their body temperature.

Transcription

1 THE EFFECT OF WORK AND CLOTHING ON THE MAINTENANCE OF THE BODY TEMPERATURE IN WATER. By W. R. KEATINGE. From the Medical Research Council, Department of Experimental Medicine, University of Cambridge. (Received for publication 20th July 1960) Twelve young naval ratings were repeatedly immersed in water at temperatures between 5 and C. Their temperatures, both rectal and cesophageal when measured, fell more rapidly when they worked than when they stayed still in water at 5 or 150 C. This was so whether the men worked as hard as possible or at a slower rate, whether they wore clothes or not, and whether or not the water (at 150 C.) was stirred when they were still. The fattest man suffered relatively small falls in rectal temperature at both 5 and 150 C. whether he worked or was still. Work had no significant effect on the rectal temperatures of unclothed men in water at 25 C. and caused a rise in water at 350 C. Work had no important effect on the falls in surface or mean temperature during 20-min. immersions at 50 and 150 C. when the men were unclothed and the water (in the still experiments) was stirred, but it increased the falls in mean temperature when the immersions lasted 40 min. and increased both when the men were clothed. Clothing substantially reduced the men's falls in both surface and deep temperature, particularly in water at 50 C. This effect was prolonged when the men were still, but when they worked it was relatively slight after the first few minutes. INTRODUCTION EXPERIENCE in the last war showed that cold, rather than drowning, was the main hazard to life after shipwreck in cold and temperate waters [Molnar, 1946; McCance, Ungley, Crosfill and Widdowson, 1956]. Many ships now carry life-rafts designed to give protection against cold, but survivors will often be immersed for a time even when such rafts are available. This paper describes an investigation in which twelve naval volunteers were repeatedly immersed in water at a wide range of temperatures in an attempt to show whether non-waterproof clothing can substantially reduce the heat lost by men in the water, and whether or not physical exertion helps them to maintain their body temperature. Earlier investigations of the latter problem have given conflicting results; Glaser [1950] considered that a man swimming hard produced enough heat to balance his heat losses even in near-freezing water and advocated that survivors should swim, but Pugh and Edholm [1955] obtained contrary evidence on a thin man in water at 16 C. As regards clothing Hervey [1955] stated on theoretical grounds that clothing is not of much value in water, but skin temperature readings made during wartime experiments [Alexander, 1946] suggest that it might provide some insulation in water. The present experiments were made in a small specially constructed indoor tank whose temperature could be adjusted by electrical heating and 69

2 70 Keatinge refrigeration, and which could be continually stirred; it was fitted with apparatus that enabled the men to make swimming movements at a controlled rate. Measurements of the men's skin, rectal and cesophageal temperatures provided the main information, but in order to provide a more complete picture of the men's heat exchanges their metabolic rates were measured during immersion. The material of this and the following paper has been the subject of a thesis [Keatinge, 1959].* PROCEDURE AND METHODS The Subjects.-There were twelve principal and two additional subjects. All were naval ratings aged who volunteered for the experiments, and none of whom had experienced unusual exposure to cold for 6 months before the experiments. All were found to be healthy at a thorough clinical examination. The Tank.-This was 8 ft. long, 4 ft. wide, and 4 ft. deep, and made of galvanized iron insulated by 3 in. of cork. Control of Water Temperatures.-The water temperature was adjusted to within ±0.20 C. of the chosen temperature (5, 15, 25, 35, or C.) by heating or refrigerating equipment at the start of each experiment and was kept within these limits throughout the immersion. The quantity of the water was so large (about 5 tons) that the temperature changed little during an experiment, but in the 50 C. immersions it was sometimes necessary to switch on the refrigerating plant to prevent the temperature from rising more than 0.20 C. Electrical heating kept the room temperature above 25 C., and a radiant heater was directed onto the subjects, when necessary, to keep them warm while they were being prepared for an experiment. Arrangement for Work in the Tank.-The subject carried out a rowing movement in which the range of movement of both the upper and the lower part of his body was fixed in the following way. A perforated sliding seat was fixed to scaffolding 30 cm. above the floor of the tank. It was constructed largely of teak and brass to resist rotting and corrosion, and since it ran entirely on roller bearings its friction was low. It was fitted with an elastic belt which fastened round the subject by a quickrelease parachute clip. Teak boards, fitted with straps for the subject's feet, could be clipped into a device on the end wall of the tank. A wooden handle held by the subject was attached by a rope to the end wall of the tank, just above his feet. In working experiments the man drew his body forward by bending his knees until the seat reached its stops, at the same time stretching his arms forward until his hands, holding the wooden handle, touched the end of the tank a foot above the attachment of his feet. He then straightened his knees, pushing his body back and at the same time bending his arms to his chest, until the seat was arrested by the stops, and his hands by the rope. The rope was 105 cm. long and the range of movement of the seat was 42 cm. A flashing light operated by a metronome controlled the men's rate of work. Slatted boards in the ends of the tank suppressed the waves set up by work. Stirring Device.-A I-h.p. electric motor, mounted above the tank and attached to a connecting shaft that ran vertically down into the tank to drive a propeller, drove water up into a metal duct which redirected it horizontally towards the subject. The current of water, about 50 cm. wide, and with a speed of cm./sec. was directed onto the subject's chest and stomach, but caused considerable turbulence around the whole of his body. * These papers give a summary of the more important experimental findings. A full account of the individual results and their statistical analysis, and of additional experiments which were made provide more precise information about the men's exchanges of heat, is available at the National Institute for Medical Research, Mill Hill, London, N.W.7.

3 Body Temperature of Man Periods of Immersion.-The men were immersed for 20 min. in the great majority of experiments. This was thought to be the longest time for which they could be left in water at 50 C. with safety, and it facilitated comparisons if immersions at different water temperatures were of equal length. However, it seemed important to have information about longer immersions, so a number lasting 40 min. were made at 150 C. Immersions at 150 C.-The largest number of immersions was made in water at 150 C. and the effect of both moderate and hard work, of clothing, of agitation of the water, and of the effect of repeated immersion were studied. A number of 40-min. immersions were also made at this temperature and so were four experiments on two extra subjects. This seemed a suitable temperature at which to make the fullest study since it is not quite low enough to cause pain. Immersions at 50 C.-It was obviously important to have information about lower temperatures. However, this temperature was very unpleasant and only the more important variables, work and clothing, were studied. Five of the twelve subjects completed this series. Immersions at Higher Temperatures.-In experiments at 25 and 350 C., which were made on all twelve men, only the effect of work was investigated with the men unclothed in all immersions. A single still immersion of all subjects was also made at C. Clothing.-This consisted of long woollen drawers, a string vest, submariner's jersey, arctic jacket and trousers (kapok lined), sea-boot stockings, half-wellington rubber boots and mitts. The jacket was secured round the waist by a belt to prevent water washing under it freely, and the legs of the trousers were tucked into the stockings for the same reason. The subjects wore brief cotton bathing trunks in all the "unclothed" experiments, which cannot have appreciably retarded the subjects' losses of heat. Leather helmets were always worn to protect the occiput and the back of the neck and to provide an attachment for the metabolic masks. Still or Working.-In all experiments the man climbed rapidly into the tank, clipped himself to the seat, and his feet were fixed to the end wall of the tank. This took sec. If the experiment was a working one the subject then began work, as described earlier. The subjects had previously practiced the movements with the tank dry, and during immersions had little difficulty in making them smoothly and to their full range. For the standard rate of 22 movements/min. the men kept in time to the metronome. For maximal work they made the same movements as rapidly as possible. In still experiments the men sat still; the water just covered their shoulders in all immersions. Experimental Design The twelve principal subjects came in groups of four, each group remaining in Cambridge for 6 weeks. All were immersed at 15, 25, 35 and 37 8 C., and seven of them, who volunteered specially, were also immersed at 50 C. 150 C. Immersions.-Six experiments were made on each of the twelve men to study the effect of work at the standard rate, clothing, and agitation of the water. These were made in random order to eliminate distortion of the results by any changes produced by repeated immersion, and an additional still, stirred and unclothed immersion was made on each man before and after this series, in order to detect any adaptive change. The maximal work experiment was made last, and was thus the ninth immersion; it was not incorporated in the cross-over pattern. A number of 40-min. immersions were made next, and were crossed-over as far as possible. Four further immersions were made on two extra subjects, at 150 C., i order to show the effect of work on men who were hot at the time of immersion; these were crossed-over. In all experiments at 150 C. and at 50 C. each man was immersed regularly every second day. 71

4 72 Keatinge 50 C. Immersions.-The series of five immersions of five men in water at 50 C. was fully crossed-over. A smaller number of experiments at 50 C. were made on two other men, one of whom was fat. Higher Temperature Immersions.-The two experiments made on each man at 25 and 350 C. were crossed-over at each temperature. The single still immersion at C. was made last. At these relatively high water temperatures each man was immersed every day. Experimental Measurements Weight and Skinfold Thickness.-The men were weighed, wearing only cotton drawers, and their skinfold thickness was measured by Harpenden calipers [Edwards, Hammond, Healey, Tanner and Whitehouse, 1955]. Sixteen measurements were made on each subject from four sites, the skinfold thickness at each site being determined twice on each side of the body. The positions used were: biceps midway between acromion and medial epicondyle, subscapular over lower corner of scapula, abdominal 5 cm. below and lateral to umbilicus, and subcostal at the lower border of the ribs directly below the mid-point of the clavicle. Readings from these sites are believed to provide a good indication of overall surface fat thickness [Hammond, 1955]. The twelve men's average weight was 69-4 kg. and their mean skinfold thickness was 7-95 mm., one man being considerably fatter than the others (84-4 kg.; 14-8 mm.). Skin Temperature during Immersion.-Four thermojunctions were attached to the skin, on the flexor surface of the forearm, extensor surface of the thigh, abdomen just above the umbilicus, and back in the midline at the level of the iliae crest. They were welded copper-constantan junctions of 28-gauge wire, in which the wires ran parallel. The wires were enclosed in a plastic sheath up to 1 cm. from the junction, the last centimetre being insulated only with "Araldite". They were held on the skin by zinc oxide plaster which covered the wire to within 3 mm. of the junction, and so kept the junction applied to the skin without covering it. The cold junction was in a vacuum flask of distilled water and ice chips, and the resulting e.m.f. led through a resistance and distributor box to a "Scalamp" galvanometer whose deflection was calibrated and was accurate to 0-1 C. The mean of these four readings, which gave the temperature of the skin-water junction, will be described as "skin temperature ". Skin Temperature in Air and Mean Body Temperature.-In order to assess the mean temperature of the men's surface tissues, the temperature of their skin was measured in air immediately before and after immersion with stirrup thermocouples. These were also made from 28-gauge copper and constantan wire, and insulated by a thin layer of "Araldite" resin. Skin thermocouples of this type are reported to give a reading accurate to 0.10 C. [Stoll and Hardy, ], except when radiant heat is falling on the skin; the subjects were, therefore, shielded from radiant heat while readings were taken. The e.m.f. was led to the direct-reading apparatus already described. Each set of readings comprised four from the trunk (front and back of chest, front and back of abdomen) two from the forearm (distal part of extensor surface, proximal part of flexor surface) two from the leg (distal part of medial side of shin, lateral side of calf) and two from the head (outer side of forehead, lower surface of chin). These sites were chosen as Burton [1935] developed a formula which can be adapted to calculate the mean temperature of the surface tissues of the body from such measurements, and for calculating the mean temperature of the entire body from them and the rectal temperature; skin temperature in air and mean body temperature, derived in this way, are reported in these experiments. Rectal Temperature.-This was followed during all experiments, and in some cases for 5 min. after the immersion was finished. The rectal leads were also made from 28-gauge copper-constantan wire, encased in semi-rigid "Portex'" plastic tubing of

5 Body Temperature of Man mm. internal diameter and 0 5 mm. wall thickness. The end of the tube was sealed by a solid filling of "Araldite", in which the junction was embedded. A rigid plastic rod, containing a bend of just over 900, was inserted into the lumen of the tube, to give it a fixed sharp curve 11 cm. from the thermojunction. When used it was inserted as far as the bend, and held in position with sticking plaster and by the swimming trunks or other clothes the subject wore. The device was safe, easy to insert and keep in place, and was very robust. It had sufficient rigidity to hold the junction against the anterior surface of the rectum cm. from the anus, thereby avoiding the errors involved in the use of a soft rubber catheter [Mead and Bonmarito, 1949]. These probes had a 90 per cent response time of 24 sec. (mean of three determinations). (Esophageal Temperature.-This was also measured in some of the 150 C. immersions, but the number of measurements was limited as some of the subjects found the cesophageal probes unpleasant. The cesophageal leads were also made from 28-gauge wire, but since this was too rigid to be inserted easily the final 50 cm. of the wire was drawn down to 34-gauge. This was enclosed in flexible "Portex" tubing of 1*57 mm. internal diameter and mm. wall thickness. The ends of these were also sealed with "Araldite", in which the junction was embedded. The 90 per cent response time of this unit was 7 sec. (mean of three determinations). These thermocouples were passed through a nostril as the subjects found this easier than swallowing them through the mouth. They were inserted cm. during immersions. The e.m.f. from both the rectal and cesophageal probes was led to a potentiometer. The relative accuracy of the potentiometer for readings taken within a few minutes of each other was better than C. although the absolute accuracy was rather less. Determination of Metabolic Rates.-These were determined by indirect calorimetry during the final 17 min. of immersion. A Kofranyi-Michaelis respirometer was used in all working experiments and was calibrated repeatedly against a Parkinson C.D.4 reference meter. During the still experiments expired air was collected in one or more Douglas bags. The oxygen content of the expired air was measured with a Hartmann and Braun automatic analyser, whose readings were accurate to 2 per cent of scale reading. The masks used to collect the expired air were high altitude oxygen masks of a type supplied to the Royal Air Force and Fleet Air Arm, and when a suitable size of mask had been found for each subject it maintained a satisfactory air seal when pulled tight on the face. Each mask was used for eight to twelve experiments. Their normal air intakes were sealed off and a single Siebe-Gorman valve used for the intake, to which air was led through a rubber tube which opened well above water level. When cesophageal thermocouples were used, they were passed through a rubber tube sealed into the mask, which was then clamped to prevent escape of air. RESULTS 20 min. Immersions at 15 C.-Table I shows that the men's mean skin temperature was within 0.60 C. of water temperature 2 min. after the start of the still unclothed immersions in stirred water and within 0 2 C. of water temperature by the end of them, and was also close to water temperature in the working unclothed experiments. Clothing kept the average skin temperature more than 50 C. above water temperature when the men were still but was considerably less effective when they worked. Their mean skin temperature, measured in air after they left the water, was slightly higher after the working than the still unclothed immersion, but lower after the working than the still clothed immersion.

6 74 Keatinge The men's rectal temperature fell on average C. during the still unclothed experiment. When they worked unclothed at the standard rate it fell over twice as fast and the difference was highly significant, and the cesophageal temperature of five men also fell considerably faster in the working than the still unclothed immersions at 150 C. Clothing reduced the fall in rectal temperature both when the men worked and when they remained still. The mean body temperature, calculated from the rectal and mean surface temperatures measured before and after the immersions, fell by about the same amount in working and still unclothed immersions. Clothing TABLE I.-OBSERVATIONS ON THE EFFECTS OF IMMERSION FOR 20 MIN. IN WATER AT 15' C. THE INFLUENCE OF CLOTHING AND WORK (All figures means for twelve subjects) Unclothed Clothed Still Work Still Work Skin temperature 'C. after 2 min t 20 7t 18 7t Skin temperature 'C. after 19 min X1 16X4 Skin temperature 0 C.in air after immersion Fall in rectal temperature 'C t 0.16* 0 33 Fall in cesophageal temperature 'C. (five subjects only) *. Fall in mean body temperature 'C :6t 4'6 Metabolic rate (k.cal./min.).... 2' * Difference from still unclothed immersion, P < 05. t Difference from still unclothed immersion, P < 01. Note.-Water stirred artificially in still experiments. greatly reduced the fall in mean body temperature in still immersions, but reduced the fall less in the working experiments. The men's metabolic rate during still immersions was lowered somewhat by clothing. It was over twice as great when the men worked unclothed than when they were still unclothed in stirred water. When they worked wearing clothing their metabolic rate was higher than when they worked without it, presumably because of the extra drag caused by the clothes. 20 min. Immersions at 50 C.-Table II shows that within 2 min. of the start of the still unclothed immersion at 50 C. the men's mean skin temperature was 1.40 C. above water temperature, and was 0. 8 C. above water temperature at the end of the immersion. It was a little lower when the men worked unclothed. Clothing kept the skin temperature on average 7.70 C. above water temperature until the end of the experiment in the still immersion, but only 3.30 C. above water temperature when the men worked. The men's mean skin temperature, measured in air after they left the water, was only slightly lower after the working than the still unclothed experiment, but was considerably lower after the working than the still clothed experiment. The men's rectal temperatures fell rapidly in the unclothed experiments at this temperature, and fell more rapidly when they worked than when they stayed still. Clothing greatly decreased the fall, reducing it to a lower level

7 Body Temperature of Man when the men were still than when they worked. The falls continued at an even greater rate in the 5 min. after the men left the water, and the effect of work and clothing on the falls was much the same during the 5 min. after leaving the water as during immersion. TABLE II.-OBSERVATIONS ON THE EFFECTS OF IMMERSION FOR 20 MIN. AT 50 C. THE INFLUENCE OF CLOTHING AND WORK (All figures means for five subjects) Clothed Skin temperature 'C. after 2 min. Skin temperature 'C. after 19 min. Skin temperature 'C. in air after immersion Fall in rectal temperature 'C. during 20 min. in water Fall in rectal temperature 'C. during 5 min. after leaving water. Fall in mean body temperature 'C. during 20 min. in water Metabolic rate (k.cal./min.) Unclothed I Still Work Still Work 14-It 11Ilt *2 15*6 1* * 0 29t 0o61t * * * 8-97 * Difference from still unclothed immersion, P < 0 5. t Difference from still unclothed immersion, P < 01. Note.-Water stirred artificially in still experiments. The mean body temperature fell slightly faster during the working unclothed than the still unclothed experiment. Clothing reduced the falls in mean temperature greatly when the men were still in stirred water, but reduced them less when they worked. The men's metabolic rate was on TABLE III.-OBSERVATIONS ON THE EFFECTS OF IMMERSION OF UNCLOTHED MEN IN WATER AT 25 AND 350 C. FOR 20 MIN. THE INFLUENCE OF WORK (All figures means for twelve subjects) 250 C. 350 C. I Still Work Still Work Skin temperature in air after immersion, 'C * Change in rectal temperature, 'C t Change in mean body temperature, 'C t Metabolic rate (k.cal./min.) * Difference from still immersion at same temperature, P < *05 t Difference from still immersion at same temperature, P < 01. Note.-Water stirred artificially in still experiments. average over 4-5 k.cal. min. in the still, and 6-9 in the working, unclothed immersions, and clothing substantially reduced the metabolic rate in the still stirred immersions. 20 min. Immersions at Higher Temperatures (all unclothed).-table III shows that men's mean skin temperatures measured in air after unclothed immersions at C. depended mainly on the temperature of the water 75

8 76 Keatinge they had been in. They were, however, rather higher after the working than the still immersions at both 25 and 350 C., significantly so at the latter temperature. In the still immersion at 250 C. the men's rectal temperature fell on average only C., but it fell more than twice as far in the corresponding experiment at 350 C. Work somewhat reduced the men's average fall in rectal temperature in water at 250 C. and converted the fall into a rise in water at 350 C. The latter effect, though small, was highly significant. Work did not affect the men's fall in mean body temperature in water at 250 C., but it eliminated their small fall in mean temperature in the 350 C. immersion. The metabolic rates were on average 0*57 k.cal./min. higher in the still immersion at 250 C. than in that at 350 C., and were also higher in the working experiment at 250 than in that at 350 C. In a further still experiment at C., the men's rectal temperatures rose C., on average, but their metabolic rates were almost exactly the same as in the 350 C. still experiment. Other Experiments.-It was found that when the twelve men worked as hard as possible without clothing in water at 5 or 150 C. their rectal temperatures fell a little less than when they worked at the standard rate, but faster when they kept still. It was also found that their skin temperature, whether they wore clothes or not, fell somewhat less in still experiments at 150 C. if the water was unstirred than if it was stirred, but their fall in rectal temperature was little affected by stirring. As regards falls in rectal temperature individual differences between men were substantial; in particular the only fat man of the group suffered smaller falls of temperature in cold water than the others, whether he worked or not. A number of other experiments were made which showed that work continued to accelerate the fall in rectal temperature of both clothed and unclothed men in immersions lasting 40 min. in water at 15 C., and that work accelerated the fall in rectal temperature of unclothed men in water at 150 C. when they were really hot before immersion. These results are available in full elsewhere (see footnote, page 70). Subjective and Clinical Observations The subjects were often distressed and gasping for breath for the first minute or two in water at 15 or 50 C. The intensity of the breathlessness and discomfort varied from subject to subject, but always decreased rapidly, and within 2-3 min. of immersion most men were fairly comfortable. This discomfort also decreased with successive immersions and most subjects found the final immersion at 15 C. less unpleasant than the first. Most subjects felt colder at the end of the working than the still immersions at 15 C., both after those lasting 20 min. and those lasting 40 min. The men were sometimes shivering considerably at the end of these immersions, particularly after work, but always remained able to co-operate well and in a reasonably composed mental state. After unclothed immersions at 50 C., however, all except the fattest subject were shivering intensely, were confused and did not respond to questions. Their mental state appeared to be

9 Body Temperature of Man somewhat less disturbed during and after working than still experiments without clothes at 50 C., and they were generally able to climb out of the water more easily after the working experiments although their rectal temperatures fell more in them. After two 50 C. experiments, two subjects were unable to remember leaving the tank, one after his still stirred unclothed immersion and the other after his maximal work immersion. Both appeared to have complete amnesia for a period starting 2-5 min. before leaving the tank to the time they went under the shower. Immediately after the men went into the hot shower after the unclothed 50 C. immersions, the shivering and discomfort always increased somewhat and one man had to be helped to a chair. The shivering made it impossible to measure blood pressures or heart rates at this stage, but since no subject lost consciousness it is unlikely that any suffered a true faint or a substantial fall in blood pressure under the shower. In the still experiments the subjective effect of clothing was striking, particularly in water at 50 C.; when the men wore clothes they were always reasonably comfortable during still immersions at this temperature and were quite cheerful and co-operative afterwards. When they worked they again remained in noticeably better condition if they were clothed, but the difference then was less great and they were in better general condition after the still clothed than the working clothed experiments. The men occasionally experienced cramp in the legs at the end of immersions at 5 and 150 C. Subject 5, the thinnest man, had them most frequently. They were commoner in the thinner men, and when the subjects were still than when they worked. They often came on only when the men started to climb out of the tank. Some men had to be assisted out of the tank after unclothed experiments at 50 C., but all subjects were able to climb out unaided after the 150 C. immersions and most were able to do so after the 50 C. immersions, although their movements were generally slow and clumsy. Penetration of Clothing by Water None of the clothing was waterproof, and the men's skin temperatures fell abruptly as soon as they entered the tank, showing that their skins were wetted immediately. Air bubbled out of the clothing for a minute or two after immersion. It then ceased, and the clothing had little buoyancy thereafter, showing that there was little air left in it. DIsCUSSION Effect of Muscular Acitivity on the Body Temperature of Stirred Water Unclothed Men in Deep Body Temperature.-Perhaps the most important finding in these experiments is the effect of work on the rectal temperature when the men were unclothed and the water in the still experiments was stirred. This was shown to depend on the temperature of the water, work increasing the fall in 77

10 78 Keatinge rectal temperature in water below about 250 C. and having the opposite effect in warmer water. It is of some importance that work accelerated the men's fall in cesophageal as well as rectal temperature in these experiments in water at 150 C., since the temperature of the deep tissues of the body is not uniform. The effect of work in increasing the fall in deep body temperature in cold water cannot be attributed to agitation of the water, since the men's skin temperatures were kept close to that of the surrounding water in the still experiments. The blood flow in muscle is increased many times by exercise [Grant, ; Barcroft and Dornhorst, 1940] and, presumably because of this, work increased the loss of heat from the central part of the men's bodies more than it increased the heat production. The rate of heat loss from the body core is determined by the temperature gradient between its core and its surface and by the thermal conductivity of the intervening tissues. In working unclothed and still stirred unclothed experiments of the present series, surface temperatures were fixed close to either 5, 15, 25 or 350 C. and the men's deep body temperatures were approximately constant at C. Work would presumably increase the thermal conductivity of the tissues by about the same amount at all water temperatures (although shivering complicated the still experiments in cold, and vasodilatation those in warm, water) and so would increase the heat loss greatly in cold water and little in warmer water. On the other hand it increased the heat production by about the same amount at all water temperatures, and so its effect on the resultant heat loss from the body core should vary with the water temperature; this can explain why work increased the rate at which the deep temperature of thin subjects fell in cold water but caused a rise in warmer water. These results do not bear out the theoretical calculation of Glaser [1950] that an unclothed man should be able to balance his heat loss by muscular work in water near freezing-point. They are in keeping with the observation of Pugh and Edholm [1955] that swimming accelerated the fall in rectal temperature of a thin man in water at 160 C., though they do not support the possibility, raised by the latter author's findings, that work might help to maintain the body temperature of a fat man in cold water; moreover, further experiments [Cannon and Keatinge, 1960] have shown that unclothed fat men achieved thermal stability in stirred water as cold as 120 C. when sitting still, while in water below that temperature work accelerated the rate at which their rectal temperature fell. It therefore seems unlikely that work would ever prolong the survival of even fat men in cold water. Surface Temperature.-The fact that the men's skin, unlike their rectal temperatures tended to be higher after the working than the still unclothed experiments at 15 C. is probably due to higher blood flow and higher heat production in peripheral muscles; skin temperatures were also somewhat higher after the working unclothed than the still stirred unclothed experiments at both 25 and 350 C. In water at 5 C. this effect seems to have been outweighed by the rather more effective agitation of the very cold water in the working than the still experiments.

11 Body Temperature of Man Effect of Clothing on the Maintenance of the Body Temperature in Water.- It is clear that clothing gave a substantial amount of protection during immersion when the men were still, and that after the first few minutes it gave relatively little when they worked. The fact that it had a proportionately greater effect in maintaining the men's rectal temperatures than their skin temperatures, particularly in water at 50 C., can be explained by the fact that the men's falls of rectal temperature increased greatly with relatively small falls in skin temperature below 150 C., for reasons which will be discussed later. Since the thermal conductivity of water is approximately cal./cm.2/ sec./0c./cm. and the thermal conductivity of air is approximately cal./cm.2/sec./0c. [Hodgman, 1947], clothes soaked in water must provide much less insulation than clothes in air. Nevertheless, although the clothing was thoroughly soaked in the present experiments, water immobilized by it appears to have provided a useful amount of insulation. Since the specific heat of water is by definition about 1 cal./cm.3/ C. and the specific heat of air only about * cal./cm.3/0c. [Hodgman, 1947], it is clear that any movement of water will carry heat away rapidly, and that movement will reduce the insulating effect of clothing much more effectively in water than in air. This probably explains the considerable reduction in the protection given by clothing when the subjects worked in the water. Water under the clothes seems to have been disturbed much more by movement of the subjects than by vigorous external agitation of the water. Rapid Cooling in Water at 50 C.-The rapid falls in the men's rectal temperatures in the 50 C. unclothed immersions may have been due in part to cold vasodilatation in their skin. Cold vasodilatation can appear in fingers cooled below 120 C. [Lewis, 1930]. It is produced by local cooling of the fingers even in men who are generally chilled by exposure to cold air or immersion in cold water [Keatinge, 1957], and appears to be due largely to a failure of blood vessels to respond to constrictor drugs when cooled to near freezing-point [Keatinge, 1958]. The loss of heat even from the extremities as a result of cold vasodilatation can be considerable [Greenfield, Kernohan, Marshall, Shepherd and Whelan, 1951], and the dilatation [Clarke, Hellon and Lind, 1958] is not confined to the extremities. The large effect of clothing in reducing the men's falls in rectal temperature in " still " experiments at 50 C. was probably due to the fact that clothing kept their skin temperatures just above the level at which a substantial degree of cold vasodilatation developed. The falls in the rectal temperatures of most subjects in water at 50 C. were considerably greater than those observed by Behnke and Yaglou [1950] for men in water at 60 C., but were of the same order as were observed in the Dachau experiments [Alexander, 1946] for clothed men in water at 50 C. The difference from the findings of Behnke and Yaglou [1950] may have been due in part to the lack of stirring in those authors' experiments, and their subjects may also have been fat; the fat man in the present experiments cooled at about the same rate as their subjects. The fact that the prisoners in the Dachau experiments cooled almost as fast as the subjects of the present 79

12 80 Keatinge experiments, in spite of the fact that the former were usually clothed, can probably be accounted for by undernutrition in the Dachau prisoners. Fall in Rectal Temperature in Bath at 350 C.-The men's rectal temperatures fell more in the 350 C. than in the 250, and almost as much as in the 150 C. still immersions. This must have been due to vasodilatation, probably as a result of the cutaneous sensation of warmth; a similar fall in the rectal temperature of men immersed in water just below body temperature was observed by Burton and Bazett [1936]. Impairment of Capacity to Perform Muscular Work at Low Temperatures.- It is of practical interest that the men were able to maintain quite high rates of work in the 50 C. immersions and were almost always able to climb out of the tank unaided after them. The ability of the forearm muscles to sustain a contraction is reduced when the forearm is immersed in water below 180 C. for 30 min. [Clarke, Hellon and Lind, 1957], and greatly reduced in water at 2 C.; while the tension developed by rat muscle at stimulus frequencies over 30 per sec. is considerably less at 9.5 C. than at higher temperatures [Doudoumopolos and Chatfield, 1959]. The absence of really gross impairment in the ability of the present men to work in water at 50 C. was probably due to the fact that most of the work was carried out by the muscles of the thigh, upper arm and trunk, which must have cooled relatively little, and to the fact that the movements were fairly slow. Fatness of the Subjects.-The average weight of the subjects was 69-3 kg. which is very close to the standard weight of 69-1 kg. quoted by Brozek and Keys [1951] for men aged 20. Their skinfold thickness was on average a, little greater than that recorded by Hammond [1955] for British men aged with the same type of fat calipers. Brozek and Keys [1951] reported that middle-aged professional men had a considerably greater fat thickness than young men, and Hammond [1955] that girls have a greater thickness of subcutaneous fat than boys and children less than adults. The present subjects therefore seem to be fairly representative of young British men. Since the rate at which men's rectal temperature falls in the cold is affected by [Winslow, Herrington and Gagge, 1937; Pugh and Edholm, 1955], and quite closely related to [Keatinge, 1960] their subcutaneous fat thickness, women and middle-aged men would probably suffer smaller falls of deep temperature in cold wivater than the present subjects while children and poorly nourished adults would probably suffer larger ones, particularly during work. Practical Conclusions Perhaps the most important practical conclusion is that physical exertion accelerated the rate at which the men's rectal temperature fell in cold water. This was true whether the men were clothed or not, whether the water was stirred or not, whether they worked hard or moderately and whether they were hot or cool when immersed, and it seems clear that men forced to remain immersed in any but tropical waters will survive longer if they float still with life-jackets or wreckage than if they swim about or struggle.

13 Body Temperature of Man 81 The effect of exertion seems to be less serious in fat than thin men in cold water and to disappear or be reversed at tropical water temperatures, over about 250 C. There also seem to be certain very limited conditions in which exertion is not harmful to men in cold water, since the men's surface and mean body temperatures fell little more in the 20 min. working than the still stirred, unclothed immersions at 50 C., and the men tended to be in somewhat better mental condition and more agile after the former. This was not the case in clothed or in longer immersions and it must be rare for a lightly clothed or naked man to be immersed in agitated water and to know that he will be rescued within 20 min., but such people would probably be as well off if they exerted themselves, particularly if it enabled them to get out of the water more quickly. These experiments also show that conventional close-fitting clothing gave a striking degree of protection in water at 50 C. and gave a useful amount of protection in water at 150 C. This protection needs to be weighed against the disadvantage of waterlogged clothing in hampering a man's rescue from water, but was so large in water at 50 C. that it probably outweighs any such disadvantage in immersions in Arctic waters; without it, a 20 min. immersion at 50 C. made most men incapable of doing much to help themselves. ACKNOWLEDGMENTS This work was supported by the Survival-at-Sea Sub-Committee of the Royal Naval Personnel Research Committee, in particular by its Chairman, Professor R. A. McCance and Secretary, Mr. F. E. Smith. Surgeon-Captain F. P. Ellis arranged for naval volunteers to be made available as subjects. Lieutenant H. Burton carried out the daily administration connected with the subjects and Mr. R. Luff and S.B.A. T. R. Simmonds gave technical assistance. The active co-operation of the subjects played a large part in the success of the experiments, particularly those at the lower water temperatures. REFERENCES ALEXANDER, L. (1946). Combined Intelligence Objectives Sub-Committee. Item 24, File Nos BARCROFT, H. and DORNHORST, A. C. (1940). J. Physiol. 109, BEHNKE, A. R. and YAGLOU, C. P. (1950). J. appi. Physiol. 3, BROZEK, J. and KEYs, A. (1951). Brit. J. Nutr. 5, BURTON, A. C. (1935). J. Nutr. 9, BURTON, A. C. and BAZETT, H. C. (1936). Amer. J. Physiol. 117, CANNON, P. and KEATINGE, W. R. (1960). J. Physiol. [In the press.] CLARKE, R. S. J., HELLON, R. F. and LIND, A. R. (1957). J. Physiol. 136, 41-42P. CLARKE, R. S. J., HELLON, R. F. and LIND, A. R. (1958). Clin. Sci. 17, DOUDOUMOPOLOS, A. N. and CHATFIELD, P. 0. (1959). Amer. J. Physiol. 196, EDWARDS, D. A. W., HAMMOND, W. H., HEALEY, M. J. R., TANNER, J. M. and WHITEHOUSE, R. H. (1955). Brit. J. Nutr. 9, GLASER, E. M. (1950). Nature, Lond. 166, GRANT, R. T. ( ). Clin. Sci. 3, VOL. XLVT, NO

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