Oxygen is one of the fuels that your body uses for energy,
and hypoxia is the condition
where your body doesn't have enough oxygen to function normally,
and that's manifested when things like your brain
start to struggle and stumble and start to shut down.
Some of the factors that will affect
the way that some people will get hypoxia,
the most important factors are altitude and time.
So, the higher the altitude, the more severe the hypoxia,
means that you'll experience hypoxia in a shorter period of time.
But then some personal factors are things like if you're cold,
well, then your body starts to burn oxygen to generate heat,
and the oxygen that's burnt to keep you warm
isn't available to help your brain function normally.
And then personal factors like smoking -
so if you smoke 20 cigarettes a day,
the amount of hypoxia that your body would have
would be equivalent to about 5,000 feet.
So if you were in a cabin altitude of 8,000 feet
and you were a heavy smoker,
the amount of oxygen that is being delivered to your brain
would be equivalent to about 13,000 feet,
and that's an altitude where we would know
that you would get hypoxia symptoms.
Some other things - like, if you're physically active,
well, then your body is using oxygen to make the muscles move.
Again, that's reducing the oxygen delivery to your brain.
And also things like your general state of health
and your level of physical fitness
can also determine how efficiently your body uses oxygen.
And if you're not very physically fit,
well, then your body uses a lot of oxygen to function,
which will lower your threshold for developing hypoxia.
But, most importantly, hypoxia is insidious
because it actually erodes the higher mental functions
that are useful in helping you
to identify and have the critical insight
to know that you're becoming hypoxic,
which is more difficult when your brain's not functioning properly.
The concept of the hypoxia signature
is really there to illustrate to aircrew
that individuals react differently to each other with hypoxia,
but within an individual it's fairly consistent,
and so if you sign your name, we know that that's your signature
and you can recognise your signature over many years,
even though it might change slightly from one year to years later.
But we can recognise that as being your signature.
So the hypoxia signature
is the group of symptoms that you would experience,
that you would recognise as being your own experience of hypoxia.
And it's that hypoxia signature
that you would be recognising during flight
that would allow you to identify that you are developing hypoxia
and then sort of give you the opportunity to respond to that.
MAN: Yes, the difficulty in recognising hypoxia
is that many people have not been exposed to it before.
So that's one of the reasons and goals of hypoxic training,
is to expose somebody so that they experience the symptoms.
The insidious nature of the onset of the hypoxia
is because we are using up the oxygen reserve
and the oxygen available in the bloodstream
progressively decreases as we use up the reserve.
And there is no magic number or line
at which we suddenly become aware
of the fact that something adverse is happening
to oxygen supply and to brain function.
So the major difficulty lies in the fact
that a brain which is already deteriorating in function
because of a reducing oxygen supply
has to make decisions about the fact that this is happening.
DR ADRIAN SMITH: The benefit of hypoxia training
is that it allows aircrew
to recognise the symptoms of hypoxia early
so they've got more time to take corrective action,
and they can recognise the symptoms of hypoxia early
because they've previously experienced those symptoms
in a safe training environment.