Development of lung diffusion to adulthood following extremely preterm birth

BACKGROUND: Gas exchange in extremely preterm (EP) infants must take place in fetal lungs. Childhood lung diffusing capacity of the lung for carbon monoxide (D(LCO)) is reduced; however, longitudinal development has not been investigated. We describe the growth of D(LCO) and its subcomponents to adulthood in EP compared with term-born subjects. METHODS: Two area-based cohorts born at gestational age ≤28 weeks or birthweight ≤1000 g in 1982–1985 (n=48) and 1991–1992 (n=35) were examined twice, at ages 18 and 25 years and 10 and 18 years, respectively, and compared with matched term-born controls. Single-breath D(LCO) was measured at two oxygen pressures, with subcomponents (membrane diffusion (D(M)) and pulmonary capillary blood volume (V(C))) calculated using the Roughton–Forster equation. RESULTS: Age-, sex- and height-standardised transfer coefficients for carbon monoxide (K(CO)) and D(LCO) were reduced in EP compared with term-born subjects, and remained so during puberty and early adulthood (p-values for all time-points and both cohorts ≤0.04), whereas alveolar volume (V(A)) was similar. Development occurred in parallel to term-born controls, with no signs of pubertal catch-up growth nor decline at age 25 years (p-values for lack of parallelism within cohorts 0.99, 0.65, 0.71, 0.94 and 0.44 for z-D(LCO), z-V(A), z-K(CO), D(M) and V(C), respectively). Split by membrane and blood volume components, findings were less clear; however, membrane diffusion seemed most affected. CONCLUSIONS: Pulmonary diffusing capacity was reduced in EP compared with term-born subjects, and development from childhood to adulthood tracked in parallel to term-born subjects, with no signs of catch-up growth nor decline at age 25 years.