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Space Shuttle Reaps New medical data


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Matters of the Heart ... And Peripheral Arteries

Women seem to faint more in microgravity, something that has NASA researchers puzzled.

It's true that women generally have lower blood pressure and higher heart rates than men, likely related to differences in how their peripheral blood vessels operate. When under cardiovascular stress -- like climbing stairs -- a woman's heart rate will increase, whereas it's a man's blood pressure that increases.

In microgravity, these differences may determine whether or not an astronaut will faint, Charles says. Fainting is scientifically known as "orthostatic intolerance," the inability to maintain blood flow to the brain during upright posture.

But the fact that women faint more -- is it due to physiologic differences, or, is it because few women have become fighter jet pilots, so few have experience with extreme G-forces? That's unclear, Charles tells WebMD.

What's certain is that it's a serious problem. Many astronauts continue to experience fainting episodes after landing, he says. "After 10 days or more in microgravity, those reflexes that normally counteract the shift of blood volume away from the upper body are not fully functional. The body has to relearn how to re-flow blood pressure to the brain."

Today's astronauts wear antigravity suits, like jet pilots wear, to combat the problem. And they take salt and water supplements immediately before landing, to replace some fluid volume they have lost.

And anybody who flies longer than 30 days comes in for re-entry while lying on their backs. "That lets them feel the G-force build-up from front to back, rather than head to fanny," says Charles. "But as missions get longer, the astronaut's cardiovascular function becomes even more atrophied -- hence the need to increase the safety margin through medication," he says.

On this flight, astronauts are testing the effects of mitodrine, a medication that helps regulate the peripheral blood vessels and could therefore prevent orthostatic intolerance.

Drugs in Space

Simply put, women are complicated -- that is, their gastrointestinal systems, liver metabolism, even hormonal changes during their monthly period. Women's gastric juices also have higher pH levels. Stuff moves through the intestines more slowly than in men. The liver enzymes that process drugs are different in men than in women.

All these factors influence how our bodies absorb and eliminate drugs. These differences may also account -- to some extent -- for the fact that women have more adverse reactions to drugs than men do, says Lakshmi Putcha, PhD, technical manager for NASA's division of pharmacotherapeutics.

In one small on-the-ground study -- with just eight male and female subjects -- Putcha found "staggering differences" between men and women in the side effects of the motion-sickness drug promethazine, which was injected into the buttocks. The drug stayed much longer in women's system, which meant that side effects also lasted longer.

Extra fat in a woman's buttocks -- a little gift from Mother Nature -- may cause the difference, she tells WebMD. "We don't know exactly why, whether it was due to site-specific absorption -- the fact that they received the intramuscular shot in the buttocks. Women do have higher fat tissue in the buttocks, so the drug may get released more slowly."

On board this space flight, astronauts will be taking the drug in pill form "as needed." They're also collecting saliva samples and making notes of the drug's effectiveness. The samples will later be analyzed to determine drug levels at varying intervals.

"If there are gender differences, then there need to be changes in the way the drug is administered," says Putcha. The next study will focus on whether the shot should be given to the buttocks or arm muscle. "It can change the picture of treatment with this drug, how it is dosed," she says.

The research also suggests that "many new active drugs need to be looked at more closely based on this information," she tells WebMD. "The effects of these drugs are critical to day-to-day performance."

Overall, she says, the pharmaceutical industry has little knowledge about the specific effects of dosages in many patient populations. What we know about drug therapies is so basic, it often is based on the weight of the person being treated, Putcha says, adding, "We don't know anything about gender differences in how these drugs are used."

The research could also have direct application to dosages in elderly populations, since many physiologic changes that occur in space are similar to age-related changes, Putcha tells WebMD.

The questions loom large, with space flights and missions getting longer -- and with the thought of a Mars mission on the horizon, Charles says.

"The NIH has been spending decades to document changes in earth-bound physiology and still isn't done," he tells WebMD. "NASA -- whose job is not primarily medical research -- is just now learning what questions to ask."

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Very interesting article! I had always heard that astronauts on reentry had problems like ours but recover within days (unlike most of us). It is interesting that they are trying drugs to prevent or reduce orthostatic intolerance. I remember there are other things that space travel "discovered" that have other useful applications so who knows maybe they will uncover something useful for our condition.

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