Hemodynamic Changes in the Transition Period in the Preterm and Term Infant: Basic Concepts.

The transition of the cardiovascular system from fetal life to extrauterine life occurs through different physiological mechanisms. The development of the lungs are parallel to the devel- opment of the cardiovascular system. Cardiac and vascular tone are affected by genetic and environmental factors, including hormonal influences and autonomic reflexes. During the tran- sition period, significant changes occur in preload, myocardial contractility, and afterload. The timing of cord clamping has a profound effect on these changes. Cerebral autoregulation is severely impaired in preterm infants, and cerebral blood flow is almost completely pressure- passive, especially in extremely preterm infants. Disrupted autoregulation is also more frequent in sick infants. Knowledge of transitional factors in different periods is essential for proper man- agement of newborn infants.