Singh B, Cable GG, Hampson GV, Pascoe GD, Corbett M, Smith A. Hypoxia awareness training for aircrew: a comparison of two techniques. Aviat Space Environ Med 2010; 81:857–63.Introduction: Major hazards associated with hypoxia awareness training are the risks of decompression sickness, barotrauma, and loss of consciousness. An alternate method has been developed which combines exposure to a simulated altitude of 10,000 ft (3048 m) with breathing of a gas mixture containing 10% oxygen and 90% nitrogen. The paradigm, called Combined Altitude and Depleted Oxygen (CADO), places the subjects at a physiological altitude of 25,000 ft (7620 m) and provides demonstration of symptoms of hypoxia and the effects of pressure change. CADO is theoretically safer than traditional training at a simulated altitude of 25,000 ft (7620 m) due to a much lower risk of decompression sickness (DCS) and has greater fidelity of training for fast jet aircrew (mask-on hypoxia). This study was conducted to validate CADO by comparing it with hypobaric hypoxia. Methods: There were 43 subjects who were exposed to two regimens of hypoxia training: hypobaric hypoxia (HH) at a simulated altitude of 25,000 ft (7620 m) and CADO. Subjective, physiological, and performance data of the subjects were collected, analyzed, and compared. Results: There were no significant differences in the frequency and severity of the 24 commonly reported symptoms, or in the physiological response, between the two types of hypoxia exposure. Conclusions: CADO is similar to HH in terms of the type and severity of symptoms experienced by subjects, and appears to be an effective, useful, and safe tool for hypoxia training.