Respiratory physiology

Respiratory system development starts in utero and continues in the post-natal period, at least up to 2–3 years of age. The intra-uterine development prepares the neonate for the transition from fetal to post-natal life. Development after birth enables the respiratory system to meet the increased metabolic demands during infancy and childhood. Therefore, the newborn respiratory system is not a small version of the adult one. Respiratory system resistance is high and compliance is low, due to the small airways and lung size. The floppy chest wall is associated with low resting volume and paradoxical breathing. The thorax has a cylindrical shape that puts the respiratory muscles at a mechanical disadvantage, and the diaphragm seems more susceptible to fatigue. The breathing pattern is very irregular due to immature control and is characterised by high breathing rates. This chapter covers the most important features of healthy newborn respiratory physiology.