The Emergence and Development of Physiological Regulatory Systems of Newborn Infants in a Neonatal Intensive Care Unit

In the life of a human being, the early neonatal period is the most prone to life-threatening events. After birth, following the transition from the intrato the extra–uterine environment, babies experience dramatic hemodynamic changes. Once babies begin life in the extrauterine environment, they must regulate their own homeostasis in order to survive. Preterm, low birth weight, newborn are even more vulnerable and require the mechanical support for proper tissue oxygenation and nutrition in order to grow and survive in the extra-uterine environment. The adaptation to extra-uterine life is a slow and difficult process for these babies because of their prematurity. At this critical period, hypothermia, apnoea, respiratory distress, and cardiac instabilities such as bradycardia and hypotension are common features in these newborn babies (Bhatt et al., 2010; Di Fiore et al.,2001; Dransfield et al., 1983; Tirosh et al., 2010; Trevisanuto et al., 2005; Upton, et al., 1992), and the resulting hypoxia may lead to brain damage and cardiac arrest if the medical support of a special incubator equipped with a ventilator and systemic monitoring is not provided a as a “primary life support system”. Therefore, the continuous monitoring of heartbeat, respiration, oxygen saturation, blood pressure and temperature has been integrated into the neonatal intensive care unit (NICU) as a mandatory tool to support the fragile clinical conditions of these infants. Monitoring data collected using non-invasive electrocardiograms have been used to understand the physiological regulatory system of these vulnerable infants. The measurement of heart rate variability has been widely examined using various analytic methods (Ardura et al., 1997; Baldzer et al., 1989; Katona et al.,1980; Patural et al., 2004; Yiallourou et al., 2010). Among them, circadian rhythms have been documented to be a prognostic marker of physiological stability and the maturation of the physiological regulatory system, which can be defined as the long-term regulatory system. The endogenous circadian rhythm is generated by the endogenous biological clock located in the anterior hypothalamic suprachiasmatic nuclei (Panda et al., 2002) and may be modulated by exogenous factors (Reppert & Weaver, 2002). It has been documented in the growing foetus