Men are not naturally adapted to extremely high altitudes, like birds,
and consequently, when they rise to great heights suddenly, all
sorts of odd things take place. The intense cold numbs them; the low
air-pressure forces them to use an artificial supply of oxygen; they
become dulled, numb, nervous, dizzy, blind and sometimes unconscious. A
detailed study of the changes which take place in the body and mind of
the aviator has lately been undertaken, with interesting results.
In its normal state the blood contains about 5,000,000 red corpuscles
per cubic millimetre. At great heights, this number is largely
increased, that is, “hyper-globia” is produced, becoming more
pronounced as the elevation attained becomes higher. The number of the
white corpuscles is not augmented.
Respiratory changes are most marked. As the tension of oxygen
diminishes the oxygen is more perfectly utilized; but at very great
altitudes, the compensation is insufficient, and asphyxiation then
commences. Muscular force diminishes, and work at great heights rapidly
produces fatigue. At still greater heights, torpor renders work
impossible, and the slightest effort becomes very painful.
The sense of hearing is greatly modified, little clicking sounds
are often heard in the ears--often noted in the act of swallowing.
Visual keenness seems, on the other hand, to be increased. The general
sensitiveness diminishes.
In the recent expedition which attempted the ascent of Mount Everest
these psycho-physiological changes were carefully studied. In every
case it was found that the oxygen content of the arterial blood was
lower than at sea level and in equilibrium with the oxygen content of
the lung-air. Arterial-blood is from 95 to 100 per cent saturated with
oxygen at sea level, but at 14,000 feet where the barometric pressure
is 460 instead of 760, which is the normal sea level reading, the blood
is from 80 to 90 per cent saturated.
These various effects, coupled with the rapid motion, the roar of the
motors, etc., produce in most persons what is known as aeroplane or
balloon sickness, identical in character with mountain sickness. It
is attended by difficult breathing, loss of appetite, nausea, loss
of muscular energy, acceleration of the pulse, venous congestion of
the face, headache, drowsiness, etc. Many persons who have taken
an aeroplane trip for the first time, anticipating a mere pleasure
excursion, have discovered these various symptoms in themselves to
their cost! But it is rather late then to “get out and walk!”
Modern improvements in aeroplane construction, however, have largely
obviated many of these more serious discomforts, and, of course, in
ordinary passenger flights such great altitudes as those here mentioned
are not attained. But the changes which take place within man’s body on
reaching these great heights are extremely interesting from the medical
and physiological point of view.