Walking the Tight Rope:
Balance Control After Space Flight
The brain gathers information about our environment
through many sensory systems. It then uses this information to direct
the body’s movement, allowing us to interact with our surroundings. In
microgravity, important information — the stimulus of gravity — is no
longer available to many of the body’s sensory organs, located in the
inner ear, muscles, joints, and skin. Fortunately, the brain is adaptive
and can adjust its processing of the remaining information to optimize
control of body orientation and movement in space. After return to Earth,
however, the brain’s processing pathways no longer expect sensory information
caused by gravity. One notable consequence of this is that balance control
is temporarily disrupted in returning astronauts, as the brain readapts
to gravity-related stimuli.
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| Astronauts learn to
adjust to the microgravity environment aboard the Space Shuttle. |
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The general objective of the Postflight Recovery of Postural Equilibrium
study is to quantify the effects that inflight neurological changes have
on postflight balance control. This study will characterize the normal
sensory and muscular response to space flight, and will define how this
response affects balance control after return to Earth. The specific objectives
are: (1) to identify how the role of sensory information in balance control
changes during postflight recovery; (2) to define how much balance control
is degraded immediately after space flight and how long is required for
full recovery of preflight function; and (3) to examine the effects of
demographic factors like age, gender, and mission duration on these responses.
This investigation has previously involved 49 crewmembers, including nine
from long duration stays aboard the Russian space station Mir. On STS-95,
data collected from four crewmembers will be compared to data from previous
space flight subjects. The presence of a septuagenarian crewmember provides
a unique opportunity to examine the effects of age on postflight balance
control. A parallel study of Earth-bound subjects is also being planned
with the National Institute of Aging’s (NIA) Baltimore Longitudinal Study
on Aging (BLSA) to characterize the normal degradation in balance control
that occurs with age. Results from this ground-based study will aid investigators
in interpreting how much Senator Glenn’s results may represent those of
others in his age group.
Balance control performance will be tested before and after the STS-95
flight using a computerized dynamic posturography system widely employed
for evaluation of balance disorders. This system has been modified to
provide complete sensory and muscular data about balance control. It consists
of a platform and a visual surround scene, both of which are motorized
to simulate motion. Subjects complete multiple tests before and after
the flight to establish stable individual performance levels and the time
required to recover them. Two balance control performance tests will be
administered. The first test will examine the subject’s responses to sudden,
balance-threatening movements of the platform. Computer-controlled platform
motors will produce sequences of rotations (toes-up and toes-down) and
translations (backward and forward) to perturb the subject’s balance.
The second test will examine the subject’s ability to stay upright when
visual and/or ankle muscle/joint information is modified mechanically.
These NASA studies of postflight balance disorders are aimed at characterizing
and eventually minimizing the safety and health risks to
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A specially modified,
computerized dynamic posturography system measures how balance control
is changed after astronauts return to Earth from space flight. |
astronauts during and after space flight. Information obtained from this
investigation is being used to design techniques for restoring lost movement
and balance control capabilities in astronauts.
A relatively large number of individuals on Earth suffer from prolonged,
frequently life-long , clinical balance disorders. Disorders like Meniere’s
disease and traumatic injuries to the inner ear can severely influence
quality of life. Currently, human space flight is the only means available
for studying the response to sustained loss and recovery of inner ear
information. The National Institute of Health’s National Institute of
Deafness and Communication Disorders (NIDCD) is using the recovery information
from this study to better understand the recovery process of inner ear
patients and to improve rehabilitation treatments on Earth.
Falls are the leading cause of injury-related deaths in the elderly and
these numbers continue to grow. By the year 2000, falls are estimated
to result in 30,000 hip fractures in the United States. This investigation
is of particular interest to the NIA because inner ear disorders are thought
to account for 10–50% of falls among senior citizens. Study data from
previous astronaut subjects have already been compared with similar data
from elderly subjects to demonstrate similarities between these balance
disorders. The NIA plans to examine these similarities in greater detail
with a ground-based study that parallels the STS-95 study.
Points of Contact:
Principal Investigator
William H. Paloski, Ph.D.
Johnson Space Center
Houston, TX
Co-Investigators
F. Owen Black, M.D., F.A.C.S.
National Institute of Health/NIDCD
Legacy Holladay Park Clinical Research and
Technology Center
Portland, OR
E. Jeffrey Metter, M.D.
National Institute of Health/NIA
Baltimore Longitudinal Study on Aging
Gerontology Research Center
Baltimore, MD
FS-1998-09-008JSC (PDF
Format)
Curator: Kim Dismukes
Responsible NASA Official: John Ira Petty
Updated: 25 October 1998
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