Physiologic circadian rhythmicity in preterm infants.

This study investigated evidence of a circadian rhythm in the physiologic variables of transcutaneous oxygen (tcPO2) level, pulse rate, respiratory rate, frequency of respiratory pauses, and skin temperature in six 34- to 37-week-preterm infants. A value for each variable was noted every 30 minutes for 24 hours, providing 245 observations for each infant. An adaptation of cosinor analysis, a least squares procedure that determines the cosine curve for a 24-hour period that best fits the observed pattern of values, was applied to the data. Statistically significant circadian rhythmicity was found for five of the six subjects with regard to skin temperature. Significant circadian rhythm was also demonstrated in two or three patients for all other variables. No significant consistent synchrony for individual variables across subjects was found. Actual peak values of respiratory pause frequency and trough values of tcPO2, however, occurred between midnight and 4:30 A.M. for every infant. Preterm infants exhibited evidence of a circadian rhythm in skin temperature, and tcPO2 and respiratory pause frequency exhibited day/night pattern characteristics.