Background: Exercise performed at high-altitude may cause a sub-clinical pulmonary interstitial edema which can worsen gas exchange function. This study aimed to evaluate whether there are changes in alveolar-capillary diffusion after exercise during a short-term exposure to hypobaric hypoxia in elite swimmers. Materials & Methods: Seven elite swimmers [age: 20.4 ± 1.4 years, height: 1.78 ± 10.8 m, body mass (BM): 69.7 ± 11.1 kg] participated in the study. Diffusing capacity of the lungs for carbon monoxide (DLCO), transfer coefficient of carbon monoxide (KCO), pulse oximeter oxygen saturation (SpO2) and heart rate (HR) were measured at sea level at rest (SL-R), and after a short-term hypobaric hypoxia exposure (4,000 m), both at rest (HA-R) and at the end of moderate interval exercise (HA-E). Results: The combined exposure to high-altitude and exercise did not change DLCO from SL-R to HA-R, or HA-E (43.8 ± 9.8 to 41.3 ± 10.5 to 42.4 ± 8.6 ml·min-1·mmHg-1, P = 0.391). As expected, elite swimmers showed large decrease in SpO2 (72 ± 5; P < 0.001) and increase in HR (139 ± 9 beats·min-1; P < 0.003) after HA-E. Conclusions: An acute high-altitude exposure combined with submaximal exercise does not change alveolar-capillary diffusion in elite swimmers
