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What are the three physiological thresholds and their corresponding altitudes?
  • A
    Reaction Threshold (8000 ft), Disturbance Threshold (13000 ft), Critical Threshold (22000 ft).
  • B
    Reaction Threshold (7000 ft), Disturbance Threshold (10-12000 ft), Critical Threshold (22000 ft).
  • C
    Disturbance Threshold (5000 ft), Distress Threshold (10000 ft), Compensatory Threshold (20000 ft).
  • D
    Disturbance Threshold (7000 ft), Reaction Threshold (10-12000 ft), Critical Threshold (22000 ft).
Syllabus reference 040.02.01.02.26: Name the three physiological thresholds and allocate the corresponding altitudes for each of them: reaction threshold (7 000 ft); disturbance threshold (10-12 000 ft); and critical threshold (22 000 ft).
EASA distinguishes three physiological thresholds:
  • Reaction threshold. The altitude of 7 000 ft is referred to as the reaction threshold. It is the altitude at which even a healthy person may start to experience symptoms of hypoxia. Above this limit, the body reacts to the decreasing oxygen supply by increasing the rate and depth of breathing as well as the stroke volume to ensure full performance.
  • Disturbance threshold. The altitude band of 10 000 to 12 000 ft is called the disturbance threshold, because the compensatory mechanisms of the body are not powerful enoughto ensure full operation. Performance will be reduced and flight safety may be impaired.
  • Critical threshold. The altitude of 22 000 ft is referred to as the critical threshold. The alveolar partial pressure of oxygen is reduced to equal the minimum required blood partial pressure, no diffusion of oxygen into the blookd will be possible.

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