Interindividual differences in the thermoregulatory response to cool exposure in sleeping neonates

The responses of the thermoregulatory effectors vary greatly among neonates . Therefore, we assume that a small decrease in air temperature from thermo neutrality induces various thermoregulatory responses within neonates that represent an energy cost due to the cold defence processes. To determine th e importance of this variability in nursing, 26 neonates were explored at t hermoneutrality and in a cool environment (-1.5 degrees C from thermoneutra lity) similar to that which occurs currently in clinical procedure. Oxygen consumption ((V)over dot O-2), oesophageal and skin temperatures, as well a s sleep parameters were recorded continuously in both conditions. Analysis of all of the data from all of the neonates revealed that the cool exposure induced thermal and sleep disturbances, but (V)over dot O-2 did not increa se and was not negatively correlated to body temperature (as might be expec ted). Analyses of individual data showed large variability in body temperat ure regulation: the neonates could be assigned to one of three groups accor ding to the direction of the individual slopes of (V)over dot O-2 versus oe sophageal or skin temperature. The groups also differed according to the sl eep changes recorded in the cool condition. The results show that the defin ition of thermoneutrality should be revised by incorporating non only chang es in the body temperature, but also the sleep disturbances (increased wake fulness and active sleep, decreased quiet sleep), which are criteria that a re more sensitive to mild cool exposure. Thermoneutrality should be defined for each individual, since the results stress that the variability does no t help to predict a general pattern of thermoregulatory responses in cool-e xposed neonates.