Role of the Chest Wall in Newborn Respiratory Function at Birth.

The chest wall significantly impacts respiratory function after birth, but its role in the newborn remains poorly understood as it is structurally and functionally different from adults. In neonates, the chest wall is highly compliant, which allows it to expand to accommodate the incoming air and the lung liquid cleared into the pulmonary interstitium during lung aeration. However, the high neonatal chest wall compliance predisposes it to distortion, which reduces breathing efficiency and necessitates respiratory muscle activation to stabilize it. This increases the work of breathing and, when combined with fewer fatigue-resistant Type I muscle fibers (slow twitch, high oxidative capacity) in the diaphragm muscle, the risk of respiratory fatigue is increased. Nevertheless, as the chest wall is highly compliant in the newborn, recent studies have demonstrated that extra-thoracic pressures can influence chest wall mechanics. Positive extra-thoracic pressures (such as those applied with tight swaddling) limit chest wall expansion, whereas a small constant negative extra-thoracic pressure stabilizes the chest wall and improves oxygenation in neonates. In this review, we aim to summarize the current evidence on chest wall function in fetuses and neonates, particularly during lung liquid clearance, lung aeration, and breathing after birth. Furthermore, we will explore how knowledge from newborn respiratory physiology may inform our understanding of the respiratory consequences of pulmonary oedema in adults, such as occurred during the initial stages of the COVID-19 pandemic.