Comparision of lung function in preterm infants at 36 and 44 weeks postconceptional age

<bold>Background:</bold> Little is known about the short-term evolution of lung function in preterm infants. <bold>Aim:</bold> Compare multiple-breath washout (MBW) and tidal breathing parameters in preterm infants at 36 and 44 postconceptional weeks. <bold>Methods:</bold> Preterm infants born between 2003 and 2006 had a lung function at 36 and 44 postconceptional weeks. We compared lung clearance index (LCI), FRC per bodyweight (FRC/kg), respiratory rate (RR), tidal volume per bodyweight (TV/kg), minute ventilation per bodyweight (MV/kg) and ratio time to peak tidal expiratory flow to expiratory time (tPTEF/tE)) by paired t-test as well as by mixed model regression analyses, adjusting for length at study visit for values not per bodyweight and CO₂-sensor for LCI and FRC. <bold>Results:</bold> We included 44 preterm infants with a mean±SD gestational age of 29±3 weeks, 66% were male. We found no difference for LCI and FRC/kg between 36 and 44 weeks. MV/kg and tPTEF/tE were higher at 36 compared to 44 weeks: mean(SD) MV/kg 474.2 (78.7) ml/kg versus 372.8 (78.9) ml/kg with a mean difference (95% CI) of 109.9 ml/kg (69.1; 150.7 ml/kg, p-value < 0.001), and for tPTEF/tE 0.40 (0.14) versus 0.28 (0.09) with a mean difference of 0.12 (0.09; 0.16 ml/kg, p-value <0.001). The other tidal breathing parameters showed no difference. In the adjusted mixed model, differences in tPTEF/tE and MV/kg remained significant. <bold>Conclusion:</bold> In our preterm cohort, tPTEF/tE and MV/kg were consistently higher at 36 compared to 44 weeks postconceptional age indicating early adaptive changes of breathing pattern, while the heterogeneous change of MBW outcomes points out the complexity of the underlying pathophysiology.