Travel Reference
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study. The effects of such hypoxemia are inconsequential in healthy individuals, but per-
sons with illnesses affecting oxygen transport could suffer adverse effects.
Temperature decreases at a rate of approximately 3.5°F per 1000 feet (6.5°C per 1000
m) gain in altitude. Cold and hypoxia combine to produce hypothermia and frostbite, and
cold may contribute to high-altitude pulmonary edema.
Because particulate matter, water vapor, and cloud cover diminish with increasing alti-
tude,solarultraviolet radiationincreases byapproximately 4percentper1000feet(300m)
gain in altitude, increasing the risk of sunburn, photosensitive reactions, snow blindness,
and,withlifetimeexposures,skincancerandcataracts.Onwindlessdays,reflectionofsun-
light from snow can produce intense heat, and heat-related illnesses are more common at
high altitudes than generally appreciated.
Becausesmalleramountsofairborneparticulatematterarepresent,altitudecanbebene-
ficial for those with allergic asthma or other allergic conditions, and for individuals whose
reactive airway disease is aggravated by pollutants. However, air pollution at high altitude
is now increasing throughout the world.
Humidity is decreased at altitude, particularly at high altitudes, because the air is cool.
(The vapor pressure of water at 5°F, or −15°C, is only 1.24 mm Hg.) Furthermore, in wil-
dernesssituationswatercanonlybeobtainedabovesnowlinebymeltingsnoworice.Such
difficultyobtainingwatercombinedwithincreasedwaterlossfromtheskinandlungsoften
leads to dehydration in healthy climbers. Compromised cardiovascular systems, diuretics
taken for heart failure or hypertension, and pregnancy (perhaps) aggravate this problem.
Drying of the airways increases the risk of tracheal and bronchial plugging, particularly in
those with chronic lung disease.
THE EFFECT OF ALTITUDE ON RESPIRATORY DISORDERS
Movement of oxygen from air to blood, the first stage of oxygen transport, is the function
of the respiratory system. Components of this system include the controls of ventilation
(the movement of air into and out of the lung), the mechanics of respiration, matching of
ventilation and perfusion by blood in the lung, and gas exchange across the alveolar-capil-
lary membrane.
Disorders of Ventilatory Control
Any disorder that diminishes ventilation or the ventilatory response to lowered oxygen
or increased carbon dioxide—such as stroke, trauma that injures the brain, neuromuscular
diseases, obesity resulting in diminished respiration (hypoventilation), chronic obstructive
pulmonary diseases (COPD) including asthma, and sleep apnea—pose a greater risk at
altitude. Medications may have the same effect. Long-acting benzodiazepines such as
diazepam (Valium®) reduce nocturnal arterial oxygen saturation at high altitude.
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