The Effects Of Altitude On Human Physiology

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change and its effect on the body mountaineers
generally define altitude according to the scale of high (8,000 - 12,000 feet),
very high (12,000 - 18,000 feet), and extremely high (18,000+ feet), (Hubble,
1995). A common misperception of the change in external environment with
increased altitude is that there is decreased oxygen. This is not correct as the
concentration of oxygen at sea level is about 21% and stays relatively unchanged
until over 50,000 feet (Johnson, 1988).
What is really happening is that the atmospheric pressure is decreasing
and subsequently the amount of oxygen available in a single breath of air is
significantly less. At sea level the barometric pressure averages 760 mmHg while
at 12,000 feet it is only 483 mmHg. This decrease in total atmospheric pressure
means that there are 40% fewer oxygen molecules per breath at this altitude
compared to sea level (Princeton, 1995).

HUMAN RESPIRATORY SYSTEM

The human respiratory system is responsible ...

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1969). The membranes in the alveoli provide a large surface area for
the free exchange of gases. The typical thickness of the pulmonary membrane is
less than the thickness of a red blood cell. The pulmonary surface and the
thickness of the alveolar membranes are not directly affected by a change in
altitude. The partial pressure of oxygen, however, is directly related to
altitude and affects gas transfer in the alveoli.

GAS TRANSFER

To understand gas transfer it is important to first understand something
about the behavior of gases. Each gas in our atmosphere exerts its own pressure
and acts independently of the others. Hence the term partial pressure refers to
the contribution ...

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