Running-induced changes in lung function are not altered by acute moderate hypoxia

The purpose of this study was to describe the acute changes in pulmonary function and volumes induced by running in a simulated normobaric hypoxic environment. Eleven men (X- = 26 years, 78 kg) ran 5 miles (run time approximately equal to 40 min) under normoxic (N) and hypoxic (H) conditions. A PO2 Aerobic Exerciser was used to approximate an altitude of 2286 m (PIO2 = 113 mm Hg). Impedance cardiography was used to measure cardiac output and segmental transthoracic impedance (Zo) was used to identify thoracic fluid shifts. Similar reductions in vital capacity (7%) and increases in residual volume (10%) occurred after the N and H runs with no change in total lung capacity. Flow rates breathing air or He/O2, closing volume, and closing capacity did not change. The DLCO breathhold maneuver caused a significant fall in pulmonary blood flow after running but diffusing capacity appeared to be unaffected. No changes occurred in Zo at the apex, middle, or base of the lung after either run. The hypoxic pulmonary pressor response failed to modify the pulmonary changes observed after equivalent normoxic exercise. The lung volume changes subsequent to either run were due to expiratory limitation. Previous speculation of an exercise-induced interstitial edema could not be confirmed.