Data on static compliance of the chest wall (Ccw) in preterm infants are scarce. We characterised the static compliance of the lung (CL) and Ccw to determine their relative contribution to static compliance of the respiratory system (Crs) in very preterm infants at 36 weeks' postmenstrual age (PMA). We also aimed to investigate how these compliances were influenced by the presence of bronchopulmonary dysplasia (BPD) and impacted breathing variables. Airway opening pressure, esophageal pressure, and tidal volume (VT) were measured simultaneously during a short apnea evoked by the Hering-Breuer reflex. We computed tidal breathing variables, lung resistance (Rl) and dynamic lung compliance (CL,dyn), inspiratory capacity (IC), and Crs, CL and Ccw. Functional residual capacity was assessed by the multiple breath washout technique (FRCmbw). Breathing variables, compliances and lung volumes were adjusted for body weight. Twenty-three preterm infants born at 27.2 ± 2.0 weeks' gestational age (GA) were studied at 36.6 ± 0.6 weeks' PMA. Median (IQR) Crs/kg is 0.69 (0.6), CL 0.95 (1.0) and Ccw 3.0 (2.4). Infants with BPD (n=11) had lower Crs (p=0.013), CL (p=0.019), and Ccw (p=0.027) compared to infants without BPD. Ccw/CL ratio was equal between groups. FRCmbw/kg (p=0.044) and IC/kg (p=0.005) were decreased in infants with BPD. Infants with BPD have reduced static compliance of the respiratory system, the lung and chest wall. Decreased Crs, CL and Ccw in infants with BPD explains the lower FRC and IC seen in these infants.
Keywords: bronchopulmonary dysplasia; chest wall mechanics; prematurity.