Physiology of Oxygen Breathing in Pilots: A Brief Review
Naval Medical Research Unit Dayton Wright-Patterson Air Force Base United States
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This non-exhaustive survey presents literature describing some effects of breathing oxygen partial pressures between normoxic 21 kPa and normobaric hyperoxic 100 kPa 160 to 760 Torr. Absorption atelectasis is a concern when the fraction of oxygen FIO2 in the breathing gas is high, but for all other risks, oxygen partial pressure PO2 is the variable of interest. Gas transport and oxygen delivery in people with healthy lungs is not improved by elevated alveolar PO2. Atelectasis absorption injury is of concern if FIO280 and small airways or eustachian tubes or sinus ostia are blocked. Absorption becomes faster as altitude increases. Pulmonary oxygen toxicity and direct oxidative injuries are improbable in flight -- No pulmonary oxygen toxicity has been found when PO2 55 Pa 418 Torr, symptoms reported for PO2 of 75 kPa 520 Torr were reported after 24-hours exposure, and the earliest signs reported at PO2 of approximately 100 kPa 760 Torr, 100 oxygen at sea level occurred after 6 hours. However, aviators who are treated for suspected decompression sickness run the risk of pulmonary oxygen toxicity. Other effects of elevated PO2 include constriction of blood vessels, changes in blood pressure control, and poor response to low blood sugar. Finally, the near zero humidity of the gas stream in which oxygen is delivered to the air crew may predispose susceptible individuals to bronchoconstriction.
- Anatomy and Physiology