HEA'F SW3 W EEEAN EN MEN mum mmm mamm E “out: {509 NM Degas M" DE. 0. MECHEGAN STATE UME’EESFE‘Y Aéafiph Richarcfl Easier 1966 |\\\\\\3\\\\t\\l§fl Mu . , LIBRARY Michigan State lflnhnnfiky This is to certify that the thesis entitled HEAT STRESS AND STRAIN IN MEN WEARING IMPERMEABLE CLOTHING presented by Adolph Richard Dasler has been accepted towards fulfillment of the requirements for Mdegree inJhliLQlogy Major professor DMe July 5, 1966 0-169 3 43. w :4 all; as.“ t . . a. ABSTRACT HEAT STRESS AND STRAIN IN MEN WEARING IMPERMEABLE CLOTHING by Adolph Richard Dasler The purpose of this study was to realistically determine the physiological tolerance of man to heat stress impermeable, full body clothing while wearing unventilated, that barred evaporative heat loss. The ambient environmental temperatures ranged from DB 18.30C and we 12°20c (65 and 54oF) to DB 32020c and WE 26.6OC (90 and BOOF). Air velocity over the surface of the 250 and 1000 feet per minute. The suit was controlled <50, variable of physical activity was limited to standing at rest, work by stepping up two 6" steps and then stepping back down at a regulated rate of 10 round trips per minute, or a combination of rest and work. A total of 10 combina- tions of the above variables were investigated; The parameters measured included temperature of the rectum, tympanic membrane, deep esophagus, 10 individual skin sites and mean skin temperature. In addition, meta- bolic rate, heart rate and blood pressure were determined. Computations and data were presented for first order Adolph Richard Dasler estimated cardiac output, and partitional calorimetry, peripheral blood flow by use of the Thermal Circulation Index. Due to the lag in rectal temperature during transient thermal states and the decrease of skin temperature during work, a series of theoretical equations were developed for mean body temperature when an unsteady state exists in man° Upon onset of work the internal temperatures in— followed by an abrupt decrease in skin tem- creased sharply, peratures. The responses were partially reversed upon onset of rest. The least active skin site (head) and more active site (calf) were most different from any intervening skin temperature site. These findings indicate that during hyper- with small heat losses, the skin temperature direct— thermia, ly over active muscles are inversely related to temperatures of the active muscles. It is hypothesized that the observed responses reflect changes in local blood flow. Partitional calorimetry showed that radiative and respiratory evaporative heat losses changed little with vary- ing air velocity. Convective heat loss was directly related to but non—linear with air velocity. Tolerance time was extended as much as 93 per cent by increasing air velocity up to 1000 feet per minute. Circulatory instability was observed as the most prominent response when tolerance to acute heat stress was Adolph Richard Dasler exceeded. Circulatory failure was indicated by both subjec- tive and objective observations. Under the specific condi- tions of this study, the upper limit of ”safe” tolerance can be defined as body temperature not exceeding 390C, heart rate not exceeding 180 beats per minute, and/or blood pres- sure not less than 90/40 mm Hg. HEAT STRESS AND STRAIN IN MEN WEARING IMPERMEABLE CLOTHING BY Adolph Richard Dasler A THESIS Submitted to »Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Physiology 1966 DEDICATED TO My wife, Louise for continued faith, support, tolerance and encouragement ii ACKNOWLEDGMENTS The author wishes to eXpress sincere appreciation to Dr. E. P. Reineke, Professor of Physiology, Michigan State University, and Chairman of his guidance committee, for untiring assistance and guidance throughout the course of his studies and this research. Sincere appreciation is also given to Dr. W. D. Collings, Dr. P. O. Fromm and Dr. Olaf Mickelson for their guidance and encouragement. Special acknowledgment is eXpressed to Dr. David Minard, Chairman of the Department of Occupational Health, University of Pittsburgh, for making it possible through numerous opportunities, valuable training and continued sup- port to develop and advance the author's interests and desires in thermal stress physiology. The initial eXperi— mental guidelines which led to this study were the product of Dr. Minard's direction as principal investigator for the previous phase of this research. In addition, Dr. Minard's participation as a member of the guidance committee is grate- fully appreciated. Dr. A. C. Burton, Professor of Biophysics, Faculty of Medicine, University of Western Ontario, London, Canada, is gratefully acknowledged for his critical review and iii Opinions regarding the internal and skin temperature data, validity of mean body temperature equations and the Thermal Circulation Index. Dr. W. E. COOper, Department of Zoology, Michigan State University is acknowledged for his guidance of the author in application of detailed statistical analyses of the voluminous data on individual skin temperatures. Sincere appreciation is given to Miss B. J. Brace, artist and technician in the Department of Physiology, Michigan State University, for her outstanding final prepara- tion of Figs. 1, 4, 7, 8, 10 and 11, and 15 through 22. .Acknowledgments are given to the Naval Medical Research Institute, National Naval Medical Center, Bethesda, Maryland, for providing facilities, materials and technical assistance. Individual thanks are eXpressed to HMC R. L. O'Brien, HM2 W. K. Mitchell and HM2 R. J. Lachapelle for their able technical assistance. HM2 Mitchell and HM2 Lachapelle are deserving of commendation as extremely cooper- ative volunteer test subjects along with HMC J. A. Gerrior, HMC F. Radcliff, HM2 J..K. Joyce and HM3 J. D. Parkinson. Special commendation is due Dr. R. A. Anderson for his per— sonal and professional cooPeration that made it possible to successfully complete the very hazardous eXperiments on tolerance to excessive heat. iv Appreciation is given to Mrs. T. P. Robinson, Head Librarian of the Medical Reference Library, Naval Medical Research Institute, for her continued valuable assistance in obtaining rare publications and government research reports that were definite assets in this study. Thanks are extended to Mr. T. J. Connor and Mr. M. Eicher, Head of the Medical Instrumentation Laboratory, Naval Medical Research Institute, for the development and maintenance of highly specialized electronics devices required in monitoring the human test subjects. The prompt technical assistance of Mr. M. H. Rhodes (Supervisor), HMC R. E. Wilder, HMC L. Lewis, Jr., HMC E. W. Maddox, HMl R. B. Beveridge, HM2 D. W. Calhoun and HM3 K. J. Smith with all of the photographic work in this study is gratefully appreciated. The medical illustration skills of HMl J. S. Vitek and DM2 J. P. Kazyaka in preparing a number of the final illustrations and teaching the author techniques of illustration were appreciated. The Surgeon General of the Navy and the Director of the Medical Service Corps Division, Bureau of Medicine and Surgery, Department of the Navy, are most gratefully acknowl- edged for providing the author with Bureau of Medicine and Surgery educational assignment to complete his studies and research reported herein. This investigation was financially supported by the Department of the Navy Bureau of Ships, under the direction of the Bureau of Medicine and Surgery Assistant Chief for Research and Military Medical Specialties as Project MR OOS.Ol-OOOl.O3. vi TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . . . . . . . . . . . . l HISTORICAL BACKGROUND . . . . . . . . . . . . . . . . 3 MATERIALS AND METHODS . . . . . . . . . . . . . . . . 15 Subjects . . . . . . . . . . . . . . . . . . . . 15 Temperature Measurements . . . . . . . . . . . . 16 Heart Rate and Electrocardiogram . . . . . . . . 24 Blood Pressure . . . . . . . . . . . . . . . . . 27 Metabolic Rate . . . . . . . . . . . . . . . . . 27 Weight Loss . . . . . . . . . . . . . . . . . . . 28 Bacteriological—Chemical Warfare Protective ClOthj—ng O O O C C O O O O O D O O O O O O O O 28 Experimental Variables . . . . . . . . . . . . . 32 Partitional Calorimetry . . . . . . . . . . . . . 34 Cardiac Output . . . . . . . . . . . . . . . . . 37 Physical Analysis of Heat Flow . . . . . . . . . 38 Statistics 0 O O O C O O O O O O O O O O 0 O O O 39 Mental Performance . . . . . . . . . . . . . . . 40 RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . 42 Exceeding Heat Tolerance . . . . . . . . . . . . 42 Internal Body and Skin Temperatures . . . . . . . 53 Partitional Calorimetry . . . . . . . . . . . . . 79 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . 91 REFERENCES . . . . . . . . . . . . . . . . . . . . . . 94 APPENDICES O O O O O O O O O O O O O O O O O O O O O 0 lo 2 vii LIST OF TABLES Description of Test Subjects . . . . . . Environmental DB and WB Combinations . . Air Velocity in Wind Tunnel . . . . . . Cycling of Individual Skin Temperatures During Work and Rest Periods . . . . . Two-Way Analysis of Variance with Replication and Equal Sample Sizes (with Single Degrees of Freedom and Orthogonal Distribution) Thermal Circulation Index . . . . . . . Effects of Air Velocity on Tolerance Time viii O Page 17 32 33 6O 61 74 81 10. 11. 12. 13. LIST OF FIGURES Tympanic Membrane Thermocouple . . . . . Tympanic Membrane Thermocouple (enlarged 5.7 times) . . . . . . . . . . . . . . Physiological Instrumentation of Thermal Stress Subjects (Human) . . . . . . . Thermocouple Wiring Scheme . . . . . . . Impregnated, Permeable, Vesicant Gas Protective Garment . . . . . . . . . . Impermeable, Unventilated, Protective Garment O O O O O O O C O O O O O O . Blood Pressure, Heart Rate and Cardiac Output When Tolerance Was Exceeded . . Blood Pressure, Heart Rate and Cardiac Output When Tolerance Was Exceeded . . Internal and Skin Temperature and Heart Rate During Work and Rest Activity . . Skin Temperatures During Work and Rest Activity . . . . . . . . . . . . . . . Skin Temperatures During Work and Rest ACtiVj—ty O O O O O O O O C O O 0 O O 0 New Multiple Range Test Applied to Ten Individual Skin Temperatures From 6 Subjects . . . . . . . . . . . . . . . Breakdown of Work Periods From New Multiple Range Test for the Ten Individual Skin Temperatures . . . . . . . . . . . . . ix 0 Page 19 20 22 23 29 31 44 46 54 58 59 62 63 Figure Page 14. Breakdown of Rest Periods From New Multiple Range Test for the Ten Individual Skin Temperatures . . . . . . . . . . . . . . . . 64 15. Thermal Circulation Index and Hypothetical BlOOd Flow Shift 0 O O O O O O O I O O O O O 78 16. Partitional Calorimetry (DB 750E, WB 650F, Work-Rest Activity, Air Velocity<:50 fpm). . 83 17. Partitional Calorimetry (DB 75°F, we 65°F, Work-Rest Activity, Air Velocity 250 fpm). . 84 18. Partitional Calorimetry (DB 75°F, WB 650E, Work—Rest Activity, Air Velocity 1000 fpm) . 85 19. Partitional Calorimetry (DB 85°F, WB 75°F, Work—Rest Activity, Air Velocity 1000 fpm) . 86 20. Partitional Calorimetry (DB 90°F, we 80°F, Standing, Air Velocity <50 fpm) . . . . . 87 21. Partitional Calorimetry (DB 90°F, we 80°F, Standing, Air Velocity 1000 fpm) . . . . . . 88 22. Heat Loss by Radiation and Convection vs. . . . . . 89 O O 0 ° 0 0 Air Velocity . . . . . LIST OF APPENDICES Appendix Page I. SUMMARY OF INTERNAL BODY AND MEAN SKIN TEMPERATURES AND HEART RATES OF THE SUBJECTS INDICATED IN TABLE 7 . . . . . . 103 II. STIMULUS PRESENTATION DEVICE . . . . . . . 114 III. CONCLUSIONS FROM: ACCURACY OF METER READING UNDER THERMAL STRESS INDUCED BY WEARING IMPERMEABLE PROTECTIVE SUIT O O O D O O O O O O O O 0 12.1- xi INTRODUC TION One rarely considers the physiological consequences of wearing clothing. It is generally understood that the basic reason for use of clothing is that of protection. However, in thinking of protection, thoughts lean toward defending the body from unwanted external forces. Rarely is thought given to the harmful effects of wearing clothing as a barrier to the liberation of metabolic heat. Therefore, when protection is emphasized, one should consider the external and internal factors that contribute to man's well- being and function. In this light, the more important fac- tor for consideration is the maintenance of body heat equi— librium. The current status of man's reaction to upper levels of heat stress is summed up by Macpherson (1960) as follows: It seems clear that none of the methods avail- able at the present time for predicting the proba- bility of endurance of extremely warm conditions is satisfactory. The only way to determine with confidence how men will react is to expose them to the conditions in question and see what happens. The purpose of this study was to realistically deter- mine the physiological tolerance of U.S. Navy personnel to severe heat stress while wearing unventilated, impermeable, full-body clothing. The availability of this clothing provided the unique opportunity to study the avenues of heat loss and tolerance to heat stress when evaporative cooling from the skin was completely blocked. Throughout the course of this dissertation first consideration was given to the physiological significance of heat stress and heat strain in men forced to dissipate excess heat like non-sweating animals. Principal attention was given to the study of deep body and skin temperatures, parti- tional calorimetry, cardiovascular reSponses and the upper limit of physiological tolerance under the given conditions. Mental performance was evaluated and was included as an appendix. HIS TORICAL BACKGROUND Medical sciences have long recognized the serious problems of heat stress. Fiske (1913), Wakefield and Hall (1927), Hall and Wakefield (1927) and Whayne (1951) have described a number of situations where heat impaired man as a functional unit. Wakefield and Hall (1927) made note of the effects of heat described in the Bible. There seems to be little question that the more stressful situations deal with industrial and military operations. Unfortunately, military settings frequently demand more prolonged exposures to wider extremes of wet— and dry-bulb temperatures than the usual civilian occupations. Further insight into the effects of heat stress may be obtained through the following selected examples cited by Minard and Copman (1963a) and Dasler-(1965): a) The notorious incident known as the Black Hole of Calcutta occurred in 1756. A recent detailed description of all factors related to the tragedy had been presented by Barber (1966). One hundred forty-six prisoners were forced to occupy the ex- tremely small prison space of Fort William, at eight o'clock the evening of June 20, 1756. This space b) C) measured 18 ft long by about 15 ft wide. "Only two holes, barricaded with iron bars, admitted air from the dark, vaulted arcade still red with the reflect- ed glow of the fires outside." By the time captives were released from the Black Hole, 10 hours follow- ing confinement, only 22 men and the sole woman were alive. Two hundred years later, in 1956, the tragedy of the Black Hole incident was repeated in Kosti town of the Sudan (Haseeb and Fayiz, 1958). Two hundred eighty-one prisoners were locked overnight in a closed ward, 63 ft long by 18 ft wide by 12.5 ft in height, which was intended for quartering 16 soldiers. The following morning 187 captives were found dead, many with pools of sweat on their depressed abdomens. Eleven of the 94 survivors were in shock; two of the 11 died on the way to the hospi- tal and five of the remaining nine died on the day of admission. In 1918 the ventilation of a fire room aboard the USS Kentucky broke down, resulting in 20 heat casu- alties among the fireroom watch (Hall and Wakefield, 1927). d) 6) More recently, during sea trials aboard the USS Des Moines in 1951, outside ventilation was secured to all Vital spaces in order to simulate nuclear- bacteriological-chemical warfare Operational pro- cedures (Yaglou and Minard, 1952; Minard, 1961). Fifteen minutes after ventilation was secured in a machinery room space, at cruising Speed where the thermal load was considerably less than at full or flank speed, three of the watch standers had to be removed because of their poor physical condition. The remainder of the crew became incapacitated and had to be removed within the next five to 15 minutes. A total of seven of the 12 man crew in the space had to be helped up the ladders and treated in the sick bay; and, A U.S. Marine Corps Division conducted an amphibious combat exercise on Mindoro Island, P.I., in the spring of 1962. Approximately 75 heat casualties, including one fatal heat stroke, were encountered by the Division. Although the incidence rate of heat casu— alties in the landing force was by no means inconsequential, the number was small com- pared to the estimated 300 rifle infantry- men rendered ineffective by the heat on the day the amphibious assault was launched. The effects of heat stress were particularly severe in the units which undertook a forced march of 13 miles to capture the air strip. Observers with the aggressor force state that in real combat these units would have been decimated by the well-accli- matized aggressor force which had been on Mindoro for approximately four weeks (Minard and O'Brien, 1964). This author has personally reviewed more than 560 publications; but, to avoid redundancy attention should be directed toward five comprehensive literature reviews perti- nent to factors involved in this study. Reference to other publications will be restricted to the clarification of specific points of concern requiring amplification beyond the review articles. J. D. Hardy (1961) examined more than 3000 refer- ences covering the period from 1885-1959. His final manu- script contained 566 citations, with principal attention to the great surge of literature since 1952. On the subject of heat, the following summary related to this dissertation appears valid: The control of internal body temperature is probably directed almost entirely from the cen- tral receptors although available evidence indi- cates that both the central and peripheral drives are required for maximal efforts in meeting the combined effects of high environmental tempera- ture and exercise. It appears that the physiologic threat of overheating is more serious than overcooling and the effort to protect against overheating of the body tissues is the major function of the physio- logic thermoregulator. Two months following Hardy's 1961 review article, C. von Euler published a review of slightly less than half the length of Hardy's. von Euler's work (1961) dealt with both the physiology and pharmacology of temperature regula— tion, but covered the literature from 1788 (A. Crawford and J. Hunter) through 1960. von Euler presented ". . . mainly those aspects of thermoregulation which seem to be of sig- nificance for the understanding of drug action on the body thermostat." However, neither the reviews of Hardy nor von Euler mentioned the work of Charles Blagden in 1775. Accord- ing to Blockley and Taylor (1948) Blagden experimented with men exposed to ambient temperatures ranging from 9OOF to 2600F. Supposedly Blagden's narrative contained notes on only scattered observations, and one cannot learn precisely the number and duration of exposures. However, Blagden did mention a few specific conditions of exposures to 2100F for three minutes, leOF for seven minutes, 26OOF for eight minutes and 2200F for 12 minutes. In addition, Blockley and Taylor (1948) have indicated that Blagden noted the protec- tive function of clothing, the relief that comes from sweat- ing, the blanket of cooler air which clings to the surface of the body, the heating effect of air movement, and the reduction in tolerable temperature with increased humidity. E. F. DuBois (1951) believed that very few accurate temperature measurements were made in man in 1740 and that the really important work began about 1850. This latter date coincides with the work of Claude Bernard. Bernard's outstanding Lecons sur ia chaleur animale, published in 1876, J— has been cited by numerous authors but none of Bernard's publications have been cited in Hardy's review. According to DuBois, Bernard and others of his time did not appreciate the significance of temperature gradients. This belief is difficult to accept in its entirety since Bernard pointed out the significance of the close arrangement of arteries and veins: therefore, helping to form the basis of what is now termed "countercurrent heat exchange.” For the purpose of clarity, the following quotation is offered from Claude Bernard (1876): Le point important des études que nous avons faites jusqu'ici, et sur leguel on ne saurait trop s'appesantir, c'est la connaissance de l'antagonisme entre les deux portions du systeme veineux: l'une étant une source d'échauffement, l'authre une source de refroidissement. Cet antagonisme dans l'état normal est constamment réglé par l'harmonisateur de toutes les fonctions, par le systeme nerveux, l‘agent de la conservation de la chaleur animale, du maintien de l'équilibre indispensable au fonc- tionnement de l'organisme.‘ There are two other outstanding reviews that are pertinent to this study. Minard and Copman (1963b) evaluated current developments in the determination of body temperature at rest and during work, and discussed opposing opinions relative to the causal mechanisms and consequence of hyper- thermia during work. Their experimental evidence, relative to thermal gradients in man at rest and during transient heat storage, indicated that body temperature measured in regions which promptly respond to changing heat loads should be considered a more valid index of heat tolerance than mean body temperature. Two extensions of this review concerning elevation of body temperature in health are found in the work of Copman, Minard and Dasler (1963) and Minard, Copman and Dasler (1964). The second review that is of importance for this study (Minard and Copman 1963a) cited pertinent reviews deal— ing with clinical and experimental aspects of fever and in- duced hyperthermia. A detailed discussion of clinical dis- orders of thermoregulation was presented emphasizing heat stroke, including the pathogenesis, clinical course, treat- ment, and pathology. They discussed the molecular basis for thermal injury and concluded that cell death which occurs during uncontrolled hyperthermia, 106OF or greater, may be described as a time—temperature relationship which may eventually result in irreversible destruction of essential cell proteins. The rarely cited work of Benedict and Parmenter (1928) indicates that up to about the mid—1920's studies on the physiology of heat emphasized internal body temperature. (According to these authors little prior attention had been given to skin temperature. Through a series of experiments, using female test subjects, they observed that metabolism increased "more than five or six hundred per cent" as a result of five minutes of muscular activity. Such a response is not surprising in itself; however, they also observed a distinctly lower skin temperature at the same time. It was 10 rationalized that the lowered skin temperature resulted from the pumping action of clothing, causing an increase in evaporation from the skin. Upon repeating the eXperiments with a nude test subject they found a similar decrease in skin temperature and an increased metabolism during work. This led Benedict and Parmenter to hypothesize that upon onset of work there may be peripheral vasoconstriction, resulting in a temporary transport of blood from the periph- ery to the muscles. Burton (1948) disagreed with this hypothesis since sweating and evaporative cooling had not been ruled out, even in the nude state. The assumption of evaporative cooling which Burton assigned to the response of decreased skin temperature dur- ing work has been held by the majority of researchers in the field of temperature regulation until recently. Robinson (1965) presented evidence from man that skin and saphenous vein temperatures decreased during work, which he attributed to heat loss by increased evaporation and convection and decreased peripheral blood flow through possible increase of cutaneous vasoconstriction. Close examination of his data indicates that upon onset of work there are concurrent rises in rectal, femoral vein and gastrocnemius muscle tempera— tures. In view of recent findings presented by Dasler and Reineke (1965) and Dasler and Minard (1966a, 1966b) further consideration of the work by Benedict and Parmenter and Robinson will be treated in the discussion section of this 11 dissertation. In addition, since there have not been any direct measurements of peripheral and muscle blood flow in man under the given eXperimental conditions, the literature review by Uvnés (1960) will lend support to an interpreta- tion of this problem. To this point, little has been said regarding the balance of heat production and heat loss. The ability of the homeothermic organism to maintain this balance has been recognized since the late 1770's. Crawford (1788) found that the metabolic rate of guinea pig was considerably greater in a cold environment than in a warm one. Greater heat production was obtained by wetting the fur, due to a greater loss of heat by evaporation. Bergmann (1845) demon- strated the importance of regulated heat dissipation to balance changes in heat production. .Adams (1959) described, in first order terms, the interactions between the homeotherm and its environment via avenues of thermal exchange. His treatment of the litera- ture serves as an elementary guide and reference source on this topic. However, to gain a better understanding of the factors involved, the works of Gagge (1936), Winslow, Herrington and Gagge (1936a, 1936b, 1937, 1938), Gagge, Winslow and Herrington (1938), and Winslow, Gagge and Herrington (1940) were carefully studied. In addition, the more recent works of Hertig and Belding (1963) and McDowell .2E,§l. (1961) were found very valuable. These latter 12 publications provide more workable first order approximation equations for radiation, convection and respiratory heat loss. A literature review on heat transfer and the influ— ence of man's clothing was published by Mortensen (1957). He emphasized the "critical studies? of heat transfer from nude and clothed men and the mechanism of heat transfer through fabrics. Mortensen's four section publication described detailed physical analysis of heat transfer, spe- cific physiological experimentation, fibers and fabrics, user requirements and protection from special hazards. Mortensen's work is not fitting for the purposes of this dissertation, in that he did not discuss the physical and physiological problems associated with impermeable garments. Even though government reports are frequently lim— ited in circulation, it was possible to locate eight reports dealing with heat stress in men wearing semipermeable and/or impermeable clothing. The reports of Clanton (1953) and Frankel _£‘ai. (1953) dealt primarily with semipermeable clothing. Hall (1952), Craig, Frankel and Blevins (1952) and Garren _E.al. (1953) were concerned with semipermeable and impermeable garments. Craig (1950a) and Robinson, Marzulli and McFadden (1950) investigated impermeable cloth— ing and the benefits of ventilating the garments. Also Craig (1950b) observed men wearing a polyvinyl alcohol suit Without internal ventilation, which is interpreted to mean 13 an impermeable, unventilated garment. Chronogically, the following summary describes the pertinent findings of these military reports: a) b) d) The physiological problem posed by impermeable cloth- ing is the blockade of one of the main avenues of heat loss from the body. Therefore, at ambient tem- peratures above body temperature the primary avenue of heat loss, namely evaporation from the skin, is of little or no value. Physiological strain was determined by: increases in heart rate, rectal temperature (measured by clinical thermometer before and at the end of each exposure), and rates of sweating (determined from nude weights before and after exposure). Development and subsequent modifications of Craig's formula (1950a) as an index of heat strain; in which terminal heart rate, rise in rectal temperature, and sweat production are combined into a single number; and, An attempt was made to partition heat losses, although radiation, convection and conduction were not separated. Also evaporation was characterized by a proposed conductance term. 14 Because of the paucity of available information on human responses to thermal stress, when complete coverage with impermeable, unventilated clothing is required, the following study will show that the consequences of wearing such clothing are more complex than previously believed. Within the limits of the given experimental design, the physical and physiological significance of hyperthermic responses in man were examined. The results will be inte— grated with those of earlier reports in the discussion section. MATERIALS AND METHODS Some of the general materials and methods were described in previous works by COpman, Minard and Dasler (1963), and Minard, Copman and Dasler (1964, 1966). Also, a portion of the procedure was given in recent presentations by Dasler and Reineke (1965) and Dasler and Minard (1966). However, for the purpose of continuity, completeness and clarity, a description of the experimental approach will be given here. Appropriate modifications of the techniques that are specific to this study will be integrated with the previously published information. Subjects Navy personnel, assigned duties as laboratory tech- nicians or scientific observers, served as thermal stress test subjects. All of these personnel were volunteers, physically fit, and were familiar with the experimental pro- cedures. No special acclimatizing methods were used, but each subject was usually eXposed to heat for 12 or 18 hours each week. No alcoholic beverages were permitted after the evening meal prior to use as a test subject. Diets were not altered in any manner other than restriction to a light breakfast and no excess fluid intake the morning of the test. 15 16 No fluid or food was permitted during confinement in the impermeable suit. Each subject received an abbreviated physical exam- ination upon arrival at the laboratory. Routine hematology studies included: red, white and differential cell counts, and micro-hematocrit. Routine urinalysis included volume, Specific gravity, pH, color, appearance, ketone bodies, albumin and microscopic examination. Extreme care was taken that the test subject for the day presented no evidence of recently past or present upper respiratory infection, fatigue, or any other symptoms which might interfere with the experiment or precipitate an incapacitating illness. Table 1 indicates the age, weight, height and sur- face area of the test subjects. The code letter assigned to a given subject has been used to identify the man in an eXperimental condition, as seen in the 10 figures of Appendix I. Surface area was determined from the DuBois body surface chart (DuBois, 1927). Temperature Measurements Rectal temperature (tr) was measured by a copper- constantan thermocouple embedded in polyethylene tubing and sealed in a copper tip that was attached to a number 16 French catheter. The rectal probe was inserted to a depth of 10 cm. beyond the internal sphincter. 17 me.H v¢.hba mmo.mh mm.hm ommuo>< em.a o oma m5.vh mm bxm Hm.H o.¢ba mh.mo mm man oo.m m.HnH om.>m pm me mw.a o.onH hb.mb mm can Hm.H o.w>H NH.¢> on sex mo.m m.mmH oa.m> mm 2x3 em.H o.nha w¢.mh mm gum NH.N m.mmH om.hm Hm amt ANEV A.Eov “.mxv A.mu>v mamaufisH Imam ooomuam .um .pz om< uuonnsm mBUmeDm BmflB ho ZOHBQHMUme H Ema/NH. 18 Tympanic membrane temperature (te) was measured with a thermocouple in the form of a loop which was held in place by a polyethylene brush. Fig. 1 shows the construction of a tympanic membrane thermocouple, and Fig. 2 is a photograph of a tympanic membrane thermocouple magnified 5.7 times. This modification of Benzinger and Taylor's (1963) design was found to be well tolerated and no functional differences were observed between their sensor and that manufactured in the Thermal Stress laboratory. The tympanic membrane thermocouple and external auditory meatus were provided additional thermal insulation by a Sponge rubber cup—shaped insert from an ear defender (MSA Noisefoe Mark II), which covered the pinna. In earlier experiments the tympanic membrane thermo- couple 100p was adjusted so that it was in direct contact with the tympanum; however, in later eXperiments the loop was adjusted first to lightly contact the tympanum and then gently withdrawn approximately 1 mm. This latter procedure provided greater comfort for the subject and did not appear to alter the temperature measurement. Cooper, Cranston and Snell (1964) and Cooper (1965) have confirmed this observa- tion. Esophageal temperature (to) was measured with a C0pper-constantan thermocouple embedded in the tOp of a polyethylene tube. The thermojunction was inserted orally until it was located 43 cm. from the incisors. 19 .6253... 0.2,: 02....mwmz. mmcmmm mz<1hmm3>qom It; awhdoo mqmaoo mm< mwo_4n_m oz< awn—.3 mmxhw>40m em: 20mm Imamm mzu4>th>qoa 6.0.0 :83 czfibh mzm4>1km>qoa Add ammo; 0253... mzmnizhufiam MJQDOOOSKMIF wzqmmimi 0_2._. <(GJLDCJHJU.Q> I: Figure l 20 F igure ' 7 2 o Tympanic membrane thermocouple (enlarged 5 t]. me ) a S . 21 In all eXperiments, skin temperature was measured at 10 points by thermocouple junctions coated with polyurethane and attached to fine mesh copper screen. The screens were held in close contact with the skin using Sanborn ECG straps; however, blood flow was not restricted. Each point was recorded individually, and the mean skin temperature was recorded as the unweighted mean of the 10 junctions. The method of recording the unweighted mean skin temperature followed a modification of the procedure of Teichner (1958). Figure 3 illustrates the positions of the thermocouples employed in these experiments. The simplified thermocouple wiring scheme, Fig. 4, is an example of how a complete thermocouple lOOp was related to apprOpriate components of the temperature measure- ment and recording equipment. Reference junctions were sit- uated in a stirred water bath accurately regulated at 39.000C (102.20F). Bath controls created a temperature cycle of ,: 0.010C (: 0.018OF) which was dampened out by positioning the reference junctions inside a 4-1iter Erlenmeyer flask resting at the bottom of the stirred bath. The thermoelectric emf's from each of the three internal body thermocouples were amplified 100 times by separate Leeds and Northrup stabilized DC microvolt pream- plifiers. In turn, the voltage was recorded by a standard lZ-channel Leeds and Northrup DC millivolt recording poten- tiometer, having a 24.2 cm. strip chart with a normal 22 0332.05 coaoEocoEoEgzom 3m; COEquOm 3w; «0.5:: mmzmmwma 000.6 . .231 309303 2.0562: 0:.an»... qun—Douozmwz... 442mmhz. O .oou :00 .13.: .23 :25 Bee. 5:534 .85 0 tom 22.. o 385 o 0 Ba... 0 86:80:55 2% o Boostgoeoemoama oom o o AcoEalv mPUMomDm mmmmkm 44.2”..th v.0 ZO_._.<._.ZwZDm._.mZ_ JIQ Figure 3 23 mmomooum l I... .538 area 20:622. mice .15... wozwmwumm 5024...: 0. 8.8.8 Sou Md booodn. kg «5 D 29822. \“ ozazmm “ 503mm . a I I l Rflzlfimeumolc rt km mueaoo 1.50 :53 e 7 5.. 8 mucsazfimo .. 5965.: 35455.» mZmrom ozizs mnenooozmmrs Figure 4 24 recording range of 36.60 to 39.000C (97.9 to 102.20F). Appropriate adjustments of the preamplifiers lowered the range to 35.4OOC (93.9OF), and by flipping a switch in the recording potentiometer the maximum range was extended to 40.200C (104.7OF). The individual skin temperatures were recorded, after intermediate amplification with a Leeds and Northrup stabilized DC microvolt preamplifier, by a lZ-chan- nel Brown (Minneapolis—Honeywell) DC millivolt recording potentiometer. The Brown recorder had a 27.9 cm strip chart recording range of 13.80 to 4l.80°c (56.8 to 107.2°F). The emf's of the individual skin thermocouples were also con- nected in series, passed through a resistance box, and recorded as the mean skin temperature by the Leeds and Northrup recorder. Heart Rate (HR) and Electro- gardiogram (ECG) Electrocardiograms were obtained by what is called "radioelectrocardiography," as described by Bellet, Deliy- iannia and Eliakim (1961) and Bellet g; 21- (1962). The radioelectrocardiograph system used was that of the Tele— medics RKG 100A telemetry system and a Sanborn electrocardio- graph, with Waters Model C224 or C225 (modified) cardiota- chometers for heart rate. The Telemedics RKG 100A system consists of: a pock— et-sized 5.5 ounce mercury battery-Operated radio transmit- ter, with a modulated frequency of 148.65 megacycles, i 10 25 kilocycles bandwidth and 2 to 3 milliwatts output; a 17 lb. compact portable receiver, with a 3 ft collapsible antenna, channel selector, skin resistance meter, and one millivolt square wave calibration; specially designed disposable snap top electrodes (Telectrodes); high conductance electrode paste; 48 inch patient cable lead; and, muscle noise filter. Because the problem of profuse sweating and high salt concentrations within the suit was encountered, it was necessary to depart from the usual procedure in utilizing this telemetry system. Following location of the right and left fifth thoracic interspace, forward of the mid—axillary line, a piece of electrical tape was applied to the pre- ferred electrode site. Tincture of benzoin was applied around the tape, forming a solid circle four inches in diameter. When the tincture of benzoin dried sufficiently the tape was removed and the underlying skin was vigorously abraded with Telectrode jelly. The Telectrodes were applied to the abraded areas and the cable lead from the subject was attached to the electrodes. Then a mole skin patch, nearly covering the benzoin covered area, was applied after leaving a small snake—like portion of cable as a strain relief under the covering. .As skin resistance plays an important role in obtain— ing uniformly good ECG's, the resistance was checked on the receiver's resistance meter. Only rare situations arose Where insufficient abrading had been obtained; those few 26 occurrences required repetition of the electrode application procedure. With the subject cable lead plugged into the RKG 100A transmitter, the telemetered ECG signal was picked up by the receiver and relayed via the muscle noise filter to a Sanborn electrocardiograph and into a Waters Model C224 Cardiotachometer, or a Model 225 (modified) cardiotachometer that served as a backup unit. The output of the cardiota- chometer was fed into the Leeds and Northrup DC microvolt strip chart recording potentiometer. In turn, heart rate was obtained continuously and ECG was taken periodically. Having prevented short-circuiting of the electrodes under the impermeable clothing, it was also necessary to prevent sweat and its electrolytes from shorting the-trans- mitter-subject cable lead junction. The transmitter and all excess cable were tightly enclosed in a saran-type bag. The waterproofing was highly efficient, even with the transmitter inserted in an inner pocket of the eXperimental clothing. .Attention is called to Fig. 3. The ECG bipolar lead II was deleted from these eXperiments when it was proven that the transthoracic lead of the RKG unit provided excel- lent ECG patterns, without the problems associated with clumsy cables and connectors interfering with the subject and observers responsibilities. 27 Blood Pressure Indirect blood pressure measurements were determined by the standard auscultatory method. The brachial artery was located and a bracelet-type stethoscope receiver attached to the skin. Care was taken so that the receiver would not slip from its position while at the same time it would not impede blood flow through the arm. A sphygmomanometer cuff was wrapped around the arm, just above the stethosc0pe receiver, and attached in a similar manner. It became com- mon practice to attach a strip of adhesive tape from the outer portion of the cuff to the subject's shoulder. The tubes leading from the stethoscope receiver and sphygmoma- nometer cuff were extended to approximately 18 inches in length so the attachments could be facilitated outside of the suit, at the wrist. Both systolic and diastolic blood pressure determi- nations were made pre-exposure, normally at one hour inter— vals during the experiment, and post-exposure. When it was suspected that heat tolerance was being reached, or a sub- ject noted unusual physical symptoms of distress, blood pressure determinations were taken at 10 and then five min- ute intervals. Mgtabolic Rate (MR) Metabolic rate was estimated by indirect calorimetry. Samples of the subject's expired air were collected in a Tissot spirometer of 150 liter capacity for timed periods of 28 three or five minutes. The oxygen concentration of the inspired and expired air was determined using a Beckman E-2 oxygen analyzer. Gas volumes were corrected to dry STP using the 21" X 7" chart prepared by Robert C. Darling (Consolazio, Johnson and Pecora, 1963). Caloric production was computed using the Weir formula (Weir, 1949). Weight Loss Subjects, wearing only undershorts, were weighed using a Buffalo Model 1100 beam-balance scale, specially constructed for use with human subjects and accurate to :_5 gm. Two weights were taken for each experiment, before and after. Bacteriological-Chemical Warfare (BU/CW) Protective Clothing The BW/CW protective clothing used in this study is divided into four basic subdivisions: a) A special impregnated, two—piece, vesicant gas pro- tective garment, with impregnated socks. Fig. 5 illustrates the impregnated clothing unit. In general, the impregnated clothing is effec- tive against chemical warfare agents of a vapor or fine aerosol nature (Fielding, 1964). Because large aerosol particles or drOplets can partially pene- trate the fabric, an impermeable outer garment pro- vides additional protection. 29 Figure 5. Impregnated, permeable, vesicant gas protective garment. b) d) 30 The impermeable, unventilated, two-piece outer assembly, which is of high—tear~strength double- coated synthetic fiber fabric having good melt-and- flame resistance and a smooth waterproof outer sur- face. Fig. 6 illustrates the tight closures at the ankles, wrists, neck and face. Press (1959) briefly described this experimental impermeable garment when he pointed out the chal- lenges for textile research. Heavy rubber gloves and boots; and, The ND MK V protective mask which is intended to provide complete protection to the face, eyes and respiratory system. A general description of the protective mask has been given by Fielding (1964). Preliminary investigations in the Thermal Stress Laboratory indicated extreme respiratory resistance with the "standard” filter canisters. Upon our request, the Protective Chemistry Branch, Naval Research Laboratory, developed "low resistance" canisters which were far superior in helping to alleviate discomforts from the clothing and heat. ' ' ' ' 'n all of "Low reSistance” canisters were utilized 1 the eXperiments reported herein. Figure 6. Impermeable, 31 ' I ( (’4' I" I J; ”’ unventilated, protective garment. 32 All of the above protective clothing components were worn simultaneously by all test subjects in the experiments to form a complete impermeable, unventilated protective assembly. Experimental Variables Ten eXperimental conditions were investigated by use of the preceding methods and an attempt was made to measure decrement of mental performance. The dry-bulb (DB) and wet-bulb (WB) temperatures of the environmental chamber air were regulated at': 0.5600 (: 1.00F) to obtain the combinations of temperatures, indi- cated in Table 2. The apprOpriate DB and WB settings pro- vided the approximate vapor pressures (VP) and relative humidities (RH) that were external to the impermeable Cloth- ing. TABLE 2 ENVIRONMENTAL DB AND WB COMBINATIONS DB WB VP RH (0C) (CF) (CG) (0F) (mm Hg) (%) 18.3 65 12.2 54 7.5 48 23.9 75 18.3 65 13.0 59 29.4 85 23.9 75 19.5 63 32.2 90 26.6 80 23.5 65 33 Air velocity over the external surface of the suit was varied under certain conditions by use of a wind tunnel. A special wind tunnel, measuring 20 ft long by 5 ft wide and 7 ft 6 inches high, was constructed of stainless steel angle irons and covered with eXpanded stainless steel with a tight outer layer of clear, heavy, gauge polyethylene sheeting. The front end of the wind tunnel was completely Open while the back end was enclosed by a partition that housed six, high velocity, waterproofed, exhaust fans. The maximum air velocity created in this tunnel was approximately 6.6 m/sec (1,300 ft/min or 12.8 knots). By operating selected fans, and apprOpriate adjustments of the exhaust ports, the rela- tively constant velocities shown in Table 3 were employed. Winslow Herrington and Gagge (1936b) showed the natural air velocity over man due to a "chimney effect," to be approx— imately 0.24 m/sec (47 ft/min or 0.46 knots) in a still room. TABLE 3 AIR VELOCITY IN WIND TUNNEL m/sec ft/min knots ozv mH.o H vm.wm ma.o H a¢.wm mH.o mm.om w~.o mm.mm om.o H mv.¢m hm.o H 0H.mm noaza Houao h Awwnomun mmwuan .2. Hm.o H 0H.bm mm.o H oo.hm Nm.o no.0m mN.o mp.mm Om.o H h¢.¢m m¢.o H o>.mm mamoam o Accumusm avmuovv hm.o H om.wm Hm.o H vw.wm Hv.o Hm.om mm.o mm.mm H¢.o H mm.¢m h~.o H hv.mm can: m Afimuoo mSEwmmfiumH .zv mv.o H om.bm H¢.o H mm.wm vm.o hh.mm mm.o Hm.mm mm.o H oo.Vm ma.o H ho.mm xomm q Auonms mfiamuouuom .zv mm.o H cm.hm b~.o H om.bm m~.o 55.0m mm.o mo.wm Nm.o H vH.mm vm.o H mo.Vm Umwnu m ”REAR nchAV wm.o H 0m.hm mm.o H on.om 0H.o ma.wm Hw.o mm.mm mwoo H ma.¢m Hw.o H n¢.mm coeocnc N Avocauonsuoum Hmuwmwooo .uxmv Hm.o H mb.bm mm.o H mo.hm mv.o H Nh.wm ov.o H ¢0.0m ov.o H ¢m.mm mv.o H Hm.vm cams H umum xuos uuom xuo3 uaom xuoz cowuwuom .oz oumq manna: >uw>auo< Hwoau>£m can acofiaummxm we wanna >Humm ouam Hauueouucm AmuOOnnsm o nah uuouuu nunvcuum H ncmozv AUOV mocha: $5. 92 58... 85.8 3593339 .58 53333 any so 96996 aw mfimemb 61 Awoaumm uuou Sunmww can oofiuwm xuo3 zucm>mmv mummy CH mung u a .uofluom anon numflm can uofluom xuo3 nunsomv mummy ca «Anna: I z Aoofiuwm umou champ van coauom xuo3 ocoowmv mummy ca >auam I m coauom ummm u m noduom xuo3 u 3 Ho>OH goo. on» an annuawflcmfin afinmfim n «g. Ho>wH H00. 0:» an ucuowwwcmam >M0> a ct H0>0H goo. wnu um cofiuonuwucH unnowwwcmau 02 u a mm.o oom nouum chm.o mm.o mv coHuomuquH . . Amumq .OHOOHS .xaummv «tom AH 60 HA m mmuwm cfixm awe ctmm.mH 6H.mH H gm .m> 2m ec¢mo.nv~ Ho.m- A am am .m> mx «ccmv.Hv v~.mm A a: .m> 23 cc.mm.oo~ ~m.mm~ H a: 2: .m> m: cccm6.mo mm.vm H q.z.mm .u> g.z.mz . . mama .OHOOA: .aauom. «6 Ho nma mv m m A . c w H >uw>wuo< umwmIXHoz h mm :00: mo mousom AZOHBDmHmBmHQ A¢2000E9¢0 02¢ EOQMNMQ ho mflflmwfla NJDZHM EBH3V mmNHw NAAZCW QEUON 924 ZOHBtUHQmNM HBH3 HUZ‘HKd5 NO MHmMQ¢Z< M¢3I03B m mHHmdflu 62 666m umonu xomm mAOOHm gnaw amass coaooam awana uoom mamo Houao chcH «Add + 2m + ”my xaco avofiumm umwm H Illlllllllllllllllll- IIIIIIIIIIIIIIIIIHII 7. l wmmm umw mmwofim on an :wEo flags? smuna e £0 X m U m 094 Hflvfio HOCCH HOOh MHflU M 04 «AA3 + 23 + mzv kaco moofluwm xuoB wm 'I'II comm umogv xomm mmoowm ocmm coE°UQ< nwwnfi smash Hock «H00 uovao Honda "gm + A: + 2m + :3 + mm + u: nuoHuom HoucaeHuomxm wBUWhmDm @ SOME mmmbfiflflflfiiflfi ZHXM AdUGHbHQZH 2N8 OE QHHQQQC BmMB ”02¢“ NAQHBHSZ 3W2 63 umwzu Ummm mmmowm Xumm cwaoond Ocmm amasa Swan? 000m «HMO uouao umccH :35 9x33 l! m m 0 mm 0 an nmwnfi o o nmdga 6 mm A 28 x mm m E 6 m .330 :9: 22 u on 3:5 .38 2:5 zxuoz ‘ W Illll m0 m0 ammo on an cwEo awash smash m 00 U E u. 3.0 .mm x. m 0 m BAN Hfivflo HGGGH NH 0 v m mmmaflmMm—Zmfi ZHXW EDA—Hagan EH. fig “Oh Ewan. Egg mAmHBHDZ BNZ SOME. WQOHMNQ :03 mo Egm «keno MXHDS Figure 13 “Dwapofihczm- nnzflm—vhs ZHVnm \H/NDQHBhflZH anuvnh ”finrflu ”nevi Irmnw-IH. "a! 02 I‘V- uLvNAIhHINL‘EE Ivan-z ZPHVQLN Klan QR 1H Yhu.§1- uwaCO EUEUK IN. TIC no. V! 1:... U Z}. '- nVQ (Th Vii. 64 @mwm #owm ummsu cmfisa amass :wEovnd mQOUHm uoom vcwm Hmuso uwccH Mano ”>HCO Aumwm soggy amass xomm ummsu vmwm mmwuwm cams Amuse GOEOUQ< uoom HOCGH wamo «haco Sumwm I! amass smash mmwm ummzu Xumm ucmm amuse mmwowm CDEO©A¢ mamo MOGGH uoom mmmbfifimmmZmB ZHXW AdDQH>HQZH «haco mumwm. 2MB NEE mOh BMWB NOZdM HAAHBQDZ 3M2 20mm mQOHMWm 9mm“ ho ZZOQKdem Figure 14 65 An evaluation of the skin temperature data and sta- tistical analysis indicates: a) b) C) (3) According to the two-way analysis of variance, Table 5, there is a highly significant difference (p<:.OOl) between periods of work and rest, and very signif— icant difference (p‘<.OOl) between skin sites. Whether one considers either work or rest periods, the early phases are more different than the middle and late phases together. There was a greater dif- ference between the work periods than between the rest periods. There is a trend toward greater differences earlier than later in the experiments, this applies to both the work and rest activity. This supports the observations of Hardy and DuBois (1938) of a ten- dency toward convergence of various body tempera- tures at an elevated level. The skin site overlying the least active muscle group had the highest temperature. In this case, the external occipital protuberance region was hotter and logically the least active in the per— formance of required work; and, 66 e) The skin site overlying the most active muscle group had the lowest temperature. In this case, the skin overlying the M. gastrocnemius region was coolest and logically the area involved with greatest phys- ical activity. The internal body temperature responses, when the resting heat production was completely stored in the body, led to the conclusion that te and t0 represented the temper- ature of over 80 per cent of the body mass, whereas tr rep— resented less than 20 per cent (Minard and COpman, 1963b; COpman, Minard and Dasler, 1963; Minard, Copman and Dasler, 1964). There is evidence from a series of studies in hot- humid shipboard working spaces that the lag in tr' while wearing normal working clothes, must introduce errors in application of tr as an index of heat strain (Dasler, 1964). Furthermore, although the lag in tr is not pronounced in this study as in others cited above, the data from this study indicate that a lag in tr cannot be overlooked when attempting to determine heat storage (Dasler and Reineke, 1965). In turn, when man is not in a steady thermal state, three widely known equations for mean body temperature will be in error since they employ heavy weighting of tr' .A recent modification of the accepted equations introduced a correction term for transient changes in ts, but no changes 67 were taken into consideration for the response to tr' For the purposes of continuity, the four equations are as follows: a) tb = 0.65 tr + 0.35 tS (8) where; tb = mean body temperature tr = rectal temperature t8 = mean skin temperature. (Burton, 1935) b) tb = 0.8 tr + 0.2 tS (9) where; tb = mean body temperature tr = rectal temperature tS = mean skin temperature (Hardy and DuBois, 1938) c) tb = 0.67 tr + 0.33 ts (10) where; tb = mean body temperature tr = rectal temperature tS = mean skin temperature (Burton and Edholm, 1955) d) TB = 0.9 TR + (0.2 — flngs/dt) TS (11) where; TB mean body temperature (in transient states) T = rectal temperature 68 a reduction coefficient for transient 3 states de = change in skin temperature dt = change in time T8 = mean skin temperature (Stolwik and Hardy, 1963) Consideration of earlier studies and the present work has led to eight possible forms of an equation for mean body temperature in transient thermal states: a) tb = (a ' tr) (12) where; a = a constant b) tb = (b . te) (13) where; b = a constant c) tb = (c - to) (14) where; c = a constant d) tb = (d ~ tr) + [(1 — d) ts] (15) where; d and (l - d) are constants e) tb = (e - ta) + [(1 - e) ts] (16) where; e and (l - e) are constants 69 f) tb = (f . to) + [(1 - f) ts] (17) where; f and (l - f) are constants 9) tb = [(1 - g) to] + [(1 - (g+ m) te] + [(1 - (g + h + 1)) tr] (18) where; g, h and i are constants h) tb = [(1 - j) to] + [(1 - (3' +16) te] + [(1- (j +k+m)) tr] + [(1 - (j + k + m + n)) ts] (19) where; j, k, m and n are constants. In view of preceding evidence, equation (19) should provide a more meaningful approximation of mean body temperatures; however, as the purpose of known equations is to prOV1de an empirical guide with simplicity of computation and involve easily obtainable measurements, it is believed that equation (16) would provide a reasonable approximation of mean body temperature when the body of man is in a transient state. The need for an empirical equation to describe mean body temperature in a transient state is apparent. However, none of these general equations can be applied and validated until the correct constants have been determined with more experimental data. It was hoped that it would be possible 70 to derive many of the constants from data presented in this paper, but there were no direct calorimetry values available to determine the reliability of derived constants. There- fore the problem of a descriptive general equation for mean body temperature of man in a transient state remains unan- swered. Three factors should be considered in attempting to explain the decrease of skin temperatures during exercise and the increase during rest: a) Evaporation of sweat from the skin. b) Convective heat exchange; and, C) Reduced cutaneous blood flow° If evaporation occurred at the skin, the skin tem- perature would decrease and the water vapors would condense on the inner surface of the suit. In the process of conden- sation the suit would show a rise in temperature. To check for this phenomenon a duplicate set of thermocouples was attached on the outside of the suit, directly over the skin .'~ d site locations. The external surface of the suit was foun to be about 0.5 to 1.00C (0.9 to 1.80F) cooler than the body . ‘ S surface temperatures. During work the skin temperature ' f 11; fell and the external surface temperature of the suit e ' ' ased and conversely, during rest the skin temperatures incre ' ' 't on, DB the external surface of the suit increased. In addi 1 ' ' ' ' at and WB temperatures were determined 1n51de the clothing 71 about mid-thigh. The DB and WB temperatures were essen- tially the same. Therefore, these observations do not con- firm the likelihood of evaporation from the skin producing the dramatic changes in skin temperature. Convective heat exchange, in the condition shown in Figs. 10 and 11, was calculated to be between 15.3 and 23.6 KCal/mz/hr. As will be seen later, this quantity of convec- tive heat loss was very small. With such low convective heat loss it does not seem likely that convection would have produced the changes found for the skin temperatures. Changes in blood flow may have produced the observed responses. Four hypotheses were considered relative to the work-rest changes: a) Muscle temperature and blood flow increased and the skin blood flow decreased. In turn, the skin temper- ature would decrease until tissue conductance and/or sufficient blood flow returned to the skin. b) Muscle temperature and blood flow increased with no change in skin blood flow. This would produce an increase in skin temperature due to heat conductance through tissues between the muscle and skin. C) Muscle temperature increased and blood flow decreased and skin blood flow was either unchanged or increased. Such a situation would most likely result in an in- crease in skin temperature; and, 72 d) Muscle temperature increased, blood flow was un- changed and skin blood flow was decreased. One might eXpect a decrease in skin temperature until tissue conductance would transfer heat from the muscle to the skin. The results of the present work can be explained by either hypothesis 3 or g, or a combination of both. Hypoth- esis b and g are obviously untenable because they do not account for the results. These findings are in accord with Burton's (1965) discussion of blood flow in the human calf muscle, and also the report of COOper, Randall and Hertzman (1959). In the present study it was necessary to rely upon physical and physiological heat transfer principles to estimate changes in peripheral blood flow. Based upon Newton's law of cooling, Burton (1934) pointed out that the ratio of the internal thermal gradient ("core" to skin) to the external gradient (skin to air) may be used as an index of peripheral blood flow. Burton termed this ratio the "Thermal Circulation Index (TCI)." Sheard (1944), in comments on the TCI, referred to Poiseuille's law of flow of liquids through a tube of small diameter. .According to this law, the flow varies as the fourth power of the vessel diameter. Therefore, small changes in blood vessel size produce marked changes in blood 73 flow, which results in marked changes in heat exchange. Therefore, when skin, internal body and air temperatures are measured, one obtains an indirect estimate of peripheral blood flow. Equation (7) for TCI employs tr as the deep internal body temperature. Although it has been shown that tr lags behind responsive and more appropriate sites (e.g., deep esophageal) in a transient thermal state, no modifications of the TCI equation were made. It was believed that consis- tency of using data from the mid-point of the selected work and rest periods would serve the purpose in comparing adjacent rest-work and work-rest periods. Table 6 indicates the trends in TCI values for the head and calf sites, using pooled data from six test subjects. It is not possible to attempt a relationship between head and calf TCI values. This is due to the fact that the TCI depends upon the length of path (thickness of tissue) which the heat must traverse from the interior of the body to the chosen skin site, on the blood supply to the site in question and upon the amount of superficial fat at the site. However, the comparison of trends between different activity states for a given site indicates that TCI values generally are decreased during work following rest, and the values all increase in the rest phase following work. The only excep- tion to this pattern was found in the comparison between the first early rest period and the succeeding work period, 74- >uu>auo< Havauazm can vc02Huomxn mo ouonm Aoocauonauoum Hauumuuoo .uxuv noon ANUUOnQQm w you 0:00! vcdnbv CAHUBV XHDZH 20HB£ADUMHO Qtldnma 0 mHHdeu .vmoH .couusmv ousuauomsou «0 noun Hocuoucn we I «a II. ouauouomEbu uo noun Hacuouxu I ta I ma I HUB a ~.H+ o.~a . . o H... H .7. m.o+ m.o+ Huh. 6 FD? m.” 0 0 . a m a e o m n.m s.~ m.H n.H Hus uuom xHOS unom uuom xuoz uuum unom Xuoz uuom EGUH upon oavvfiz sauna xuw>auo¢ Hoowm>na can ucoaauOQXN mo ouunm Anawfiocoouunom .zv MHGU o.m+ TN: Tm... «.ou w.n+ m.o+ H24 «.ma «.5 m.m 5.0 v.0 m.o h.m m.n o.N HOB nova xuoz unou puma xuoz you: uuou xuoz anon EOUH ouoq canon: sauna r\ I“! 75 which is believed to be the result of the body beginning to warm up while there was still an ample volume of blood in splanchnic regions that could be shifted peripherally for heat dissipation. Benedict and Parmenter (1928) observed decreases of skin temperatures in working regions of the body during five minute exercise periods where metabolism was increased five- to sixfold. They hypothesized that during work there may be a peripheral vasoconstriction, resulting in a temporary transport of blood from the periphery to the muscles. In contrast, Cooper, Randall and Hertzman (1959) reported the heating of skin overlying a working muscle and attributed this to direct vertical vascular convection of heat from muscle to the skin. McCook, Wurster and Randall (1965) pointed out that the functional control of this response remains unknown. This author believes that both the findings of Benedict and Parmenter and COOper, Randall and Hertzman are correct, but, the eXperimental conditions were such for each group of researchers that their findings describe two differ- ent physiological responses. The combination of clothing and marked elevation of heat production in Benedict and Parmenter's study resulted in a generalized hyperthermia. It is possible that a sizable portion of normothermic splanchnic blood volume was in cutaneous regions during the np-exercise state, and during exercise the muscle demand for 76 blood resulted in restricting a considerable quantity of blood from reaching the skin because of increased demands by the muscle. When a reduced volume of hot blood was supplied to the skin, the skin temperature fell. The study of COOper, Randall and Hertzman was conducted at environmental tempera- tures varying from 20 to 330C (68 to 910E), with relative humidity varying between 40 and 60 per cent. Their subjects were very lightly clothed with shorts and with or without undershirts. Based upon the brief description of the type of exercise used, the metabolic rate of their subjects was apparently much less than in the study by Benedict and Parmenter. Therefore, in consideration of the eXperimental design and findings it is possible that there were suffi- cient reserves of blood in internal body regions to provide an adequate supply to meet working muscle demands without restricting blood flow to the skin. ‘ Uvnas (1960) suggested a number of factors that may be interrelated to eXplain the phenomenon of decreased skin temperature during muscular work. He indicated that the increase in cardiac output during exercise is distributed chiefly to the muscles by shifts of tone in the peripheral vessels. Eliasson and co-workers (Uvnas, 1960) were able to localize hypothalamic areas which when stimulated activated the sympathetic vasodilator outflow to skeletal muscle and simultaneously produced cutaneous and visceral vasoconstric- tion. Also, adrenals were activated and epinephrine was 77 selectively liberated. Uvnas believed that even though the quantities of epinephrine were not sufficient to produce vasomotor reactions in the muscles and skin, the amount was sufficient to increase the metabolic processes in the mus- cles, heart and other organs. From this form of reasoning, Uvnas stated "one is tempted to assume that the sympathetic vasodilatory nerves are activated in circumstances which require optimal conditions for muscular effort." Shepherd (1963) has indicated the same physiological responses as cited by Uvnas (1960), but Shepherd describes the effect of epinephrine on skin and muscle blood vessels in terms which aid in additional clarification of data from this study. He presented evidence that epinephrine produces vasoconstriction in skin vessels, whereas vasodilatation results in muscle vessels. The effects of epinephrine are such that muscle blood flow is increased, skin blood flow is decreased, heart rate shows a transient increase, systolic blood pressure rises, diastolic blood pressure decreases, and pulmonary ventilation rate increases (Cobbold, Ginsburg and Paton, 1960). These responses are like those observed in this study. The relationship between internal and skin tempera— tures is graphically summarized in Fig. 15. The decrease in TCI values during work and rise during rest demonstrates that under these experimental conditions the skin blood flow was decreased during work and increased during rest. The THERMAL CIRCULATION INDEX (TCI)' t.-= RECTAL TEMPERATURE I; SKIN TEMPERATURE (,- AIR TEMPERATURE 78 HYPOTHETICAL BLOOD FLOW SHIFT REST (A TO PV; MUSCLE TO P'V) (A TO IV; PV TO MUSCLE) A= ARTERY PV= PERIPHERAL VEIN IV= INTERNAL VEIN AI... ' INTERNAL GRADIENT (I, - I.) At“, - EXTERNAL GRADIENT Tim " TISSUE INSULATION (t,-I,,) .m : t.-t. . EXTERNAL DROP AFTER SCHMIDT-NIELSEN. Ir't. INTERNAL DROP . 196! (MODIFIED) (BURTON, I934) Figure 15 79 hypothetical blood flow shift is shown in the diagram modified from Schmidt—Nielsen (1961). As illustrated by this diagram, when heat production was increased during work blood was shunted to internal vessels resulting in heat retention in deep body tissues and active muscles. This caused a rapid spiraling of internal body temperatures. Partitional Calorimetry Research conducted prior to commencement of the present study clearly indicated that heat stress with the complete clothing assembly was extremely restrictive under ambient conditions that were normal for men in usual work clothes. It was concluded in the initial research (Dr. David Minard, unpublished data) that tolerance time of the subjects was directly related to the rate of body heat storage. Furthermore, a limited number of experiments demonstrated that tolerance time could be extended by in- creasing the air velocity over the external surface of the suit. The experimental conditions in the present study were based upon control of air velocity while using three pre-established upper levels of ambient temperatures and two physical activity levels. "Control” conditions for the different activity levels were selected by the subjective judgment of comfort in the suit, and objective observation of relatively constant internal body temperatures. The 10 80 eXperimental conditions utilized throughout this study are given in Table 7, along with the effects of air velocity on tolerance time. Table 7 clearly supports the concept that air move- ment can increase tolerance time in the heat, provided a critical air speed is not exceeded. The tolerable eXposure time was found to be a function of dry bulb temperature, physical activity and air velocity. Since tolerance time was extended from 26 per cent to 93 per cent, depending on the conditions, the logical explanation had to be either increased convective heat loss or increased evaporative cooling. As has been shown, evaporative cooling within or on the surface of the suit was not possible under the experimental conditions. However, the relationship between convection and air velocity will be shown more clearly from the results of the first order partitional calorimetry. The most commonly used methods to determine body heat storage, those of Burton (1935) and Blockley, McCutchan and Taylor (1954), have mean body temperature (tb) as a key element of their equations. As has been shown, the calcula« tion of tb by available equations is not appropriate in transient thermal states. To avoid the underestimation of heat storage during rapid storage and an overestimation dur- ing rapid loss by using equations dependent upon tr' the data were applied to the general eXpression for heat balance, equation (1). Substitution of radiation from equation (2), i. 8]. case I + .mmOA I I : Agave sueuofiw> Aa< .Amov m3\Amov an a I Aonv mk\nmv A mm + am - on o « om.~ N oooH .mk\mw -I--- #0 a. WM 0 .“ HOQH m omv amN\nw Roam .mo\mkv A om + .Aomv mo\mkv A ma + m + SN o « no m m coca .mo\mk Aomv .mo\nkv A mm + «A - m~.o « mm.~ m omm .mo\mm nuns: he I H~.o P mm.~ m omv .mo\nm ----- ----- m~.o « ~n.m k Aaouucoov omv .qn\~o "mmuummxm me ¢H< ho mHQmmhm h mHHmdfir 82 convection from equation (3), respiratory evaporation from equation (4) and metabolism into equation (1) yielded the estimated partitional calorimetry of body heat as shown in Figs. 16-21. It is usually believed that evaporation from the respiratory tract is an important avenue of heat loss. Under the conditions of these experiments however, respira~ tory heat loss was negligible in every instance. It is also of interest that radiative heat loss showed comparatively little change in contrast to the substantial changes obn served in heat storage and convection. It is shown most clearly in Figs. 16-18, at DB 750F and WB 6SOF, that there is an inverse relationship between heat storage and convec— tive heat loss. A similar relationship can be deduced from the data in Figs. l9—Zl. However, the comparison is compli— cated by the fact that several different variables were included in these experiments. The values for radiation and convection given in Figs. 16-21 are plotted versus air velocity in Fig. 22. It is apparent that radiation is relatively unaffected by air velocity, whereas convection is directly related to but non- linear with air velocity. At <50 fpm air velocity, radia- tion is two times greater than convection, at 250 fpm convecM tion exceeds radiation, and at 1000 fpm convection is about two and one-half times greater than radiation. Leithead and Lind (1964) point out that a gradual increase in air movement 83 PARTITIONAL CALORIMETRY DB 75°F WB 65°F ACTIVITY -WORK- REST AIR VELOCITY- <50 FPM -+2£K)P W/a\a +l50- 'tKNDE’“”§‘--_w@_ ———— ’S\\ V +50- 0: I I' Nr‘ C) -- --;:5- ----- 1:"'2 """""""" 5 ‘Ev 3 " R 7'7 '—" 3 -SOE\@~ —o—o X -I00- -I50- -200- L I l 1 l l i l I 1 0 30 60 90 I20 I50 I80 2IO 240 270 MIN. 0 I 2 3 4 HR. TIME Figure 16. R = metabolic rate; 8 = heat storage; M C = convection; R = radiation; and E v = respiratory evaporation. 84 PARTITIONAL CALORIMETRY 08 75°F we 65°F ACTIVITY- WORK- REST AIR VELOCITY- 25o FPM +200F L «MR J #3 [21—0 E}—' ‘4 +l50I- +I00- S -—:"_-'"“*@-‘----%——---—---—ae—~"x +50- 0: I b N\ E OZjE'"-z ---- A """" A "———z“ "’ 2% E F? K “A O O 400)- -I50- —200L 1 1 l l l l 1 IL I L_ MIN.0 30 60 90 I20 I50 I30 2l0 2:0 270 HR.0 I 2 TIME Figure 17. MR = metabolic rate; 5 = heat storage; C = convection; R = radiation; and EV = respiratory evaporation. 85 PARTI TIONAL CALORIME TRY 08 75°F we 65°F ACTIVITY-WORK—REST AIR VELOCITY- I000 FPM +200 3 [ MR @_ ‘a/ \[3\ [B / +I50- +I00- ’/X\~\~ m +50- L"X~-~-~X/’/ \X\ 3: ”'T’ \X “§ 0 ET ----- *- ----- z' ----- 2.- TTTTT 5;?- ) V 7“ g R fiO— C C N X -50 C 400? fig; A—i ——0 O\. -I50- -200- I ' I . I I I I . OL 3'0 60 90 I20 I50 I80 2I0 240 270MIN. 0 I 2 3 4 HR. TIME MR = metabolic rate; S = heat storage; C = convection; R = radiation; and EV = respiratory evaporation. Figure 18. 86 PARTITIONAL CALORIMETRY 08 85°F we 75.F ACTIVITY-- WORK-REST AIR VELOCITY- I000 FPM + 200 DE] L MR 3/ . D . +I50- +IOCM- 0: “*5C)- E .. Q! s o--,-----.—____. --------- M- 4 EV - .1 5 RR V ‘9 0'0 5: ‘5C) C e 7_—.t ‘l_7 5‘40. -I00- ‘50- “200- l I I I I l I I I MIN.0 30 60 90 I20 I50 I30 2I0 220 27 HR. 0 I 2 TIME = metabolic rate; 8 = heat storage; . . R O o Flgure 19 g — convection; R = radiation: and Ev = respiratory evaporation. +200- +I50 - +IOO - 87 PARTITIONAL CALORIMETRY DB 90 ° F WB 80" F ACTIVITY — STANDING AIR VELOCITY— <50 FpM -lOO- .450- -ZOOI- I I I I I I I I I__ MIN. 0 30 60 90 I30 I50 I850 2|O 2’10 270 HR. 0 | TIME Figure 20. R = metabolic rate; S = heat storage; M I o C = convection; R = radiation; and E = respiratory evaporation. v 88 PARTITIo DB IggLF caquMETRY ACTIVITY - STANDING AIR VELOCITY— I000 FpM +200 +I50- +IOO- ‘gE .F50$jafifiia¢,a’lj‘--\-‘fl3 SE .- S °"7$‘~.. XJ’F \. —J OAK ’V“’r"""\.§k.——"""’K—=-HM"' -- 3 1R MVO‘G ‘50-— aw -I00- -I50- L I I I I I I I I I MIN. 0 3O 60 90 I20 I50 I80 2IO 240 27 HR. 0 I 2 3 4 TIME Figure 21. MR = metabolic rate; S = heat storage; C = convection; R = radiation; and EV = respiratory evaporation. I-\ .I- \JIJ‘! gain-(ICI‘n 89 HEAT LOSS BY RADIATION AND CONVECTION VS. AIR VELOCITY RADIATION (KCAL/MZ/HR) I .‘ (To '50r ‘~~~ )(0 ~.. 75/65. WORK-REST -40 P M ___________ “T. "5?? N451- 90/80 STANDING WORK pESTCYQ": -20 E" ~"~.--— X0; —G ""'"'""“"'"“""""'""""'"'"' -l0 - ________,_.__.__-_____-_.-_____-__-__- K O L T’ -IOO - ”I ’ / 64 85/75 2... , WORK -REST T I—” d ‘ d‘ CONVECTION (KCAL/MZIHR) a. C) L. L J I l L l J 0 I00 200 300 400 500 6023;: 700 800 900 I000 AIR VELOCITY PM) Figure 22. T = time zero; '1‘t = time terminal; and R— = mean. 0 90 in warm to hot air temperatures will be beneficial at first, but above some critical speed it will become detrimental. The data in Fig. 22 shows the non—linearity between convec- tion and air movement, where increasing the air speed four times greater than 250 fpm produced only a twofold increase in convective heat loss. Therefore, to greatly exceed 1000 fpm would yield less convective loss per unit of velocity until the critical air speed would be reached, at which time the friction of air movement would impose a heat load on the test subject. The practical advantage of employing first order partitional calorimetry has been demonstrated. This ap- proach appears to provide a reasonable way of estimating heat storage for this study, and at the same time to provide an opportunity to evaluate the various avenues of heat loss in a rational fashion. Among the experimental variables tested, the only one which shows promise in reducing the heat load under the experimental conditions is convection. Parallel experiments, not reported herein, showed that sub- stantial improvements in tolerance time could be obtained by using an evaporative cooling garment and water spray on the external surface of the suit (Dr. David Minard, unpublished data). A logical sequence for these experiments would be to combine convection and evaporative cooling in a future study conducted under controlled conditions. SUMMARY AND CONCLUSIONS Heat tolerance was studied in volunteer human test subjects clothed in an impermeable, unventilated bacterio— logical—chemical warfare protective assembly that barred evaporative heat loss. Data are presented to show condi- tions needed to approach the upper limit of heat tolerance in man. The physiological consequences of exceeding the heat tolerance limit are also described. The ambient environmental temperatures ranged from DB 16.3% and we 12.2% (65 and 54%) to DB 32.2% and we 26.6OC (90 and 800F). Air velocity over the surface of the impermeable suit was controlled at <50, 250 and 1000 fpm. Physical activity was limited to standing at rest and work- ing by climbing two 6" high steps and then stepping back down at a rate of 10 round trips per minute. The parameters measured included temperatures of the rectum, tympanic membrane, deep esophagus, 10 individual skin sites and mean skin temperature. In addition, metau bolic rate, heart rate and blood pressure were determined. Computations and data were presented for first order parti- tional calorimetry, estimated cardiac output, and peripheral blood flow by use of the Thermal Circulation Index. 91 92 Theoretical equations were developed for mean body tempera- ture in a transient thermal state. It is concluded that: 1. Under the specific conditions of this study the upper limit of "safe" tolerance can be defined as body temperature not exceeding 390C, heart rate not I exceeding 180 beats per minute, and/or blood pres- sure not less than 90/40 mm Hg. 2. Circulatory instability was observed when the heat a tolerance limit was exceeded, resulting in imminent circulatory failure. 3. When heat storage is rapid and continuous, rectal temperature is not a reliable index of body tempera— ture; whereas deep esophageal and/or tympanic mem- brane temperatures do reflect sudden changes in internal body temperature. 4. When man is in a transient thermal state the widely used equations for mean body temperature cannot accurately predict mean body temperature or heat storage. 5. During work, deep body temperatures rise and skin temperatures fall; conversely, during rest skin temperatures rise and deep body temperatures fall. 93 Based upon physical principles of heat transfer, the decrease in skin temperature during work and rise during rest was not the result of evaporation or con- vection, but the result of changes in peripheral blood flow. Tolerance to severe heat stress, with unchanged air temperatures, was increased with increasing air velocity. Convection heat exchange is the most practical avenue of heat loss when evaporative cooling is not possible. 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APPENDICES APPENDIX I SUMMARY OF INTERNAL BODY AND MEAN SKIN TEMPERATURES AND HEART RATES OF THE SUBJECTS INDICATED IN TABLE 7 (Note that the code letters A-H at the bottom of each figure, correspond with the respective subject indicated in Table l.) 9P“) HEART RATE I 327335333 ’C T E WE RATURE I 104 PROTECTIVE CLOTHING 395 DOUBLE SUIT -‘ I03 08- 62 ’F WB-M ’F AIR VELOCITY - ‘ 50 F PM _, I02 AVERAGE 0 “EN, ”83'“ 303 >- '* IOI 38.0 '- 37.!) '- -* 99 310 '- ‘I 90 365 '- ‘I 97 36.0»- -‘ 96 35.5 '- 330 I- 4 95 3&3 ,_ _, 94 m >— ‘I 93 I- 335 .. 92 33.0 '- -‘ 9| 32.3 32.0 ./ 3° sure TIME °P TEMPERATURE (8PM) 32323 HEART RATE 39.5 39.0 38.5 3&0 37.5 37.0 36.5 'C 4.05:5; ooooOO TEMPERATURE 355 35.0 345 L: 34.0 335 '- 33.0 32.5 ‘- 32.0 105 PROTECTIVE CLOTHING DOUBLE SUIT Figure 2 - IO3 0.- 90 ’F 'I-CO " ACTIVITY- STANDINO -‘ I02 AIR WLOGTY- (50 PPM AVERAGE 0 MEN, I903-“ -* IOI - IOO -* 99 -* 90 -‘ 97 -I 96 _. 95 —I 94 -I 93 .. " 92 _ 9| HR -‘ 90 _ E A II 2 I 6 ° 89 1 I 1 1 IOO 21") MIN. 0 3O 60 90 I20 3 HR. ' 2 TIME TEMPERATURE ° F (I'M) 33385835883 MART RATE 106 PROTECTIVE CLOTHING IXIEKEI SUN 3» I03 u-fl‘f II-Io-I no» ACTIVITY-91M _m In vuocmr- too"- Ivuuu 7 In. Ion-u su- -I0I uo- -Ioo use'fi «99 up- Th 'B -u o 305-- 0 III ‘91 5 no- 2 I «It 3 an» -95 ”OI- TS yuP- “3 340- a» 335— a: no- HR «II 32.5— no I..- I I I I I 0 ‘ 09 1 I I l 1 I ‘ $0 an 240 um. o no I? ’0 f3 5° 3 4 In TIME Figure 3 TE’ERATWE ' F IBPM) HEART RATE 3366 TEMPERATURE ”0 I50" I50- I40- I30- I20" ”0'- fl 107 PROTECTIVE CLOTH IN G DOUBLE SUIT 395 00- 90 'F '03 wa— 00 ‘F 39.0 b ACTIVITY- STANDING AIR VELOCITY- I000 FPII -« I02 AVERAGE I IIEII . Ins-u 3&5 - - IOI 300*- - I00 325 - - 99 37.0 - H98 365 - - 97 360 - - 96 35.5 - 35.0 - T5 7 95 34.5 I— .. 94 34.0 - T 93 310R HR - 9| 325*- 1 90 320 — r o l R ' as I 1 l l l 2.40 "IN '30 2I0 ' 0 90 Ii? '50 3 4 HR. TIME TEMPERATURE 'F 108 PROTECTIVE CLOTHING DOUBLE SUIT 39.5 '03 DO- 62 'F Ila—34 °I= 3,0 _ ACTIVITY - Mom: - REST ' AIR VELOCITY -<50 FPM 7. I02 AVERAGE 7 IIEN . I963-34 I 305*- - IOI 3&0 « IOO 37.3 - 99 I 37.0 i 9 I... III 365 3 I- 3 U -I_ 97 t 1 3&0- III " I 4' 96 33.3 — 95 350'- 34.5 r- -4 94 —- 34.0 493 50- I50 )- 335 . IQOI- 92 - I30 - I20 - 33.0 « 9I I! II0 - I00 - 325 “’90r- .490 ”E T5 70 32.0 — E r . ‘ o H 109 1 ____..iI M L___.__Lri..iil_— I..~-_._.1_._--—",50 I80 me 240 MIN. 0 3o 60 9° '2° 3 4 HR I 2 TIME Figure 5 'F TEMPERATURE HEART RATE (8PM) I70 I50 I40 l20 I I0 IOO 80 70 'C TEMPERATURE TR 109 PROTECTIVE CLOTHING 395 DOUBLE SUIT -* l03 DB— 75 'F W8-65 'F 39.0 _ ACTIVITY- WORK. REST AIR VELOCITY- <50 FPII 1.02 AVERAGE a IIEN, I963-64 385 I- .4 IOI 38.0 *- - I00 375 ’- -99 37.0 ’— - 98 36.5 - "‘ 97 360‘- -I 96 35.5 '- 350 L- 7 95 345 - a 94 340- J93 330e HR - 9I 32.5 — TS - 90 32.0 - l A c I g r E z ,3 j 89 I l l 0 MIN I i_.i__...L————A-————— . 24 . I TIME Figure 6 'F TEMPERATURE ’C TEMPERATURE 110 PROTECTIVE CLOTHING 395 DOUB_LE SUIT '03 09-75°P w9-35°F ACTIVITY - WORK, REsT 39.0 T AIR VELOCITY- 230 PPM - I02 AVERAGE a MEN. I933-64 33.5 . IOI 330 - I00 37.5 J I -I 99 I 37.0 I . . I . I99 I 36.5 - Te ‘ . I -4 97 360‘ H96 355 _ i I... 35.0 P 345 ‘ _ 9‘ 34.0 -« 93 33.5 ' - J 92 330 ‘ ' 1 9| 325 I— .1 90 32.0 D I L 1 P I 1 _g___,_,I I30 2,0 240 MIN. 0 30 9° '20 I50 3 4 HR. TIME Figure 7 'F TEMPERATURE l- HEART RA E o 5 o I o T 'C TEMPERATURE |70r ROE 5 T O O T 4 O 111 PROTECTIVE CLOTHING DOUBLE SUIT 3” ’ 09-75° r 4 I03 III—65° F ACTIVITY-MORK-ResT AIR VELOCITY- I000 FPM 39° ‘ AVERAGE 3 MEN, I963—64 A .02 335 - -‘ IOI 35.0 — ~ IOO 37.5 - TI 4 99 37.0 - TO T 198 6 36.5 - — 97 36.0 — < 96 35.5 P « 95 35.0 — - 94 34.5 e 340— ~ 93 33.5 P — 92 33.0 ~ «9' 32.5 — 490 32.0- ; r H ‘ “ « 89 [41,422 I. 240 MIN. 0 310 60 90 I20 '50 ‘330 2'0 4 HOUR TIME Figure 8 'F TEMPERATURE (IPM) HEART RATE 3333 I40 I20 I I0 112 PROTECT IVE DOUBLE SUIT CLOTHING 39.0 315 310 'C 365 TEMPERATURE I- 33.0... 32.5)- HR . A F _____L——————-—L— ——‘—‘—-‘L_.’_ I 2 TIME Figure 9 00-95 'F WO-TO‘F ACTIVITY - WORK . REST AIR WEMENT- < 50 PPM AVERAGE 3 MEN— ”63-54 I80 I 2|O I 240 4 j” -* I03 -I I02 -‘ IOI -I97 "96 495 ~94 —-93 ‘92 49I HR. 'F TEMPERATURE (8PM) HEART RATE ‘C TEMPERATURE I70 ‘— I60 L- I50 I— I40 I— I30 - I20 P IIO I. Ioo A 90— 90- 70 L PROTECTIVE CLOTHING m _m_ __ DOUBLE SUIT 09- 95 'F I '03 99-75 °r ACTIVITY - wORR.REST 39.0— AIR VELOCITY- IOOO FPM AVERAGE 2 MEN, I963-64 7 '02 39.5 - I «IOI 390- I I T} /\\Yr/4\\n RICO 375 ~— I To . - 99 370- I Te I " 98 365‘»- ‘ ” - 97 360- /‘K P I/ -\ 355°— ,)3\ / -96 350- T8 - 95 345 _ A \f 7 9‘ 340— - 93 335- ; - 92 I 33.0I- If), /°\ / )5 — 9I 325:- HR -90 320+— C . 939 _,11 I_,_ I , I 1 - I _ i_I .._ 1."____L__ L 0 3O 60 90 I20 l50 I90 2lO 240 MIN. I 2 3 4 HR TIME Figure 10 TEMPERATURE ‘F APPENDIX II STIMULUS PRESENTATION DEVICE 115 Stimulus Presentation Device BY Mr. M. Eicher Head, Medical Instrumentation Laboratory Naval Medical Research Institute An instrument was constructed to measure and record reactions of thermal stress subjects under varying tempera- ture conditions, while the subjects were wearing BW/CW pro- tective clothing being evaluated for the Bureau of Ships. The basic objective of the stimulus presentation device was established by Dunlap and Associates, Inc., who are experts in the field of assessing mental performance of subjects submitted to heat stress. The stimulus selected was a reading on a standard three (03) inch panel meter. This stimulus remained in position on the meter for a fixed interval of time and then changed to another reading, proceeding through a random sequence of fifty (50) readings of twenty (20) different values, then repeating the cycle. The subject responded to the stimulus by depressing one (1) of twenty (20) buttons which correspond to the stimulus presented. A twenty-pen Operations strip chart recorder indicated the stimulus pre- sented as well as the button which was depressed in response to the stimulus. Figures 1, 2 and 3 illustrate the device and how a subject uses the device. A rate of presentation of stimuli of 30 per minute was used for the testing procedure, although an optional slower rate of 15 per minute was available when needed for teaching a new subject. The reading of the panel meter, mounted at eye level (Fig. 1), represented a typical task required of shipboard personnel. The meter face was marked with twenty (20) numerical divisions, O to 4.0 in 0.2 incre- ments. The meter needle read coincident with the divisions, requiring no interpolations or estimating. The twenty (20) response buttons were one inch in diameter with the numbers engraved on the faces of the buttons. They were arrayed on an 8" X 10 5/8" sloping panel in four (04) rows and five (05) columns. The numerical order was left to right, top to bottom, starting with O and ending with 3.8. In all tests the top of the meter was at a 10 per cent depression from a straight line (horizontal) sight of the subject, which minimized the physical strain of the subject. 116 The record obtained on the Esterline-Angus event recorder was twenty printed parallel lines each showing a deflection when its correSponding stimulus was presented (Fig. 2). At a paper speed of six (06) inches per minute, a two (02) second stimulus was l/5 inch long. Depressing a response button caused its corresponding pen to deflect with a distinctive oscillating mark which was superimposed on the stimulus deflection for a "correct" response. In this way, correct and incorrect responses would be distinguished as well as response time relative to the time of the stimulus presentation. Also, this method immediately gave a perma- nent record of the test result, which could be summarized later. Construction of the pulser and stepping switch is shown in Fig. 3 and a block diagram of the basic flow scheme is illustrated in Fig. 4. The indicating timed pulses were produced at fifteen (15) to thirty (30) per minute by a synchronous motor driven cam and switch. These pulses Operated a six-level lO-position stepping switch. Five (05) levels were used with minor switch to transfer the signal to the succeeding level. This permitted fifty (50) stimulus presentations before the pattern was repeated. Each of the stepping switch contacts operated one of twenty relays whose contacts passed a signal to the panel meter and also made the corresponding pen on the recorder deflect. Since there were only twenty (20) different stim- uli, the stimuli were all presented twice and ten of them three times in the pattern of fifty. 117 Figure 1 ’f’C/u; 118 Figure 2 119 Figure 3 120 Cum—100mm. .ll mmZOm mm: IUF_>>m 07...:um mDADZCM moan mohadazmmwmm mafia—Ham me gum ISM 0H3 KmmJDm Figure 4 APPENDIX III Conclusions From: ACCURACY OF METER READING UNDER THERMAL STRESS INDUCED BY WEARING AN IMPERMEABLE PROTECTIVE SUIT (Dunlap and Associates, Inc., Report DRD-64-109) By Dr. R. D. Pepler Conclusions 1. Subjects wearing an impermeable protective suit were generally able to maintain a reasonably high level of accuracy in reading the meter values under all condi— tions of work, ambient temperature and air movement. Heat and work reduced the consistency with which the more motivated subjects read the meter accurately. These conditions appeared also to reduce the average levels of accuracy of the more motivated subjects, but these latter trends in performance were not statistically significant. Increases in speed of air movement from 50 to 250 fpm and from 250 to 1000 fpm resulted in approximately equal improvements in the Consistency with which the more motivated subjects read the meter accurately. The more motivated subjects were almost as consistenly accurate at reading the meter under the most stressful set of conditions (stepping and standing at 850/75O with 50 fpm) as under the cool conditions of 620/54 F° This finding demonstrates that well motivated men wear~ ing an impermeable suit are able to sustain a high degree of accuracy in reading a meter under conditions of severe thermal stress, even until the time the suit becomes intolerable and is removed. 121 "’IIIIIIIIIIIIIIIII‘IIII