Mechanical properties of the lungs during acclimatization to altitude

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Abstract
Mechanical properties of the lung were studied in 9 healthy lowlanders during a 6-day sojourn at an altitude of 3457 m. In comparison to sea-level values, at altitude, lung volumes measured by plethysmography including total lung capacity, vital capacity, and functional residual capacity (FRC) presented small changes not exceeding 300 ml; static and dynamic lung compliances were not modified but static pressure-volume curves of lungs were shifted progressively to the left (the decrease in lung elastic recoil averaged .apprx. 2 cm H2O on days 4-6); and maximal midexpiratory flow, forced expiratory volume in 1 s, and maximal expiratory and inspiratory flows were increased and airways and pulmonary flow resistances were decreased on most days at altitude. The unchanged FRC in the face of a decreased lung recoil may be explained by an increase in thoracic blood volume at altitude, but other possible mechanisms are discussed. The decrease in resistances and increase in maximal flows may be partly explained by the decreased air density at altitude, but another contributing factor such as a bronchodilatation is also suggested. Changes in lung mechanics at altitude may account for some of the changes in the pattern of breathing and mouth occlusion pressure (P0.1) observed during acclimatization of lowlanders to altitude.