High altitude induced extravascular lung fluid accumulation

Exposure to high altitude is associated with changes in body fluid compartments, and spirometric changes suggestive of extravascular lung fluid accumulation can appear. Both exercise and hypoxia have been reported to have an additive effect on body fluid shift. With regard to the extravascular lung fluid accumulation, exposure to high attitude is known to induce changes in spirometry, including an increase in flow rates, and a fat in vital capacity (VC) and forced vital capacity (FVC): in fact many papers report a reduction of FVC and of flows at the last part of FVC at high attitude as compared to sea level. The potential explanation for reduced FVC and VC at high altitude can be summarized as follows: an increase in pulmonary blood volume; the development of interstitial lung oedema; respiratory muscles weakness. The presence of interstitial lung oedema is supported by numerous data, especially the increase in closing volume, indicating small airways compression by extravascular lung fluid accumulation, reported in 74% of recreational climbers at 4,559 m. According to this paper, increased pulmonary extravascular lung fluid would track centrally along major pulmonary vessels and airways. Peribronchial fluid accumulating in this way would be expected to compress airways increasing the volume at which airways close. An increased permeability of capillary endothelium could at least in part explain the increase of interstitial lung fluid. There is growing evidence that hypoxia increases capillary endothelial permeability both in vivo and in vitro. Preliminary data from our laboratory, aimed at investigating at which attitude the lung interstitial oedema appears and whether it appears also in elite climbers, seem to show that these changes in lung function appear also at lower altitudes but do not preclude successful climbing at extreme attitudes.