Imaging lung aeration and lung liquid clearance at birth

Abstract

Aeration of the lung and the transition to air-breathing at birth is fundamental to mammalian life and initiates major changes in cardiopulmonary physiology. However, the dynamics of this process and the factors involved are largely unknown, because it has not been possible to observe or measure lung aeration on a breath-by-breath basis. We have used the high contrast and spatial resolution of phase contrast X-ray imaging to study lung aeration at birth in spontaneously breathing neonatal rabbits. As the liquid-filled fetal lungs provide little absorption or phase contrast, they are not visible and only become visible as they aerate, allowing a detailed examination of this process. Pups were imaged live from birth to determine the timing and spatial pattern of lung aeration, and relative levels of lung aeration were measured from the images using a power spectral analysis. We report the first detailed observations and measurements of lung aeration, demonstrating its dependence on inspiratory activity and body position; dependent regions aerated at much slower rates. The air/liquid interface moved toward the distal airways only during inspiration, with little proximal movement during expiration, indicating that trans-pulmonary pressures play an important role in airway liquid clearance at birth. Using these imaging techniques, the dynamics of lung aeration and the critical role it plays in regulating the physiological changes at birth can be fully explored.

Effect of sustained inflation vs. stepwise PEEP strategy at birth on gas exchange and lung mechanics in preterm lambs

“…t he respiratory transition from fetal to ex utero life involves rapidly aerating the fluid-filled lung to establish a functional residual capacity (FRC) (1). In premature infants, this process often requires augmentation with positive pressure ventilation (PPV).…”

Emphysema diagnosis using X-ray dark-field imaging at a laser-driven compact synchrotron light source

“…Multiple air-tissue interfaces present in the inflated lung result in a high degree of X-ray phase contrast and low absorption contrast. Among the phase-contrast imaging methods available-namely, interferometric methods, propagation-based methods, and analyzer-based methods-the latter two were intensively studied in lung imaging (9,13,14).…”

Establishing lung gas volumes at birth: interaction between positive end-expiratory pressures and tidal volumes in preterm rabbits

“…For all levels of PEEP and V T , the PIPs required to initiate lung aeration were high (40-45 cmH 2 O), which was likely to be due to the initial presence of liquid in the airways rather than any other factor (19,34). However, the PIP required to achieve a set V T markedly and rapidly decreased as soon as the lung began to aerate.…”

“…This was capped to prevent air entering the lungs before PPV commenced. The umbilical cord was cut and the pup placed in a purpose-built water plethysmograph (34) to record respiratory function during imaging. After the experiment, rabbits and their pups were humanely killed using an overdose of sodium pentabarbitone (>100 mg/kg).…”