Assessment of pulmonary function in preterm infants without bronchopulmonary dysplasia. A pilot observational study

Preterm birth is a major cause of neonatal respiratory morbidity and increases the risk of bronchopulmonary dysplasia (BPD). Tidal-breathing flow-volume loops (TBFVL) enable non-invasive early detection of respiratory abnormalities. While there is extensive data on TBFVL in preterm infants with BPD, data in those without BPD are limited. This prospective cohort study evaluates TBFVL and the impact of prematurity-related variables in preterm infants without BPD.

Subjects were recruited from the Neonatology Unit of Buzzi Children's Hospital in Milan, Italy, from 1st February to 31st December 2025. TBFVLs were performed during natural sleep at term-equivalent postmenstrual age. Time-to-peak expiratory flow to total expiratory time (tPTEF/tE, measuring airway size), respiratory rate, tidal volume/kg and minute ventilation/kg were analysed, comparing them with reference values for term subjects and stratifying the sample by gestational age (GA) (≤32 vs > 32 weeks). Several perinatal variables were collected, to identify potential associations with respiratory outcomes.

38 infants (mean GA 32.76 weeks) were included. The mean tPTEF/tE was significantly lower compared to a previously published cohort of healthy term infants (p < 0.001). Infants born ≤32 weeks had significantly lower values than those born >32 weeks (p < 0.001). Gestational age at birth was the only variable significantly associated with tPTEF/tE.

Preterm infants, even without BPD, show greater signs of airway obstruction at term corrected age. GA at birth emerges as the main determinant of respiratory performance, suggesting a key role for intrauterine lung maturation. Longitudinal studies are needed to define its long-term clinical significance.