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 (DLCO) relative to individuals born at term (CONT). Low DLCO may predispose PRET to diffusion limitation during exercise, particularly while breathing hypoxic gas because of a reduced O-2 driving gradient and pulmonary capillary transit time. We hypothesized that PRET would have significantly worse pulmonary gas exchange efficiency [i.e., increased alveolar-to-arterial PO2 difference (AaDO(2))] during exercise breathing room air or hypoxic gas (FIO2 = 0.12) compared with CONT. To test this hypothesis, we compared the AaDO(2) in PRET (n = 13) with a clinically mild reduction in DLCO (72 +/- 7% of predicted) and CONT (n = 14) with normal DLCO (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 O-2 saturation (SaO(2)), were made prior to and during exercise at 25, 50, and 75% of peak oxygen consumption ((V) over dot o(2peak)) while breathing room air and hypoxic gas. In addition to DLCO, pulmonary function and exercise capacity were significantly less in PRET. Despite PRET having low DLCO, no differences were observed in the AaDO(2) or SaO(2) pre- 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 DLCO resulting from very preterm birth does not cause a measureable reduction in pulmonary gas exchange efficiency.