Life, Heat, and Altitude: Physiological Effects of Hot Climates and Great Heights [Reprint 2014 ed.] 9780674431003, 9780674180963

Citation preview

LIFE, HEAT, AND ALTITUDE

LONDON : HUMPHREY MILFORD OXFORD

UNIVERSITY

PRESS

LIFE, HEAT, AND ALTITUDE PHYSIOLOGICAL EFFECTS OF HOT CLIMATES AND GREAT HEIGHTS

By DAVID B R U C E DILL Fatigue Laboratory,

Harvard

University

CAMBRIDGE HARVARD U N I V E R S I T Y PRESS 1938

COPYRIGHT,

1938

B Y THE PRESIDENT AND F E L L O W S OF HARVARD COLLEGE

PRINTED AT THE HARVARD UNIVERSITY PRESS CAMBRIDGE, MASSACHUSETTS, U. S. A.

To H. T. EDWARDS, 1897-1937 Friend and Collaborator

PREFACE The ideas presented in this volume are less diverse than first impressions may suggest: they all relate to the physiological responses of living organisms to stress. These responses show certain uniformities even among different species and, on the other hand, instructive differences within the same species. A courageous man is apt to think he can reach any goal attained by his fellows despite the demonstrated absurdity of this idea in the field of sport. Studies of life in heat and high altitudes reveal the superior adaptability of some species and demonstrate concretely the extent to which the variations in adaptability in man depend on his physiological endowments. Many of the investigations to be discussed have been carried out in the Fatigue Laboratory, both at home and in the field. Without the support of Professor L . J. Henderson these could not have been undertaken, and without the collaboration of Dr. Α . V . Bock, Dr. J. H . Talbott, and Mr. H . T . Edwards they could not have succeeded. Dr. E. F . Adolph of the University of Rochester and Dr. F . G. Hall of Duke University shared with me the planning and execution of a study at Boulder City in 1937 of acclimatization to heat. I am particularly indebted to the many foreign research fellows supported by the Rockefeller Foundation, by the Commission for Relief in Belgium Foundation, or by special government fellowships, who have worked in the Fatigue Laboratory. During ten years sixteen of these men

vili

PREFACE

have come to us from eleven countries and three continents; the interchange of ideas and techniques have been mutually advantageous. For permission to use copyrighted material I am indebted to Akademische Verlagsgesellschaft, Leipzig (Folia haematologica) ; Dr. Isaiah Bowman (Desert Trails of Atacama) ; Dr. W. B. Cannon (paper in Proceedings of the Royal Society of London Bço); J. & A. Churchill, London (The Physiology of Human Perspiration, by Yas Kuno); The Engineer, London; Lea & Febiger, Philadelphia (.American Journal of the Medical Sciences) ; Royal Geographical Society, London (Geographical Journal)·, Georg Thieme, Leipzig (Deutsche Medizinische Wochenschrift) ; The Williams & Wilkins Company, Baltimore (Aviation Medicine, by L. A. Bauer) ; The Wistar Institute of Anatomy and Biology, Philadelphia (Journal of Cellular and Comparative Physiology) ; Yale University Press (Civilization and Climate, by Ellsworth Huntington). The stimulus for preparing this survey of life in hot climates and high altitudes came as an invitation from Mr. A. Lawrence Lowell to lecture in the Lowell Institute. In preparing the eight lectures for publication I have had the encouragement of Professor A. B. Hastings, member of the Board of Syndics of the Harvard University Press. D. B. D. Boston April, 1938.

CONTENTS I. II. III.

ENERGY EXCHANGE AND ENVIRONMENT

VI.

3

PERSPIRATION

24

THIRST

50

IV. MAN IN HOT CLIMATES, WET AND DRY V.

. . .

ANIMAL LIFE IN DESERTS

. . .

73 96

ANIMAL LIFE IN GREAT HEIGHTS

120

VII.

MAN IN HIGH ALTITUDES

I44

VIII.

HIGH ALTITUDE FLIGHT

175

INDEX

203

ILLUSTRATIONS FIG.

1. The volume of air expired and the heart rate at various metabolic rates

10

2. Respiratory patterns in a manic and in a schizophrenic patient

12

3. Oxygen dissociation curves of human blood in relation to pH of serum

13

4. Carbon dioxide dissociation curves of oxygenated and reduced human blood 5. An exercise experiment on Clarence De Mar

18 . . .

. 2 0

6. Perspiration on the palm and on the forehead during mental arithmetic (from Kuno)

28

7. Relative changes in chloride of sweat during acclimatization to dry heat

37

8. Current ideas regarding the movement of ions through cell membranes 9. Pressure changes in the esophagus (from Mueller)

65 . . .

71

10. The effect of restricted evaporation of sweat on the heart rate

92

h . H. T. Edwards and Chihuahua at the conclusion of two hours' walk in the desert

106

12. Speed of locomotion of ants (Liometopum apiculatum) in relation to their temperature (from Shapley) . . .

118

13. The relation between air (and oxygen) pressure and altitude (from Keys)

123

14. Oxygen dissociation curves for animals native to high altitudes and animals native to sea level

128

15. Relative viscosity of blood as measured in tubes of various diameters (from Fâhraeus and Lindquist)

134

16. Counts of red blood cells at high altitudes (from Talbott)

149

xii

ILLUSTRATIONS

17. Blood proteins in relation to altitude

152

18. Muscle hemoglobin (myoglobin) in various tissues of the dog at sea level and at high altitudes (from Hurtado)

156

19. Arterial pCO s , total C0 2 , and p H of serum in relation to altitude

158

20. Chilean workmen at the sulphur mine on Aucanquilcha

162

21. Observations on Christensen in exercise at altitudes ranging from sea level to 5.34 km. (after Christensen and Forbes)

168

22. Soccer team representing the 'Quilcha mine workers

170

23. Soccer game between 'Quilcha and Santa Rosa

. .

. . . .

170

24. Group at the temporary laboratory quarters: 17,500 feet

176

25. Three men under observation after an exposure of six hours to a simulated altitude of 16,000 feet

178

TABLES ι. Four American dietaries

5

2. Energy and water derived from foodstuff

8

3. Harvard records — one-mile run

23

4. Water exchange and urine constituents of subject D at Boulder City

31

5. Chloride concentration in sweat

32

6. Protocol of a walk at Boulder City, June 14, 1937

. . .

36

7. Individual variation in chloride content of sweat . . . .

39

8. Chloride concentration in sweat in relation to rate of sweating

40 .

40

10. Individual in rates ture rise variations in one hour's workof weight loss and tempera-

9. Chloride content of sweat in relation to grade of work

42

1 1 . Temperature rise in one hour's work — weight loss approximately constant

43

12. Weight loss in one hour's work — temperature rise approximately constant

44

13. Chloride in body sweat and hand sweat

45

14. Distribution of body water

87

15. Weight losses in man and dog at Boulder City

. . . .

16. Plasma chloride before and after work

101 101

17. Plasma protein before and after work

102

18. Physiological changes in the burro in work and recovery

106

19. Relation between water loss and serum chloride in the burro

107

20. Effects on the chuckwalla of continuous exposure to the sun

114

21. Oxygen transport capacity within fixed limits of p0 2

. .

129

22. Hemoglobin and red cells of some vertebrates

131

23. Relation of red cell count to oxygen combining capacity

151

24. Used and unused hemoglobin in two hypothetical cases .

153

25. Acid-base balance in serum

160

26. Relation between alveolar and arterial p0 2

162

27. Dependence of arterial oxygen on pulmonary ventilation

195

LIFE, HEAT, AND ALTITUDE

I ENERGY E X C H A N G E A N D

ENVIRONMENT

Man is endowed by nature with a love for adventure and a curiosity about the unknown. While historians are prone to ascribe the migrations of peoples to economic or religious motives, it is a fair guess that their leaders are sometimes dominated by curiosity about the unknown country beyond the next mountain range. A wise leader would conceal this motive beneath some such happy description of their destination as "a land flowing with milk and honey," "El Dorado," or a region containing a spring of perpetual youth. If such promises tempted early Americans to make southward migrations from cold, rigorous climates of the north, their arrival in desert regions must have stirred up bitter complaints about the lack of water, the inhospitable plants, and the burning heat. Hardy individuals stayed on, however, and today their descendants are still wresting a precarious living from the desert. Others pressed southward and after emerging from the tropical jungles climbed to treeless highlands swept by cold, dry winds. Here exertion left them breathless; their animals were often barren, and newcomers were stricken with a strange illness. Eventually hardy races found this environment to their liking; hundreds of thousands of their descendants, now living in these highlands, attest the ability of man to become adapted to strange conditions. The hot, low-lying deserts of the southwestern United

4

LIFE, HEAT, AND ALTITUDE

States and the high, cold prairie or puna of South America have little in common. In both, however, life for man or animals is an arduous undertaking depending for success upon adaptations to hot and dry air on the one hand, and to cold and thin air on the other. Thus a close link between these two extremes of environment is provided the physiologist. He is enabled to compare the results of his numerous studies of man in the laboratory at comfortable temperatures and the usual concentration of oxygen with observations made during and after the process of adaptation to adverse conditions of temperature, humidity, and oxygen supply. In this introductory chapter a background will be provided for a physiological description of life in hot climates and in high altitudes. Attention will be paid to the processes involved in the transformation of energy: the materials used, the supply of oxygen, the maintenance of body temperature, the elimination of waste materials, and the maintenance of water balance. The fuels upon which all higher animals depend consist of carbohydrate, protein, and fat. The composition of four ordinary American diets is shown in Table i. For each the minimum requirement for maintaining the machine in an idling state is about 1500 to 2000 kilogram-calories per day. The sedentary worker may add only 750 kilogram-calories to this requirement for his day's work, the man doing moderate work twice as much, and the worker in heavy industries four to six times as much. Students of human physiology are taught that sugars, or compounds like starch derived from them by polymerization, are the only carbohydrates available as fuels. Herbivorous animals are not so closely restricted; they are able to

ENERGY EXCHANGE AND ENVIRONMENT

5

derive much value from more highly polymerized carbohydrates such as celluloses. They are enabled to do so because of especially potent enzymes which hydrolyze these celluloses to simpler carbohydrates. These enzymes are not TABLE

I

FOUR AMERICAN DIETARIES

Subjects City workers * . . . . Soldiers" Lumbermen ° . . . . Schoolboys d

Protein gm.

90 122 206 166

Fat

Carbohydrate

gm.

gm.

123 387 200

344 483 963 630

124

Kilogramcalories

Calories from fat percentage

2,932 3.624 8,140 5,124

39 32 43 36

* Personal communication from H. K. Stiebeling, U. S. Bureau of Home Economics. The data apply to employed adults of North Atlantic cities. In 1935 the estimated weekly cost was $2.50—$3.12. b J. R. Murlin and F. M. Hildebrandt in American Journal of Physiology 49> 53 1 (1919) - Average figures for 427 messes in U. S. Army training camps in 1917-18. c C. D. Woods and E. R. Mansfield, U. S. Department of Agriculture Experiment Station Bulletin 14g (1904). Measurements were made in Maine in December 1901 and November 1902. d F . C. Gephart in Boston Medical and Surgical Journal 176, 17 (1917). Observations were made on boys of the St. Paul's School, Concord, New Hampshire.

necessarily secreted by the herbivores but may be produced by bacteria or protozoa of their intestinal tract. It has been reported by Cleveland 1 that termites are able to digest 1 L . R. Cleveland in Memoirs of the American Academy of Arts and Sciences 17, 185 (1934). According to Mansour and Mansour-Bek, solid wood particles are ingested by protozoa which are eventually digested by their host. They do not believe the relationship is properly termed symbiotic. Not all termites depend on this relationship. Those that are dependent are referred to by these authors as micro-organism feeders. See

6

LIFE, HEAT, AND ALTITUDE

cellulose because of a symbiotic relationship with a protozoan native to their digestive tract. In ruminants, the rumen is the site of extensive chemical changes, including the hydrolysis of celluloses and pentosans. While plant enzymes help to catalyze these reactions, bacteria are thought to be chiefly responsible for the conversion of these inert substances to simple, active molecules.2 It has been reported by Voltz and others 3 that urea may be utilized by ruminants under suitable conditions. If so, it is probably used by bacteria, in part synthesized to protein, and bacteria are in turn utilized by the host. Herbivorous animals differ in their ability to survive on the tough and desiccated vegetation of the desert. The burro of the desert and the llama of the arid puna thrive on provender which the cow and horse are unwilling to eat and possibly unable to digest. Protein is the chief fuel of carnivorous animals, but while proteins may be used as fuel their most important function consists in providing material for building and repair. Aside from water, protein is the chief constituent of most tissues; the mammalian body is about seven tenths water and two tenths protein. The desert mammalian carnivore has the advantage that its food contains a large proportion of water, but there is the disadvantage that it has to excrete through its kidneys the nitrogen-containing end products of protein digestion along with a good deal of water. In the K . Mansour and J. J. Mansour-Bek in Biological Reviews and Biological Proceedings of the Cambridge Philosophical Society 9, 363 (1934). * H. H. Dukes, The Physiology of Domestic Animals (Ithaca, Ν . Y . : Comstock Publishing Co., 1 9 3 5 ) . 3 W. Völtz, W. Dietrich, and H. Jantzon in Biochemische Zeitschrijt 130, 323 ( 1 9 2 2 ) .

ENERGY EXCHANGE AND ENVIRONMENT

7

case of birds and reptiles this loss of water is avoided by the excretion of crystallized urates. Fat is useful to the animal as a condensed source of energy; for a given weight it has more than twice the energy value of carbohydrate or protein. It is less labile than carbohydrate; most physiologists believe that mammals are unable to convert fat to carbohydrate, while it is agreed that most fats can be synthesized from protein or carbohydrate. The great virtue of fat is its inertness. It can be stored as a water-insoluble substance without modifying the osmotic pressure of the body and yet can be mobilized in emergencies as a source of energy. It is of special importance to hibernating and estivating animals; their fat depots enable them to survive long periods of starvation. For many desert animals, solid food provides not only their energy but also their water. Aside from the water present as such, a considerable amount is produced by oxidative processes. In the breakdown of carbohydrate and fat all of the hydrogen is oxidized to water; about two thirds of that contained in protein follows a similar course, the remainder being used in building end products of nitrogen excretion such as urea, uric acid, and allantoin. The quantity of water thus supplied to play a role in the internal economy of the organism is shown in Table 2.4 It is dear that for the transformation of a given amount of energy, carbohydrate is the foodstuff which yields the largest proportion of water. The intermediate reactions involved in the production of mechanical energy from the ingested foodstuffs are not 'Compiled from J. P. Peters, Body Water: The Exchange of Fluids in Man (Springfield, 111.: C. C. Thomas, 1935).

8

LIFE,

HEAT,

AND

ALTITUDE

identical in all animals. Meyerhof and Lohmann,® for example, have shown that phosphocreatine, a substance important in muscular contraction in mammals, is replaced by phosphoarginine in crustaceans. Nevertheless, the net result of metabolic reactions is similar: the foodstuffs are oxidized to produce a large proportion of heat and a small proportion of mechanical energy and two quantitatively important subTABLE

2

ENERGY AND W A T E R DERIVED FROM FOODSTUFF

Carbohydrate Energy per gram of foodstuff (kg.-cals.) Water per gram of foodstuff (gm.) ... Water per kilogram-calorie (gm.) . . . .

4.1 0.556 0.136

Fat

Protein

9-3 1.071 0.115

4.1 0.396 0.096

stances — carbon dioxide and water. In man, 6 in the horse,' and in the dog,8 the efficiency with which work is performed is about 20 per cent. In other words, in the transformation of energy involved in the oxidation of stored fuel, about one fifth of the stored chemical energy may be converted to useful mechanical work measurable on an ergometer or a treadmill, the remainder appearing as heat. So far as I know, no measurements of mechanical efficiency have been 5 E. Meyerhof and K. Lohmann in Biochemische Zeitschrift ιφ, il (1928). 6 F. G. Benedict and E. P. Cathcart, Muscular Work.: A Metabolic Study with Special Reference to the Efficiency of the Human Body as a Machine (Carnegie Institution of Washington, Publication No. 187, 1 9 1 3 ) . 7 S. Brody and E. A. Trowbridge, Efficiency of Horses, Men and Motors (University of Missouri Agricultural Experiment Station Bulletin 383,

1937)·

8 B. Slowstoff in Archiv für die gesammte Physiologie und der Thiere {Pflüger's Archiv] 83, 494 (1901).

des

Menschen

ENERGY EXCHANGE AND ENVIRONMENT

Ç

made on intact cold-blooded animals, but since most of the reactants and end products are the same as in warm-blooded animals it is a fair guess that the mechanical efficiency is of the same order of magnitude. The supply of oxygen is an integral part of the process of energy transformation. It depends upon the regulation of air supply to the lungs, the diffusion of oxygen through the broad surface of the pulmonary capillary bed, its uptake by the blood, and its transport to the areas of oxidative reactions where it diffuses into the tissues. Even at sea level the blood is not fully saturated with oxygen and at high altitudes the diminished concentration of oxygen in the air increases the difficulty of oxygen uptake by the blood in its passage through the lungs. With a lowered partial pressure of oxygen ( p 0 2 ) in the blood, the delivery of oxygen to the tissues is handicapped and their capacity for work correspondingly diminished. Along with other tissues, the heart muscle experiences a deficient oxygen supply. As a result, its output of blood is restricted, and until compensatory changes occur the organism must be content with a lower level of muscular activity than is possible at sea level. The whole process of respiration, outlined above, cannot be considered in all its phases here, but only in respect to those phases which are of particular interest in connection with adaptations to high temperatures or to high altitudes. First of all, we must consider the regulation by the central nervous system of the air supply to the lungs. This is so effective that every ordinary demand for a change in oxygen supply meets a prompt and suitable response by the respiratory muscles. If we plot the volume of expired air against the level of oxygen consumption, as in Figure i, we find a

IO

LIFE, HEAT, A N D

ALTITUDE

linear relation throughout easy, moderate, and hard work. Eventually a critical level of activity is reached in which the pulmonary ventilation increases out of proportion to the increase in oxygen consumption — an indication that this part 10a

-1I60

90

80

S

ß

70

•^eol if *• 50|„ z" o Κ < 40 -J I-

//

"0

/

/

/y

0.5

/

/ I40 120

/

80!

«/

Z3d

10

///

ρ / y

y

20

t

/

SO

/o

40

4

1.0

li

2.0

2.5

30

3.5

O,CONSUMPTION. LITERS/MIN.

4.0

FIGURE I

T h e volume of air expired, measured at standard conditions, and the heart rate in various metabolic rates. T h e subject was De Mar, the marathoner.

of the machine does more than its share in supplying the demands of the tissues for oxygen. The respiratory center responds to other stimuli than oxygen lack. It is even more sensitive to the level of carbon

ENERGY EXCHANGE AND ENVIRONMENT

II

dioxide in the blood; we shall see later that in the adjustment of breathing to high altitude both the oxygen supply and the concentration of carbon dioxide play a part in determining the volume of air breathed. In high temperatures we find that a third factor, temperature regulation, may also influence respiration. In man the effect is small and except in extreme circumstances of minor importance. In animals with few sweat glands, however, excess heat production may produce a several-fold increase in the volume of air breathed — the familiar phenomenon of panting. While we associate panting with dogs, it is a general phenomenon among animals which are not well provided with sweat glands. Cats pant on occasion, but the occasions are rare because they are careful not to overexert themselves in hot weather. It is not unusual to observe birds panting, and at Boulder City the members of our party have seen reptiles pant when their body temperature was elevated to 40 or 45 ° C . T h e pattern of breathing as revealed by kymographic records shows a remarkable variation from person to person. Figure 2 contains the record of two pathological subjects studied by D r . John Thompson of our laboratory

and

D r . William Corwin of the Metropolitan State Hospital.

9

If

certain psychoses prove to be associated with characteristic patterns of breathing, the accuracy of early diagnosis might be increased. Normal subjects usually fall between these extremes; we shall see that the nature of the respiratory pattern in part determines the adaptability to high altitude. T h e passage of oxygen from the alveoli of the lungs into the capillaries is believed to take place by diffusion. It has been thought by some that after adaptation to high altitudes, * Unpublished observation by J. W. Thompson and W. Corwin.

12

LIFE, HEAT, AND ALTITUDE

secretion might occur, resulting in building up a higher partial pressure of oxygen in the blood than exists in the air spaces in the lungs. This theory never had irrefutable ex-

TIMC IN MINUTES; FIGURE

2

Respiratory patterns in a manic and in a schizophrenic patient. Normal subjects usually lie between these extremes.

perimental support; as we shall show later, examination of arterial blood from men and animals in high altitudes has not revealed a higher percentage of saturation of hemoglobin with oxygen than can be accounted for by simple diffusion from a given pressure in the alveoli to a slightly lower level in the blood.

ENERGY EXCHANGE AND ENVIRONMENT

I3

T o the biochemist the most interesting phase of respiration is the part played by hemoglobin. This iron-containing protein combines reversibly with oxygen to form oxyhemoglobin and is so constituted that it becomes 95 per cent saturated with oxygen in the lungs under ordinary condi-

FIGURE

3

Oxygen dissociation curves of human blood in relation to pH of serum.

tions. Figure 3 illustrates the uptake of oxygen by normal h u m a n blood at various oxygen pressures and at four levels of alkalinity ( p H ) . W e see that when the partial pressure of oxygen ( p 0 2 ) drops to zero, oxyhemoglobin gives up all its oxygen. W h e n the p 0 2 is 30 m m . H g (about one fifth that of ordinary air) and the p H value is 7.4, blood is onehalf saturated, and at a p 0 2 of 100 m m . it has taken on

14

LIFE, HEAT, AND ALTITUDE

nearly a full load of oxygen. The oxygen-combining capacity of blood is roughly 100 times the concentration of oxygen dissolved in arterial blood. Physiologists have frequently pointed out the importance of this fact; clearly, without some such substance as hemoglobin active life for large animals would be impossible. While hemoglobin may vary in physico-chemical properties, it plays the same role in all animals : that of an oxygen carrier which can take on nearly a full load in the lungs and, if necessary, can discharge nearly all its load as the blood passes through the tissue capillaries. It is important to emphasize the fact that it is able to do so primarily because of the character of the reversible compound it forms with oxygen. There are secondary factors involved in the transport of oxygen which deserve attention, although the importance of these factors has been exaggerated by many authors. In the first place, the combination of hemoglobin with oxygen is affected by acidity; the more acid the blood, the lower the affinity for oxygen. The advantage of this property is that the release of carbon dioxide as the blood passes through the lungs — since the blood thereby becomes more alkaline — aids in the uptake of oxygen and there is a similar reciprocal relation in the tissues. It has been shown that some species have hemoglobin without this property, yet they are able to carry on their gas exchange satisfactorily. Oxyhemoglobin is also sensitive to temperature; high temperature favors its dissociation. This seems to be a general property of hemoglobin; a given increment in temperature produces a constant decrement in affinity. Hemoglobin from different species may vary, however, in respect to the

ENERGY EXCHANGE AND ENVIRONMENT

I5

affinity for oxygen at a given temperature and degree of acidity; in general, the oxyhemoglobin of cold-blooded animals dissociates more readily than that of warm-blooded animals. Even among mammals the affinity of hemoglobin for oxygen varies greatly. One of the important characteristics of the hemoglobin of animals native to high altitudes is the high affinity for oxygen which their blood possesses. This question will be dealt with more fully later. The transportation of hemoglobin with its load of oxygen from the lungs to the tissues depends upon the action of the heart as a pump. In rest the heart of a man supplies about 4 liters of blood per minute to the tissues, to which about 240 cc. of oxygen are delivered, or about 60 cc. per liter of blood. Christensen 10 has shown that the output of the heart, no matter how hard the work, is almost directly proportional to the rate of oxygen consumption. The heart of a healthy man is able for a short time to circulate 25 liters of blood to the tissues per minute where 3 liters of oxygen are unloaded, i.e., about 120 cc. per liter. The most powerful athlete studied by Christensen had a cardiac output of 37 liters per minute when he was using 3.94 liters of oxygen per minute. The capacity of the heart, as has already been suggested, is restricted at high altitude because of the deficiency in supply of oxygen to it. The ability of the circulatory system to deliver oxygen to tissues is restricted at high temperatures because of the conflicting demands for heat dissipation. This brings before us the question of temperature regulation. Every warm-blooded animal is provided with a mechanism for the control of its body temperature. One of the 10

E. H. Christensen in Arbeitsphysiologie 4, 470 (1931).

16

LIFE, HEAT, AND ALTITUDE

most successful of such mechanisms is that of man. By virtue of it and his development of artificial devices for tempering his environment, his species has spread more completely than any other over the earth's surface, whether it be hot or cold, wet or dry. His friend, the dog, has done nearly as well and without so many artificial devices. Dogs have aided him in reaching the poles, they follow him to high altitudes, and they have been with him in the tropics from prehistoric times. The dissipation of heat by man is accomplished by radiation, by conduction, and by evaporation of water from the skin and lungs. In a cool environment, the amount of water evaporated may be less than a liter per day; we shall see that strenuous activity in a hot environment may demand the evaporation of ten times as much. Regulation of body temperature is difficult in hot climates because the dissipation of heat tends to lag behind its rate of production. It is difficult in high altitudes because the rate of dissipation may outstrip the rate of production, and in addition the peripheral circulation may be slowed down dangerously; frostbites are a common experience among mountain climbers. The oxidative reactions which have been mentioned have, besides water, only one other quantitatively important product — carbon dioxide. This substance is often referred to in textbooks as a waste product, but it cannot be dismissed so simply. T o the engineer, the carbon dioxide produced in furnaces must be disposed of — nothing is gained by keeping part of it in the combustion chamber. The living organism, on the contrary, keeps the carbon-dioxide concentration of every tissue at a constant and relatively high level. One

ENERGY EXCHANGE AND ENVIRONMENT

V]

thousand cubic centimeters of arterial blood, for example, contain about 500 cc. of carbon dioxide, free and combined. T h e range in the resting adult male is rarely outside the limits of 450 and 550 cc. Aside from the bones, which consist of calcium and magnesium carbonates and phosphates, the body probably contains over 20 liters of carbon dioxide — as much as a resting man produces in about two hours. T h e constancy of the carbon dioxide level in body fluid implies that there is some sensitive mechanism responsible for its regulation. T h e respiratory center, already referred to in connection with oxygen supply, is even more responsive to variations in the carbon-dioxide concentration. This can be shown by adding carbon dioxide to inspired air; the increase in volume of air breathed can be predicted with astonishing accuracy if one knows the concentration of carbon dioxide. If the sensitivity to oxygen lack is measured by lowering the concentration of oxygen in inspired air, the response will be more sluggish and less uniform. Figure 4 describes the uptake of carbon dioxide by blood saturated with oxygen (oxygenated) and by blood free of oxygen (reduced). This specimen of blood when oxygenated contains 49 per cent by volume of carbon dioxide when the partial pressure of carbon dioxide is about 40 mm., the usual value in arterial blood. This corresponds to about 5.5 per cent of carbon dioxide in air saturated with water vapor at 37 o , the condition in the lungs. In other words, as venous blood takes on its load of oxygen it gives up, not its entire load of carbon dioxide, but only enough to come into equilibrium with the carbon dioxide of alveolar air.

In

higher animals there is only one tissue, the lungs, which provides free interchange of gases with the external world;

l8

LIFE, HEAT, AND ALTITUDE

hence the frequent statement that man lives in an atmosphere of 5 to 6 per cent carbon dioxide. Uninformed people, on the assumption that carbon dioxide is an undesirable waste material, have advocated deep-breathing exercises to sweep poisons out of the system. T h e vertigo which may

FIGURE

4

Carbon dioxide dissociation curves of oxygenated and reduced human blood.

result from such intemperate exercises is a message from the central nervous system to the effect that it prefers to maintain the status quo. T h e mechanisms by which carbon dioxide is carried in the blood will not be discussed in detail here. About one twentieth is free, about one tenth is combined with hemo-

ENERGY EXCHANGE AND ENVIRONMENT

I9

globin, and the remainder is bicarbonate. The properties of carbonic acid and its salt, in conjunction with the amphoteric nature of protein, account for the capacity of the blood to combine with considerable quantities of acid or alkali without much change in reaction. Other waste products, such as residues from protein digestion and the excess inorganic constituents, are eliminated by the kidneys, and for this purpose a certain amount of water is necessary. Mention has already been made of the advantages of birds and reptiles over mammals in this respect: their principal end products of nitrogen metabolism, uric acid and its salts, are relatively insoluble and may be excreted as crystals. The example of water economy just given is only one of the mechanisms upon which desert animals depend for maintenance of their water balance. The healthy organism maintains a constant quantity of water and also a constant ratio of water to dissolved substances — that is, a constant osmotic pressure. A large intake of an osmotically active substance such as salt will produce a desire for water; when the excess salt is excreted by the kidneys, enough water will be put out to maintain the proper balance of water and dissolved substances in the body. The state of edema in certain types of nephritis is one in which the kidneys have failed to excrete certain substances, such as salt or urea, and water has been retained to keep the osmotic pressure near normal. At the other extreme one may have a depletion of body water without thirst if an excess of salts is lost, as through sweating. If pure water is ingested in such a circumstance, it will not be retained. Not only the osmotic pressure of the body as a whole is

20

LIFE, HEAT, AND ALTITUDE

kept within narrow limits but the separate parts of the body are in osmotic equilibrium. Even the digestive juices, 11 much as they differ in chemical make-up from one another, are in osmotic equilibrium with the blood and so with the body as a whole. When a sudden change is produced in the osmotic pressure of one tissue, the blood by transfer of water restores equilibrium. In severe exercise there is a temporary increase of considerable magnitude in the osmotic pressure of muscles, due to the conversion of large molecules into small molecules of greater osmotic activity. Dependently, the blood promptly delivers a considerable quantity of its own water to the muscles; later, as the small molecules are removed by oxidation or resynthesis, water returns to the blood. Having surveyed the processes involved in the transformation of energy in the body, let us turn to a few illustrations of experiments designed to measure quantitatively some of these processes. Figure 5 shows the world-renowned marathoner, Clarence De Mar, running on our treadmill. He is breathing outdoor air through the mouthpiece, and his expired air passes through a rubber tube into the gasometer. Here the volume of air expired in a given time is measured and samples are taken for analysis. From these measurements we can calculate the rate of carbon-dioxide output, the rate of oxygen consumption, and the ratio between them. This ratio represents the proportion of fat to carbohydrate being oxidized. The straps about the runner's chest carry electrodes which pick up the electric current generated at each contraction of the heart. This current is amplified enough a

Saliva is an exception.

FIGURE

5

A n exercise e x p e r i m e n t on C l a r e n c c De M a r . Collecting expired air, recordi n g the heart

rate, a n d s a m p l i n g

capillary

blood

observer is M r . S. R o b i n s o n .

are

in progress.

The

ENERGY EXCHANGE AND ENVIRONMENT

21

to operate a relay and a pen on a moving tape, thus yielding a record of the heart rate as work is going on. The observer holding the right hand of the runner is withdrawing a sample of blood from the finger; by use of micromethods it is possible to determine the concentration of hemoglobin, of serum protein, of lactic acid, and of blood sugar in a few drops of blood drawn while the subject continues his activity. The treadmill is motor-driven and can be operated at eight speeds and at any angle up to 25 per cent. It is possible to make the work so easy that an ordinary individual can continue for hours, or so severe that the most powerful runner will be exhausted in a few seconds. The external conditions can be varied from zero to 50 °C., or from pure oxygen to as low a partial pressure of oxygen as can be tolerated. The treadmill cannot be transported easily; in field studies we fall back on other types of activity — using the bicycle ergometer or merely walking over a measured course. Such experiments as these I have described enable us to assay the fitness of the individual and to determine the extent of the handicap placed upon him by high temperatures or low oxygen. Apart from our interest in these questions, we have been making measurements for several years on a group of schoolboys. Some of these are athletic and others are non-athletic; we hope to learn something about physical development during the adolescent period in relation to the participation in competitive sports. Some of our were made on our laboratory rest and then

most interesting observations of the past year a group of champion runners who came to and underwent a thorough examination in went through several exercise experiments

22

LIFE, HEAT, AND ALTITUDE

of the type I have described. These men are able to run the mile in 4' 1 0 " or faster: they owe this ability not to blood of unusual properties, nor to an unusual type of breathing, nor to phenomenally large lungs, but to beautifully integrated muscular and nervous systems and to a remarkably developed capacity for supplying oxygen to their tissues. Lash, who weighs only 65 kg., and who holds the world's record in the two-mile run, was able to transport 5.35 liters of oxygen per minute to his tissues — showing nearly twice the capacity of the ordinary man of his size. While doing so, his heart beats 190 times per minute, which is a normal maximal figure for men of his age. Since he must have been delivering to his tissues at least 35 liters of blood per minute, it follows that he has a heart of great power and size: this is the organ which is apt to be phenomenal in distance runners. However, there need be no fear of unhappy consequences from such physiological hypertrophy. The record of De Mar, who has been running marathons for twentyfive years, should allay such fears. Still more convincing are Dublin's statistics,12 which show that college athletes have a life expectation greater than that of their fellows. As a final illustration of athletic feats, in Table 3 the records are presented of Harvard's first mile runners; the table is copied from a tablet which hangs in the Dillon Field House. There are many sound reasons for Mr. Lowell's being affectionately known as the first citizen of Boston, but not many are familiar with his early performance in distance running. The record he set in 1875 was not surpassed for three years. Some years later two of his cousins, Guy Lowell and Julian Lowell Coolidge, held the u

L. I. Dublin in Harper's Monthly Magazine, July 1928.

ENERGY EXCHANGE AND ENVIRONMENT

23

record in the family for a period of five years, from 1891 to 1896. T h e foregoing picture of the processes of energy transformation provides a background for the study of life in hot climates and high places. T h e attainment of high levels of TABLE

3

HARVARD RECORDS — ONE-MILE RON

Charles S. Bird '77 Oct. 24, 1874 A. Lawrence Lowell '77 May 22, 1875 A. Lawrence Lowell '77 Nov. 6, 1875 C. S. Hanks '79 May 24, 1878 J. S. Bell '81 May 22, 1879 J. S. Bell '81 1 Albert Thorndike '81 J May 19, 1880 J. S. Bell '81 May 28, 1880 Albert Thorndike '81 May 28, 1880 G. B. Morison '83 May 20, 1882 G. B. Morison '83 May 26, 1883 G. Lowell '92 May 4, 1891 G. Lowell '92 May 28, 1892 J. L. Coolidge '95 May 4, 1895 R. Grant '97 May 9, 1896

Minutes

Seconds

5 5 5 5 4

41% 14 2% 2^ 56

4

50%

4 4 4 4 4 4 4 4

44% 42% 39 38% 34 y* 33% 30% 28%

Present Official World's Record Glenn Cunningham

June 16, 1934

4

6

energy transformation by athletes, the successful survival in regions of scanty food, little water, and high temperature, and the adaptive processes called into play in high altitudes — in short, the responses of living organisms to stress — furnish rich materials for students of physiology, biochemistry, and kindred sciences.

II PERSPIRATION In animals which can maintain a high rate of work output in hot climates there is only one important means for dissipation of heat, and this involves the evaporation of water. Certain properties of water give it a peculiar usefulness to living organisms, a thesis developed by Henderson. 1 T w o properties which render water so valuable in the regulation of body temperature are its high heat capacity and its high heat of vaporization. The body, consisting as it does largely of water, has a high heat capacity and so is well buffered against variations in temperature which might otherwise result from fluctuations in the rates of heat production and heat loss. If a resting man were placed in an environment where he neither lost nor gained heat, his body temperature would rise as a result of his own heat production less than 2 ° C . in an hour, while if his heat capacity were that of steel, for example, the temperature rise would be about eight times as great. Heat is transported by the blood from the tissues where it is produced to the lungs and respiratory passages and to the skin, where it is dissipated. The blood, like other tissues, has a high heat capacity and can transport a large quantity of heat for a given circulation rate. For the same reason a small temperature gradient suffices to take up a 1 L. J. Henderson, The Fitness of the Environment (New York: Macmillan & Co., 1927).

PERSPIRATION

25

large amount of heat as the blood passes through the tissue capillaries and to dissipate it as the blood passes through the skin. T h e maintenance during exercise of a skin temperature 3 ° C . or 4 ° C . below that of the blood coming to the skin depends chiefly upon the high heat of vaporization of water. T h e evaporation of one liter of water at a skin temperature of 33 o absorbs about 580 kilogram calories — as much heat as may be produced in one hour of moderately hard work or in 6 hours of rest. When a man works hard in the hot desert the quantity of water evaporated in one hour may exceed 1.5 liters. While the sweat glands provide the chief avenue by which water reaches the surface of the human body, a considerable amount is constantly passing through the skin in some other manner; this is known as the insensible perspiration. There have been numerous opinions advanced regarding the mechanism by which this water passes through the skin and the degree to which its passage is influenced by external conditions. Kuno

These opinions have been reviewed critically by 2

as follows :

( 1 ) The rate of insensible perspiration is fairly uniform over the whole body surface, except for a few regions such as the palms and soles. . . . (2) This rate can vary to a very limited extent only. . . . (3) The physical passage of water through the epidermis is quite possible, and subjects with no sweat glands can discharge as much water as normal subjects do. . . . 3 2 Y a s Kuno, The Physiology of Human Perspiration (London: J. & A. Churchill, 1934), p. 79. 3 Kuno implies that the normal subjects are not sweating. The most convincing evidence for the third conclusion is furnished by Richardson's study of a young man with congenital absence of the sweat glands. See H. B. Richardson in Journal oj Biological Chemistry 67, 397 (1926) and

26

LIFE, HEAT, AND ALTITUDE

From these facts we may be convinced that the cutaneous insensible perspiration is due to a physical process, probably the diffusion of the tissue fluid through the epidermis. It has been shown by Benedict and R o o t 4 and by numerous other investigators that the total volume of water lost insensibly, that is, from both skin and lungs, is roughly parallel to the resting metabolism. Some claim the deviations in the relationship are ± 10 per cent, others =fc 20 per cent, while still others find a wider divergence. Some have optimistically concluded that the measurement of weight loss during sleep gives a satisfactory measure of basal metabolism, but as Lusk remarked, "a measure of basal metabolism which is no more accurate than ± 27 per cent is not likely to come into general use."

5

A s suggested above, the water lost insensibly consists of that evaporated in the lungs and respiratory passages and of the insensible perspiration through the skin. T h e quantity of the former depends both on the level of activity and on the external conditions. T h e inspired air may be saturated or nearly free of water; it may be hot or cold; it may be inspired at the rate of 5 liters per minute or 100 liters per minute. T h e expired air has relatively constant properties — it is saturated with water vapor at about 33°C.

Knowing

the external conditions, the volume of air breathed, and the temperature of expired air, one can calculate the water lost in the external respiration. In twenty-four hours under ordiA . G. R. Whitehouse in Transactions of the Institution of Mining

Engineers

93, 18 (1937)· 4 F . G. Benedict and H. F. Root in Archives of Internal Medicine 38, ι (1926). E Graham Lusk, The Elements of the Science of Nutrition, 4th ed. (Philadelphia and London: W . B. Saunders Co., 1928), p. 146.

PERSPIRATION

Τ]

nary conditions it amounts to about 400 cc. while the total insensible water loss is about 1200 cc. In contrast to the passive nature of the insensible loss of water through the skin, the sweat glands are subject to nervous control and vary widely in their level of activity. T h e sweat glands of man are classified into eccrine, the small glands distributed generally over the surface of the body, and apocrine, the large glands found chiefly in the axillary and pubic regions. Apes have a mixture of the two glands over the body while other mammals, notably the horse, have only apocrine glands over most of the body surface. T h e products of these glands are unlike. That of the eccrine glands consists of little else than a dilute solution of sodium chloride, sodium lactate, and urea, while the apocrine glands contain other substances which vary in nature from animal to animal. T h e eccrine glands of man are chiefly responsible for his profuse secretion of sweat when the ordinary channels for dissipation of heat are inadequate. T h e anatomy and the innervation of these glands are subjects remote from our field of interest, but a word should be added about the stimuli which produce sweating. These are of two kinds, emotional and heat-regulatory. W e are all familiar with the "cold sweat" of emotional disturbances. K u n o has shown that the sweat glands of the palms and soles are always active;® emotional stimuli may cause a sudden increase in sweat production in these areas. T h e simultaneous nature of the response in palms and soles suggests that a common sweat center is functioning. Figure 6, from Kuno, illustrates the great rise in perspiration on the palm in mental arithmetic and the absence of a rise on the forehead. ' Kuno, The Physiology

of Human Perspiration, p. 208.

28

LIFE, HEAT, AND ALTITUDE

Thermal sweating is the term given by K u n o 7 to the production of sweat over the whole body surface by thermal agents. He differentiates it from sweat produced by exer-

vA V

T» **·« -

ΤΛ

s·

IVI 0

IO

20

30

40

MINUTES FIGURE

6

Perspiration on the palm (SA) and on the forehead (SB) during mental arithmetic (M). TA, skin temperature of the palm; TB, that of the forehead. (From Kuno, The Physiology of Human Perspiration, by permission.)

eise and shows that there are differences in respect to the areas involved. In both these types, however, sweating begins simultaneously over the entire body surface, indicating that the autonomous nervous system provides or at least 7

The Physiology

oj Human

Perspiration,

p. 84.

PERSPIRATION

29

transmits the stimulus. Whether the message reaches the centers by way of heated blood or by afferent fibers from the skin is not known. Most physiologists, however, agree with Bazett 8 that nervous reflexes are chiefly responsible for the part played by the sweat glands in temperature regulation. While an extreme temperature rise produced artificially in the brain causes sweating, moderate rises do not, at least in animals. Cloetta and Weser 9 found that an increase in brain temperature of i ° C . by diathermy does not cause sweating, and Hasama 1 0 found that the subthalamus of the cat had to be heated to ¿μ°0. before sweating occurred. While the evidence on this subject is not wholly conclusive, the statement of K u n o 1 1 seems most acceptable : "Sweating on the general body surface is as a rule produced by a nervous reflex. The afferent path of this reflex arc consists of heat nerves, or other sensory nerves, as well as of fibers . . . from higher nervous centers. All these fibers run to the cerebral sweat center from which the efferent fibers go to all the sweat glands along the sympathetic nerves." Perhaps the most valid criticism of Kuno's theory is that it oversimplifies the operation of the sweat center: some mechanism must exist for coordinating the sweat center with the vasomotor, respiratory, and cardiac centers. Bazett 1 2 and Barbour 1 3 may be consulted for further information about these questions. " H . C. Bazett in Physiological Reviews 7, 531 ( 1 9 2 7 ) . Έ . Cloetta and E. Weser in Archiv für experimentelle Pathologie und Pharmakologie 77, 16 ( 1 9 1 4 ) . 10 B. Hasama in Archiv für experimentelle Pathologie und Pharmakologie 146, 129 (1929); 158, 257 ( 1 9 3 0 ) . 51 Kuno, op. cit., p. 207. 12 Bazett, loc. cit. 13 H . G. Barbour in Physiological Reviews 1, 295 ( 1 9 2 t ) .

30

LIFE, HEAT, AND ALTITUDE

Our principal interest in this field concerns the measurement of sweat volume and determination of its composition in relation both to internal and to external conditions. A t the outset it was necessary to make a choice of methods. We desired to study day-to-day changes in the composition of sweat while the subjects were carrying on their usual activities. In the first series of experiments, 14 carried out in the hot desert at Boulder City, Nevada, in 1932, we employed an indirect method which possessed the advantage that little of the subject's time was required; he could carry out his duties in the laboratory and engage in outdoor activities with complete freedom. Each man went on a constant diet, with all portions of food carefully measured. The daily output of sodium, potassium, chloride, and nitrogen in the urine was determined. Three of the subjects spent a preliminary period in a cool environment where little sweating took place. After reaching Boulder City, the decrement in urinary output of the significant substances was ascertained, the sweat volume was estimated from water intake and its output by other avenues, and the composition of sweat could then be calculated. The degree of accuracy depends on the constancy of the diet, the volume of sweat, and the duration of the experiment. Table 4 contains a record of observations on me during fourteen days at Boulder City following a four-day vacation in California. It will be seen that the water intake, excluding water in foods, varied from 3.6 to 10.5 liters per day, and that during the first week only about one tenth of the chloride of the diet was appearing in the urine, pre" D . B. Dill, B. F. Jones, H. T. Edwards, and S. A. Oberg in Journal of Biological Chemistry 100, 755 (1933).

PERSPIRATION

3I

sumably because of the large losses in the sweat. During the second week, more than one half of the chloride ingested was being excreted in the urine. Without presenting the details of experiments on the other five subjects in these TABLE

4

WATER E X C H A N G E AND U R I N E C O N S T I T U E N T S OF S U B J E C T D AT BOULDER

Period

Water intake

Water

liters

liters

8.01 6.51 9-21 8.16 7.96 10.51 4.91 5-41 4-71 7.11 5.11 3·6Ι 7·3ΐ 4·2ΐ

1.08 0.72 1.13 0.85 0.78 0.78 0.79 °·9° ι·« 0.92 0.94 1.29 0.95 0.96

CITY

Urinary output Chloride Sodium

Potassium

mE

mE

mE

24 10 22 20 14 21 51 125 197 140 109 190 113 m

33 15 33 23 21 30 79 125 173 123 144 173 Ι0*> 106

56 97 85 89 80 85 66 93 97 99 72 89

Estimated daily output in urine and sweat July 18-24 212 July 25-Aug. ι 208

200 195

July 18 19 20 21 22 23 24 25 26 27 28 29 30 3ΐ

102

ιοί 94 83

first experiments at Boulder City, it is enough to say that they responded in a fashion which was like my record qualitatively but unlike it quantitatively. It appeared from these experiments that sweat is much more dilute than many previous reports indicated. In few

32

L I F E , H E A T , AND A L T I T U D E

cases d i d the c o n c e n t r a t i o n of

chloride in sweat

o v e r a 24-hour p e r i o d exceed 2 5 m E p e r liter.

excreted

Our

results

are c o m p a r e d w i t h those of other investigators i n T a b l e 5. I t is a s a f e i n f e r e n c e t h a t w h e n p r o f u s e s w e a t i n g o c c u r s d a y a f t e r d a y , the c o n c e n t r a t i o n of salt in s w e a t c a n n o t rem a i n as h i g h as m a n y o f t h e v a l u e s g i v e n i n t h e t a b l e b e l o w . TABLE

5

CHLORIDE C O N C E N T R A T I O N I N

Observer

Conditions

Adolph * Berry b D i l l et al." Fishberg and Bierman H a n c o c k et al.' Hunt1 Moss ' Talbert and H a u g e n 1 1 Whitehouse 1

SWEAT

d

Hot room; no work W o r k in hot r o o m Varied activity in s u n a n d shade Radiothermy; n o w o r k Hot room; no work H o t r o o m in saturated air; no work W o r k in hot r o o m Rest and w o r k i n hot r o o m Rest and w o r k in hot r o o m

Chloride mE per liter 24-88

6-37 6-27 64-85 21-64

31-34 20-56 74-142

9-43

* E . F. Adolph in American Journal of Physiology 66, 445 ( 1 9 2 3 ) . b E . Berry in Biochemische Zeitschrift 72, 285 ( 1 9 1 5 - 1 6 ) . c D. B. Dill, B. F. Jones, H. T. Edwards, and S. A. Oberg in Journal of Biological Chemistry 100, 755 ( 1 9 3 3 ) . d Ε. H. Fishberg and W. Bierman in Journal of Biological Chemistry 97, 433 ( 1 9 3 2 ) . " W. Hancock, A. G. R. Whitehouse, and J. S. Haldane in Proceedings of the Royal Society of London Β ios, 43 (1929—30). Έ . Η. Hunt in Journal of Hygiene 12, 479 ( 1 9 1 2 ) . * K . N. Moss in Proceedings of the Royal Society of London Β 95, i 8 i (1923-24). b G. A. Talbert and C. O. Haugen in American Journal of Physiology 81, 74 ( 1 9 2 7 ) · 1 A. G. R. Whitehouse in Proceedings of the Royal Society of London Β io8, 327 ( 1 9 3 1 ) .

PERSPIRATION

Hunt

15

33

records that while working outdoors in dry heat in

India he drank 13.6 liters in a day with scanty secretion of urine. After returning to England, Hunt found his sweat produced in a hot room contained 31 to 34 m E of chloride. If this concentration characterized his sweating in India, the daily salt intake would have had to exceed 25 gm. Such a high figure is barely possible, but a concentration as great as that reported by Fishberg and Bierman (see Table 5) would have called for a salt intake of 60 gm. per day. This is five times the salt content of most diets. It was concluded from our first experiments at Boulder City that in the process of acclimatization to high temperature the concentration of salt in sweat decreases. In addition to the evidence given in Table 4, two other subjects showed a decrease in sweat chloride when the first period at Boulder City was compared with the last. T h e mean value for four men dropped from 18 to 1 2 m E , or one third. T h e evidence for a decreasing salt concentration in sweat during the process of acclimatization was complicated by other factors not subjected to control. Variation in day-today activities and in prevailing temperature resulted in large variations in daily sweat volume.

T h e sweat of

D . B . D . and S.A.O. had the greatest mean volume and the greatest absolute daily variation. It was noted that the concentration of dissolved substances in sweat appeared to be roughly proportional to the volume of sweat. W e shall see later that the suggestion that there might be some dependence of sweat composition on its rate of secretion was an important one. Another conclusion reached after our first stay in Boul15

Ε . H. Hunt in Journal of Hygiene 12, 479 ( 1 9 1 2 ) .

34

L I F E , H E A T , AND ALTITUDE

der City was that there may be large individual differences in respect to the concentration of dissolved substances in sweat. When comparison was made after acclimatization, and when the daily sweat volumes were of the same magnitude, it was found that the concentration of chloride in the sweat of D.B.D. was twice that of S.A.O. There were no significant differences in the properties of the blood nor in the rate of sweating to account for these individual characteristics. These experiments at Boulder City led to conclusions so different from those generally accepted that it seemed desirable to continue the study with alterations first in the selection of climate, then in method. During the following summer in the humid heat of Boston, Daly and 1 1 8 used the same method with the many refinements which were possible because of our first experiences. Sodium and chloride concentrations decreased strikingly in these experiments after six days of activity which followed a control period when sweating had been kept at a low level. Subjects F . C. and W . C. took part in both the early Boulder City and the Boston experiments. The salt content of their sweat after acclimatization was of the same order of magnitude in the two places, although the volume of sweat was somewhat less in Boston. While the method used in the above experiments is suitable for long-range studies, it is not accurate for hour-to-hour or even day-to-day measurements. In later experiments we have used another method, adaptable only to an arid environment, since it depends on evaporation of the sweat 18

C. Daly and D. B. Dill in American Journal of Physiology ii8,

(1937)·

285

PERSPIRATION

35

in situ and its quantitative removal by washing the body with distilled water. The subject bathes and is weighed to o.oi kg. before beginning the period of observation. Weighings are made frequently during the period of sweating and the water intake is measured. At the end of the period, after the final weighing, he is washed down with 5 liters of distilled water as he stands in a bathtub. The few clothes he has worn are washed out in the same water, after which a sample is taken for analysis. The volume of sweat corresponds to the weight lost with the following corrections: Positive Fluid intake during the experiment Weight of 0 2 used Negative Weight of CO2 output Water from the lungs and respiratory passages17 Insensible perspiration Table 6 records the details of a typical experiment of this sort. Similar experiments were carried out on members of our party at Boulder City nearly every day from May 23 to July 9, 1937· During this time the maximum daily shade temperature varied from 28 o to 44°C. by the government thermometer. The relative humidity occasionally fell as low as 6 per cent and was rarely above 30 per cent even at night. The sky was usually but not always cloudless. Indoors the temperature range was smaller and the humidity varied from 40 to 70 per cent. In addition to this range of climatic 1 7 T h e water loss from lungs and respiratory passages is calculated from the observed volume of expired air as measured at atmospheric pressure and the observed temperature of expired air, the observed relative humidity of inspired air, and the assumption that expired air is saturated with water vapor at its observed temperature.

hO Λ

Jf

« 3 O B·O

60 M M bc M ¿. W 1 1

< H

rt Ò, ΓΛ. T!" -Äΐ cO· ir, OC ra jy 1

e o •a o tv Κ. rrj m

3 a. » ÌS δ ^ δ

όν νο tv tv

r

0

o o o o o o

M ro m M o tv tv ri ,ξρ ÙÔ O oó CO d\ Ó\ O U -V tv tv t-v tv tv £

§ S H ¿

+

V •M

rt

ut

t» c O 3 ι

& C4

« * S¡ o £ 'β « Ö 2 κ" υ t-1 o S c ζ Ε £ £ υ fe «J s δ s Ί> S ä -tí u 'ο Ο » u j * Μ Ü .2 o o 2 O O Mr° H H O Η Ο U oo° od oo } POΓΤ) cri

V

rt i3 is . s '

W M ε e η Ι-

ΙΑ ο\ κ. tv

« rrj m ο rtΓΛ tv V? π ΙΛ ir\ co rö ró

tí .2 ñ a

PERSPIRATION

37

conditions, each subject was studied at different levels of activity — rest, slow walking, fast walking such as that described in the protocol, and playing tennis. In many cases sweat was also collected directly in a rubber glove worn on

FIGURE

7

Relative changes in chloride of sweat during acclimatization to dry heat.

one hand; a suitably adjusted elastic band about the wrist prevented evaporation or contamination.

T h e results of

enough typical experiments are included to illustrate the following points: ι . Figure 7 confirms our previous conclusion, based on

38

LIFE, HEAT, AND ALTITUDE

earlier experiments, that in the process of acclimatization sweat becomes more dilute. Taking the chloride concentration in sweat produced in a hot dry room in winter as unity, we see that the concentration is about three fourths as high on arrival at Boulder City and in most cases drops considerably during the first few days of residence there. The grade of work, the temperature, and the humidity were of the same order of magnitude in the artificial environment in Boston as outdoors at Boulder City. It appears that the major step in acclimatization was accomplished before reaching Boulder City or at any rate within twenty-four hours of arrival. Progress in acclimatization appears to be of a very temporary character; the most concentrated sweats, other than those produced on the first days at Boulder City, were produced on the first day of a hot wave or after a period of inactivity or after a stay of three or four days at the seacoast. 2. The variation among individuals was unexpectedly large, as appears from the measurements of Table 7. My son and I usually produced the most concentrated sweat; that of Hall and of Adolph was most dilute. This difference could not be related to age, physical condition, or properties of the blood. 3. It will be recalled that the experiments of 1932 at Boulder City suggested that there is a relation between the concentration of salt in sweat and its rate of production. Under such conditions not only temperature but also humidity and rate of air movement are factors upon which the rate of production depends. This rate may be considered a rough measure of the burden placed on the heat-dissipative mechanism of the body. Table 8 is the 1937 record of

è

•a

M

ω W

fi

8 ei

È -ti ^ -is s V. ~ s "f w S • ^ •5 fe S 8 δ . κW ν

¿ Ü fi 03 rt rt υ J 66, 1 7 6 Mueller, L . R., 55, 58, 70, 7 1 M u l e in h i g h altitudes, 138 M u r l i n , J. R., 5 Myerson, Α . , 187 increase

156 Nielsen, Η . E . , 186 Nielsen, J. M . , 181 Nielsen, M . , 1 7 9

fishes, 6 3 - 6 4 Ostrich ( S o u t h A m e r i c a n ) , properties of h e m o g l o b i n , 1 3 6 ; red cells of blood, 131 O x y g e n , administration, 2 0 1 ; consumption, 9, 20, 22, 99, 1 1 7 ; diffusion, 12, 1 6 1 , 1 6 2 ; limiting factor in flight, 200; partial pressure and altitude, 1 2 1 - 1 2 3 , 145, 1 4 7 ; secretion, 161—163; utilization in the brain, 1 8 7 ; utilization b y m a n and animals, 129 O x y g e n - a b s o r b i n g p o w e r , 181 O x y h e m o g l o b i n dissociation, in animals at h i g h altitudes, 128; effect of p H , 1 3 ; effect of temperature, 14, 1 1 6 , 1 1 7 ; in m e n in h i g h altitudes, 1 5 1 — 1 5 4 , 162, 1 6 3 ; in m e n in l o w o x y g e n , 1 7 7 , 1 9 5 Pack, G . T . , 56

Missiuro, W . , 192

Myoglobin

ι6ι

with

altitude,

in reptiles, 1 1 4 Pappenheimer, A . M., Jr., 154, 1 6 1 Parker, G . H., 1 1 5 Perspiration, insensible, 25, 26, 3 5 ; sensible, see Sweat Peters, J. P., 7, 50, 61 Petersen, W . F . , 89 Pheasants in h i g h altitudes, m o d e of capture, 1 3 7 Phosphoarginine, 8 Phosphocreatine, 8 Physical fitness, assay, 2 1 , 164, 169, 182; llama and vicuña in h i g h altitudes, 124 Pierce, H . F., 182

210

INDEX

Pigs in high altitudes, 139 Pilocarpin and thirst, 55, 57 Poikilothermism, 1 1 2 Poiseuille, 1 3 2 Polyuria in relation to thirst, 52 Pons, J., 1 5 6 Potassium, in urine, 3 1 ; in tissues, 64-65 Potassium chloride ingestion and thirst, 64 Pressure chamber at Wright Field, 197 Priestley, J. G., 146, 180, 194 Protein, 4-6, 8 Rabbits, in the desert, h i ; red cells of blood, 1 3 1 Redfield, A. C., 154 Regan, W. M., h i Respiration, pattern of breathing, 12, 1 8 1 ; regulation, 17, 145, 157, 1 6 3 - 1 7 2 , 179, 195; effect of ammonium chloride, 195; effect of carbon dioxide, 1 7 , 179, 196; in temperature regulation, 99 Rice, Η. Α., 98, 103 Richards, J., 149 Richardson, Η. B., 25 Root, H. F., 26 Roth, P., 1 8 1 Rotta, Α., 1 5 6 Rowntree, L . G., 55 Ruminants, 6 Salivary flow in thirst, 52, 58 Salivary glands congenitally absent, 58 Sand grouse, i n Schechter, A. J., 66 Schlutz, F. W., 99 Schneider, E. C., 148, 154, 182, 184, 186 Schneider test, 169 Scott, J. C., 85

Sensory functions in low oxygen, 189 Shapley, H., 1 1 7 Shattuck, G. C., 92 Sheep, red cells of blood, 1 3 1 ; tolerance to high altitudes, 139; use as pack animals, 140 Skin color and energy absorption, 46 Skin temperature, 25 Sleep, 88 Slowstoff, B., 8 Smith, C. A. M., 94 Smith, H. W., 63 Soccer in high altitudes, 170 Sodium, distribution in body, 64, 83; in sweat, 46; in urine, 3 1 , 83 Sodium chloride, added to drinking water in steel mills, 83; daily intake, 81, 95 Soil temperature, 73, 75, 1 1 2 Solar radiation, 74—76, 90; effect on reptiles, 1 1 4 - 1 1 7 Steggerda, F. G., 58 Steinhaus, Α. Η., 98, 103 Stevens, Α. W., 1 2 1 Stiebeling, H. Κ., 5 Stratosphere, 1 2 2 Stumme, Ε. Η., 83 Sub-stratosphere plane, 190 Sundstroem, E. S., 80, 93 Sweat composition, 31—38, 44, 48 Sweat glands, apocrine, 27; of burro, 106; congenitally absent, 25; eccrine, 27; emotional stimulation, 27; nervous regulation, 27, 29, 42, 48 Sweat volume, dependence on acclimatization, 42, 48; individual differences, 42, 45, 48; measurement, 30, 35, 100 Talaat, M., 154 Talbert, G. Α., 3 2 Talbott, J. H., 82, 83, 85, 149, 154, 158

INDEX Termites, 5 Thirst, in absence of saliva, 54, 57, 68-70; Bernard's theory, 59; Cannon's theory, 5 1 , 62; definition, 69; dependence on cellular dehydration, 70; in diabetes insipidus, 5 5 ; and esophageal fistula, 59; and extracellular dehydration, 66; after ingesting potassium salts, 64; after ingesting urea, 67; in marine bony fishes, 62; and pilocarpin, 5 5 ; post-prandial, 5 3 , 6 1 ; in polyurea, 5 2 ; in relation to contraction of esophagus, 70—71; in relation to sweating, 68, 1 0 0 ; satisfaction, 70, 8 1 ; successive stages, 69 Thompson, J. W., 1 1 , 194 Tortoise's response to heat, 1 1 5 Training and acclimatization to heat,

43

Treadmill, 8, 2 1 Trowbridge, Ε . Α., 8 Truesdell, D., 186 Urea in sweat, 46 Urea ingestion and thirst, 67 Uric acid, 7, 1 9 Urine in desert heat, 3 1 , 80 Valenti, Α . , 5 2 Van Wagenen, W . P., 56 Ventilation of the lungs, see Respiration

211

Viault, E., 1 4 8 , 1 7 3 Vicuna, 127—131 Viscacha, 1 3 6 Völtz, W., 6 von Tschudi, J. J., 140 Ward, R . DeC., 77 Water, and climate, 7 3 , 79, 8 1 ; deficiency in heat cramps, 83; economy in birds and reptiles, 1 9 ; of external respiration, 2 6 ; ingestion by fishes, 63; loss in high altitudes, 1 5 9 ; of oxidation, 8; quantity evaporated by man, 25, 3 3 ; requirement of burro, 1 0 4 ; and thirst, 50, 53, 60, 8 1 , 1 0 0 Weather and health, 89 Weser, E., 29 Wettendorff, 61 Wheeler, W . M., 1 1 7 Whitehouse, A . G . R., 26, 3 2 Wier, J. F . , 55 Woodbury, Α . M., 1 1 6 Woods, C. D., 5 Work capacity, in dry heat, 1 0 3 ; in high altitudes, 146, 1 7 1 ; in humid heat, 9 1 Workmen, in high altitudes, 1 6 2 , 1 7 0 ; in steel mills, 83, 93 Yannet, H., 66 Youngstown Sheet and Tube Co., 83 Zapus, 1 1 4 Ziegler, Ε . E . , 1 8 1