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by the body's normal working
processes. The problem is that these
gases expand and contract as the
aircraft climbs and descends. Some
Human Factors 411
need a way out, and some need a
way back as well.
·  Gas in the ears is normally vented
via the Eustachian tubes. If
these are blocked (say with a
cold), the pressure on either side
of the eardrum is not balanced,
which could lead (at the very
least) to considerable pain, and
(at worst) a ruptured eardrum.
·  Sinus cavities are also vulnerable
to imbalances of pressure, and
are affected in the same way as
eardrums.
·  Gas in the gut can be vented from
both ends.
·  Teeth may have small pockets of
air in them, if filled, together
with the gums. Although
dentists nowadays are aware of
people flying, and pack fillings
properly, the general public
don't fly every day, as you do, so
it's best to be sure. High altitude
balloonists actually take their
fillings out.
Motion Sickness
This is caused by a mismatch
between the information sent to the
brain by the eyes and ears.
Accelerating from straight and level
may give you the impression of
pitching up, because the sensors in
the inner ear perceive the body
weight as going rearwards and
downwards. As the most dependable
source of sensory information is
your eyes, believe your instruments.
Decompression Sickness
Where pressures are low, nitrogen in
the blood comes out of solution
(typically above 18,000', but more so
at 25,000'). Bubbles can form, and
are especially painful in the joints
(e.g. the bends, for the joints, the
creeps (skin), chokes (lungs) and the
staggers (brain).
Unfortunately, these bubbles do not
redissolve on descent, so if you are
affected you may need to go into a
decompression chamber. For this
reason, diving before flight should
be avoided, as extra nitrogen is
absorbed while breathing pressurised
gas and will dissolve out as you
surface again. Don't fly for 12 hours
if you have been underwater with
compressed air, and 24 hours if
you've been below 30 feet.
Circulatory System
Made up of the heart, arteries,
arterioles, capillaries, venules, veins
and blood.
The Heart
This item does not rest in the
same way as other muscles –
instead, it take a mini-rest for a
microsecond or two in between
beats (a normal pulse rate is
around 70 beats per minute).
The systolic blood pressure is the
peak pressure as blood is
412 Canadian Professional Pilot Studies
pumped from the heart to the
aorta. The diastolic pressure is
the lowest, produced when
resting between beats. Normal
blood pressure lies between
110-145 mmHg (systolic) and
70-90 mmHg (diastolic) – you
might see a figure of 120/80
(120 over 80).
Blood
55% plasma, for transporting
CO2, nutrients and hormones,
and 45% cells. Red cells
transport oxygen via
haemoglobin, and white cells
(leukocytes) fight infection.
Platelets are for clotting blood.
Heart Disease
Heart disease can be grouped
into 3 categories:
·  Hypertensive—from high
blood pressure, working
the heart harder so it gets
enlarged (anxiety, etc.).
·  Coronary, or Arteriosclerotic—
hardening of the arteries
through excessive calcium,
or cholesterol, which again
makes the heart work
harder (bad diet).
·  Valvular or rheumatic—
where valves are unable to
open or close properly,
allowing back pressure to
build up (old age).
Adrenaline increases the speed
and force of the heart beat.
To reduce the risks of heart
disease, double your resting
pulse for at least 20 minutes 3
times a week.
Fatigue
It’s not so much the amount of sleep
you get, but when you get it that
counts, so fatigue is just as likely to
result from badly planned sequences
of work and rest. A surprising
amount (over 300) of bodily
functions depend on the cycle of day
and night—we have an internal
rhythm, which is modified by such
things. You naturally feel best when
they're all in concert, but the slippery
slope starts when they get out of
line. The best known
desynchronisation is jet lag, but it
also happens when you try to work
nights and sleep during the day—
bright light can fool your body into
　
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