A comparison of laboratory and field studies of cold response

A Comparison of Laboratory and Field Studies of Cold Response

JOEL M. HANNA Pacific Biomedical Research Center, University of Hawaii, Honolulu, Hawaii

ABSTRACT The recent application of physiological techniques to anthropological studies of cold stress in different human groups has produced evidence of considerable variation in response to cold. The usual anthropological procedure has been to com- pare the adult males of two different ethnic groups under standardized laboratory conditions, and then to generalize the conclusions in an evolutionary or ecological context. Several assumptions behind this procedure are examined.

Four studies of response to cold in the same Quechua Indian group of Southern Peru are discussed. Two of the studies deal with variation in response to cold in a standardized laboratory situation. The other two describe responses as detected under actual cold conditions experienced by the subjects as they go about their daily routines. The results of the laboratory and field studies are compared. It is suggested that adult males studied in the laboratory may represent only a minor part of the variation which exists in the group and that their responses may not be indicative of those of the entire population. It is also proposed that the validity of laboratory studies for an evolutionary interpretation may be limited by the laboratory approximation of the actual cold stress experienced by the group.

Anthropological interest in cold adaptation has led to a number of studies in which members of two or more ethnic groups were compared in situations of cold exposure. These studies show considerable variation in response to cold when such diverse groups as Eskimos, Bushmen, Abo- rigines and urban Europeans are considered. It has been proposed that these fit into an evolutionary scheme which re- traces man’s migration from the tropics to more arctic environs (Hammel, ’64). A typical study of ethnic differences com- pares the responses of unclothed or lightly clothed adult males of different ancestry as they are exposed to a similar cold experi- ence. Any differences in response may be variously assigned to genetic adaptations, acclimatization, body composition or any of a number of other features which could produce individual response differences (Buskirk, ’66). Because the number of subjects actually studied is usually small, in- trapopulatjon variation is seldom considered. Yet it is well known that biological parameters common to all populations, age and sex for example, may produce variety in response.

Anthropological interest in ethnic differences is usually directed toward their evo-

lutionary or ecological implications. Differ- ences are ascribed to the differing environ- ments inhabited by various groups. Thus each group is “adapted’ to its environment through a process of genetic and individu- ally acquired mechanisms. Physiological studies of ethnic differences within this framework often have two implicit assump tions: (1) The response exhibited by small groups of adult males is indicative of the response of their entire population; and (2) the patterns of cold response detected have validity outside of laboratory conditions.

This study was undertaken to examine the validity of these assumptions. Labora- tory estimates of cold response and actual measurement of cold response in everyday situations were compared. The population considered is known in great detail and is described in Baker, Escobar, Dejong, Hoff, Mazess, Hanna, Little and Picon-Reategui (’68).

LABORATORY STUDIES

The first of the laboratory studies compared men and women under identical cold stress to examine the variation which might be related to sex differences. Eight- een men and 18 women, all residents of

Am. J. PHYS. ANTHROP., 32: 227-232. 227

228 JOEL M. HANNA

Nuiioa and of predominantly Quechua ancestry were recruited as subjects. Anthro- pometric measurements are presented in table 1. They correspond to other published material from the Nuiioa region (Baker et al., '68). As might be expected, the women show greater skinfold thickness than men.

The general methods were described by Baker, Buskirk, Kollias and Mazess ('67). Subjects, tested in like-sexed pairs, reported to the laboratory at 8 : O O AM in a fasting condition. They rested for one hour after which they were conducted to a preparation room where they disrobed and re- clined on cots. After an hour's exposure to 78°F (covered with blankets if desired), the subjects entered a cold chamber. Cham- ber temperature was carefully maintained at 50 f 0.5"F. Surface body temperature was recorded every four minutes through thermocouples placed on the skin and core temperature through a rectal thermocouple. Metabolic gas (expired air) was collected through an open circuit system and analyzed with a paramagnetic analyzer.

RESULTS

Although a number of temperatures were recorded, the following will be used to illus- trate the basic patterns in the data: Rectal temperature (Tr), Finger temperature (Tf), and Toe temperature (Tt). Mean weighted skin temperature (Tmws) was calculated from skin temperature measurements ac- cording to the methods of Baker et al. ('67). The first three variables were analyzed for

TABLE 1

Biological and anthTopometric characteristics of laboratory subjects

Characteristic

Male Age - years Stature - mm Sitting height - mm Average skinfold - mm Weight - kg

Female Age - years Stature - mm Sitting height - mm Average skinfold - mm Weight - kg

Mean S.E.

29.7 1,586.2

858.4 6.0

55.6

26.3 1,449.5

791.0 9.8

44.5

3.1 14.2 5.9 0.3 1.1

2.1 10.8 8.5 0.5 1.4

sex differences using an analysis of variance.

Figure 1 illustrates the Tf and Tt for male and female subjects. The females maintain higher finger temperatures (Tf ) at a statistically significant level (P < 0.01), the males have significantly higher toe temperatures (Tt) (P < 0.05). Figure 2 illustrates Tr and Tmws. The women were warmer than the men on both of the measurements with the Tr being significantly different (P < 0.01). No statistical analysis was performed on Tmws.

Sex related differences did exist and showed a definite pattern. Women tended to maintain higher skin and core temperatures. The only exception is in foot temperature where the men were warmer.

The second of the laboratory studies examined the effects of clothing on the pat-

FINGER "1 a,

160-1 , , , , , I , , , ,

a TOE & 90

? 80

50 0 24 48 ' 72 96 120

EXPOSURE I N MINUTES

--MALE(UCL) -FEMALE (UCL) --- MALE (CL) '--A FEMALE ( CL)

Fig. 1 A comparison of finger and toe temperatures of clothed (CL) and unclothed (UCL) Quechua men and women during exposure to 50°F for two hours.

COLD RESPONSE VARIATION 229

'O"] \ RECTAL

5 90 c

MWST

\

70 0 24 48 72 96 120

EXPOSURE IN MINUTES - MALE (UCU FEMALE(llCL) --_ MALE(CL1 L - 4 FEMALE( CL)

Fig. 2 A comparison of rectal and mean weighted skin temperature (MWST) of clothed (CL) and unclothed (UCL) Quechua men and women during exposure to 50°F for two hours.

terns established in the previous study. The same 36 subjects were used and the experimental procedure was the same; the only difference was that subjects wore na- tive clothing (except sandals and ponchos).

Figure 1 shows the finger and toe temperatures of the subjects with clothing su- perimposed over those without clothing. There were no changes in the relative posi- tions of the male and female groups. How- ever, there was a general elevation of skin temperature. Figure 2 shows no major shift in patterning in Tr and Tmws. Women seemed to get some special benefit from the addition o€ clothing for they show a disproportionate increase in finger temperature (fig. 1).

These laboratory studies reaffirm the ex- istence of sex related differences in response to cold. The differences were not appreciably modified by the addition of clothing.

FIELD STUDIES

Baker ('66) described two periods during which the Indians of Nufioa reported the cold stress to be greatest. The first was during the nights of the dry season and the second during the daytime in the wet season, Baker studied the temperature responses of the Indians as they slept in their houses during the nights of the dry season. He collected hand, chest, foot and rectal temperatures on 18 men, 10 women and 28 children over 8 hours of night-time cold exposure. Chest and hand temperatures were similar in all three groups. Women maintained the highest rectal temperatures, men intermediate, and children the lowest. The ranking is reversed in foot temperature where the children are highest, men intermediate and women lowest. Baker considered the rectal temperature of children to be of special interest for it showed a rapid fall to equilibrium while that of the adults declined gradually.

The pattern of responses of men and women while sleeping at home was quite similar to that in the laboratory. The men have higher foot temperatures while the women have higher rectal temperatures. Chest and hand temperatures are similar for the two groups.

The second period of cold stress reported by the Indians is during the daytime in the wet season when there is considerable precipitation in the form of sleet, snow, rain, and hail. This precipitation is usually ac- companied by considerable wind activity. The responses of the Nufioa residents to this climate were measured during their waking hours (Hanna, '68).

Fifty-two subjects, 26 adults of both sexes and 26 children of both sexes were followed as they went about their daily activities. Surface, rectal and environmental temperatures were measured every two hours. Because of observer and equipment error, only five observations per subject are available for all 52, and the analysis is based on these. Temperatures were compared through an analysis of variance, and F tests were performed. Table 2 shows the mean temperatures for each of the four groups and table 3 shows the results of the analysis.

230 JOEL M. HANNA

TABLE 2

Mean temperatures (“C) during field studies by age and sex. {See text fa explanation.)

Site Young male

No. of subjects

per group

Old male

Young female

Old female

Forehead Chest Arm Hand Finger Leg Foot Toe Rectal Environmental

temperature

13 31.6 13 33.4 13 30.3 13 26.4 13 22.3 13 29.0

13 11.4

31.7 33.5 32.7 28.7 2.1.7 30.9 28.2 22.6 37.2

10.8

31.3 33.5 29.9 24.9 21.5 26.6 23.5 20.2 37.3

11.2

31.7 33.7 31.5 28.3 26.0 28.5 27.3 22.5 36.8

11.7

TABLE 3

F tests of differences between sites i n field studies. (See text fur explanation.)

Site Sex Inter- Age action

Forehead Chest Arm Hand Finger Leg Foot Toe Rectal Environmental

temperature

1.24 0.12 1.31 2.19 0.54 24.43 7.50 a 0.91 4.32

0.63

0.15 0.32 0.20 0.02 15.262 2.26 18.49 0.63 11.77* 1.02 14.74 0.00 17.402 2.12 3.32 0.60 11.892 0.74

0.30 0.96 5% level of confidence.

2 1%.

There were significant sex differences in leg, foot and rectal temperatures. In each case men were warmer, and table 2 shows this to be a tendency in children as well. Age differences were observed in arm, hand, finger and leg temperatures; the adults were warmer, but children showed significantly higher rectal temperatures. There were no significant differences in environmental air temperatures measured coincident with skin temperatures which might otherwise explain these age and sex differences.

This field study represents a partial re- versal of the observations of Baker (’66). In the present study the adult males had higher rectal, and lower-extremity temperatures, than the adult females. The adults had higher surface temperatures than children, while the latter maintained higher core temperatures.

DISCUSSION It should now be possible to evaluate the

two assumptions as they apply to the Nuiioa area. First, adult males represent the responses of the entire population under consideration.

Results described in earlier sections indicate that this is not necessarily the case in the Nuiioa area. In controlled laboratory conditions men and women show different patterns of response. Women maintain higher Tr and Tmws; the only exception seems to be the higher temperatures of men in the lower extremities. This basic pattern was reproduced in both clothed and unclothed subjects in laboratory studies. Baker’s (’66) nighttime cold observations also reported this pattern to some de- gree. The skin temperatures of the women and men at night were generally similar; however, the women still maintained higher rectal temperatures and the men higher foot temperatures. During daytime cold stress the pattern is somewhat different: men maintained higher foot and rectal temperatures. As in the study of sleeping In- dians, both men and women tended to have similar skin temperatures over the other parts of the body. The only consistent re- lationship between the temperature responses of the two sexes was that the men maintained warmer foot temperatures in all conditions.

In addition to variation in temperature due to sex, there were age mediated responses as well. In both of the field studies where children under 15 years were considered, they responded in a manner dis-

COLD RESPONSE VARIATION 231

tinct from adults. During night exposure they maintained lower rectal but higher foot temperatures; during daytime exposure the pattern was reversed.

Adult males, then, represent only one segment of the population. Women and children respond in different manners. Any attempt to construct ecological or evolutionary pictures of a population in terms of climatic adaptation should consider other segments of the population as well as adult males.

The second assumption is that the patterns of cold response discovered have validity beyond the laboratory situation. The current observations suggest limitations on this assumption as well. The response patterns resulting from sex differences in the laboratory were not faithfully reproduced in the field. In the laboratory, women were generally warmer with higher skin and rectal temperatures. Baker's ('66) night time field studies showed some aspects of this pattern remain while others were not observed. Thus, women maintained warmer rectal and men higher foot temperatures. Surface temperatures, however, as esti- mated by chest and hand measurements were the same for both groups. When the daytime field observations were considered, the laboratory-determined sex differences were no longer evident. Both sexes maintain similar surface (skin) temperatures, but men had higher rectal temperature (Tr) and only the higher leg and foot temperatures of the men were reminiscent of laboratory findings. Based upon these observations it would be unwise to charac- terize the population's response to cold stress in terms of the single laboratory conditions described in these experiments.

Sex differences in response to cold as detected by laboratory work and by Baker's ('66) field study are quite similar. Men had warmer lower extremities and women higher rectal temperatures. This probably re- sulted from the general similaritity in the testing situations. In both cases the subjects were inactive, exposed to similar lev- els of cold stress, and there was only limited air movement. Apparently, the laboratory studies could predict the responses of sleeping Indians because night time conditions were reproduced in the laboratory.

If this be the case, laboratory studies which approximate actual conditions of cold exposure would seem most desirable (Baker, '65). Studies to determine actual types of stress might be undertaken and these ap- proximated in the laboratory. In this manner more meaningful conclusions in anthropological studies of human adaptation might be anticipated.

ACKNOWLEDGMENT

This study was supported by U.S. Army Medical Research and Development Con- tract DA-49-193-MD-2260. The author wishes to express his thanks to Drs. P. Baker, F. Hulse and H. Bleibtreau for their useful comments during the collection and analysis of data.

LITERATURE CITED Baker, P. T. 1965 Multidisciplinary studies of

human adaptability: Theoretical justification and method. In: International Biological Pro- gramme Guide to Human Adaptability Propo- sals. J. S. Weiner, ed. Central Office, I.B.P., 7 Maryleborne Road, London.

-- 1966 Micro-environment cold in a high altitude Peruvian population. In: Human Adap- tability and its Methodology. H. Yoshimura and J. S. Weiner, eds. Japan Society for the Pro- motion of Sciences, Tokyo, 67-77.

Baker, P. T., E. R. Buskirk, J. Kollias and R. B. Mazess 1967 Temperature regulation at high altitude: Quechua Indians and U.S. Whites during total cold exposure. Hum. Biol., 39(2): 169.

Baker, P. T., G. Escobar, G. DeJong, C. J. Hoff, R. B. Mazess, J. M. Hanna, M. A. Little and E. Picon-Reategui 1968 Human Adaptation to High Altitude, Occasional Papers in Anthropol- ogy No. 1, Department of Anthropology, The Pennsylvania State University, University Park, Penna.

Buskirk, E. R. 1966 Variation in heat produc- tion during acute exposures of men and women to cold air or water. Ann. N. Y. Acad. Sci., 134

Hammel, H. 1964 Terrestrial animals in cold: Recent studies of primitive man. In: Adapta- tion to the Environment. D. B. Dill, ed. Hand- book of Physiology, Section 4, Amer. Physiol. Soc., Washington, D. C., 413-434.

Hanna, J. M. 1968 Cold stress and microclimate in the Quechua Indians of Southern Peru, Ap- pendix H in Baker et al. ('68), University Park, Penna.

(2): 733-742.

DISCUSSION

DR. JAMES GAVAN: Your second figure (2) appears to indicate that there are sex

232 JOEL M. HANNA

differences in the opposite direction from those at the beginning of the experiment. How do you explain this? DR. HANNA: These graphs, drawn by

hand on the blackboard, are not very ac- curate. The data actually show that after we wait 15 minutes, the sex differences do remain consistent. I'm afraid it's due to my faulty graphing technique.

DR. GAVAN: I notice that they start out more similar than they end up.

DR. HANNA: Initially, both are placed in a preparation room under identical conditions. When they were placed in the cold room, it would take 15 minutes for the effects of the cold to become noticeable, and after that there is a divergence in each of the groups. Now this divergence continues over the rest of the study.

DR. GAVAN: Wouldn't the similarity at the beginning be just as important as at the end of the experiment.

DR. HANNA: The similarity at the beginning is due to the unstressful preparation room conditions under which they were placed. The question should be, are there any different laboratory conditions that would produce responses similar to actual field situations?

DR. GAVAN: I don't know the answer to that question; should there be any differences?

DR. HANNA: Actually that may be the point. I would rather doubt that preparation room conditions would produce meaningful response differences in Peruvian In- dians, but conditions of cold stress should.

DR. MICHAEL LITTLE: I might say that I agree with Dr. Hanna's feelings about males not being representative of the total population. However, males are easier to use as test subjects than females since females are quite difficult to get to come to the laboratory. Perhaps we might cover this problem in the discussion section.

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A comparison of laboratory and field studies of cold response