May 13, 1998 WASHINGTON, D.C. -- A technique developed to help astronauts stave off problems with their blood vessels in zero gravity may become an important tool in helping prevent strokes among the estimated 50 million Americans who have high blood pressure.
The technique, which involves placing the patient's lower body in a vacuum, would let doctors know which of their patients with high blood pressure could suffer a stroke if their blood pressure is lowered too much with medication, said Dr. John Absher, assistant professor of neurology at the Wake Forest University Baptist Medical Center.
"People with high blood pressure have hardening of the arteries, and when your arteries get hard, too much of a drop in blood pressure can produce problems," Absher said.
Absher presented the results of his small-scale study involving 10 patients today at a meeting of the Space and Underwater Research Group of the World Federation of Neurology. The meeting is being coordinated by the Stroke Research Center at the Wake Forest University Baptist Medical Center.
In space, astronauts spend time wearing special pants hooked up to a vacuum that lowers the pressure around their legs. This pulls blood to their legs, mimicking the effect of gravity and preventing "vascular deconditioning," Absher said.
By adapting this technique, doctors could determine at what blood pressure a patient might be a risk of stroke or "silent stroke" -- a gradual loss of adequate blood flow to the brain that can go unnoticed.
Doctors have long known about the problem, Absher said, "but no one has had a way to test it."
In his study, Absher sealed off the lower bodies of patients with high blood pressure in a plastic drum and then used a vacuum to lower the pressure inside the drum. This lowers blood pressure in the brain by pooling blood in the legs. During this process Absher took images of blood flow in the brain with a PET scan to determine at what point the blood pressure dropped to the point that the brain was not getting enough oxygen.
"It's a safe and reproducible way to see what happens when blood pressure drops," Absher said.
He compared the technique to the standard treadmill test for heart disease patients. Doctors stop a treadmill test when the patient begins to exhibit signs of interrupted blood flow, and it takes a few minutes to settle down. With his test, once symptoms begin, the test is stopped and "flow returns to normal in 10 seconds."
"We know we have 25 percent of the people who have high blood pressure and even though we are treating these people with medication to lower their blood pressure, some of them continue to have strokes," he said.
"Part of the reason might be we don't know how low they can go safely and we haven't had a way to measure that risk," Absher said. "This technique may be able to help us do that."
The American Heart Association estimates that 50 million Americans have high blood pressure. High blood pressure is the leading risk factor for stroke, which is what happens when a blood vessel serving the brain is blocked by a blood clot or hemorrhages, impairing the flow of oxygen to that part of the brain. About 500,000 Americans suffer stroke every year. Stroke is the third leading cause of death and the leading cause of disability in the United States.
The four-day meeting -- the Congress on Cerebral Ischemia, Vascular Dementia, Epilepsy and CNS Injury: New Aspects of Prevention and Treatment from Space and Underwater Exploration -- concludes at noon Wednesday at the Washington Marriott Wardman Park Hotel, formerly the Sheraton Washington.
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The above story is reprinted from materials provided by Bowman Gray/baptist Hospital Medical Center.
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