Shuttle test to measure impact of weightlessness

Hopkins lab rats to help in study of effects on blood vessels, organs

January 16, 2003|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Today's scheduled flight of the space shuttle Columbia will be the first for an Israeli astronaut, and the last for 10 Johns Hopkins lab rats.

The rats are being launched into orbit as part of a NASA-funded study to discover the cause of the debilitating effects of weightlessness on astronauts' cardiovascular systems, which leave them feeling weak, with a loss of coordination and a tendency to faint when they return to Earth.

As soon as Columbia lands after 16 days in space, the rats will be killed so that Hopkins scientists can study the effects of weightlessness on their blood vessels and other organs.

Astronauts are treated better when they return to Earth. But many feel lousy. And their physical difficulties could impair their ability to control the shuttle, or to escape the spacecraft in an emergency.

"It's a dangerous situation," said Janice V. Meck, director of the cardiovascular lab at NASA's Johnson Space Center in Houston.

As part of a continuing effort by NASA to find a solution, the space agency is funding a $1 million research project by Hopkins anesthesiologist Dr. Dan E. Berkowitz and his team at the Johns Hopkins School of Medicine.

They're betting that cardiovascular changes they expect to find in the rats after their time in zero gravity will shed light on the astronauts' problems, and might even lead to new treatments for Earth-bound patients who have difficulty regulating their blood pressure.

"Gravity is one of the most profound stressors placed on the cardiovascular system on a regular basis," said Berkowitz, 41, of Pikesville, co-investigator in the NASA rat study with Hopkins physiologist Artin Shoukas.

For most of us, healthy nervous and cardiovascular systems keep blood flowing to our brains against the tug of gravity.

But prolonged bed rest, aging and diseases such as diabetes can impair those systems in ways similar to the effects of weightlessness in space.

"Our long-term goals are to understand the mechanisms by which these regulatory mechanisms are changed," Berkowitz said, "and to design countermeasures."

The shuttle, with 80 scientific experiments and seven crew members, was scheduled to lift off from the Kennedy Space Center between 10 a.m. and 2 p.m. today.

The Hopkins rats will be on their own, floating in a cage designed to provide all their food, water and ventilation. Their posthumous contribution to science will begin immediately after their landing, set for Feb. 1.

In a laboratory at the space center, Berkowitz and his team will euthanize the animals and divide up their organs for a battery of well-rehearsed tests.

"We'll probably work through the night," he said. All the dissections and studies must be completed within 24 hours of the rats' return from zero gravity - before their organs have had time to re-adjust to Earth's gravity.

Weightlessness triggers changes in virtually every system in the body, said Meck, whose team at the Johnson Space Center in Houston studies the effects of weightlessness on returning astronauts.

Until the body figures out how to respond to weightlessness, she said, "crew members feel lousy." Most feel bloated and nauseated as fluids shift toward the head and portions of the middle ear that regulate balance struggle to make sense of zero gravity.

All the mechanisms that usually keep blood flowing to the brain against the pull of gravity suddenly have nothing to do, and begin to shut down.

The heart begins conducting electricity differently and beats more slowly in response to the lighter workload. Muscles weaken.

"We're starting to understand, if we don't use a system, how rapidly it will remodel," Meck said.

But on landing, all that remodeling works against the crew. Some astronauts climb from the shuttle on their own. But others - especially those returning from several months aboard the International Space Station - frequently need intravenous fluids and must be carried off. Full recovery can take days or weeks.

Efforts to keep the crews' cardiovascular systems in shape with exercise gear while in orbit have shown no real benefit, Meck said, except to prevent the loss of calcium from their bones. NASA crews wear pressurized flight suits when they land, which squeeze on their extremities to keep blood flowing to their brains. Astronauts on six flights also have tried a drug frequently prescribed for diabetics, midodrine, which boosts blood pressure.

The effects of prolonged weightlessness on future crews launched to Mars could be serious. "There isn't going to be anybody there to greet them and take care of them," Meck said. "It takes six months just to get to Mars."

The challenge for researchers has been to figure out where the returning astronauts' cardiovascular problems lie - in the heart, the blood vessels, the brain or in the electrical and chemical mechanisms that regulate blood pressure under normal gravity.

In the laboratory, Berkowitz and his team have simulated zero gravity by suspending rats' hindquarters on a tether. They found that the animals' aortas and smaller blood vessels had weakened responses to signals that would usually cause them to contract - which helps to control blood pressure.

Now it's up to the astro-rats to verify that the same thing happens under real weightless conditions, in space.

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