Entwicklung des circadianen und ultradianen Biorhythmus bei Frühgeborenen

Summary Background: Many physiological processes in humans like hormone secretion, activity-rest patterns or body temperature regulation underlie cyclic patterns, so-called biological rhythms. Environmental influences such as light-dark cycle, food ingestion, sleep-wake cycles and social cues are major determinants in synchronizing human circadian rhythm. The foetal circadian system is mainly synchronized by the maternal circadian rhythm; however, neonates lose this circadian rhythm after birth which needs time to adapt to the extra-uterine life. Preterm infants are exposed early to medical and caregiving interventions, which can be a reason of stress for preterm infants. To date, only few and inconsistent results exist about the development of the circadian rhythm of preterm infants in the literature. The purpose of this study was to examine the biologic rhythm of preterm infants during their first weeks of life by measuring circadian cortisol levels and their activity-rest behaviour. Methods: 62 preterm neonates with gestational age between 30 and 37 completed weeks and a postnatal age of less than ten days were included in the study. Actographic monitoring was used to record the activity and rest patterns of the preterm continuously over 24 hours on day one, seven and fourteen. Additionally, saliva samples were obtained from 22 preterm neonates at seven predefined time points of those days. Cortisol and activity data were analysed by Least Squares Spectral Analysis (LSSA) to assess periodic characteristics and frequencies. Hierarchical Linear Modeling was further performed for statistical analysis. Results: The cortisol rhythm analysis indicated a circadian rhythm pattern for only one premature infant, the majority of the neonates showed no circadian or ultradian rhythm of the hormone cortisol. Furthermore, the cortisol level of the premature neonates was significantly higher on the first day of study (p < 0.005) compared to day seven and fourteen of the study (day 1: median=16.5 nmol/L, day 7: median=9.8 nmol/L; day 14: median=10.0 nmol/L). Notably, cortisol levels at night declined significantly (p < 0.05) during the study period (night 1: median=17.1 nmol/L; night 7: median=9.6 nmol/L; night 14: median=9.8 nmol/L). The activity-rest rhythm of the preterm neonates was dominated by ultradian rhythm patterns with a period length of four hours in the first weeks of life. 12 preterm infants showed a circadian pattern of activity-sleep-rhythm at one time point during the study. The duration of resting phases (low activity frequencies) increased significantly during the observation period (day 1: 55%; day 7: 61%; day 14: 60%). In addition, the sleep duration of the infants increased significantly (p < 0.05) from 66% of day one to 72% of day seven. Conclusion: No stable circadian rhythm was found during the first four weeks of life of the examined preterm infants. An ultradian rhythm of the acitivity-rest behaviour with a period length of four hours could be detected in a subgroup of these infants. The study population showed higher cortisol levels and higher activity frequencies at earlier time points after birth which may reflect difficulties in the adaptation process of neonates after birth, e.g. intensive care or medical interventions. Further studies are necessary to better understand the correlation between stress processes, illnesses, extra uterine adaption and cortisol concentration as well as the activity-rest behaviour of preterm infants in order to optimize treatment and nursing of preterm infants.