The International Biological Program (IBP) is the successor in the biological field to the International Geophysical Year in the physical field. This report discusses one of the methods, approved by a Working Party of the IBP, for determining the cold tolerance of various ethnic groups under field conditions. A standardized cold stress for an eight-hour period during the night is provided by a portable environmental chamber developed by the contractor. Measurements of metabolism and body temperature, with a high degree of accuracy, and the obtaining of EEG and EMG tracings during the cold exposure, are necessary. These parameters can be obtained by either modifying standard medical laboratory equipment available from commercial sources, or constructing new equipment according to the instructions of the contractor.
Adaptations which equip a mammal to cope with the cold stresses of the Arctic environment must at the same time be accompanied by responses which enable it to dissipate large quantities of heat produced during exercise. Some aspects of the heat producing and heat dissipating mechanisms were investigated in the reindeer, an example of a large well adapted Arctic mammal. The oxygen consumption of a reindeer while standing quietly was 606 ml/minute; while pulling a heavily loaded sled, 2390 ml/minute. The evaporative heat loss from the respiratory tract of a standing reindeer was 12 kcal/hour, or seven percent of the heat production; of a vigorously exercising reindeer, 130 kcal/hour, or 20 percent of the heat production. The temperature of the air expired at the nostril was as low as 14° C when the reindeer was standing in a wind at -16° C, and about 30° C at ambient temperatures near 0° C. After the animal exercised, the nostril temperature was 35° to 37° C. The heat production of the rumen ingesta was found to be as high as 0.09 kcal/hour per kilogram of body weight soon after feeding, or 5% to 10% of the basal heat production. The average surface temperature of the thinly furred parts of the reindeer was 5° to 11° C above ambient temperature, the hoof temperature 5° to 9° above ambient and the thickly furred parts only 2° to 4° C above ambient when the reindeer was conserving heat during rest. On the other hand, during vigorous exercise the thinly furred surface was 18° to 22° C above ambient temperature, the hoof was 21° to 28° C above ambient, and the thickly furred surfaces 12° to 15° C above ambient.
Studies were made of 10 adult male Bushmen and four Europeans during night-long exposure to ambient temperatures of approximately 6° C using only single-blanket sleeping bags . Four Bushmen were studied twice. Measurements were made of oxygen consumption, rectal and skin temperatures, muscle activity and sleep. Five Bushmen were also studied during a night with extra blankets. Rectal temperature of both groups started at about 36. 8° C, but in the Bushmen fell O. 7° C lower than in the Europeans during the cold night. Calculated mean body temperature also fell lower in the Bushmen. Mean skin temperature of the Bushmen started higher but was the same as that of the Europeans at the end of the night, although the foot temperatures of the Bushmen were lower. The heat production of both groups was the same at the start, expressed as kcal per kg lean body mass per hour (approximately 1.5). Both rose during the cold night but the Bushmen increase was only half as great as that of the Europeans . Shivering in the Bushmen was less than in the Europeans and sleep was interrupted less in the Bushmen. The results indicate a difference between Bushmen and Europeans in response to cold.