Respiration in newborns: development of the control of breathing.

The pattern of breathing has been studied in human infants at 10, 60, and 90 min, and at a few days after birth. The major characteristics of the pattern of breathing in the immediate period after birth is a marked variability that decreases progressively with time. Interruptions of expiration and peak expiratory flows occurring late in expiration are common findings at 10 to 90 min of age but are infrequent at a few days. From 10 to 90 min to a few days of life the tidal volume increases and respiratory rate decreases with no changes in minute ventilation. The decrease in respiratory rate is due to proportional increases in both inspiratory and expiratory time. Infants born vaginally behave similarly to those delivered by cesarean section except with regard to tidal volume, which at 10 min is closer to the value measured at a few days; this may be the result of the mechanics of the vaginal delivery, which results in less fluid to be absorbed from the lung at birth. Vagal respiratory reflexes are present at birth and the prolongation of inspiratory time during occlusion at end expiration appears to decrease from 10, 60, and 90 min to a few days of age. Values of mouth pressure at 0.1 s after an occlusion at end expiration are higher at 10 min after birth than at 60 and 90 min. Because mean inspiratory flow is similar in this time period it could indicate a progressive increase in the compliance of the respiratory system, possibly reflecting the absorption of pulmonary fluid.