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Matt Hurst
Professor Kinnamon
English 112.[section no.]
11 November 2000

Thesis: Microgravity in space can be harmful because of its effects on the health of astronauts through muscle depletion, bone deterioration, and breakdown of the cardiopulmonary system.

Outline

                Introduction

I. Microgravity and depletion of muscle mass

    A. Inability to adapt fully to microgravity

    B. Evidence of depletion

    C. Inadequate benefits of exercise

II. Microgravity and bone deterioration

III. Microgravity and breakdown of the cardiopulmonary system

    A. The function of the system

    B. The health of the heart

                Conclusion

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    The popular view of space flight has long ignored questions of health in favor of a focus on the marvels of soaring among the stars. In 1953, for example, well before any actual experience of outer space, Arthur C. Clarke published an essay with the enticing title, "Vacation in Vacuum," which he reprinted with only a modest disclaimer in 1972 (Report 45-56). Just four years before the reprint and several years after the Gemini flights had taken place, Clarke published another essay, which, although considerably less fanciful than the "Vacation" piece, contained the assertion that, up to 1968, "adaptation to weightlessness had been astonishingly easy" (Promise 116). Even government experts today seem relatively unconcerned about the harmful effects of space flight on the human body. With the apparent depletion of muscle, quick bone deterioration, and breakdown of the cardiopulmonary system, however, it is time to learn the facts about the effects of space travel on the human body before further exploration can occur.

    Because there is no certain understanding of why astronauts are losing great percentages of muscle while in space, there is definite need for further studies of microgravity. In the fledgling science of space medicine, one of the deepest mysteries is why astronauts lose muscle mass during weightlessness. There is, thus, an urgent need "to build a profile of what goes wrong with the muscles during space flight" ("Space Travel"). Studies have just begun to find out the reaction that takes place in human muscle tissue during periods of weightlessness. Scientists have tended to believe that organisms adapt to microgravity quickly and acquire a new biological condition to compensate for the change. But Wesley Hymer, a Pennsylvania State researcher, has stated that adapting to space or readapting on earth "may not be 'straightforward'" (qtd. in Joyce 22). His study of rats showed that in a weightless environment they were able to produce only half (or less) of the normally expected amounts of pituitary growth hormone. The pituitary helps to control growth of muscle, as well as bone and immune system cells, so Hymer's results imply that "pituitary cells package hormone molecules differently in weightless conditions" (Joyce 22). Supporting general evidence of lack of full adaptation to drastic changes in gravity is cited by David (157) and Goldsmith (2040).

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    With NASA itself doing extensive research with rats, more evidence of muscle depletion is now available. In one study, rats lost up to 36 percent of their muscle mass in only seven days of space flight. In another, they lost up to 40 percent in twelve and a half days ("Space Travel"). Relying heavily on comparisons of preflight and postflight measurements of muscle girth and strength, muscle studies have demonstrated a reduction in both factors (Goldsmith 2043). When looking further into the loss of muscle, Danny A. Riley, professor of anatomy and cellular biology of Wisconsin University, conducted an experiment with rats that showed that there is a degeneration of nerve connections to muscles and a breakdown of blood vessels within muscle tissue during and after weightlessness (McDonald). Riley's study offers this explanation:

Muscles can function only if they "receive signals from the brain which are transmitted down motor nerves to the muscle," but Riley's examination of other rat muscle specimens showed that nerve terminals had deteriorated. Because of the decrease in nerve input, cell death or muscle fiber shrinkage can occur. (qtd. in McDonald)

Some corroborating evidence came from studies of giraffes. Because the environment of the womb is very close to zero gravity, baby giraffes are born with minimal muscle development around the arteries in the lower extremities. By analogy, astronauts will also lose arterial muscle if they live for long periods without gravity ("Gravity" 92). This study sheds light particularly on problems associated with the former Soviet space program. It "helps to explain why cosmonauts faint and get oedema [swelling from accumulation of fluid] after long missions. . . . When they return from space their withered arterial muscles cannot cope with the force of gravity," which "will pull blood away from the head and down to the feet" ("Gravity" 92). While we continue to send more astronauts up into space, it is no wonder that researchers remain puzzled by the possibly death-related questions of losing muscle mass or worse.

    While NASA struggles to find ways to improve or overcome this problem, there have been interesting new ideas for using exercise to compensate for muscle mass loss. The answer may be for astronauts to use some bizarre training equipment for a few hours each day while they are in space. One idea is to put the astronaut into an airtight bag reaching up to his or her stomach and then suck out the air inside the bag. This procedure pulls blood down to the lower half of the body, rather like filling an old-fashioned fountain pen ("Gravity" 92). Dr. Ankadi Ushakov of the former Soviet Academy

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of Sciences believes that muscle atrophy can be largely prevented by exercise. A strict workout on a treadmill helped keep Soviet cosmonauts' muscles toned; the regimen also reduced calcium loss to a minimum, at least for a limited time ("Perils"). On the other hand, this machinery is bulky and does little to provide the "shock" to bones of earth-bound exercise that human beings apparently require for health. Moreover, muscles need different types of exercise; exercise that contracts muscles but does not elongate them may not be adequate (Joyce 21). In spite of the little breaks that have worked to some extent for astronauts in the past, the risk is still very high for extreme muscle loss. What the effect of long-term space flight will be is still unknown.

    Many astronauts and NASA officials also fear that there may be overall bone deterioration after space flight. The effects of microgravity on the musculoskeletal systems have been determined through a series of preflight and postflight measurements involving the use of X-ray densitometry to examine the weight-bearing bones before and after flight. The crews of later Apollo, Skylab, and Spacelab missions were studied with photon abseptiometry--a more sensitive indicator of bone mineral content. These methods indicated that bone mineral loss ranging from 3.2 percent to 8 percent occurs on flights longer than two weeks and varies directly with the length of the voyage (Goldsmith 2043). Bone loss has also been estimated through calcium-balance studies. Throughout the flights, fecal calcium continued to increase steadily and thus, by implication, leach from bones throughout flight (Goldsmith 2043; see also Miller). Indeed, some researchers believe that long-term bone loss may be the most serious problem facing Mars-bound astronauts. A post-Skylab NASA report warned that osteoporosis may set in after four to eight months of flight. Although all astronauts quickly regained their bone mineral once back on earth, the report speculated that there might be a "point of no return," beyond which bone damage becomes permanent (Noland 79). With no answers clearly in sight, the chances of negative side effects are still high for those who go into space.

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There are still other worrisome physiological changes prompted by microgravity. One of the most serious is an alteration of the heart's functions. The cardiopulmonary system--which controls ventilation, blood flow, gas exchange, and pressure of air in the lungs--is affected. When exposed to microgravity, the body fluids shift to the upper body, with blood tending to pool in the chest, neck, and head (David 157). The result is an unaccustomed feeling of fullness in the head, stuffy sinuses, and puffy eyes that the Skylab astronauts called fat face. Simultaneously, the legs noticeably shrink. One of the most troubling problems associated with fluid shift is the resulting diuretic effect, leading to reduction of blood volume, as well as frequency of urination and possible dehydration. Typically, blood volume starts decreasing within three hours; within the first day it can shrink by 10 percent (Noland 77). Thus, blood flow is a major cause of concern for the health of astronauts.

    One of the greatest fears even to those on earth is the health of the heart. Without gravity, the heart begins to relax, adjusting to its lower work load by slowing down and shrinking (Noland 78). Cardiac size was also measured radiographically before and after the space flights. There has been a slight decrease in the cardiac-thoracic ratio on short flights and a major decrease on longer flights (Goldsmith 2042). Goldsmith reports still other significant findings. It was also learned, for instance, that the left and right ventricles underwent extreme decreases throughout the tested flight, but returned to its normal state within hours of landing. The mean resting heart rate increased by 20 percent. And this elevated heart rate, in connection with the increased stroke volume--a result of an increase in left ventricle volume--raised mean cardiac output substantially during the first day of flight. In subsequent days, as left ventricle volume declined, mean cardiac output returned to preflight level (Goldsmith 2042). According to other reports, however, even with its returning to previous states, the shift in blood from the lower limbs to the chest seems to suppress lymphocyte and red cell

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production, which in turn could impair the immune system ("Space May Be Bad"). With the heart pulling more than its share in gravity, it cannot be expected to continue to perform at peak capacity during long stays in microgravity. Noland concludes that, regardless of all the strategies being considered, "a weightless astronaut's circulatory system will . . . never operate as vigorously as it does on Earth" (78).

    If we continue to neglect the safety of human life because of pushing forward in space exploration, we may pay the price in another major NASA disaster. We need to establish a data base for further research of microgravity to ensure the safest possible environment for our astronauts. Further progress may also come from recent research on cell development in the bioreactor by the NASA Microgravity Research Program ("Bioreactor"). If we hope to fulfill the exhilarating promise of a philosophically complex film like 2001: A Space Odyssey--another challenging work from the speculative imagination of Arthur C. Clarke--we must be prepared to address the very real threats of actual space exploration to the men and women who assume the risks for the rest of us.

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Works Cited

"Bioreactor Expands Health Research." Microgravity Research Program. 9 Sept. 1998.

     NASA. 28 Oct. 2000. <http://science.msfc.nasa.gov/newhome/br/bioreactor.htm>.

Clarke, Arthur C. The Promise of Space. New York: Harper, 1968.

---. Report on Planet Three and Other Speculations. New York: Harper, 1972.

David, Leonard. "Artificial Gravity and Space Travel." Bioscience 42.3 (1992): 155-59. 

    Research Library. ProQuest. Renfro Library, Mars Hill College. 28 Oct. 2000.

Goldsmith, Marsha F. "The Body Pays a Penalty for Defying the Law of Gravity." Journal

    of the American Medical Association 256 (1986): 2040+.

"Gravity and Blood Circulation: A Tall Story." Economist 21 Nov. 1987: 90-92. Research 

    Library. ProQuest. Renfro Library, Mars Hill College. 28 Oct. 2000.

Joyce, Christopher. "Mars: Is It Mission Impossible." New Scientist 16 Feb. 1991: 21-22. 

    Academic Search Premier. EBSCO. Renfro Library, Mars Hill College. 28 Oct. 2000.

McDonald, Kim. "Weightlessness and Muscle Damage." Chronicle of Higher Education 29 June

    1988: A5.

Miller, Patricia L. "Nursing in Space: A New Frontier for Nursing." Nursing Management 22.8 

     (1991): 36-37. Research Library. ProQuest. Renfro Library, Mars Hill College. 28 Oct. 2000. 

Noland, David. "Zero-G Blues: Three Decades after the Mercury Mission, the Biggest Obstacle to

    Prolonged Space Travel Remains the Frailty of the Human Form." Discover May 1990: 74-80.

    Academic Search Premier. EBSCO. Renfro Library, Mars Hill College. 28 Oct. 2000.

"The Perils of Zero Gravity." Time 18 July 1988: 52. Research Library. ProQuest. Renfro Library, 

    Mars Hill College. 28 Oct. 2000.

"Space May Be Bad for Your Health." Science 71 (1990): 1491. Academic Search Premier. EBSCO. 

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"Space Travel: Why Astronauts' Muscles Weaken." USA Today 18 June 1990: 12.