Basic Aviation Physiology and Health Maintenance
What the domain covers
This domain covers the body in flight: hypoxia, hyperventilation, decompression, barotrauma, spatial disorientation, vision, hearing, fatigue, circadian rhythm, and the effects of alcohol, drugs and smoking. Candidates must understand oxygen partial pressure and how it falls with altitude, the difference between hypoxic and hypemic hypoxia, and the time of useful consciousness (TUC) at various cabin altitudes.
Concepts to master
- Hypoxia types: hypoxic (low alveolar oxygen), hypemic (anaemia, carbon monoxide), stagnant (G-force, cold), histotoxic (alcohol, drugs).
- Hyperventilation: produces dizziness, tingling and cramps by washing out CO2; often confused with hypoxia. Trap: both improve with 100% oxygen, but only hyperventilation improves with slowed breathing.
- Decompression: explosive versus rapid; always don oxygen first, then descend.
- Spatial disorientation: somatogravic illusion during acceleration (false climb sensation), leans, and the somatogyral illusion.
- Fatigue and circadian rhythm: worst performance around 0300-0600 body time; sleep debt is cumulative.
Question traps
Questions often ask for the first action after a decompression (oxygen mask on, then emergency descent) or confuse the cause of a symptom. Another classic: alcohol is a histotoxic hypoxia and also increases dehydration. Carbon monoxide binds haemoglobin about 200-250 times more readily than oxygen.
Worked example / rule of thumb
At 35,000 ft cabin altitude, TUC is roughly 30-60 seconds. Rule of thumb: above 35,000 ft, treat TUC as seconds, not minutes, and oxygen must be immediate.