularly to the heart. Limitations imposed by heart disease may be often assessed by measurements of maximal heart performance. Many experts have emphasized the need to measure cardiac reserve through exercise stress testing, and this has become a useful clinical means for checking physical reserve while diving. Since heart disease is one of the common causes of sudden death underwater, fitness for sport diving must include assessment for heart disease risk.
*Underwater swimmers with full scuba gear have been tested for the amount of work involved; divers must be in good physical condition to do a sustained swim at 1 knot (101 feet/minute, or about a 1.15 mph ). One met = 3.5 ml/kg/minute, and since VO2 Max is 40, a diver swimming 1 knot should be able to reach and sustain 13 mets on the treadmill. (Some feel that this speed is quite slow and 13 mets is high.)
Swimming at about 60 % of maximum [about 24 ml/kg/min] is slightly below the anaerobic threshold can be sustained for long periods of time since it is not lactate producing. *
Physicians planning to evaluate sport divers require a basic knowledge of the physiology of diving and a fundamental understanding of the diving environment. It is helpful if the physician is also a diver himself. Assessment of fitness for diving must consider physical conditioning as well as limitations imposed by medical conditions.
The medical evaluation should consider absolute, relative, or temporary disqualifying conditions as well as excessive smoking and substance abuse. Poor muscle tone, lack of conditioning, obesity and other evidence of dietary indiscretion should be a stimulus to advise the diver about fitness. A medical condition that could injure the diver or his buddy diver should disqualify the diver. The buddy-diver system is the universally recognized practice of pairing scuba divers for mutual safety and implies that each of the pair is fully capable of providing effective aid to the other. Limitations in one of the buddy pair upsets this balance of safety.
Obesity represents a hazard to divers because of the common lack of adequate physical condition in obese individuals and because inert gas exchange and its relationship to decompression sickness are modified unfavorably. Total body fat of less the 22% in males, and less than 28% in females is desirable.
DIVER FITNESS AND AGE
The majority of elderly people do not exercise adequately. For diving good physical condition is essential. Although physical capacity is known to decline with age (Bruce et aI 1974; Raven and Mitchell 1980), it is unclear whether the loss of physical capacity is related to age or to the inactivity common in older individuals. Because of the reduced physical activity experienced by older individuals, there is a deconditioning effect. Most elderly divers are not capable of sustaining the work load of younger individuals. The reduction in physical capacity must be accounted for when accompanying older divers. Studies in older athletes suggest that the decline in physical capacity with age can be minimized by continued physical training (Heath 1980). Elderly divers should be healthy, and possess a level of physical condition that allows them to dive safely.
Chronic diseases known to be of higher incidence in the elderly present special problems in diving. A significant and important problem in the elderly is the high incidence of cardiovascular disease. Atherosclerosis can affect flow to the brain, heart. kidneys, or skeletal muscles. These disorders may go undetected and high exercise demands induced by swimming with diving gear may result in inadequate oxygen supply and abnormal function of a tissue or organ. Of most importance is the presence of coronary atherosclerosis with coronary artery disease, heart attack or sudden death may occur in unfit divers with coronary disease. Avoidance of serious cardiac problems while diving can be achieved through appropriate screening evaluation (Linaweaver 1977). Exercise testing is a useful means of screening in elderly individuals prior to instituting a diving program.
Fitness considerations for young divers are directed towards emotional maturity, ability to learn and understand the requisite physiologic, physical and environmental data needed for safe diving, and towards strength requirements necessary for handling diving equipment (Dembert and Keith 1986).
Sport diving imposes no legal limits on age, but most diver training organizations require candidates to be 15 years old for full certification. Training is provided to younger candidates who receive conditional certification until age 15. Children divers should use dive profiles which minimize risk for decompression sickness to eliminate concern for injury to growing tissues. Equipment must be properly fitted to the young diver. Equipment designed for adults may be unsafe for a child of small body habitus. Individual variation in development, strength, maturity, and intelligence is too wide to set a fixed minimum age for diving. Customarily, 15 years is the usual minimum age for sport diving in the United States.
WOMEN AND DIVING
Many women have learned the sport of diving, and are active divers. Although there are few limitations to diving in women when compared to men, most diving physicians recommend against diving while pregnant. Other than pregnancy , there are no unique concerns regarding fitness of women divers.
Women usually have a lower strength capacity than men and a lower aerobic capacity. Women have a higher percentage of body fat. Sedentary women approximate 25% body fat while trained athletic women reach 10-15%. Trained males however average 7-10% body fat. Increased body fat in women provides better insulation from heat loss during diving, and increased buoyancy.
In assessing fitness to dive in women, the same considerations applied to men regarding general health, physical capacity, mental stability, and training should be used.
EAR PROBLEMS IN DIVING
Ear problems are the most common medical problems in diving. The ears, including the ear drums must be healthy in order to dive safely. Fitness evaluation requires a thorough evaluation of the ears. Aural barotrauma (ear squeeze) occurs in all divers, and can be avoided by careful attention to ear clearing during descent, and the maintenance of open air passages in the ears and throat. A perforated ear drum, chronic ear infections, and unilateral hearing loss should make a candidate unfit to dive.
Avoidance of pulmonary overpressure injury (barotrauma) is a primary concern of all divers, because of the potential seriousness of the lung conditions which can result from diving (Linaweaver 1963). Pneumothorax, mediastinal emphysema, and traumatic arterial gas embolism can occur from lung overpressure. In arterial gas embolism the overpressure forces air into the arterial circulation, and usually to the brain where it can obstruct blood flow. This event leads to permanent brain damage unless treated rapidly by recompression therapy (Linaweaver 1963). To prevent injury divers must be free of spontaneous pneumothorax, chronic pulmonary disease and asthma.
Divers with neck and back problems may develop nerve injuries from heavy lifting, climbing and other diving related activities. Some individuals with severe disease of the spine (herniated disc), may be unable to dive safely due to limitation of motion or severe pain.
Cardiovascular fitness in diver candidates requires the absence of heart disease, hypertension and disease of the blood vessels. The use of drugs for CV disorders may also render a diver unfit.
CORONARY ARTERY DISEASE
Coronary artery disease is the most highly prevalent, life-threatening disease in the United States. Its seriousness and prevalence demand special mention in divers. Two million people per year develop this disease, and over 500,000 people per year die from coronary artery disease (American Heart Association 1981). The basic abnormality of coronary disease is partial or complete obstruction of one or more arteries which supply the heart. In the presence of increased work demands, the heart becomes oxygen starved.
There are several consequences of inadequate oxygen supply to the heart during diving. Oxygen deprived heart muscle may develop sudden reduction in pumping function.. Marked shortness of breath and lung congestion will occur with exercise. Although coronary heart disease is usually manifested by chest pain in most afflicted people, the most troublesome person with coronary disease is the person who has no symptoms but who develops marked oxygen deprivation detected only by electrocardiogram. Such people are at greater risk for sudden death since they developed no premonitory symptoms when oxygen deprivation to the heart occurs.
HEART SURGERY AND ANGIOPLASTY
Patients with successful coronary bypass surgery or balloon angioplasty have returned to sport diving. Careful evaluation of the diverâ€™s condition after recovery from surgery and successful demonstration of acceptable exercise capacity will allow some individuals to return to diving.
Detection of heart disease is particularly important in divers beyond the age of 40. Significant coronary disease may exist without symptoms, only to become evident during stress induced by exercise or anxiety. Diving is an environment which can provoke the first symptoms of coronary disease. In many cases the first symptom is sudden death.
Testing for coronary heart disease can be done by exercise stress testing, and should be done in diver candidates over the age of 40 or those with known or suspected coronary heart disease (Bruce and Hornstein 1969).
Two medical conditions which deserve special mention are seizure disorders and insulin dependent diabetes. Both of these chronic disorders can increase the risk for sudden unexpected unconsciousness underwater.
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