Basic Aviation Physiology and Health Maintenance
Domain 2 tests the body in the flight environment: hypoxia, hyperventilation, gas laws, barotrauma, decompression sickness and health maintenance. Questions often ask for the first action or the distinguishing sign.
Oxygen and altitude
- As cabin altitude rises, alveolar oxygen pressure falls; hypoxia impairs judgment and vision before the pilot notices.
- Approximate time of useful consciousness: FL180 20-30 min; FL250 3-5 min; FL300 1-2 min; FL350 30-60 s. Individual variation is large.
- Treat suspected hypoxia with 100% oxygen and descent; do not rely on feeling euphoric.
Pressure and health
- Boyle's law explains barotrauma and trapped gas; Henry's law explains decompression sickness after diving.
- Hyperventilation causes tingling, dizziness and cramps; hypoxia can cause cyanosis, confusion and euphoria.
- Alcohol, sedatives, antihistamines and smoking degrade performance; carbon monoxide raises carboxyhaemoglobin and reduces altitude tolerance.
Worked example
A pilot at 12,000 ft cabin altitude feels dizzy, tingly and anxious, but is not cyanosed and improves when told to slow breathing. This is hyperventilation, not hypoxia. Hypoxia would worsen with breath-holding and may show cyanosis or confusion. Initial management: reassure, slow breathing, and if doubt remains give oxygen and descend.
Traps
Assuming hyperventilation and hypoxia cannot coexist; ignoring a recent scuba dive; treating 'one drink' as safe; forgetting that smoking and CO reduce time of useful consciousness.