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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