An experiment aboard the 1998 Neurolab space shuttle mission has found the cause of orthostatic intolerance, which affects two-thirds of astronauts. The results have down-to-earth applications as well: About 500,000 Americans suffer from the condition, which is marked by lightheadedness, dizziness, palpitations and difficulty concentrating upon standing.
Researchers discovered that orthostatic intolerance results from excessive reductions in blood volume while standing, which causes the heart to stiffen and shrink. It was earlier thought to be due to a malfunction of the sympathetic nervous system.
Many forms of the condition can be prevented or reversed without the use of drugs, says Benjamin Levine, M.D., medical director of the Institute for Exercise and Environmental Medicine, operated by the University of Texas Southwestern Medical Center and the Presbyterian Hospital of Dallas.
"Increased consumption of salt and water, both endurance and strength training to increase heart size and flexibility and expand blood volume, and behavior modification to facilitate return of blood back to the heart have helped more than 75 percent of [our patients] with orthostatic intolerance," he says.
The report was published in the Journal of Physiology.
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