ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 359

CHAPTER 25
ALTITUDE AND COMMON MEDICAL CONDITIONS
Peter H. Hackett, M.D.
Principal Contributor
More and more people with a variety of medical conditions are traveling to altitude for re-
creation or work. Many are choosing to live at altitude, particularly retirees. The increased
needforknowledgeaboutthemixofillnessandaltitudehasstimulatedinvestigation,butfor
many conditions not enough information is available for conclusions about the risks. This
chapter considers the effect of altitude on preexisting illnesses, pregnancy, children, and the
elderly, as well as the converse effect of illnesses on altitude acclimatization.
ALTITUDE STRESS
Ascenttoaltitudeaffectspeopleinvariousways.Expansionofairfromthereducedpressure
cancauseproblemsinanyspacethatcontainsairorgas,suchassinuses,middleears,lungs,
the intestines, even a pneumothorax. Dysbarism, as such problems are called, is more com-
mon with rapid ascent in airplanes, but even gradual ascent to terrestrial elevations can be
associated with problems such as dental pain produced by expansion of gas trapped beneath
a filling.
In contrast, less dense air may flow through airways more easily and improve lung func-
tion. Decreased air resistance improves performance in athletic events such as jumping,
vaulting, and sprinting, and allows balls to travel farther.
The major physiologic stress of altitude is, of course, hypoxia. As barometric pressure
fallswithincreasingaltitude,thepartialpressureofoxygendeclines.Comparedtosealevel,
Denver, Colorado, has 17 percent less atmospheric oxygen pressure, Aspen has 25 percent
less, and only half the sea level pressure of oxygen is present at approximately 18,000 feet
(5500 m). In addition, weather, season, and latitude affect barometric pressure. Low atmo-
sphericpressureproducesbadweather.Pressureathighaltitudeislowerinwinter,andlower
farther from the equator for any given altitude. Environmental hypoxia is directly related to
barometric pressure, not altitude.
Many individuals experience hypoxemia—lower arterial blood oxygen—in everyday
life, such as during sleep, during airline travel, or as the result of lung disease. Commercial
aircrafthavecabinpressuresequivalenttoaltitudesashighas8500feet(2600m)andairline
crewmembersexperiencehypoxemia.Oxygensaturationsof80to93percent(normalatsea
level is 95 percent or higher) and an average low point of 89 percent were found in a recent