Imaging the Respiratory Transition at Birth: Unravelling the Complexities of the First Breaths of Life.

Rationale: The transition to air-breathing at birth is a seminal respiratory event common to all humans, but the intrathoracic processes remain poorly understood. Objectives: The objectives of this prospective, observational study were to describe the spatiotemporal gas flow, aeration and ventilation patterns within the lung in term neonates undergoing successful respiratory transition. Methods: Electrical impedance tomography was used to image intrathoracic volume patterns for every breath until six minutes from birth in neonates born by elective cesearean section and not needing resuscitation. Breaths were classified by video data, and measures of lung aeration, tidal flow conditions and intrathoracic volume distribution calculated for each inflation. Measurements and Main results: 1401 breaths from 17 neonates met all eligibility and data analysis criteria. Stable functional residual capacity was obtained by median (IQR) 43 (21, 77) breaths. Breathing patterns changed from predominantly crying (80.9% first minute) to tidal breathing (65.3% sixth minute). From birth tidal ventilation was not uniform with the lung, favouring the right and non-dependent regions; p<0·001 versus left and dependent (mixed effects model). Initial crying created a unique pattern with delayed mid-expiratory gas flow associated with intrathoracic volume redistribution (pendelluft flow) within the lung. This preserved functional residual, especially within the dorsal and right regions. Conclusions: The commencement of air-breathing at birth generates unique flow and volume states associated with marked spatiotemporal ventilation inhomogeneity not seen elsewhere in respiratory physiology. At birth neonates innately brake expiratory flow to defend functional residual capacity gains and redistribute gas to less aerated regions.