STS-95 PAYLOADS - Human Research
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.

Mission Specialist Scott Parazynski demonstrates agility in microgravity, but balance control could be an issue upon his return to Earth.

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 Baltimore Longitudinal Study on Aging 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 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, or 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 to 50 percent 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.

A specially modified, computerized dynamic posturography system measures how balance control is changed after astronauts return to Earth from space flight.

With preparations underway for establishing a continuously crewed space station, a healthy immune response becomes more important to mission success. Increased crew size and mission duration may influence the long-term immune response of crewmembers, as they are confined to the closed quarters of the space station for long periods of time. Decreased immune response is also found in a number of environments on Earth, where close confines create an environment similar to that found in a spacecraft. These environments include polar stations, submarines, hospitals and nursing homes. In particular, the elderly are susceptible to immune-related diseases and infection because of a decreased immune cell response that occurs with age. Research into immune system suppression and infection-fighting response during spaceflight will provide important insight into patients affected by immune suppression on Earth.

Nearly all of us come into contact with some form of infection every day but we rarely contract an illness because of our healthy immune response. The Epstein-Barr virus, for example, infects approximately 80 to 90 percent of the general population, but few people actually contract the disease because viral activity levels are low. Research into the regulation of the immune sytem during spaceflight will add to our understanding of the immune system in general and may reveal new avenues of research into immune disorders.