Development of lung diffusion to adulthood following extremely preterm birth

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.

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.

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.

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.