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Researcher explores heart problems tied to space flight

"Chicken legs" caused by a lack of gravity for circulating blood to the lower extremities, decreased blood flow out of the heart and irregular heartbeats are a few of the problems experienced by astronauts on prolonged space flights, Dr. Richard Cohen told researchers at MIT's Center for Space Research on Feb. 12.

Cohen, the Whitaker Professor in Biomedical Engineering at the Harvard-MIT Division of Health Sciences and Technology , was the featured speaker at this month's National Space Biomedical Research Institute seminar.

The most important issues for astronauts is a reduced capacity for exercise while on the spacecraft and possible manifestation of pre-existing cardiovascular disease or silent coronary artery disease. Screening people for these conditions may be one possible answer, Cohen said in his talk titled "Cardiovascular Stability on Earth and in Space."

Some of our body's reflexes get "down-regulated" because they are not in use during space flight, Cohen said. When astronauts stand upright after being in a reclining position on the spacecraft, they can experience pooling of blood in the large veins of the lower extremities. Before gravity helps blood return to their legs, Cohen said it looks like they have skinny "chicken legs." The current remedy of drinking saltwater before re-entry is not sufficient to address this problem, he added.

In addition, decreased blood flow out of the heart and reduced arterial pressure can cause fainting upon return to Earth, he said. Women are more susceptible to this than men.

Cohen pointed out that Russian astronauts had to be carried out of the spacecraft after a long stint in Mir. This raises the question of whether astronauts would be able to exit a spacecraft or space station quickly in case of emergency. "This is an operational problem for NASA," he said. "When a spacecraft gets to Mars, there will be no extraction crew waiting for them."

Long-duration space flight also causes a loss of cardiac mass, Cohen said, although no one is sure why.

Cohen is leading a bed-rest study to see how people's hearts react to 16 days of strict bed rest while tilted at a 4-degree angle. He also is proposing animal studies and flight studies. "It's important to identify the physical mechanism of cardiology problems tied to space flight and suggest countermeasures," he said.

The National Space Biomedical Research Institute is a NASA-sponsored program that addresses the medical obstacles to safe, productive, long-term human presence in space and applies the knowledge gained from space research to medical problems of people on Earth.

A version of this article appeared in MIT Tech Talk on February 27, 2002.

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