REGULATION OF SLEEP AND BODY-TEMPERATURE IN RESPONSE TO EXPOSURE TO COOL AND WARM ENVIRONMENTS IN NEONATES

Background and objective. Thermoregulation is impaired during desynchr onized sleep in animals and in adults. This can lead to a conflict bet ween homeothermy and sleep in nonthermoneutral conditions. This study aimed to analyze thermoregulation during sleep, especially during desy nchronized sleep (active sleep, AS) and to determine whether the confl ict between thermoregulation and sleep might exist in the newborn slee ping in warm or cool conditions. Methods. Esophageal and skin (cheek a nd abdomen) temperatures, local sweating rate (ventilated sweat collec tion capsule stuck on the abdomen), metabolism (indirect respiratory c alorimetry), and sleep variables were recorded in 10 newborns exposed, in an incubator, to thermoneutraI, warm, and cool environments. Body movements and apneas were also considered. Exposures were performed af ter a first habituation condition. Results. Sleep structure was not mo dified by the first exposure nor by the warm environment. Exposure to cool temperatures increased AS duration (+13% of total sleep time) and the quantity of body movements during AS (+11.3% of AS duration), whe reas these parameters were not modified during quiet sleep. The thermo regulatory response to warm and cool environments was not impaired dur ing AS. During exposure to mild thermal load, analyses revealed large interindividual differences in the strategy for thermoregulation durin g AS. Depending on the newborn, the thermoregulatory response to cool temperatures could be described by an increase either in nonshivering thermogenesis or in frequency of body movement. In warm conditions, mo st newborns exhibited an increased sweating rate. The interindividual differences (lack of increase sweating in three newborns) seemed to be linked to changes in the sensitivity of the sweating response. Conclu sion. Because thermoregulation is not impaired during AS, this sleep s tage seems to be a well-protected one from a thermoregulatory point of view. This difference from adults and animals may be due to the impor tant role of AS in newborn's nervous maturation.