High-altitude exposure of three weeks duration increases lung diffusing capacity in humans

Area of Science:

• Physiology
• Altitude Medicine
• Respiratory System

Background:

• High-altitude exposure leads to increased arterial oxygen partial pressure (PaO2).
• Improved lung gas exchange contributes to better arterial oxygenation alongside increased ventilation.
• Previous studies suggest reduced alveolar-capillary barrier resistance with prolonged hypoxia, but early adaptation effects are unknown.

Purpose of the Study:

• To investigate changes in lung diffusing capacity and its determinants during early high-altitude adaptation.
• To examine hemoglobin, alveolar volume, pulmonary capillary blood volume, and alveolar-capillary membrane diffusion at high altitude.

Main Methods:

• Lung diffusion was measured in 33 healthy lowlanders at sea level and after 2 weeks at 5,400 m on Mount Everest.
• Measurements included hemoglobin, lung diffusing capacity, alveolar volume, and membrane diffusion, adjusted for hemoglobin and inspired oxygen.
• Subjects experiencing mountain sickness were excluded from the analysis.

Main Results:

• Hemoglobin oxygen saturation increased significantly after 2 weeks at high altitude.
• Lung diffusing capacity, membrane diffusion, and alveolar volume showed significant increases compared to sea level.
• Pulmonary capillary blood volume remained unchanged, while membrane diffusion normalized for alveolar volume increased substantially.

Conclusions:

• Lung diffusing capacity improves with acclimatization at high altitude due to increased hemoglobin, alveolar volume, and membrane diffusion.
• Reduced alveolar-capillary barrier resistance may be mediated by increased sympathetic tone.
• These physiological adaptations can develop within approximately 3 weeks of high-altitude exposure.