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    Space Research Eases Dizziness on Earth

    WebMD Health News

    Feb. 19, 2002 -- The dizzying heights reached by astronauts traveling in outer space can make even the hardiest of souls a bit tipsy. About two-thirds of space shuttle astronauts have problems standing up when they return to Earth. But a new discovery about what causes them to go weak in the knees may help both astronauts and Earthbound individuals affected by the same dizzying condition.

    It's called orthostatic disorder, and about 500,000 people who never even step foot into outer space suffer from it. Symptoms include lightheadedness, quickening heartbeat, trembling, and brief loss of consciousness.

    Previous studies had indicated that the condition was caused by a malfunction in the sympathetic nervous system, a group of nerves that help maintain normal blood flow and pressure.

    But a new study, published in The Journal of Physiology and highlighted in this week's Journal of the American Medical Association, debunks that theory. After studying six astronauts from the 1998 Neurolab space shuttle mission, researchers found that the condition was due to the heart shrinking and becoming stiff as changes in gravity reduced blood volume during space travel -- and not to a nervous system malfunction.

    "Microgravity causes conditions that bring the control mechanism out of line, but the mechanism itself is unchanged," writes study author C. Gunnar Blomquist, MD, professor of internal medicine at University of Texas Southwestern Medical Center. For astronauts, that means drug therapy designed to boost the activity of the sympathetic nervous system after space flight may not be necessary.

    For those suffering from the condition without ever leaving home, researchers say the study suggests that the condition can be prevented or reversed without the use of drugs. Other studies have hinted that increasing salt and water intake, or engaging in endurance and strength training can help by increasing the heart's size and flexibility. Other possible behavioral remedies may include bouncing on your toes or crossing your legs while standing to encourage the return of blood flow to the heart.

    Researchers say this was a small study, but the lessons learned from it should lead to better understanding and treatment of the condition in both astronauts and Earthbound people.

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