DEVELOPMENT OF CIRCADIAN RHYTHMICITY OF TEMPERATURE IN FULL-TERM NORMAL INFANTS

Twelve full-term infants (7 girls and 5 boys) with normal neurological , behavioral and somatic development were followed at regular interval s during the first 5 months of life to appreciate the development of c ircadian rectal temperature rhythmicity. Activity and temperature (ora l at birth, rectal thereafter) were monitored for a minimum of 60 hour s on seven separate occasions: at birth, 3 weeks, 6 weeks, 8 weeks, 10 weeks, 16 weeks and 20 weeks of age. Activity was measured using an a ctigraph worn on the infant's wrist, and rectal temperature was measur ed using a rectal probe attached to a portable microprocessor (Vitalog (TM)). Data points were collected every 2 minutes. No fewer than ten i nfants were monitored at each session, and no infant missed more than one session. Missing recordings were due to equipment malfunctions, pr obe expulsions and minor health problems. Six infants out of 12 were s uccessfully monitored at each of the first four sessions, from birth t o 8 weeks of age inclusively, and two subjects were successfully monit ored at all seven sessions. Periodic regression analysis was performed by least squares curve fit with secondary analysis of variance. Analy sis of covariance was performed on repeated measures. There was no evi dence of rectal temperature circadian rhythmicity at 3 weeks. Two infa nts demonstrated a circadian rhythmicity at 6 weeks, and all infants h ad a circadian rhythmicity at 10 weeks post-natal age. At the time of the first observance of circadian rhythmicity of rectal temperature, t he mean delta in temperature from peak to trough was 0.6 +/- 0.3 degre es C. This delta was greater at the 16th week, with a mean value of 1. 2 +/- 0.3 degrees C. The trough was seen during the first part of the long nocturnal inactivity period. Circadian rhythmicity of rectal temp erature was always observed in the studied subjects before the establi shment of a consolidated, long daytime wake period.