What effect does crying after birth have on intrathoracic pressure?

Crying after birth is crucial for the establishment of normal respiratory function in newborns. When an infant cries, it creates a significant change in intrathoracic pressure. During crying, the diaphragm and intercostal muscles contract vigorously, which leads to a decrease in the pressure inside the thoracic cavity. This action generates a greater negative intrathoracic pressure, which aids in the expansion of the lungs and promotes airflow into the alveoli.

This negative pressure is essential for drawing air into the lungs after birth, allowing for adequate oxygenation and removal of carbon dioxide. It contributes to the transition from fetal circulation to normal respiratory physiology, helping to ensure that the newborn can breathe effectively outside the womb. Such physiological changes support the establishment of normal ventilation and gas exchange, vital for the newborn's health and survival.