Pulmonary gas exchange efficiency during exercise breathing normoxic and hypoxic gas in adults born very preterm with low diffusion capacity

Adults with a history of very preterm birth (<32 wk gestational age; PRET) have reduced lung function and significantly lower lung diffusion capacity for carbon monoxide (DL_CO) relative to individuals born at term (CONT). Low DL_COmay predispose PRET to diffusion limitation during exercise, particularly while breathing hypoxic gas because of a reduced O₂driving gradient and pulmonary capillary transit time. We hypothesized that PRET would have significantly worse pulmonary gas exchange efficiency [i.e., increased alveolar-to-arterial PO₂difference (AaDO₂)] during exercise breathing room air or hypoxic gas (FIO₂= 0.12) compared with CONT. To test this hypothesis, we compared the AaDO₂in PRET (n = 13) with a clinically mild reduction in DL_CO(72 ± 7% of predicted) and CONT (n = 14) with normal DL_CO(105 ± 10% of predicted) pre- and during exercise breathing room air and hypoxic gas. Measurements of temperature-corrected arterial blood gases, and direct measure of O₂saturation (SaO₂), were made prior to and during exercise at 25, 50, and 75% of peak oxygen consumption (V O_2peak) while breathing room air and hypoxic gas. In addition to DL_CO, pulmonary function and exercise capacity were significantly less in PRET. Despite PRET having low DL_CO, no differences were observed in the AaDO₂or SaO₂pre- or during exercise breathing room air or hypoxic gas compared with CONT. Although our findings were unexpected, we conclude that reduced pulmonary function and low DL_COresulting from very preterm birth does not cause a measureable reduction in pulmonary gas exchange efficiency.