Health in Space
Back when science fiction was first hustling to keep ahead of science fact, some tales featured the medical possibilities of near zero-gravity conditions. Surely humans would thrive once they could get away from the wearying, unceasing pull of Earth. Hearts wouldn’t have to pump so hard not muscles strain against gravity. Perhaps, some authors speculated, brains would work better too.
It’s beginning to look as if healthy space living has gone the way of boating on Martian canals. Fiction is being replaced by more disagreeable fact.
Though the health of astronauts has been of great concern since the days when only dogs or apes were sent into space, intensive biomedical studies have played a fairly small part in the National Aeronautics and Space Administration’s efforts. According to Science magazine, the space shuttle mission completed this past June was the first major life sciences project flown by NASA since 1974. Animals studied aboard the flight were 2000 jellyfish, 29 rats—and seven humans.
Preliminary results of the studies were given at a briefing in mid-September. They don’t make encouraging reading for someone who’s dreamed of an eventual vacation on Mars.
The physiological changes brought about by weightlessness appear quickly. The classic effects of space travel—those noted before by American and Soviet spacefarers—include shift of blood volume from the legs to the upper torso, increased heart rate, reduced intake of food and drink, and decrease in plasma volume.
The effect that immediately bothers astronauts is motion sickness. All but one of the crew on the June flight suffered from the nausea that much of humankind feels on a rolling boat or in a jouncing car. Two-thirds of the people who have flown in space have felt motion sickness, some to the point of virtual incapacitation.
The theory explaining motion sickness assumes it comes from conflicting signals. An astronaut can see that he or she is in a stable position and can touch and feel the deck. But the positioning sensory apparatus in the mammalian inner ear depends on gravity to work; without the gravitational guide, those sensors misread what’s happening. Forced to process the conflicting information reported by the senses of vision, touch, and balance, the brain reacts by generating feelings of nausea.
Like earthside sailors, astronauts seem to adapt eventually to the erroneous messages sent by their inner ears. Microscopic examination of tissues from the spacefaring rats showed that physical changes may help spacesick voyagers. The rats’ inner ear sensors seem to grow more receptor synapses in zero gravity. In effect, they’re compensating for weaker signals by building better receivers.
That physiological change may be the only beneficial one astronauts can expect. The shift in blood from legs to chest, for example, seems to suppress production of both reed and white blood cells, which could impair the immune system. Without gravity’s encouragement, bones begin to demineralize; astronauts undergo a kind of hastened osteoporosis. And kidneys change in space, filtering at a faster rate while the plasma flow decreases. That means kidney stones could become a common ailment on long space voyages.
For the medical researchers, one of the most interesting results of their studies was something that didn’t change in space. Air collects at the top of lungs, while more blood is concentrated in their lower portions, and scientists assumed that gravity played an important role in producing that pattern. But the same imbalance continued in space, which means that lung physiology isn’t as well understood as everyone thought.
The NASA life scientists are concerned enough about their findings to suggest that artificial gravity should be a feature of any manned Mars flight. Cynics think it would be far less expensive to stick with robot-manned flight—though other life forms could go along. Those 2000 jellyfish, for example, didn’t seem to miss gravity at all.
