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Computer generated
diagram of the Integrated Cardiovascular investigation onboard the ISS.
Image Credit: NASA/JSC
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Astronauts
Getting to the Heart of the Matter
When
humans venture into space for long periods, their muscles tend to
weaken. The heart of the matter is that muscles don't have to work as
hard without gravity.
Of course, the most important muscle in the body is the heart.
While
doctors are well aware of this weakening of the heart in space --
known as cardiac atrophy -- a new study aboard the International Space
Station seeks to find out exactly how much the heart muscle decreases
in size over a standard six-month station tour and how quickly it
occurs.
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In
addition to evaluating cardiac health in space, the Integrated
Cardiovascular investigation also will determine how effective the
astronauts' current exercise program is at protecting the heart from getting
smaller or weaker.
"This study also will help us determine if there is a risk of abnormal
heart rhythms and how significant the risk is in order to develop
appropriate countermeasures," said Dr. Deborah Harm, international
project scientist for the International Space Station Medical Program at
NASA's Johnson Space Center in Houston.
According to Harm, many crew members experience a brief period of
lightheadedness and a drop in blood pressure when standing still after
coming home to Earth from long-duration missions. Fainting can occur when
the heart cannot generate enough force to pump the necessary blood to the
brain and the rest of body -- either because the muscle is too small or
weak, or because there is an abnormal heart rhythm.
"At this time it is unknown if heart muscle weakening continues
throughout a mission or if it levels off at some point. That's what we want
to find out," Harm said.
Crew members on Expedition 20, which began in May and will continue through
October, are the first to participate. Before, during and after flight, they
are measuring their heart rates, heart rhythms and blood pressure for 24- to
48-hours before and after exercise sessions. They're also performing
on-orbit cardiac ultrasound scans on each other before and after exercise to
look at how effectively the heart fills with blood and pumps it to the rest
of the body.
"MRI scans will be done on crewmembers' hearts before and after flight
to measure exactly how much heart muscle is present and will be compared to
the cardiac ultrasound information to better understand how changes in heart
muscle are related to cardiac function," said Dr. Michael Bungo of the
investigator team.
"Such an extensive and sophisticated study of the cardiovascular system
was virtually impossible before we had six crewmembers onboard the
station," Harm added. "There simply was not enough crew time
available to complete all the procedures required for this experiment."
While in space, crewmembers will wear four
devices: a portable Holter monitor that measures heart rate continuously for
extended periods; a Cardiopres that measures blood pressure with every heart
beat; and two Actiwatches -- one on an ankle and one on a wrist -- to
monitor and record body movements.
The data collected is being beamed down to the Payload Operations Center at
NASA's Marshall Space Flight Center in Huntsville, Ala., and delivered to
the investigator’s team for analysis.
This study shows the breadth of international cooperation and collaboration
that occurs on the space station. Three international partner agencies are
working together to get the best science for everyone. The European Space
Agency (ESA) is providing the Cardiopres device for monitoring blood
pressure, and the investigators will be sharing the Holter data with teams
for two Canadian-sponsored experiments. One of these experiments also
includes ESA investigators.
All of these investigator teams are studying different aspects of the
cardiovascular system. Sharing this data among scientists greatly enhances
the overall science return. That, in turn, allows us to more efficiently and
quickly understand the full range of cardiovascular changes than any one
investigation could, Harm said.
"As we move toward exploration missions where astronauts could be in
space for longer periods of time, it is very important that we know to what
degree they could experience cardiovascular risks, and prepare
countermeasures to protect them," said Dr. Julie Robinson,
International Space Station program scientist at the Johnson Space Center.
"We are eager to see the results from this study."
Knowledge gained in the Integrated Cardiovascular study may help doctors
treat patients on Earth who have been confined or on bed rest for long
periods. Patients with heart diseases that change their normal cardiac
function may also benefit.
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