Ventilatory function and oxygen delivery at high altitude in the Himalayas.

This study aimed to evaluate changes in lung function assessed by spirometry and blood gas content in healthy high-altitude sojourners during a trek in the Himalayas. A group of 19 Italian adults (11 males and 8 females, mean age 43 ±15 years, and BMI 24.2 ±3.7kg/m) were evaluated as part of a Mount Everest expedition in Nepal. Spirometry and arterial blood gas content were evaluated at baseline in Kathmandu (≈1400m), at the Pyramid Laboratory - Observatory (peak altitude of ≈5000m), and on return to Kathmandu 2-3 days after arrival at each site. All participants took 250mg of acetazolamide per os once daily during the ascent. We found that arterial hemoglobin saturation, O and CO partial pressures, and the bicarbonate level all decreased (in all cases, p<0.001 with R=0.70-0.90), while pHa was maintained stable at the peak altitude. Forced vital capacity (FVC) remained stable, while forced expiratory volume in 1sec (FEV1) decreased (p=0.010, n=0.228), resulting in a lower FEV1/FVC ratio (p<0.001, n=0.380). The best predictor for acute mountain sickness was the O partial pressure at the peak altitude (p=0.004, R=0.39). Finger pulse oximetry overestimated peripheral saturation relative to arterial saturation. We conclude that high-altitude hypoxia alters the respiratory function and the oxygen saturation of the arterial blood hemoglobin. Additionally, air rarefaction and temperature reduction, favoring hypoxic bronchoconstriction, could affect respiration. Pulse oximetry seems not enough to assist medical decisions at high altitudes.