Low-frequency oscillatory mechanics in very preterm infants with and without Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is characterised by inflammation in the developing airways and lung parenchyma. The ability of low-frequency forced oscillation technique (LFOT) to measure the impact of BPD on peripheral lung growth and function is unknown. We aimed to measure airway and pulmonary tissue mechanics in very preterm infants with/without BPD. We hypothesised that BPD alters the pulmonary mechanical properties compared to infants without BPD. LFOT (1-12 Hz) was applied to unsedated preterm infants during a short apnoea (4-7 s) provoked via the Hering-Breuer reflex (1-4 rapid manual inflations). Peak inflation pressure was 20cmH2O. Outcome variables were determined by fitting the constant phase model to the data, and analysed using t-test and multiple linear regression. 70 of 85 infants had acceptable tests: [median (range) GA 286w (234-316)] at a median (range) 355w (340-374) postmenstrual age. 25 infants had BPD (mild n=10, moderate n=7, severe n=8) according to the NICHD criteria. Newtonian resistance (R) (mean difference (SD): 3.88 (1.71); p 0.026) was significantly lower in infants with BPD than infants without BPD. Presence of BPD did not impact tissue damping, elastance, or hysteresivity. Length independently predicted all outcome variables. Duration of nCPAP was independently associated with R. In our cohort of infants, length rather than presence of BPD was the primary determinant of parenchymal mechanics: our findings may be explained by similar tissue mechanics in infants with/without BPD due to mild BPD, or that the effect size of BPD on LFOT outcome variables is low. Funding: NHMRC (1047689,1057514,1077691), MHRIF, Hungarian Scientific Research Grant #105403