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High-Altitude Breathing May Be in One's Blood
By Guy Gugliotta
Washington Post Staff Writer
Monday, December 23, 2002; Page A09
The mathematics are inescapable. The higher the altitude, the less oxygen
the air will hold, and the more difficult it is to breathe. Either the body
adapts, or the person dies.
For decades scientists accepted an "Andean man" model for acclimatization:
The body at altitude will grow a higher concentration of oxygen-absorbing
red blood cells to mop up scarcer oxygen from rarified air.
Add bigger lungs and deeper breathing, and equilibrium is reestablished. The
result is a blocky fellow with a washtub chest, like the musicians who play
the panpipes and wooden flutes of Andean mountain music.
"Their lungs are 25 percent bigger than ours," said Case Western Reserve
University anthropologist Cynthia Beall. "Andean highlanders are very
distinctive."
Earlier this month, however, Beall and five colleagues reported on another
distinctive people -- a community of Ethiopians who live at 11,650 feet, and
whose blood, by several common measures, is exactly the same as if they
lived at sea level.
"I'm flabbergasted; I don't see how they do it," said exercise physiologist
David Martin of Georgia State University. "I'm left with a dozen questions.
It's a fascinating kind of story."
And it is not just a curiosity. For Martin, a consultant for USA Track &
Field, and others like him, the extraordinary success of African distance
runners -- principally Ethiopians and Kenyans -- has been a source of wonder
ever since barefooted Abebe Bikila won the 1960 Olympic marathon. Is there a
secret that others cannot possess?
"Efforts to find a genetic explanation have been dismal failures," said
Dallas cardiologist Ben Levine, an expert in exercise medicine. "My personal
opinion is that these successes are cultural. A distance runner in Ethiopia
or Kenya is a national hero."
In an online article to be published in the Proceedings of the National
Academy of Sciences, Beall's team reported on 300 people living in the
Semien Mountains about 300 miles north of Addis Ababa. Testing showed they
had neither elevated red-cell concentrations nor low levels of oxygen
saturation in their blood -- two key indicators of the Andean model.
"We were stunned," Beall said. "The Ethiopians are finding the same amount
of oxygen we find, even though the amount of oxygen in the air they breathe
is two-thirds of what we have at sea level."
Humans transport oxygen via hemoglobin, a protein in red blood cells that
binds to oxygen molecules and moves them from the lungs to muscles and other
tissues. At sea level, between 95 and 97 percent of the body's hemoglobin is
saturated with oxygen during every breath.
At altitude, reduced oxygen logically means lower oxygen saturation. In the
Andes, highlanders compensate by producing more red cells to create a
heightened "hemoglobin concentration" -- a higher proportion of red cells in
the blood. That way the blood has more hemoglobin to sponge up scarce
oxygen.
Lowlanders need at least 10 days for this process to begin. In the meantime,
however, they will acquire the other characteristic of high altitude
survival -- deeper and more frequent breathing. The Andean barrel chest
comes from being born and raised at altitude.
Scholars were satisfied with this explanation until studies in Tibet in the
1970s showed that highlanders there had both low hemoglobin concentrations
and low oxygen saturation levels. In theory, the Tibetans should have been
oxygen-starved.
"But they breathe faster, and there's also some evidence that they are
better able to modulate blood flow," Beall said. "When they exercise, their
blood flow increases more rapidly, so they may have a larger cardiac output.
We don't really know."
The Himalayan research triggered a debate over a possible evolutionary
explanation for high altitude adaptation. The Andeans, whose lowland
ancestors migrated from Asia perhaps 16,000 years ago, adjust to altitude
essentially the same way as any lowlander would today -- and it is not a
perfect solution.
"Creating more red cells is a pathological response," said Temple University
anthropologist Charles Weitz. "If you have too many red cells, the blood's
too thick, and it's like pumping oil. Eventually you have to move downhill."
Tibetans or their ancestors, however, have been in Asia for 1 million years
or more -- time enough, some scholars theorize, to evolve a different
approach.
Exercise physiologists were moving along a different track. Realizing that
ultra-high hemoglobin concentrations were no good for athletes -- syrupy
blood doesn't flow well -- they still sought enhanced athletic endurance by
increasing red cell counts, but only in the context of a larger overall
blood volume.
"Over time -- four weeks minimum, or many months -- you can elevate both red
cells and volume, therefore keeping [sea level] hemoglobin concentrations,"
Levine said. Athletes with this training have hearts that "pump more blood."
So why is it that the Andean nations -- except for Colombia's cyclists -- do
not produce more such athletes? There is no scientific answer, but Georgia
State's Martin suggests that many Andeans may "live too high -- 12,000,
13,000, 14,000 feet" -- so high that "the blood turns to sludge."
Altitude training seeks to expand the competitor's blood volume using a
combination of lowland workouts and highland living, varying the amounts of
time in each milieu. Finding the optimum times and altitudes is a Holy Grail
of athletic trainers.
In Ethiopia, the two tracks may converge. Human ancestors first arose there
and in Kenya as much as 4 million years ago. If Darwinian adaptation has
played a role, there may be no likelier places.
Ethiopia and Kenya are also countries where the runners come from high
altitudes, but not too high: Ethiopia's Haile Gebrselassie, who holds the
world's 10,000-meter record at 26 minutes, 22.75 seconds, lives at 7,900
feet in Addis Ababa, and trains in the surrounding hills.
In the Semien mountains, Beall's team tested people of all ages, mostly
herders with no particular athletic bent. Unlike the Andeans, their
hemoglobin concentrations were the same as those of lowlanders. But unlike
the Tibetans, they also had high, sea-level oxygen saturation levels.
Beall does not know how this can be, but her team did not look at blood
volume, which might at least explain the hemoglobin concentrations: "If
Ethiopians have a bigger blood volume, they could do a better job of
transporting oxygen," Martin said. "If an athlete in Ethiopia has this huge
blood volume, he's going to have an enormous advantage at sea level."
