Onset of hypoxia is insidious (like CO poisoning) and can be recognised only by being very aware of the symptoms.
Arrow Symptoms of Hypoxia
• Concentration difficulties.
• Impaired judgement, mood changes, euphoria (euphoria can be experienced above 10,000 ft)
• Drowsiness and lethargy.
• Light headedness, dizziness, nausea.
• Loss of muscular co-ordination.
• Pallor and cyanosis.
• Failure of the basic senses, especially colour vision, which becomes affected by 8000 ft. Night vision affected above 8000 ft.
• Unconsciousness, coma and death.
Arrow Factors Affecting Hypoxia
Following factors increase the onset of hypoxia:
• Exercise
• Cold: Increases the body’s demand for oxygen which is required to burn carbohydrates in order to generate heat to keep the body warm.
• Illness
• Fatigue
• The use of drugs/alcohol
• Smoking. Inhalation of CO binds to haemoglobin blocking oxygen transfer. It can raise the physiological altitude by 4-5 thousand feet above the actual cabin altitude as the ability to transfer oxygen is reduced by 4% to 10%.
Arrow Time of Useful Consciousness
It is the length of time during which an individual can act with both mental and physical efficiency and alertness.
It is measured from the moment at which an individual is exposed to hypoxia.
It varies with altitude.
Altitude in ft … Time of Useful Consciousness
18,000 … 30 minutes
22,000 … 4 to 8 minutes
25,000 … 2 to 4 minutes
30,000 … 30 seconds to 1 minute
35,000 … 15 to 30 seconds
43,000 … 8 to 12 seconds
Time of useful consciousness for people doing light to moderate work (effective performance time) fall by 40%.