Operation Everest. II: Spirometric and radiographic changes in acclimatized humans at simulated high altitudes.

We report spirometry and radiographic data on eight normal male human subjects during prolonged graded altitude exposure to as high as 8,848 m above sea level in a hypobaric chamber. We found a significant and progressive drop in FVC by 14 +/- 3% over 40 days, which resolved slowly during the first 48 h after descent. With altitude, midrange forced expiratory flow (FEF25-75) increased by 82 +/- 3%, probably because of reduced air density. FEV1, however, did not change. Chest radiographs on subjects taken 2 h after descent to sea level showed a pattern of pulmonary artery enlargement and interstitial edema. These data suggest that increased pulmonary blood volume and edema may be causes of the restricted pulmonary function pattern.