Short-term hypoxic exposure at rest and during exercise reduces lung water in healthy humans

Hypoxia and hypoxic exercise increase pulmonary arterial pressure, cause pulmonary capillary recruitment, and may influence the ability of the lungs to regulate fluid. To examine the influence of hypoxia, alone and combined with exercise, on lung fluid balance, we studied 25 healthy subjects after 17-h exposure to 12.5% inspired oxygen (barometric pressure = 732 mmHg) and sequentially after exercise to exhaustion on a cycle ergometer with 12.5% inspired oxygen. We also studied subjects after a rapid saline infusion (30 ml/kg over 15 min) to demonstrate the sensitivity of our techniques to detect changes in lung water. Pulmonary capillary blood volume (Vc) and alveolar-capillary conductance (D_M) were determined by measuring the diffusing capacity of the lungs for carbon monoxide and nitric oxide. Lung tissue volume and density were assessed using computed tomography. Lung water was estimated by subtracting measures of Vc from computed tomography lung tissue volume. Pulmonary function [forced vital capacity (FVC), forced expiratory volume after 1 s (FEV₁), and forced expiratory flow at 50% of vital capacity (FEF₅₀)] was also assessed. Saline infusion caused an increase in Vc (42%), tissue volume (9%), and lung water (11%), and a decrease in D_M (11%) and pulmonary function (FVC = -12 ± 9%, FEV ₁ = -17 ± 10%, FEF₅₀ = -20 ± 13%). Hypoxia and hypoxic exercise resulted in increases in Vc (43 ± 19 and 51 ± 16%), D_M (7 ± 4 and 19 ± 6%), and pulmonary function (FVC = 9 ± 6 and 4 ± 3%, FEV₁ = 5 ± 2 and 4 ± 3%, FEF₅₀ = 4 ± 2 and 12 ± 5%) and decreases in lung density and lung water (-84 ± 24 and -103 ± 20 ml vs. baseline). These data suggest that 17 h of hypoxic exposure at rest or with exercise resulted in a decrease in lung water in healthy humans.