Body temperature and sleep architecture in response to a mild cold stress in women.

Six women participated in a seven consecutive night polygraphic sleep study during which both 24-hour rectal, body temperature and wrist activity were continuously sampled and stored at one-minute intervals. The study was designed to investigate the effects of a mild nocturnal cold stress on thermoregulation and sleep. On nights 4 and 5, subjects slept naked, without any bedcovers (mild cold stress) in a warm (26.7-28.3 degrees C) room. The daily mean rectal temperature and the daily nadir (low point) of the circadian temperature rhythm (CTR) showed a significant decrease between the baseline and cold stress conditions. The lowered nadir resulted in a significant amplitude increase in the daily CTR between the baseline and cold stress conditions. There were no significant changes in activity levels across experimental conditions. The ability to maintain a sleep state was significantly impaired during the cold stress. Stage 4 slow wave sleep increased, while Stage 3 decreased in response to the cold stress condition, and there was an associated lengthening of the first NREM period. These data suggest that challenges to the thermoregulatory system can be used as a vehicle to systematically alter sleep architecture in humans.