BACKGROUND: It remains unclear how the lung is aerated after birth in human infants. We aimed to describe volume changes over the first breaths of life. DESIGN: Prospective observational study in healthy infants after vaginal delivery. METHODS: Electrical impedance tomography (EIT) data were collected continuously after birth. End-expiratory lung volume (EELV), tidal volume (VT) and markers for regional ventilation distribution including center of ventilation (CoV), silent spaces (SS), functional lung size (FLS) and coefficient of variation (CV) for each of the first ten breaths and at each full minute until ten minutes after birth. MAIN RESULTS: 10'546 breaths from 46 infants were analyzed. During the initial five breaths of life, EELV increased rapidly, and VT were approximately three-fold higher than post-transitional VT (linear mixed-model, both p<0.001). During the initial two breaths, there were unique regional inhomogeneities with preferential ventilation occurring sequentially in the right and left lung (CoVRL first vs second breath: 29.2+/-12.3 vs 53.5+/-9.5, post-hoc test, padj=0.003), before resolving quickly to a more even distribution of lung volume (decrease in CV, LMM: p<0.001). Finally, the lung periphery is less ventilated during the initial ten breaths, which improves over the subsequent ten minutes (increase in FLS, LMM: p<0.001). CONCLUSIONS: This study visualizes and characterizes the first breaths of life, describing lung physiology during this crucial moment. Functional residual capacity is largely established within the first five breaths. The first breaths are characterized by large VT and show highly interesting regional inhomogeneities, likely reflecting complex anatomical and positional factors.
