It takes a lot of heart to become an astronaut, leave Earth, and hang out in a dangerous and weightless environment for two weeks. More than anyone knew, in fact.
Upon returning to Earth, some two-thirds of astronauts report lightheadedness, dizziness and difficulty concentrating when standing up. New research done during a 1998 Space Shuttle flight has found the cause: Astronauts hearts grow stiff, shrink, and pump less blood.
The condition causes similar symptoms in some 500,000 Americans, mostly elderly, who've never been to space.
Cures may now be on the horizon, scientists said today.
"This research has led to a better understanding of the type of blood-flow problems that affect astronauts on return to Earth and that can also cause an elderly person who stands up too quickly to become dizzy," said Gunnar Blomqvist, former director of the NASA Specialized Center of Research and Training in Physiology at the University of Texas, where the study was conducted.
The new study involved six male astronauts aboard a Neurolab shuttle mission, designed specifically to study the human nervous system and to test what's called sympathetic nerve activity, which researchers had thought was behind the wooziness.
"Drug therapies aimed at boosting sympathetic activity in astronauts after space flight in response to standing upright may not be necessary," said Benjamin Levine, who led the study. "Rather, efforts to combat the primary problem, namely an excessive reduction in stroke volume while standing, which causes the heart to stiffen and shrink, may be effective."
Levine said many forms of orthostatic intolerance, as the condition is known, can be prevented or reversed without the use of drugs.
"Markedly increasing the consumption of both salt and water, exercise training -- both endurance and strength training to increase the heart size and flexibility and expand the blood volume -- and behavioral modification to facilitate return of blood back to the heart has helped more than approximately 75 percent of patients," Levine said.
The researchers examined the astronauts before, during and after the 16-day spaceflight, monitoring the astronauts' blood pressure and how the cardiovascular system is stressed by gravity.
Neurolab was a part of the shuttle program's Spacelab, which was used extensively for medical research prior to the construction of the International Space Station.
The research will be published in the January issue of the Journal of Physiology.
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