Cold acclimatisation and thermal status of Antarctic divers
Results of the first investigation into possible acclimatisation to cold and thermal status of Antarctic divers are presented. Over a year, on average one subject dived on alternate days and the other four subjects once a week. Divers wore 7mm or 10mm wet suits in water ca-1oC. Mean dive duration was 30min, and mean depth of immersion 9m. Surface mean wind speed was 10 knots and mean ambient temperature -2oC. Over the year subjects rectal and skin temperatures, and thermal comfort were monitored before, during and after immersion on 26 dives. Severe body cooling (Hall 1972) occurred on 75%, rectal temperature decreased to below normal (although never to clinically hypothermic levels) and there was a marked, exponential drop in skin temperature. End-of-dive finger temperatures were always at a level at which impairment of function would be expected. Divers were usually uncomfortably cold at the end of dives. During the year repeated monthly measurements were made of: skinfold thickness, body weight, body fat weight and fat-free mass: basal metabolic rate: rectal and skin temperatures, metabolic rate, shivering, thermal comfort, adrenaline, noradrenaline and cortisol excretion during immersion to the neck in water at 20oC for one hour: time of onset of cold-induced vasodilatation, temperature and pain responses of left index finger immersed at 0oC for half an hour. Differences between the responses of divers at different months of the year and between divers and nondivers were tested by analysis of variance. It was found that divers shivered less and had less thermal discomfort (by verbal rating scales) than nondivers (as they had similar metabolic rates this suggests greater nonshivering thermogenesis). It was also found that divers extracted more oxygen from inspired air while immersed to the neck than nondivers. In both divers and nondivers there was a winter increase of skinfold thickness and body fat weight and a winter decrease of fat-free mass, and while these may be an adaptation to cold, it is possible that other stimuli were responsible. No significant differences were found between any of the other parameters tested. Monthly measurements of physical fitness, and time spent outside and in various activities indicated that these were not important complicating factors in the acclimatisation studies. A comparison of Antarctic dives and laboratory cold water immersions showed that while dives led to a greater fall of peripheral temperature and lower peripheral thermal comfort the laboratory immersions led to a greater fall in rectal temperature and trunk skin temperature. In this thesis, it is proposed that while Antarctic divers were subject to considerable thermal stress there was little evidence of cold acclimatisation.