Lung function at term in extremely preterm-born infants: a regional prospective cohort study

Abstract

Objectives: To compare lung function of extremely preterm (EP)-born infants with and without bronchopulmonary dysplasia (BPD) with that of healthy term-born infants, and to determine which perinatal characteristics were associated with lung function at term and how predictive these measurements were for later respiratory health in EP-born infants.

Methods: Perinatal variables were recorded prospectively, and tidal breathing parameters were measured at term-equivalent age using electromagnetic inductance plethysmography. Respiratory morbidity was defined by hospital readmissions and/or treatment with asthma medications during the first year of life.

Results: Fifty-two EP-born infants (mean gestational age 261, range 226-276 weeks) and 45 term-born infants were included. There was evidence of significant airway obstruction, higher tidal volumes and increased minute ventilation in the EP-born infants with and without BPD, although generally more pronounced for those with BPD. Male gender, antenatal steroids and number of days on continuous positive airway pressure were associated with lung function outcomes at term. A prediction model incorporating two unrelated tidal breathing parameters, BPD, birth weight z-score and gender, predicted respiratory morbidity in the first year of life with good accuracy (area under the curve 0.818, sensitivity and specificity 81.8% and 75.0%, respectively).

Conclusion: Lung function measured at term-equivalent age was strikingly abnormal in EP-born infants, irrespective of BPD. Tidal breathing parameters may be of value in predicting future pulmonary health in infants born premature.

Trial registration number: NCT01150396; Results.

Keywords: bronchopulmonary dysplasia; lung disease; lung function test; prematurity; tidal breathing.

Conflict of interest statement

Competing interests: None declared.

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Figures

Figure 1

Receiver-operator characteristic (ROC) curves comparing the ability of different tidal breathing parameters to discriminate between extremely preterm-born infants (n=52) and healthy term-born controls (n=45). If the 95% CI of the area under the ROC curve (AUC) includes 0.5 (no discrimination), the tested variable does not distinguish between the two groups. The optimal cut-off point is the point for which sensitivity+specificity is maximal. For abbreviations of lung function variables, please see list in table 2.

Figure 2

Receiver-operator characteristic (ROC) curves comparing the ability of tidal breathing parameters and clinical variables to discriminate between extremely preterm-born infants with and without bronchopulmonary dysplasia. If the 95% CI of the area under the ROC curve (AUC) includes 0.5 (no discrimination), the tested variable does not distinguish between the two groups. The optimal cut-off point is the point for which sensitivity+specificity is maximal. For abbreviations of lung function variables, please see list in table 2.

Figure 3

Receiver-operator characteristic (ROC) curves comparing the ability of TEF50/PTEF and BPD, and additionally a compound model incorporating TEF50/PTEF, Vt/kg, BPD, birth weight z-score and gender, used to predict development of respiratory distress requiring readmission or treatment with asthma medication during the first year of life of extremely preterm-born individuals (n=35). The compound model achieved the best sensitivity and specificity, that is, respectively, 81.8% and 75.0% at a cut-off value of 0.34. If the 95% CI of the AUC includes 0.5 (no discrimination), the parameter does not predict later respiratory distress. The optimal cut-off point is where the sensitivity and specificity are maximal. This value corresponds with the point on the ROC curve farthest from the diagonal line. AUC values for other breathing parameters and clinical variables are given in (online supplementary table S4). AUC, area under the curve; BPD, bronchopulmonary dysplasia; TEF50/PTEF, ratio of tidal expiratory flow at 50% of expired volume to peak tidal expiratory flow; Vt/kg, tidal volume per kilogram body weight.