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How hypoxia affects me?

  Hypoxia

When altitude increases as a result of an emergency or rapid depressurization, the air pressure falls. Atmospheric pressures is reduced to half its sea level value at 18,000 feet. Thus, partial pressure of oxygen will also fall. The body is capable of coping with the fall of alveolar partial oxygen quite well, but as altitude is increased above 10,000 feet, the body will become less able to cope with the effect of reduced partial pressure.

The brain is particularly sensitive to oxygen lack, and an early effect is that the subject may have no insight into his condition and has no ability to criticize his own actions. As a result it is unlikely that the corrective actions will be taken and the condition then progresses to unconsciousness.

Cabin altitude and hypoxia

Symptoms will depend on the partial pressure of the alveolar oxygen and time of exposure and these will in turn, depend on cabin altitude and degree of oxygen failure.

Breathing air at 4000 feet or above, night vision is affected. Above 10,000 feet and up to 18,000 feet, the effect of oxygen lack become important, though they seldom occur suddenly and, at rest, consciousness will be maintained (not a problem to those Nepalis who live in the Himalayas).

Above 25,000 feet, there is a marked increased in hypoxic incidents and the rapid reduction in time of useful consciousness. Above 33,000 feet, breathing 100 % oxygen is necessary.

Typical symptoms of slow onset at 15,000 feet

  • Blueness of lips and finger nails
  • Tiredness, sleepiness, headache
  • Light-headedness, dizziness
  • Sickness and sweating
  • Mental impairment, poor judgment and loss of self criticism

          Typical symptoms of rapid onset at 25,000 feet

  • Blueness of lips and finger nails
  • Dizziness, light-headedness, possible feelings of detachment and well being.
  • Mental impairment, difficulty in concentration, making simple mistakes, lack of self-criticism and impairment of judgment.
  • Visual symptoms, either blurred vision, tunnel vision or double vision.
  • Tingling in hands and feet.
  • Muscular weakness, incoordination in fine movement, leading to muscle tremor, usually first seen in the hands
  • Semiconscious state, mentally switched off and unresponsive, with eyes open and head upright.
  • Unconscious

Time of useful consciousness

This is the period between the individual being deprived of his oxygen and become so affected by hypoxia that he is unable to cope with an emergency. Typical examples are as follows:

Altitude (feet) Moderate Activity Sitting quietly
22,000 5 minutes 10 minutes
25,000 2 minutes 3 minutes
30,000 45 seconds 75 seconds
40,000 18 seconds 30 seconds

Conclusion

I have been subjected to a hypoxic demonstration in a decompression chamber personally. Despite all the symptoms elaborated above, I was not aware that I became hypoxic until the Aviation Medicine Doctor pointed out to me later when the decompression was back to normal.

The doctor was on the oxygen mask and he conducted experiments on us. He told us we could not even add two plus two ! All the while, we felt euphoric (happy) and did not know what was happening ! ..so much for the symptoms !!

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