Thermal changes observed before and after J.-L. Etienne's journey to the North Pole. Is central nervous system temperature preserved in hypothermia?

The thermoregulatory responses of a French doctor, Jean-Louis Etienne, were examined in a standard cold test before and after his journey to the North Pole, to investigate whether general and/or local cold adaptation had occurred. The two tests were carried out in a climatic chamber for 2 h at rest (dry bulb temperature, 1 degree C; relative humidity, 40%; wind speed, 0.8 m.s-1). After his journey, Etienne showed a general hypothermic-hypometabolic adaptation, i.e. a decrease in rectal temperature (Tre) and metabolic heat production (M), and an increased local skin temperature of the extremities. Between the two tests, a change occurred in the relationship between tympanic temperature (Tty) and M. During the post-journey cold test, Tty [as representative of the central nervous system (CNS) temperature] increased while the decrease in Tre was accelerated, probably due to a redistribution of blood volume towards the CNS. Such a mechanism would protect the central core with special reference to the CNS.

Physical fitness and thermoregulatory reactions in a cold environment in men.

The relationship between the physical fitness level (maximal O2 consumption, VO2max) and thermoregulatory reactions was studied in 17 adult males submitted to an acute cold exposure. Standard cold tests were performed in nude subjects, lying for 2 h in a climatic chamber at three ambient air temperatures (10, 5, and 1 degrees C). The level of physical fitness conditioned the intensity of thermoregulatory reactions to cold. For all subjects, there was a direct relationship between physical fitness and 1) metabolic heat production, 2) level of mean skin temperature (Tsk), 3) level of skin conductance, and 4) level of Tsk at the onset of shivering. The predominance of thermogenic or insulative reactions depended on the intensity of the cold stress: insulative reactions were preferential at 10 degrees C, or even at 5 degrees C, whereas colder ambient temperature (1 degree C) triggered metabolic heat production abilities, which were closely related to the subject's physical fitness level. Fit subjects have more efficient thermoregulatory abilities against cold stress than unfit subjects, certainly because of an improved sensitivity of the thermoregulatory system.