Space Takes its Toll

For space enthusiasts, it’s almost like the good old days again. The nine-day flight of shuttle Discovery beginning later this month is expected to draw nearly as much public attention as the historic Mercury and Apollo missions did a generation ago. The reason, of course, is that America’s original space hero, John Glenn, the first American to orbit the Earth, is making his second space flight. This time the 77-year-old senator has signed on as a medical guinea pig.

When Glenn first went up in 1962, next to nothing was known about the effects of space flight on the human body. Now nearly 700 individuals have flown, on missions ranging from Glenn’s five hours to Russian Valeri Polyakov’s 438 days. Scientists now know that space flight has dramatic and harmful effects on physiology. Astronauts get space sick, they lose bodily fluids including blood, their bones and muscles atrophy, their balance is upset, and they suffer sleep deprivation. They’re also exposed to radiation; the longer the flight, the more radiation increases the risk of cancer. On Discovery, Glenn will participate in 10 medical experiments aimed at helping figure out what will happen to humans who live in space for extended periods, such as a two-year trip to Mars and back.

The most delightful aspect of space travel – weightlessness – is also the most problematic. Even though astronauts and cosmonauts undergo extensive weightlessness training in airplanes, about 75 percent suffer form of space motion sickness, including queasiness, headache, lack of ability to concentrate, and drowsiness. About a third vomit repeatedly over several days, although drugs can reduce symptoms. “The good news is, almost everyone gets over it in two to four days,” says Charles Oman, director of the Massachusetts Institute of Technology’s manned-vehicle laboratory, who is studying the body’s balance mechanisms and space motion sickness.

Freed from the pull of gravity, the body immediately changes the distribution of bodily fluids. Blood that normally pools in the legs because of gravity migrates toward the head. Neck veins bulge, faces become puffy, sinuses fill, noses run, and legs get skinny. The brain thinks the body has at least a quart too much fluid, and the excess is eliminated through decreased thirst and increased urination. In order to avoid problems such as lightheadedness after returning to Earth, crew members take salt tablets with a quart of water just before landing.

Getting taller. The composition of the blood is altered, too. The percentage of blood volume made up of red blood cells declines, production of new red cells decreases, and the blood’s oxygen-carrying capacity, as a result, is reduced. It takes astronauts about a month after they return home for their blood to return to normal.

Without the downward pull of gravity, space fliers soon grow up to 2 inches taller. That’s because pressure on the discs separating the vertebrae in the back is gone, and the discs expand. When they return, they shrink to their usual height.

Astronauts also consistently report that they don’t get enough sleep. They average only six hours a night, says David Dinges of the University of Pennsylvania School of Medicine. He is on a National Space Biomedical Research Institute team studying sleep and the body’s circadian rhythms, which are regulated by the rising and setting of the sun. Terrestrial studies simulating space travel show that by the seventh night “the performance of that individual looks like someone who has been awake 36-to 48 hours,” Dinges says. Lack of sleep slows thought processes, impairs judgment, and blunts memory.

Glenn and Japanese astronaut Chiaki Mukai, 46, each will wear a cap with electrodes to monitor brain activity while they snooze. Their eye and facial muscle twitches will be recorded to gauge the depth of their sleep, and they will wear vests that measure respiration. Older people often suffer disturbed sleep, but the elderly Glenn may not be a good example of this. “He sleeps like a log,” NASA researchers report.

As part of the circadian rhythm research, every day Glenn and Mukai each will swallow a pill that contains a thermometer and tiny radio transmitter. The pill will broadcast their core body temperatures, which vary over the course of a day, to receivers they’ll wear on their belts.

Because Glenn is spending less than two weeks in space, he won’t experience the more devastating long-term effects of weightlessness. After several months on the Russian Mir space station, Russians and Americans typically lose about 15 percent of their muscle mass and strength.

Most of the loss is in muscles in the legs and back that keep the body balanced and erect in Earth’s gravity, says Frank Sulzman, deputy of NASA’s life sciences division. Further, astronauts use their arms to move themselves around in space, so leg muscles don’t get a workout.

On Discovery, Glenn will be given amino acids involved in muscle buildup and breakdown that have been chemically altered slightly so they can be detected in blood and urine samples. The amounts found in the samples should help re searchers understand muscle loss.

Vigorous exercise appears to be effective countermeasure to muscle loss, but it’s hard to make astronauts do the required work. Shannon Lucid, who spent six months on Mir, reported afterward that “the daily exercise was what I disliked most.” The twice-daily 45-minute exercise sessions on Mir, alternating between pulling against bungee cords and running on a treadmill, were hard, long, boring – and smelly, since it’s not possible to take a shower after every workout.

Brittle bones. But muscles can be rebuilt back on Earth. Bone loss in space could be a much more serious problem. Astronauts and cosmonauts lose about 1 percent of their bone mass a month in space, and there is no indication that the rate of loss ever stops or levels off. This rate of bone loss is 10 times as high as that of osteoporosis, the bone-loss disease suffered by older people. Bone loss is not serious for short shuttle flights like Glenn’s, but it could be worrisome for a two-year flight to mars. Some researchers fear that the loss not be reversible, in which case ex-astronauts could be more likely to break bones back on Earth.

So far, it’s not clear what should be done to reduce or prevent bone loss. Exercises such as hard running while tethered by elastic bands to a treadmill don’t seem to slow the loss. Some researchers say that drugs used to control osteoporosis might help. As a last resort, it may be necessary to build centrifuges on long-duration spacecraft in which crew members could spin part of the day in artificial gravity. Providing artificial gravity with centrifuges or by rotating part or all of a space vehicle, however, would add cost and complexity to the mission.

There is also preliminary evidence that space travel harms the immune system. On long flights astronauts may not be able to fight off viruses and wounds may not heal quickly, according to William Shearer, an immunologist at the Baylor College of Medicine who leads a team studying the issue. He says that stress, confinement, isolation, lack of sleep, and radiation all can affect the immune system.

The medical problems of space travel aren’t likely to ground future astronauts. Instead, they are puzzles to be unraveled and overcome. With the International Space Station, which will be built starting late this year, researchers hope to learn how to live for long periods in space.

by William J. Cook from U.S. News & World Report, October 1998

2) Recall the situations with the following words, word-combinations and phrases: a generation ago, the effects on the human body, dramatic/ harmful effects on physiology, medical experiments, undergo extensive weightlessness, body’s balance mechanisms, eliminate through, thirst, increased urination, return to normal, vertebrae, terrestrial studies, to impair judgment, to blunt memory, to monitor brain activity, circadian rhythm research, amino acids, urine samples, bone loss disease, artificial gravity, fight off viruses.

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