week or more at high altitude, the num- 
ber of red blood cells can increase by up 
to 50 percent, depending on the altitude 
and the length of time spent there. Since 
hemoglobin is the major transporter of 
oxygen in the blood, an increase in the 
number of red blood cells has generally 
been interpreted as a means of increas- 
ing hemoglobin and getting more oxy- 
gen to the tissues. Among altiplano na- 
tives, however, evidence for increases in 
red blood cell number has been variable. 
At extremely high altitudes ( 1 4,700 feet 
and above), red blood cell counts 50 to 
60 percent above sea-level norms have 
been reported, while among Quechuas 
tested at Nunoa, red blood cell counts 
are reported to be only about 10 to 12 
percent above sea-level norms. By con- 
trast, red blood cell counts of Sherpa 
adults and children are considerably 
lower, actually in the low end ol the 
normal range for sea-level populations. 
As oxygenated blood circulates 
through the body, the oxygen is released 
for use in the tissues. The unbinding, or 
dissociation, of oxygen from hemoglobin 
is enhanced among the Quechuas be- 
cause at high altitudes more C0 2 is 
picked up by hemoglobin as red blood 
cells pass through the capillaries. As this 
happens, hemoglobin’s affinity for oxy- 
gen is reduced, and more oxygen can be 
released to the tissues. Travelers to high 
altitudes and Andean natives also show 
an increase in their blood of a compound 
called 2,3 diphosphoglycerate, which 
has the effect of increasing the amount 
of oxygen released to the tissues. When 
oxygen concentrations are low, as in the 
capillaries, the 2,3 diphosphoglycerate 
reacts with hemoglobin, interfering with 
hemoglobin’s affinity for oxygen. To- 
gether with an increase in the size and 
number of capillaries perfusing the ac- 
tive tissues, these characteristics insure 
delivery of sufficient oxygen to the tis- 
sues. 
Unlike the Quechuas, Sherpas may 
not have increased levels of 2,3 diphos- 
phoglycerate — at least at altitudes be- 
low 14,000 feet. Since they also do not 
exhibit large lung capacities or elevated 
red blood cell numbers, the question is, 
what sort of adaptation do they have? 
Unfortunately, the answer is not yet 
clear. Some data seem to show a slightly 
lower carbon dioxide concentration in 
the lungs, perhaps indicating a slightly 
higher ventilation. It is also possible, 
according to one study, that the affinity 
between oxygen and hemoglobin is 
greater for the Sherpas than for the 
Quechuas. But Sherpas don’t appear to 
possess any special type of hemoglobin, 
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