Respiratory and chest wall mechanics in very preterm infants

Data on static compliance of the chest wall (C_cw) in preterm infants are scarce. We characterized the static compliance of the lung (C_L) and C_cw to determine their relative contribution to static compliance of the respiratory system (C_rs) in very preterm infants at 36 wk 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 (V_T) were measured simultaneously during a short apnea evoked by the Hering-Breuer reflex. We computed tidal breathing variables, airway resistance (R), and dynamic lung compliance (C_L,dyn), inspiratory capacity (IC), and C_rs, C_L, and C_cw. Functional residual capacity was assessed by the multiple breath washout technique (FRC_mbw). Breathing variables, compliances, and lung volumes were adjusted for body weight. Twenty-three preterm infants born at 27.2 ± 2.0 wk gestational age (GA) were studied at 36.6 ± 0.6 wk PMA. Median and interquartile range (IQR) C_rs/kg is 0.69 (0.6), C_L/kg 0.95 (1.0), and C_cw/kg 3.0 (2.4). Infants with BPD (n = 11) had lower C_rs/kg (P = 0.013), C_L/kg (P = 0.019), and C_cw/kg (P = 0.027) compared with infants without BPD. C_cw/C_L ratio was equal between groups. FRC_mbw/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 lungs, and chest wall. Decreased C_rs, C_L, and C_cw in infants with BPD explain the lower FRC and IC seen in these infants.NEW & NOTEWORTHY Data on chest wall compliance in very preterm infants in the postsurfactant era are scarce. To our knowledge, we are the first group to report data on static respiratory system compliance (C_rs), lung compliance (C_L), and chest wall compliance (C_cw) in preterm infants with and without bronchopulmonary dysplasia (BPD) in the postsurfactant era.