Effects of gestation and antenatal steroid on airway and tissue mechanics in newborn lambs

The aim of this study was to partition airway and parenchymal mechanics in newborn lambs at different gestations and following variable exposure to an tenatal maternal betamethasone using the forced oscillation technique (FOT) . Pulmonary impedance data were collected in 37 sedated and intubated apnei c lambs with the FOT between 0.5 and 20 Hz and fitted by a model to estimat e airway resistance (Raw) and inertance (law) and the coefficients of tissu e resistance (GL) and elastance (HL). Total respiratory resistance (Rrs) wa s also determined during tidal ventilation by using the multiple linear reg ression technique. Advancing gestation or increasing antenatal steroid expo sure had no clinically significant effect on the values of Raw and law, whe reas Rrs and both GL and HL decreased markedly. There was a decrease in tis sue hysteresivity (GL/HL) with repeated antenatal steroid exposure. Partiti oning of lung mechanics highlights the dominant contribution of the tissues to the total respiratory resistance in the immature ovine lung. Clinically relevant changes in lung mechanics associated with structural and function al maturation of the immature ovine lung are primarily confined to the tiss ue compartment.