Lung injury related to extreme environments.

Hydrostatic lung injuries The evolution of fish to amphibians, reptiles to endothermic birds and mammals has been accompanied by a progressively thinner pulmonary blood gas barrier, to accommodate the constraint of increased oxygen uptake and carbon dioxide output [1]. Accordingly, pulmonary circulation has evolved as a separate high flow–low pressure system. In humans, mean pulmonary artery pressures (PAP) are 8–20 mmHg, pulmonary wedge pressures are 5–14 mmHg and pulmonary capillary pressures are 8–12 mmHg [2]. A low-pressure regimen preserves the integrity of an alveolar capillary membrane only 0.3 mm thick. However, this structure is vulnerable to increased pressures during strenuous exercise or environmental hypoxic exposure as a cause of stress failure of the pulmonary capillaries and accumulation of extravascular lung water [3]. Reports of lung injury related to extremes of exercise and variations in ambient pressure and altitude confirm this vulnerability. The resulting lung injury takes the form of noncardiogenic pulmonary oedema.