Prolonged bedrest is used by NASA to reproduce the harmful affects of microgravity environment in space exploration. Why do you think that they use bedrest as a model for degeneration in microgravity?
Human Space Adaptation Helps us Understand Aging
Astronauts: Simulating the Aging Process
Life on Earth evolved in the presence of gravity. For this reason, gravity plays a role in all life processes, and exposure to the microgravity environment of space affects living things significantly. Certain physiological changes that occur in space also occur with aging: for example, cardiovascular deconditioning, balance disorders, weakening bones and muscles, disturbed sleep, and depressed immune response. An important difference, however, is that these changes are reversible in astronauts.Research has shown that insufficient exercise- due to aging, paralysis, weakness, injury, or prolonged bedrest, for example- can cause a downward spiral in an individual's health over time, increasing susceptibility to bone fractures and slowing recovery from injuries and other ailments. What researchers learn about the physiological effects of the inactivity that accompanies space flight may yield ways of limiting the deconditioning symptoms of the inactivity that comes with aging.Are these changes inevitable?
Gravitational biology has the objective of understanding how cells perceive and respond to gravity and how whole organisms use this information. This knowledge is essential for promoting human adaptation to the microgravity of space and to furthering our understanding of how organisms function on Earth.
* Major problems facing astronauts in flight and on return to Earth are neurological disorders of the vestibular system. Similar disorders occur in the general population as a result of infection, intracranial tumors, and head injuries. These lead to significant disabilities because of the profound influence of the vestibular system on posture, balance, and eye and head movements. Ground-based research jointly sponsored by NASA and the National Institute on Deafness and Other Communications Disorders (NIDCD) is making significant headway in understanding the biomechanical and behavioral properties of vestibulospinal postural stabilizing systems. The goal is to discover the neural mechanisms controlling posture and how these processes change in altered gravity environments. This project has generated the first comprehensive model of the head and neck system in which each bone and muscle is modeled as a well-defined element. This multilevel research project illustrates the progress that NASA has made in its cooperation with other agencies in pursuing cutting-edge research that benefits multiple agencies.
The most overt change affecting an astronaut in space flight is the immediate response of the neurovestibular system to changes in gravity. Astronauts experience orientation illusions, posture and locomotion disturbances, vestibulo-occular function and gaze changes, space motion sickness, and possible structural changes affecting sensory-motor behavior and reorganization. Research and technology efforts include ground-based tests of neurological adaptation, operational implications, countermeasures, and impacts on other physiological systems; and instrumentation, models and methods to improve preflight adaptation and better understand individual responses. Countermeasures include artificial gravity, preflight training and adaptation, automated landing systems, inflight exercises, and advanced VR systems.
Cardiovascular adaptation to spaceflight is rapid, with no evidence of functional impairment during spaceflight. Risks include: occurrence of serious cardiac dysrhythmia; impaired cardiovascular response to orthostatic stress; impaired cardiovascular response to exercise stress; manifestation of previously asymptomatic cardiovascular disease; and diminished cardiovascular function. Research and technology focuses on: understanding the mechanisms and processes underlying cardiovascular alterations; risk assessment strategies; models to derive thresholds of operational significance; and potential crew screening and selection criteria. Countermeasures may include pharmacological agents, exercise regimes, artificial gravity, nutritional supplements, mechanical aids, and electro-myostimulation to minimize these risks.
Bones of the legs, pelvis and spine are subject to decreased stress in weightlessness, leading to the release of calcium, leaving the bone more brittle and weak. Risks include: acceleration of age-related osteoporosis; fracture and impaired fracture healing; injury to soft connective tissue and joint cartilage, and intervertebral disc rupture; and renal stone formation. It is unknown whether these changes continue unabated, nor whether they can be totally reversed. Countermeasure research and technology efforts focus on diagnostic tools to monitor and measure critical parameters, including the cellular and molecular mechanisms of bone loss. Prevention and rehabilitation involves pharmacological, exercise and nutritional regimens, artificial gravity options, and crew screening and selection criteria to identify "at risk" individuals.
It's actually astonishing that something as tiny as sperm could be affected by gravity. Physicists, says Tash, "might argue that the size of molecules critical to sperm movement are not big enough to be sensitive to gravity." But, he points out, the head of a sperm is about the same size as statoliths in plants -- small floating granules that help plants tell up from down. Gravity may in fact affect things that are even smaller. Researchers, says Tash, are now beginning to find evidence that even the individual proteins that form the structures of the sperm tail may be sensitive to gravity changes.No one knows exactly how gravity affects cells. It may have to do with the cytoskeleton: the structure that gives a cell its shape. Proteins that send signals are often physically connected with the cytoskeleton, says Tash. Perhaps, he says, there is a mechanism in which the gravitational forces on the sperm head are somehow transmitted into the cytoskeleton, which then affects the signaling pathways that alter movement.
SPACE RESEARCH PROVIDES NEW EVIDENCE ON THE ROLE OF GRAVITY IN FERTILIZATION
Oct. 12, 2001Dwayne Brown
(Phone: 202/358-1726)RELEASE: 01-196NASA researchers have uncovered evidence that gravity, or the lack thereof, may play an important role in the development and evolution of life. The study suggests fertilization is gravity-sensitive and works differently in the near-weightless environment of space than it does here on Earth.Using sperm from tiny sea urchins, the research team conducted both ground- and space-based experiments to examine the impact gravity has on the reproduction process. According to a paper authored by Dr. Joseph Tash, a NASA researcher and a professor at the University of Kansas Medical Center in Kansas City, scientists found gravitational changes may influence a species' ability to reproduce. His team's findings were published in a recent issue of Biology of Reproduction."The research shows that fertilization is altered in a microgravity environment," said Tash. "Such alterations have implications for reproduction of plant and animal food and for long-term space habitation by humans. This research will be essential for prolonged space exploration."The experiments were conducted under a grant from NASA's Office of Biological and Physical Research in Washington. The research program provides investigators with the opportunity to use microgravity or low-gravity environments to investigate the role this fundamental physical force and other space-flight factors have on biological and ecological systems."All life is influenced by the pull of Earth's gravity. NASA scientists are conducting research to explore the role of gravity at all levels of biological processing," said Dr. Kathie Olsen, Acting Associate Administrator for Biological and Physical Research at NASA Headquarters. "Without the presence of Earth's gravity, we are able to pursue answers to questions of how living organisms develop."
Science Objectives for Everyone
Early studies on astronauts found that anemia (decrease of red blood cells in the blood stream) of individuals returning from a space flight was due to selective hemolysis (destruction of red blood cells), neocytolysis. The Neocytolysis investigation, can lead to treatments of different types of anemia, especially those related to renal failure or acute infections.
Science Results for Everyone
Exploding red blood cells!? Less of that, please. Astronauts experience significant, symptomatic anemia caused by neocytolysis, a process that selectively ruptures new red blood cells. This happens under certain conditions on Earth as well, such as moving from high altitude to sea level. Blood cell volume, hemoglobin concentration, and red blood cell counts did not significantly differ from pre- to post-space flight. The percentage of new red blood cells did decrease after flight, and young cells lost viability, indicating that destruction of red blood cells occurred in space. Researchers observed no significant changes in red blood cell population in the control group. A programmed cell death characteristic in the organism could trigger the cell destruction.