Thermal sensation during experimental hypothermia

Ten subjects were cooled to a deep body temperature (T DB)∼35°C by the passage of cold air and water over the skin. Four subjects repeated the exposure on 3 more occasions. Subjective assessments of thermal comfort were recorded using an automated 10 cm line device. Multiple regression analysis showed that comfort was related to the levels and gradients of T DB and mean skin temperature (T s −) as well as the presence or absence of shivering. First exposures were characterized by extreme discomfort associated with the initial rapid fall of T s − at the conset of cooling and an improvement in thermal sensation as T s − plateaued before T DB started to fall. This response was not seen in subsequent experiments. In these, discomfort occurred initially with falling T s − and then remained constant, finally increasing further as T DB fell, suggesting habituation to steep gradients of T s −. Other indications of habituation, leading to less discomfort at given levels of T s − + T DB during later stages of cooling, were not statistically significant. There was no evidence of physiological acclimatisation to cold in those subjects undergoing repeated exposures.