ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 362

High-Altitude Residents
Lung disease is the most common cause of impaired oxygen transport and would be ex-
pected to impact those living at altitude. Studies of high-altitude residents have found an
increased morbidity from COPD, as well as a propensity to migrate to lower altitude.
In South America and Asia, the problem of acquired lung disease is greater. A high in-
cidence of pneumoconiosis—lung disease resulting from inhalation of particulate foreign
material—is found at high altitude in central Ladakh, located at the base of the Korakorum
range in Pakistan and Kashmir. This disorder is attributed to dust storms that stir up silica
and the absence of chimneys in residents' homes.
Cigarette smoking is also a major cause of lung disease. Altitude and smoking are in-
dependently associated with mortality from COPD in the United States. In an analysis by
states, COPD mortality rose by 1 per 100,000 population for every additional 5.4 packs of
cigarettes smoked per person per year, and for each 300 feet (95 m) increase in altitude.
Stable Hypoxemic Disease in Lowlanders
Sea-levelandlow-altituderesidents—lowlandersforshort—withlungdiseasewouldbe
expected to tolerate high altitude less well. In addition, altitude might unmask lung disease
that has gone undetected. Acute hypoxemia associated with air travel has received consid-
erable attention, but much less is known about more prolonged hypoxia, such as a stay at
a ski resort. In one study of eight hypoxemic individuals with moderate, uncomplicated
COPDwhoascendedto6300feet(1920m)forfourdays,thepersonshadonlymildsymp-
toms on ascent, primarily mild fatigue and insomnia. However, arterial oxygen pressure
declined from 66 at sea level to 51 mm Hg while at rest and from 63 to 47 mm Hg with
exercise. (Normal resting arterial oxygen pressure at sea level for healthy young adults is
85to100mmHg.)Theindividuals didacclimatize. Their arterial carbondioxide pressures
dropped abruptly and declined further over four days, and their arterial oxygen pressures
increased, the responses seen in healthy persons. The authors concluded that travel to this
moderate altitude is safe for such persons and speculated that their preexisting hypoxemia
may have produced the equivalent of altitude acclimatization, decreasing the likelihood of
AMS. Despite the authors' plea for further investigations with sicker individuals at higher
altitudes, subsequent studies have not been done.
In studies of acute hypoxia and air travel, the ability to blow out a match to ensure ad-
equate expiratory flow, and the ability to walk up a flight of stairs without distress, have
been recommended as simple screening tests. Supplemental oxygen during flight has been
suggested for those who “failed.” These and other much more sophisticated tests may pre-
dict oxygenation during transient (up to four hours) modest hypoxia, but their usefulness
is limited because sea-level arterial oxygen levels do not correlate well with how people
fare at altitude. These studies also did not address how individuals might do with longer
stays at altitude and with associated stresses such as sleeping, physical activity, smoking,