Aims Eighteen patients with asthma were evaluated during preparation to climb to extreme altitude in order to study the effects of low fractional inspired oxygen (FiO₂), prolonged exposure to cold air and high altitude on lung function, asthma control and airway inflammation.

Methods Spirometry and airway inflammation (fractional exhaled nitric oxide (FeNO) and induced sputum) were studied under different test conditions: hypoxic (FiO₂=11%) exercise test, 24-hour cold exposure (−5°C) and before, during and after an expedition that involved climbing the Aconcagua mountain (6965 m).

Results Forced expiratory volume in 1 s (FEV₁) and FeNO values were slightly lower (p<0.04) after 1 h of normobaric hypoxia. FEV₁ decreased (p=0.009) after 24-hour cold exposure, accompanied by increased sputum neutrophilia (p<0.01). During the expedition FEV₁ and forced vital capacity decreased (maximum FEV₁ decrease of 12.3% at 4300 m) and asthma symptoms slightly increased. After the expedition the Asthma Control Test score and prebronchodilator FEV₁ were reduced (p<0.02), sputum neutrophil count was increased (p=0.04) and sputum myeloperoxidase levels, sputum interleukin 17 mRNA, serum and sputum vascular endothelial growth factor A levels were significantly higher compared with baseline. Patients with asthma with the lowest oxygen saturation during the hypoxic exercise test were more prone to develop acute mountain sickness.

Conclusions Exposure to environmental conditions at high altitude (hypoxia, exercise, cold) was associated with a moderate loss of asthma control, increased airway obstruction and neutrophilic airway inflammation. The cold temperature is probably the most important contributing factor as 24-hour cold exposure by itself induced similar effects.