ABSTRACT
Abrupt decompression and consequent gas expansion cause an almost instantaneous fall in partial pressure of gases within the lung. Delivery of 100% oxygen immediately upon decompression is essential for preservation of consciousness. Delivery of 100% oxygen for the earliest breaths following decompression requires system ‘dead space’ to be purged rapidly of gas still containing nitrogen. Post-decompression severity of hypoxia will be determined by lung volume and effectiveness of pulmonary ventilation to eliminate alveolar nitrogen – deep breaths essential even when breathing against pressure breathing for altitude protection (PBA); hypoventilation will delay alveolar oxygenation and could cause severe hypoxia. The physiological consequences of PBA include increased breathing effort, increased pulmonary ventilation, distension of lungs and chest, soft tissue distension, raised intrapleural pressure, respiratory counter-pressure and cardiovascular effects. For use in space, pressure suit requires closed-circuit system to remove CO2, water vapour, heat and odour, and to add O2; limited radiation and micrometeorite protection also required.
