Respiratory Studies in Newborn Infants. II: Pulmonary Ventilation and Mechanics of Breathing in the First Minutes of Life, Including the Onset of Respiratio1

Summary 1. Respiratory volume changes and intra‐esophageal pressure changes have been simultaneously recorded beginning before or during the first breaths in 18 infants. 2. Respiratory adaptive changes for successful extra‐uterine existence occur rapidly. Some of the features are summarized below. 3. The average air exchange in the first 20 seconds after the first breaths is 2–3 times the resting minute volume observed later in the neonatal period. 4. A residual volume is established in some infants beginning with the first breath. In others this was not recorded and evidence is presented which suggests it may occur prior to the first breath. 5. The total pressure change of the first breath ranged from 40–100 cm O. In succeeding breaths this decreased. Typical pressure‐volume diagrams (“respiratory loops”) are illustrated and their possible significance discussed. 6. During the first few breaths the lung compliance was one‐fifth to one‐third and the pulmonary flow resistance 24 times that found in older neonates.