Volunteers' body core temperatures were lowered by immersion in water at 15 degrees C. Aspects of cognitive function were subsequently tested after rewarming had been started in water at 41 degrees C when their skin was warm and they felt comfortable but their body core temperature remained low. Memory registration was found to be impaired progressively when core temperature fell from about 36.7 degrees C; at core temperatures of 34-35 degrees C the impairment caused loss of approximately 70% of data that could normally be retained. However, recall of previously learned data was not impaired at these core temperatures. On a two-digit calculation test, speed of performance was impaired by about 50% at a core temperature of 34-35 degrees C, but provided enough time was available, accuracy of performance was not reduced.
Deep body temperature fell progressively by 0.5-1.4 degrees C during 3-h immersions in 29 degrees C water. Both in unacclimatized volunteers and, to a lesser degree, in divers in cold-water training, cooling the hands and feet for 1 h in 12 degrees C water during such immersion caused sensation of cold, shivering, and rise in metabolic rate; it caused body temperature to rise in unacclimatized subjects and halted its fall in divers. Tissue conductances generally fell a little in divers but rose in unacclimatized subjects, probably because of muscle blood flow associated with the greater shivering in the latter. Soaking the skin for 4 h produced no major changes in cutaneous thermal sensation assessed in the forearm, though with seawater it sometimes reduced cold sensation and with distilled water sometimes reduced warm sensation, a little. It is concluded that uniform skin temperature of 29 degrees C often induces insufficient heat-gain reflexes to maintain body temperature and that cooling of the extremities can restore adequate thermoregulatory response.
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