The emergence of body temperature biorhythm in preterm infants.

The biorhythm of body temperature was studied in five hospitalized, medically stable preterm infants, gestational age 30 to 34 weeks and postnatal age 5 to 10 days. Abdominal skin temperature, as well as incubator air temperature, were measured by thermistors and recorded at one-minute intervals throughout a 24-hour day using a computerized data acquisition system. Data were analyzed using autocorrelation, a form of time series analysis. A cyclic pattern of temperature was observed in three of the five subjects. The length of time of the cycles were two, three, and six hours. Incubator air temperature did not exhibit similar cyclicity, and it is therefore assumed that incubator operation is not responsible for the observed cyclic variation in infant temperature.