ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 373

Abnormal Hemoglobin
The hypoxia of high altitude is a well-recognized problem for those with sickle cell
disease. Even pressurized aircraft cabin altitudes (up to 8250 feet or 2500 m) will cause
20 percent of those with hemoglobin SS, SC, and sickle-thalassemia to have a thrombotic
vaso-occlusive crisis. Indeed, ascent to altitude for some has triggered their first awareness
oftheircondition.Peoplewithsicklecelldiseaselivingathighaltitude(10,000feetor3000
m) in Saudi Arabia have twice the incidence of crises, hospitalizations, and complications
as their counterparts at low altitude.
Splenicinfarctionataltitudemaybemorecommoninthosewithsicklecelltrait(hemo-
globin AS) than those with homozygous disease (hemoglobin SS), who totally infarct their
spleens early in life. The differential diagnosis of left upper quadrant pain at altitude (even
as low as 5000 feet or 1500 m) should include splenic infarction—in Caucasians as well as
those of African ancestry. The incidence of problems in individuals with sickle cell trait,
however, is quite low, and ascent to altitude, even with vigorous exercise, is not contrain-
dicated, in contrast to those with sickle cell disease. The U.S. Army, for example, does not
consider soldiers with the trait unfit for duty at high altitude.
Oxygen Affinity
Hemoglobin with altered oxygen affinity may affect acclimatization to high altitude.
When individuals with genetically left-shifted oxygen dissociation curves were taken to
10,200 feet (3100 m), surprisingly they did not develop a fast pulse or rapid respirations
and were superior in their exercise performance. At least at this altitude, increased loading
of the hemoglobin in the lung presumably resulted in improved oxygen transport. Whether
a decreased oxygen affinity would be detrimental has not been addressed.
Anemia
Giventhecentralroleofhemoglobininoxygentransport,alowhemoglobinlevelmight
be expected to affect tolerance to high altitude. However, neither the extent of ventilatory
acclimatizationortheincidenceorseverityofAMShasbeenfoundtocorrelatewithhemo-
globin concentration.
Persons with iron deficiency, even without frank anemia, have reduced exercise per-
formance at high altitude (as at sea level), as well as reduced erythropoietic (bone marrow
stimulation) response. Iron deficiency is particularly common in women who are not care-
fulaboutreplacingironlostinmenstrualblood.Nodataareavailableontheroleofanemia
in susceptibility to high-altitude illness.
THE EFFECT OF ALTITUDE ON NEUROLOGIC CONDITIONS
Migraine