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5.0.0 TEMPERATURE 5.1. 0 Low Temperature In addition to the great variation in surface water temperatures in differ- ent areas and seasons, a sizable differential between surface and deep-water tem- perature exists in many localities. Superimposed upon the wide range of environmental temperatures are large variation in the diver's rate of metabolic activity and heat production. Since it is usually impractical for the free swimmer to perform effectively while bur- dened with excessive protective clothing, he is to a considerable degree limited in capacity by his environmental temperature. 5.1.1 Circulation Most of the current studies of hypothermia, stimulated by interest in its applicability to specialized surgical procedures, are directed toward elaboration of the effects of considerably reduced body temperatures. Work in the area of prolonged exposure to low-water temperatures with moderate depression of body temperature, such as may be encountered in underwater swimming, is receiving very little attention. Not only the effects of exposure but phenomena such as the dangerous after-drop in body temperature following removal from cold water im- mersion require further study. Although no method of adequately protecting the free swimmer from the loss of effectiveness during prolonged exposure to cold water is yet available, it is unlikely that this is a totally insoluble problem. Considerable progress has been made recently in the development of light exposure suits offering protection against cold air and water for individuals exposed at the surface with minimal need for mobility. Considerably more work is necessary in the more difficult de- velopment of insulating suits for the free swimmer. Furthermore, although the possibilities of the use of electricity for providing heat during submergence have not yet proved encouraging, the chemistry of certain heat producing substances and even the use of compact combustion chambers hold out considerable hope for a method of supplying external heat to the swimmer. In the diver's favor is the fact that his metabolic heat production is high while swimming vigorously; the major problem therefore becomes one of conservation rather than substitution of body heat. 5. 1. 2 Dietary Influences Very little is known about dietary influences on the tolerance to cold water. Among those experienced in arctic living, there is the opinion that dietary influences are quite important in chronic situations. However, most of the evi- dence seems to have been obtained from exposure to dry cold and on relatively in- active individuals. This work has not been extended to the swimming man ex- posed to cold water. 23
5.1. 3 The Extremities In studies of exposure suits it has been found that one of the greatest prob- lems of protection concerns the hands and feet. In the extremities, the relatively large surface exposed, the distance the blood must travel, and the normal vaso- constrictor response to cold, all lead to exaggerated lowering of temperature. As yet no great success has been achieved in maintaining hand and foot temperatures or manual dexterity in cold water. That this may be a fruitful area for research is suggested by the unique tolerance to cold water demonstrated by the hands of some of the Maine lobstermen. On the basis of present knowledge any extensive physiological or pharma- cological modification of human intolerance to lowering of body temperatures is not promising. Quite possibly, the principal long-range activity must be in the direction of human engineering and design of external protective mechanisms that will allow the diver to maintain a relatively constant environment inthe immediate vicinity of his skin. 5. 2.0 High Temperature Although exposure to cold in diving has received most attention, the prob- lem of exposure to high water temperatures cannot be ignored. In the actively swimming individual the metabolic heat production is high and, if dissipation of this heat is impeded, considerable discomfort and physiologic derangement can result. Heat dissipation is considerably abetted by the high conductivity of water but if the water temperature is near or above skin temperature, this physical factor is no longer an aid to the swimmer and body temperature must rise. As in exposure to cold the end result is determined by the rate of heat loss relative to metabolic heat production. 24
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