Effects of acclimatization to cold baths on men's responses to whole-body cooling in air.

The purpose of this study was to investigate the thermoregulatory mechanisms underlying artificial acclimatization to cold and to compare them with those of naturally acclimatized men. Six white men were cooled, nude, in air at 10 degrees C for 2 h before and after they had been acclimatized by ten daily cold (15 degrees C) baths of 30-60 min followed by rapid rewarming in hot (38-42 degrees C) water, and again 4 months later after acclimatization had decayed. Six control subjects also underwent the same tests, providing an opportunity to discriminate between changes caused by the immersions and those caused by extraneous influences. Acclimatization significantly reduced heat production and heat loss (P < 0.05) but did not change heat debt. The reduced heat production was accompanied by reductions in shivering (P < 0.10) and in cold-induced muscle tenseness; no evidence of nonshivering thermogenesis or active brown fat was found. These findings are attributed to increased tissue insulation, mediated by an enhanced vascular response to cold that did not involve the cutaneous circulation and was probably located in skeletal muscle. Thermal sensation and discomfort did not change, although perceived strain tended to increase (P = 0.08). Acclimatization was accompanied by, but was unrelated to, slower cooling of the finger and toe. The main conclusions, and many specific findings, agree with those of two previous studies made by the same techniques in naturally acclimatized men wintering in Antarctica. Other significant findings included changes--in particular reduced thermoneutral rectal temperature and a delayed onset of shivering--that are commonly regarded as evidence of acclimatization but were in fact unrelated to it as they also occurred in the control group. They are attributed to extraneous influences, in particular the relaxation of heightened arousal ('first-time effects') found in the baseline tests.

Cardiovascular and metabolic responses to noradrenaline in men acclimatized to cold baths.

The purpose of this study was to see whether artificial acclimatization to cold would reduce the pressor response to noradrenaline (NA) as natural acclimatization has been shown to do, and whether it would induce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 microgram.kg-1.min-1 (2-23 micrograms.min-1), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatization was induced by ten daily cold (15 degrees C) baths of 30-60 min followed by rapid rewarming in hot (38-42 degrees C) water, and was confirmed by tests of the subjects' responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Acclimatization substantially reduced the pressor response to NA at 0.150 and 0.300 micrograms.kg-1.min-1, confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P < 0.05 for both changes). Acclimatization did not change the response to NA of heart rate, subjective impressions, skin temperature of finger and toe, pulmonary ventilation, or plasma free fatty acids and ketone bodies. At no time did NA increase oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show that acclimatization to cold reduces sensitivity to the pressor effect of NA but does not induce nonshivering thermogenesis, and that the reduced sensitivity is replaced by a hypersensitivity to NA when acclimatization decays.

The physical characteristics of the members during the International Biomedical Expedition to the Antarctic.

Twelve male medical scientists formed the International Biomedical Expedition to the Antarctic (IBEA). Their physical characteristics and maximum oxygen uptakes (VO2max) were measured in association with three series of thermal tolerance tests in Sydney, twice before and once after going to the Antarctic. In the Antarctic they lived in tents and spent 15 days travelling by motor toboggan. Their body mass (BM) and skinfold thickness (SFT) were measured four times during the 69 days the expedition spent in the field. The characteristics of the group were (ranges): age 26-52 years, height 1680-1889 mm, BM 58.5-103.4 kg, fatness 16-34% BM and VO2max 33-49 ml X kg-1 X min-1. In the Antarctic 9 men lost between 0.7 and 5.5 kg (mean 2.7 kg) of BM with a decrease in SFT, whilst 2 men increased BM by 1.2 and 1.9 kg without change in SFT. One man retired early from the expedition. BM and SFT were regained and physical fitness lost during the return voyage to Australia. Consequently there was no difference in average SFT between the pre- and post-Antarctic laboratory tests, but BM was greater after the Antarctic implying gains in fat free mass. VO2max was lower in the final laboratory tests than in the tests before Antarctica.