Membrane and Capillary Components of Lung Diffusion in Infants with Bronchopulmonary Dysplasia

Rationale: Autopsied lungs of infants with bronchopulmonary dysplasia (BPD) demonstrate impaired alveolar development with larger and fewer alveoli, which is consistent with our previous physiologic findings of lower pulmonary diffusing capacity of the lung for carbon monoxide (DLCO) in infants and toddlers with BPD compared with healthy controls born at full term (FT). However, it is not known whether the decreased DLCO in infants with BPD results from a reduction in both components of DLCO: pulmonary membrane diffusing capacity (D-M) and Vc. Objectives: We hypothesized that impairment of alveolar development in BPD results in a decrease in both D-M and Vc components of DLCO but that the D-M/Vc ratio would not differ between the BPD and FT groups. Methods: DLCO was measured under conditions of room air and high inspired oxygen (90%), which enabled D-M and Vc to be calculated. Measurements and Main Results: D-M and Vc increased with increasing body length; however, infants with BPD had significantly lower D-M and Vc than FT subjects after adjustment for race, sex, body length, and corrected age. In contrast to D-M and Vc, the D-M/Vc ratio remained constant with increasing body length and did not differ for infants with BPD and FT subjects. Conclusions: Our findings are consistent with infants with BPD having impaired alveolar development with fewer but larger alveoli, as well as a reduced Vc.