Lungs begin to function only from the moment of birth. The lungs of the newborn are well vascularized, they have little elastic tissue. The upper respiratory tract is not developed enough, their enlightenment is narrow, the mucous membrane is rich in blood vessels.
In newborn infants, the ribs are characterized by a slight bend and an almost horizontal arrangement, the relative weakness of the intercostal muscles is noted. Upper ribs with a shoulder girdle are located high. These features determine the predominance of diaphragmatic breathing in newborn infants (with minor involvement of intercostal muscles).
At the time of birth, the formation of the respiratory center is not yet complete, but it provides a rhythmic change in inspiration and expiration, the so-called respiratory cycle. In newborn children, the excitability of the respiratory center is low. Breathing is frequent and superficial, its frequency fluctuates significantly (40-50 per minute during sleep and 50-60 per minute during wakefulness). A high respiratory rate remains adequate for ventilating the lungs. By the end of the neonatal period, the volume of respiration in term infants is on the average 30 ml, and the minute volume of respiration is 650-700 ml.