PAYLOADS - Human Research
Getting Pumped Up in Space: Cardiovascular Investigations
In the microgravity
of spaceflight, bodily fluids are shifted to the upper body. As
the body seeks to regulate this fluid movement, the cardiovascular
system is affected during and after spaceflight. During spaceflight,
pressure sensors in the head, neck and chest are stimulated by
the fluid shift, which the central nervous system interprets as
excess fluid volume in the heart and lungs. To reduce this perceived
excess, body fluids are either directly eliminated through urination
and decreased thirst or redistributed throughout the blood vessels.
After a few days, the body adapts to the microgravity environment
and the process of fluid redistribution is complete. A new difficulty
arises when the astronaut returns to Earth and again feels the
effects of gravity. The reduced blood volume, combined with less
responsive reflexes, may not provide adequate blood pressure to
the head during entry or landing. Astronauts often experience
lightheadedness, and sometimes even fainting, when they stand
for the first time upon returning to Earth. The natural loss of
body fluids in space may also upset the chemical balance of the
blood and thereby interfere with the normal functioning of the
heart, possibly resulting in irregular heartbeats.
planned for STS-95 will address the cardiovascular effects of
spaceflight, with a focus on the older individual. Each cardiovascular
investigation for STS-95 requires multiple repetitions of the
experiment procedure before and after the flight.
Responses to Standing Before and After Spaceflight will build
upon an existing database of 43 shuttle astronauts, including
three who flew long-duration missions on the Russian space station
Mir. This investigation will assess the many physiological responses
involved in standing up in the normal gravity environment after
the body has adapted to 9 days in microgravity. Immediately after
landing, astronauts are transported to the clinical test facility,
where the cardiovascular response to Earth's gravity can be examined
with the enhanced tilt test procedures. These procedures allow
researchers to collect detailed cardiovascular measurements as
the astronaut is telted upright after lying down. Cardiovascular
response mechanisms will be measured with a blood pressure monitor,
an electrocardiograph for collecting heart rate and rhythm information,
and an ultrasound echocardiograph for measuring the volume of
blood pumped by each heart beat. With this information, the degree
of arterial constriction can be calculated both at rest and under
the gravitational stress of standing. A second, minimally invasive
technique involves the re-breathing of a small amount of carbon
monoxide to allow the calculation of blood volume.
astronaut dons his launch and entry suit, which contains
a compact blood pressure monitor and tape recorder for measuring
Function During Entry, Landing and Egress (with an existing
database of 66 shuttle astronauts, including five from Mir) will
focus on two parameters, blood pressure and heart rate, during
the entry and landing phases of the flight. A compact blood pressure
monitor and a small tape recorder will record cardiovascular data
for the intervals before, during and after entry and landing.
These deveces are integrated into the landing and egress suit.
Data collected during these phases will document the real-time
response of the cardiovascular system to Earth's gravity after
more than 9 days of exposure to microgravity. Comparison with
data from the Cardiovascular Response experiment will indicate
how much readaptation takes place in the first hours after landing.
The third investigation, In-flight Holter Monitoring (with
an existing database of 24 shuttle astronauts, including four
who flew on Mir), will use a standard Holter recorder to collect
24 hours of electrocardiogram data. The Holter recorder is a vest-like
garment with embedded sensors. Data collected before, during and
after the flight will reveal what difference, if any, exists between
the occurrence of irregular heartbeats in spaceflight and on Earth.
Holter monitor consists of an electrode set and data recorder
that continuously measure electrocardiograph data.
of an inadequate cardiovascular response to entry and landing
and to the gravitational loading on Earth could compromise the
health and safety of crewmembers after spaceflight. Development
of improved countermeasures and treatments for astronauts requires
a complete understanding of how the body adapts to the microgravity
of spaceflight. Similar mechanisms may be involved in the development
of many cardiovascular diseases on Earth, such as abnormal blood
pressure, blood loss and heart failure. These diseases are particularly
prevalent in older people. The same knowledge that benefits returning
astronauts may be applied to protecting patients here on Earth,
young and old alike.