ARKORYD MEDICAL RESEARCH LABORATORY

Fort Knox, Kentucky

S"Project 1o. 1-19 31 May 1946SPMIA 727-1

1. PROJXCT NO. 1 - Cold Wearther Operations. Third Partial Reporton Sub-Project 1-19. Study of the Physiologic Iffects of Cold.

a. - Letter Commanding General. Headquarters Airmored

Force, Fort Knox, Xentueky, File 400.112/6 GNOHD, dated September PA. 1942.

2. DIACUSSIOgr:

Military operationo- in cold weather naturally pose many problems.One of the most important is related to immobilization of men for long periods oftine, preventing them from indulging in even the smallest movements from fear ofhaving their presence detected. The experimental work being reported is concernedwith the reactions of soldiers sitting quietly for periods of two to three hoursin environmental temperatures ranging from 41 to -40 0 C.

3. C0•CIUsIoNS:

The data here presented illustrxte some of the phyliologicel changerthat occur in mmn exposed to low environmental temperatures. The responses of mento cold is complicated by a number of extraneous factors which are, at present,poorly understood. Physiological and psychologictl studies 41n progress at the presenttime will, it is hoped, clarify a number of po!nta regsirding thi variability of theresponse of clothed men to very cold environments.

4. RY-CWt4E2DATIONS:

No specific recommendations Fxe made.

Submitted by-Steven M. Horvath, Major, SaUHoward Gclden, Tec 3

John Wagar, Tec 3

',PR077D T I)--~-~-- '

(/7 1JY 'N0FLAUaT{"Lt. Colonel, Mc

3 Incls. 0'am= nr,~#1 - A~ppendix

#2 - Tables 1 - III

,K _TTIMi No,

O

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APP)WMX

"THQODI Forty-five younr men in excellent physical condition served aosubjects for a total of 430 tests. The largest number of exposures for a stnglsindividual wni thirty-five. Two to five tests were performed on each subjectin a 'ingle environment. 0tt group of five subjects was exposed to all environ-ments with thn exception of 11.10C. The average characteristics of the entiregroup were az follows: Age, 20.5 years; height, 67.6 inches; weight, 140 p•vfled5end surface area, 1.79 square meters.

All exposurem were made in the morning between 8 and 12 o'clock. Thesubjects ate a light breakfast two to three hours prior to their entrance intsthe cold room. The men put on thermocouple harnesses of five to flfteen copper-constantan couples and after donniug their underwear remained lyinAg quietly forat least one-half hour in a control room, environment 220 C., 50% relative humidi-ty. Basal measurements of skin and rectal temperatures (with a thermocouple ora calibrated rect&l thermometer) were then obtained and the men proceeded todress in their Arctic clothing'.

RESZMT Te data obtained are presented in Tables I, II sad IIZ andFigures 1 to 11. All data presented in the tables are mean values, but in orderto indicate to some extent the variability that was encountered, ranges are alsogiven.

N•TABOL30I5 0F §AT3D. CLT=1D M) ' s When sen quietly seated in a relatlve*7cool environment of 220C. for a three hour period, only slight alterations ofapproximately 5 per cent in metabolism were observed (Table 1). Nzposure tocold environments was accompanied by increased metabolic rates and this wasevident even in the very first hour of the sitting period. However, irr*gulr-ities in response were common, varying from no chenge to increases of over 30per cent. This latter value, obtained at an environmental temperature of 2.10C.,was exceptional for the first hour; the majority of the increases were around10 per cent. Durine, the second hour of exposure a striking rise of the metabolicrAte occurred at all environments. The highest increase of 53% was observed atthe lowest environmental temperature, -40 0 C., although no correlation betweenambient temperature and metabolic response was notea. The metabolism contiiUedto rise during the third hour, reaching in the -40 0 C. envirovzent a value ofalmost 74 per cent above basal.

§XIN AND ANTAL TINPERAEURx: The data are presented in Tables 11 and UIIand -,gures I to 11. The man dcin temperatures were calculated from the fiveskin areas included in Table U1. The major portion of fall in mean skin

"*§Arctic clothingt' with insulative value of approximately 4 clo, conaisted oft

Underwear, wool 50-50 Socks, cushion sole, 1 pairTrousers, field, alpaca pile (3/81) Socks, ski, wool, 2 pairTrousers, field, cotton Shoes, flet orJacket, field, pile (3/8") Xuklaks, with burlap insolesParka, field, pile (3/8") Mittens, woolParka, field, cotton Mittens, shell, outer

teoiqrats'o ecovirred in the first hour of exposure. The average seaa canves91olted in ncoe 1 illustriste this rapid fall. The rate of decreasing tamper-atures w*a very slow in the lUet half of the exposure. While this may be relatedto the Intreased metabolism of the later perti&, more probably it indicated theattainmeat of a equilibrium between input and lose of heat from the clothedbody. The relative etabilitt. of the rectal temperature in this last one and aae-half to two hours of expo•ure (Table 1U1) aeds additional emphasis to this Mwg'gested leveling-off phenomenon. Vith the exception of the curves for environ-Sento of -26.lMnd -34.4 0 C., thew. appearod at the end of three hours to be agreater drop and a lover final mean Odn temperature the colder the environment.

The ranes of skin and rectal teup,;.atures are preosnted is an indicationof tha variability to be erpectd and the futility of depending upon observationsm&oe on a few subjects in exporiments of tht.a nature. The frequency distributionof the mea& skin temperature durinr the threc hour exposure to four of the environ-ments stn-lked, vii., -17.860 -23.30; -28.90, and -40.000. ar* showa in Figures293,4. and 6, They eaphasise the rapidity of drop in mean abin values an=4 thesecmtter that caa bA expected. Unfortunately thi fail to show that an tudivldualzaiF atart off with one of the higher initial temperatus but end the period ofexposure with one of the lowest. For example, at the -4MO.C envron•menta onesubject hai an Il•tial value of 35.°C. and a final value of 17.24C. wilhz anotherstarted with 3,20C. and ended with 28.2C. In these cases neither subjectcomplained of the cold; only tho firat subject shivered and this occurred after170 minutea of exposure.

The data on values obtained for arz, chest# thlgb, calf, and toe are alsogivon In Table 11 as a'ditional evidence of variability uad to show the regionaldifferences in rate and degree of change in the t~aperatures of these parts,The susaeptability of the extremities to low gnvironuental temperatures and theprogressively greater inadequacy of foot protectioA Arx Indicated by the frequeacy"istribution diagrams of ?igures 6 to 11 inclusive. Tze temperutures below 000.

vere recorded in environments of -234C. and below. Thaso occurred in a mibevof cases before two hours of the exposure had elupwed. In some individmle aphastc type of retponse was observed in which the toe temperature, after the abovemount of eoollug, sudaenly rose 6 ta 10 degrees, but retumed again very rapidlyto lower levels. Other tndividuals remained at theso low levels. No cases offrostbite wore observed in any of tho subýects. Subjective complaints re"ardingtoes and other areas could not be definitely related to the temperature of thepart. Frequently the complaints wore more vigorous with the higher temperaturesthan with ýhe lower.

The obsorvatioss made on the divernity in rate ad extent of fall in meanekin or individual part teaperatires were aleo observed with rectal temperatures(Table Z11). Considerable caution must be exercised in the Interpretation ofanW single individual value. An interosting observation was the finding thatafter the men returned to a comfortable environaent, 200., their rectal t•emper-aturoes continued to fall This is probably a reflection of the coctinuing trans-port of cooled blood from the body surface to the body core.

M12gJs T• variability observed In the reactions of sme to coldeuviroments are related, althou&, not as a positive correlatlomn to the vuawtlons

in metabolim, in mean skin, body and in unit area temperatures. Since allsubjects wore clothing offering essentially similar ingulative protection aadsince tests were made ot each man in several environments, these findings areof importance in the final evaluation of protective clothing akd susceptibilltrof son to the effects of cold. Most subjects followed a regular pattern inthat the colder the enrironment the more uncomfortable they were by both sub-jective and oblective criteria. However, a few men were comfortable at lowertemperatures and uncomfortable at certain higher ones. The cause of thesevariations could not be determined and remains a major stumbling block to adelineation of the physiologic responses cr men to cold environments.

On exposure to cold the total metabolism is increased (Table 1). Thecause of the increased heat production is not clear and considerable dispute hasarisen as to whether the increase is induced solely through muscular movements.Including shivering, or whether other mechanisms are brought into play. Cannoaet &.L, favors a humoral factor, i.e., adrenelin, as being the factor, suggzstiagthat Increased metabolism is due to the increased secretion of this hormone.Other inveotigitors while favoring the humoral theory, feel that the adrenalcortex plays the more significant role in adaptation of animals to cold environ-mente. [rogh believes that the increased activity of the animal exposed to coldmay be the factor increasing muscle tonus at rest and so affecting the basalrate.

There is no doubt that even adequately clothed individuAls shiver, some-times quite violently, while sitting in the cold and that the large increases JAheat production observed in the lant hour to hour and a half in our subjects weremainly due to this activity. It was difficult to explain the increases in thefirst hour on this bacis as gross shivering was generally absent. Although Is-creased muscular tonus may be the cause it was impossible by methods emplored todetermino Wa evidence of greater tension. The following table is An analysisof subjective data on shivering obtained at an ambient temperature of -28.90C.

SARosu. 2ime at Onset,ober of SubgtsierA

10% Under 66 minutes25% Under " minutesU4 Under 0 minutes76% Under -. minutes90% Under 181 minutes

At this environment of -28.9 0 C., only a mall fraction of the group exhibttedeven the mildest shivering in the first houw, although the heat production ofthe group had increased almost 13 per cent.

These data substantiate neither the chemical nor the mnscular actiW~tytheories of Increased metabolism. Alterations in usecular tone cannot be elimi-nated as a cause of the raised heat production, and since it was impossiblq Inthese experiments to demonstrate an increased secretion of epinephrine the roleof this factor cannot be clearly evaluated. However, since the experiments ofdo Barenno, et al. indicated that Increased muscle toce is not associated withana' high degree of metabolism, the chemical theory is en attractive explanationfor the initial increase in the metabolism of clothed mon sitting quietly in a

//

cold environment. Furtheomre, Hicks has performed experiaents on the Australian,borigine suggesting that the inersased heat production at low environmentaltemperatures are not brought about by shivering.

Higher skin temperatures were sometimes associated with high metabolic rates,but the ccntrar was also observed - high metabolism with lowered skin tompera-tures. 1'wift reported that his partially nude subjects began to shiver when theskin temperature reached 1900. Io such correlation was found in the presentobservatious, but heav7 clothing worn by these men may have Interfered with theIrresponses, When shivering did occur, skin temperatures of 290C. to 160C. wererecorded, Individuals had different responses on differGnt days under identicaloenvironmental conditions.

7b& changes in rectal toeperature bore no relation to the metabolic rate.Swift's data on lightly clothed subjects indicated that changes in rectal temper-atures were not a stimulus to shivering and, therefore, were not related to theincreased metabolic rates observed. Vaughn's metabolic studies on subjects whoserectal tempiratures had been lowered to approximately 8407., disclosed that therevas a relationship between rectal temperatures and metabolism since all subjectshad a mrkedly lowered metabolic rate. However, Dill and Forbes in similar ex-periments reported the total energy exchange to be above basal levels due to shiver-ings, voluntary activity, end a muscular rigidity of unknown origin.

vWJ Continuous observations were made of the metabolic rate, skin andrectal temperatures of men while dressed in Arctic uniforms and sitting quietly _in extremely cold environments. Ambient temperatures ranged from(ýl.l to 40O.4*'

The heat production in the cold was above basal values during the enti"atest period. In the -4 0*C°,environment, avevage metabolic increase of 13, 53and 74 per cent were recorded for the first, second and third hours respectively.The rise in heat output during the first hour could not be explained on the basisof shiverIng. In the third hour, shivering was present in the majority of thesubjects.) Neither the role of chemical mediators nor that of increaned musculartonus.omfeld be clearly delineated and requir. additional investigation.

-?2he fall in rectal temperatures was moderate although values of 35..04°were occatsionally obseriod. The absolute value was not correlated with the pres-ence of shivering and, therefore, low rectal temperatures could not be consideredas the stimulus for shivering.

Mean skim temperatures fell precipitously during the first hour of exposureand were stabilised before the end of the test period. Considerable variabilitywas observed in both the rate and extent of fall not only in different mon, butin repeat tests on the same subject.

Of all the skin areas, the hands and feet exhibited the great*!) temperaturechanges in both rate and degree of fall. Toe temperatures below OOC.- were not4din several instances. The susceptibility of the extremities to cold environmentswas related to their sensitive vasomotor ;-echanisms and to the fact that theywere provided with the least amount of insulative protection. / _

The responses of mon exposed to cold environments are subject to considerable

'4

variation and extreme care must be exercised in the interpretation of data obtained,Ohether on a few or a large number of subjects.

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TABLE III

Rectal Temperatures (0c) of Men Sitting %uietlyat Designated Environmental Temperatures

Room Banal First Hour Second Hour Third HourTemperature -

Men Rne Me an 1Range Men Rge M ag

22.2 37.8 37.4 38.1 37.1 -06.1 37.6 37.0 36.4 37.4 37.0 36.3 .

1.1 37.-4 37.2 37.6 36.9 36.6 37.2 36.8 36.4 37.0 - - -

-17.8 37.4 37.0 37.9 37.2 36.6 38.1 j136.9 36.3 37.7 3o.7 36.3 3.31

-23.3 37.8 36.9 38.4 37.2 36.7 37.5 36.8 35.9 37.6 136.8 35.8 37.6-26.1 37.4 37.0 37.8 37.0 36.8 37.4 36.7 36.4 36.9 - - -

-28.9 38.0 36.1 38.2 37X0 36.0 37.6 .36.8 35.8 37.2 36.7 35.4 37..1

-34.4 37.3 36.9 37.6 37.1 36.8 37.3 1f36.6 136.4 36.7' (J6~.4 J6.1 36.7

-40.C 37.4 37.0 3e.1 36.9 36.8 _ .2 33.8 136.7 36.1 37.-1

FIG. I

MEAN SKIN TEMPERATURES OF SITTING MEN

EXPOSED TO LOW ENVIRONMENTAL TEMPERATURES

35

0

0

404a-

Z5 -4000

20o I I0 2 3

EXPOSURE - HOURS

*1.

FREQUENCY DIST'RIBUTIOINJ IN MEAN SKIN TEMPERATURLIE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO - 17.8* C

40 -

30K

BASAL

10

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cr FIRST HOU

zuJI

LL30

20SE0OND HOU

0I0

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20THIRD HOUR

10

0o - - -- I I20 22 24 26 26 30 32 34 36 38 40

DEGREES CENTIGRADE

FREQUENCY DISTRIBUTION IN MEAN SKIN TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -23.3 C

40

30-

20 - BASAL-

10

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SECOND HOUR10-

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TEHIRD HOURI0 - l

20 22 24 28 30 32 34 36 38 4'

DEGREES CENTIGRADE

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FREQUENCY DISTRIBUTION IN MEAN SKIN TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -26,90.C

r BASAL

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DEGREES CENTIGRADE/cy #.

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FREQUENCY DISTRIBUTION IN MEAN SKIN TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -40.0 °C

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DEGREES CENTIGRADE

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FREQUENCY DISTRIBUTION IN TOE TEMPERATURE OF MEN SITTINGDURING A TWO HOUR EXPOSURE TO i.1 0C

50 ~

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-2 0 2 6 10 14 18 22 26 30 34 38

DEGREES CENTIGRADE

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FREQUENCY DISTRIBUTION IN TOE TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -178 0C

I30 -4

20

SECONDASAL

cTHIR HOUR~

r 7

FREQUENCY DISTRIBUTION IN TOE TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -23.3 OC

30

20

0

~-30

20

uj0 FIRST hOUR

z

LJ

-o

0020

, 0-V SECOND HOUR

,0 THIRD HOUR

-2 0 2 6 0 14W Is 22 26 30 34 38

DEGREES CENTIGRADE

FREQUENCY DISTRIBUTION IN TOE TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -28.9 0C

20

10 SAL-

20

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Q.

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0ui 20 ru-

10 SECONC HOUR

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-2 0 2 6 10 14 22 26 30 34 38

DEGREES CENTiGRADE.

f

FREOUENCY DISTRIBUTION IN TOE TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -34.4 @C

60

50

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0 0 2 6 10 14 !8 22 26 30 34

DEGREES CENTIGRADE ,

FREQUENCY DISTRIBUTION IN TOE TEMPERATURE OF MEN SITTINGDURING A THREE HOUR EXPOSURE TO -40.0 *C

t ~30

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DEGREES CENTIGRADE

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