Flow‐resistive loading and diaphragmatic muscle function in term and preterm infants

Abstract Purpose We aimed to assess diaphragmatic function in term and preterm infants with and without history of bronchopulmonary dysplasia (BPD), before and after the application of inspiratory flow resistive loading. Methods Forty infants of a median (range) gestational age of 34 (25–40) weeks were studied. BPD was defined as supplemental oxygen requirement for >28 days of life. Seventeen infants were term, 17 preterm without history of BPD, and six preterm with a history of BPD. The diaphragmatic pressure–time index (PTIdi) was calculated as the mean to maximum trans‐diaphragmatic pressure ratio times the inspiratory duty cycle. The PTI di was calculated before and after the application of an inspiratory‐flow resistance for 120 s. Airflow was measured by a pneumotachograph and the transdiaphragmatic pressure by a dual pressure catheter. Results The median (interquartile range [IQR]) pre‐resistance PTIdi was higher in preterm infants without BPD (0.064 [0.050–0.077]) compared with term infants (0.052 [0.044–0.062], p = .029) and was higher in preterm infants with BPD (0.119 [0.086–0.132]) compared with a subgroup of preterm infants without BPD (0.062 [0.056–0.072], p = .004). The median (IQR) postresistance PTIdi was higher in preterm infants without BPD (0.101 [0.084–0.132]) compared with term infants (0.067 [0.055–0.083], p < .001) and was higher in preterm infants with BPD [0.201(0.172‐0.272)] compared with the preterm subgroup without BPD (0.091 [0.081–0.108], p = .004). The median (IQR) percentage change of the PTIdi after the application of the resistance was higher in preterm infants without BPD (65 [51–92] %) compared with term infants (34 [20–39] %, p < .001). Conclusions Preterm infants, especially those recovering from BPD, are at increased risk of diaphragmatic muscle fatigue under conditions of increased inspiratory loading.