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 bodyís movement, allowing us to interact with our surroundings. In microgravity, important information ó the stimulus of gravity ó is no longer available to many of the bodyís 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 brainís 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.


  
Astronauts learn to adjust to the microgravity environment aboard the Space Shuttle.  
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 Agingís (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 Glennís 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 subjectís 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 subjectís balance. The second test will examine the subjectís 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
     
  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 Meniereís 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 Healthís 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 10Ė50% 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


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