Extreme environments—flying, altitude, diving

Flying presents potential physiological challenges: modest hypoxia, gas expansion/ contraction with ascent/ descent, recirculation of air with increased risk of air-borne infection. Hypoxia of high altitude may lead to high altitude illness, comprising acute mountain sickness, which is generally minor and self-limiting, and high altitude pulmonary or cerebral oedema, which are serious and even life threatening. Increased recreational diving has raised the awareness of respiratory problems at depth. These can essentially be divided into five: barotrauma, e.g. ruptured bullae and pneumothorax, worsening of pre-existing disorder whilst at depth, e.g. asthma, nitrogen gas evolved from solution in body fluids (the ‘bends’), breath-hold diving and ascent hypoxia, pulmonary oedema.