Biological rhythm development in preterm infants: does health status influence body temperature circadian rhythm?

Twenty-six preterm infants, postconceptional age from 28 to 35 weeks and postnatal age approximately 14 days, were included in a study of the development of temperature circadian rhythm. Insulated abdominal skin temperature and incubator air temperature were recorded continuously at 1-min intervals for 24 hr. Using cosinor analysis, cycle mesor, amplitude, and acrophase were determined. Initial results from regression analysis did not confirm a predicted linear relationship between postconceptional age and amplitude; however, dividing the sample according to health status into sick (N = 15) and not sick (N = 11) groups revealed differing regression models. For not sick infants, amplitude increased with postconceptional age (R(2) =.405), whereas no relationship was found between postconceptional age and cycle amplitude in sick infants (R(2) =.069). These results indicate that healthy preterm infants demonstrate emergence of circadian temperature rhythm. Implications include potential time-based periods of vulnerability, overheating and hyperthermia, and management of incubator operation. Copyright 2001 John Wiley & Sons, Inc.