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By Peter Rejcek
Sun staff
Scientists and support personnel have been traveling to
the South Pole for nearly 50 years now, taking that giant
leap from sea level to nearly 3,000 meters on the polar
plateau to further our understanding of the continent,
the world and the universe.
Dr. Bruce D. Johnson wants to better understand, in part,
why that jump in altitude affects some people more severely
than others.
Johnson is the principal investigator for a research team
from the Mayo Clinic in Rochester, Minn. The group arrived
in early October at McMurdo Station to begin a three-year
study on altitude illness called Altitude Symptoms at
South Pole (ASAP).
“This go-around we’re just quantifying the frequency,
intensity and duration of symptoms, and trying to come
up with the key predictors that will increase your susceptibility
to altitude illness,” Johnson explained during an
interview at the Crary Science and Engineering Center,
where the team is screening patients in a small lab room
adjacent to the aquarium.
The group is hoping to recruit 150 people for this year’s
field season, with the goal of capturing statistics and
data on 300 individuals during the team’s two deploying
seasons.
Johnson said the South Pole serves as an ideal laboratory
for this kind of study for several reasons. At approximately
2,800 meters, the Pole represents a moderately high altitude
where many people may reasonably travel or live as opposed
to extreme Mount Everest-type heights. People traveling
to Pole represent a broad but very healthy cross-section
of people in terms of demographics and physiology rather
than a sub-group of elite climbers.
In addition, people en route to the bottom of the world
start at the same baseline, as they travel through Christchurch,
New Zealand, and on to McMurdo Station, which are both
at sea level.
“What’s unique about the South Pole, about the
Antarctic, is that it’s a very structured population,”
Johnson said. “It’s kind of a unique laboratory
setting here.”
And what is unique about going to altitude at Pole is
the climb itself. Most people arrive at 90 degrees south
on a U.S. Air National Guard LC-130 ski-equipped plane,
rocketing to elevation in the course of about three hours.
While the physical altitude of the South Pole is 2,800
meters, a couple of factors can change the equation dramatically.
At the South Pole, the barometric air pressure averages
about 20 percent lower than expected for that elevation.
Atmospheric pressure is the weight of the overlying air
column. As altitude increases, pressure decreases. Under
less pressure, oxygen molecules are more widely dispersed
throughout the atmosphere, making the air feel thinner.
Cold only exacerbates the process, meaning greater variability
in what’s called physiological altitude as pressure
drops, particularly during the cold winter months.
The physiological altitude at Pole can typically hit 3,500
meters and has gone as high as about 3,783 meters. (For
a more detailed explanation of physiological altitude,
see the Feb. 2, 2003, issue of The Antarctic Sun at antarcticsun.usap.gov.)
Aside from having to adapt to the physiological shifts
in altitude, many Polies hit the ground running to squeeze
every working minute possible out of the relatively short
austral summer season, which generally lasts from late
October to early February.
“We do know how quickly you go to altitude does play
a role in the symptoms [of altitude illness],” Johnson
said. “We’re trying to quantify does cold play
a role, does activity play a major role.”
The team has already recruited about 120 volunteers. Amnesty
Kochanowski, a South Pole air cargo handler on her second
season, said that as an outdoor person who regularly hikes
at altitude she was eager to participate in the study.
“Living high in Colorado and climbing high in the
mountains, I’ve seen how [altitude] affects people,”
said Kochanowski, from Grand Lake near Rocky Mountain
National Park. “I wanted to be sure I was involved.”
Some South Pole stats
Mild symptoms of altitude illness include headache, fatigue,
shortness of breath, nausea, lack of appetite and lightheadedness.
More severe cases can result in High Altitude Cerebral
Edema (HACE), which causes swelling of the brain due to
fluid leakage, and High Altitude Pulmonary Edema (HAPE),
which involves fluid leaking into the lungs and impairing
the transfer of oxygen to the blood stream.
Dr. Will Silva served as the South Pole physician for
the last year and has done a total of three full years
at the station. Last summer, he said, was a mild year
for altitude illness, with the clinic recording only a
dozen visits and one case of HAPE. Normally, the clinic
averages 20-plus cases of altitude sickness during the
summer.
“I suspect a growing awareness on the part of veteran
managers of the need to go easy on people for the first
couple days, plus our opening on Saturdays several seasons
running (so people get a rest day), plays a role here,”
Silva wrote in an e-mail, explaining last year’s
decline in clinic visits.
Serious cases of HAPE or HACE do periodically occur at
the South Pole, according to Silva, and require immediate
evacuation back down to sea level. In 2002, he sent three
patients back to McMurdo, one of whom was deteriorating
with cerebral edema. Silva stressed that low-level activity
is key to successful acclimatization.
“Once again, the most important thing is to do as
much nothing as possible the first two days,” he
noted. “Vigorous exercise before acclimatization
is a major risk factor for HAPE, which can be rapidly
fatal if untreated.”
To quantify that factor and others, the ASAP team performs
a series of tests before subjects leave McMurdo. Each
person fills out a questionnaire that captures basic medical
history and general activity level, along with information
regarding such things as previous trips to Pole and whether
someone has a history of motion or carsickness.
ASAP staff members then draw blood and perform several
physiological tests to determine such things as lung function
and capacity and oxygen saturation — the percentage
of arterial hemoglobin saturated with oxygen. Subjects
continue to fill out daily symptoms worksheets for seven
days after reaching the South Pole.
“What we’re trying to get at is if [subjects]
have symptoms, how severe they are and try to relate that
back to their blood work, function test, genetics, to
how well they’re sleeping, how much their activity
is,” explained Maile Ceridon, a Mayo graduate student
working with the ASAP team. “We’ve got a number
of things we’re trying to do comparisons on.”
The medical team will collect additional information about
sleep habits and activity levels from a smaller group,
about 50 subjects, using Vivometric LifeShirts and BodyMedia
activity monitors.
The shirts monitor an array of physiological responses
during sleep, such as rapid eye movement, or REM, and
brain activity. The sleeveless black vest also has a voice
recorder to tape snoring noises. There is some evidence,
Johnson said, that people who snore or have sleep apnea
may be more prone to altitude illness. Subjects wear the
shirts one night while in McMurdo and then during their
first night at South Pole to determine how the sudden
increase in altitude may affect sleep.
Sleep may play an important role in acclimatization because
a person’s ability to adapt early to altitude relies
mainly on breathing, which increases to compensate for
the lower partial pressure of oxygen at higher elevations.
During sleep, a person naturally breathes slower; someone
with difficulties, such as apnea, will have periods where
the arterial oxygen levels in the blood will drop, which
becomes even more prominent at altitude.
Silva said that new arrivals at South Pole usually have
an oxygen saturation of about 87 to 89 percent (at sea
level, saturation is normally at 97 to 99 percent). Individuals
struggling to acclimate can drop into the low to mid 80s.
“In contrast, those with HAPE have audible pulmonary
congestion with rales (crackles) and sometimes a little
wheezing, and O2 [saturation] in the high 60s to mid 70s
by the time they arrive in Medical, and are often coughing
up a little pink froth,” he wrote from Pole.
Although HAPE cases occur, what Johnson says are “life-threatening
maladaptations” to altitude affect relatively few
people at South Pole. “Our laboratory has evidence
that there are likely much more subtle changes in lung
fluid balance in a larger percentage of people going to
altitude than previously appreciated,” he said.
The other device the group is using is a BodyMedia activity
monitor, which is worn around the upper arm. The unit
possesses a number of bells and whistles, such as an accelerometer
that detects movement in any direction and a galvanometer
that measures skin temperature. The device is able to
work out the metabolic rate and tell the researchers the
kinds of activities a person is doing, from walking to
running to standing still.
“It does a very good job at quantifying what we are
doing,” Johnson said.
The bigger picture
By identifying people who get various strains of altitude
illness and matching that data with their physiological,
chemical and genetic profiles, researchers may be able
isolate certain markers that pre-dispose people to altitude
sickness.
“Physicians could use that algorithm and tell people
if you have this background you need to spend more time
at moderate altitudes adapting or you need to be less
active when you go to altitude … or take medication,”
Johnson said.
Interests in this type of research go well beyond altitude
studies, according to Johnson. Agencies like NASA could
use the data to calculate ideal pressurization for long-term
spaceflights. The study also has implications for research
on heart and lung diseases, which share some of the same
pathology as altitude illness, particularly concerning
low oxygen levels and constriction of blood vessels in
the lungs.
“There is a lot of synergy between disease and humans
trying to adapt to high altitude,” Johnson said.
- The
Antarctic Sun -
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