Formerly, the great explorers, navigators, conquerors of the impossible traveled incredible distances across seas and oceans, propelled by their technical progress. Land unexploited and unexplored by civilization has therefore "disappeared" from the face of the globe.
Today, astronauts soar into space and spend six months in Earth orbit aboard the International Space Station, virtually free of gravity. Tomorrow, space stays towards the Moon or Mars could last several years. Big changes for the human body.
Indeed, environmental changes in space are very important and permanently modify the functioning of living beings which, until then, have evolved slowly to adapt to environmental modifications, such as their environment or the climate. “Space biology” applies to understanding the phenomena induced by changes in the living environment of space explorers, and support is necessary to better control its consequences on the organisms of our astronauts.
Bodies without gravity
Gravity has shaped the animal and plant world for millions of years. If it didn't exist, we wouldn't need such a complex cardiovascular system. For example, the protective mechanism that allows us to maintain normal cerebral circulation when we change position quickly (lying down to standing in particular) is linked to the existence of gravity. It's'orthostatism. It is the same for the bone and muscular systems, adapted to the terrestrial gravity, because we spend most of our life to fight against gravity.
All physiological functions are addressed in space medicine. Some are particularly important for the well-being and performance of astronauts, as they require adaptation to the space environment. These are for example the cardiovascular, musculoskeletal, neuro-sensory systems, nutrition, energetics, radiobiology and psychology. All of this research in space biology actually has applications in everyday medicine.
Blood circulation, at the heart of studies since Laïka
The absence of gravity, but also confinement and cosmic radiations, have repercussions on cardiovascular regulation.
From the very beginning of the space conquest, we had to study whether the heart and the vessels supported a journey in microgravity. Thus, the blood pressure and heart rate of the dog Laïka were monitored throughout her flight in 1957. These measurements showed that the cardiovascular system can adapt relatively well and paradoxically to this environment, because the constraints on it are imposed are in fact weaker than on Earth.
It is upon returning to Earth that the cardiovascular system is mismatched to gravity. Then occurs a cardiovascular deconditioning syndrome, caused by physical inactivity and fluid transfers induced by microgravity. The deconditioning syndrome, quickly reversible after returning to Earth, was described as early as 1945 in another context, by A. Keys, in patients who were bedridden for a long time.
Of the need for the space gym
The musculoskeletal system allows us to walk and run "against gravity", with a specific perception of movement and orientation. It was shaped by constant gravity on Earth (worth 1g), but it is obviously very difficult to do experiments that change the value or direction of the gravity field ... except by going into space (or in flight parabolic, but the experience is much shorter).
Testing individuals living in modified gravity therefore makes it possible to study the specific role of gravity on bone tissue in particular. Indeed, the absence of gravity modifies its mass, its structure and its resistance, and the time necessary to recover them. is longer than the duration of the mission.
Exposure to microgravity during space flight also causes spatial disorientation, changes in body pattern, and impaired arm movements and precision gestures. These alterations are due to the absence of a gravitational reference frame provided by the otoliths, small crystals located in the inner ear, which move when the head moves and thus modify proprioceptive signals, but which malfunction in the absence of gravity. In space, astronauts show a preference for visual information.
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What if gravity disappeared ...
Space flight also results in a drastic reduction in physical activity, which can lead to the development of metabolic disorders, such asinsulin resistance or dyslipidemia. Their role is increasingly evident in pathologies linked to a sedentary lifestyle on the ground: obesity, diabetes, arterial hypertension, or as a risk factor for psychopathologies.
Watch out for cosmic rays! What sunscreen for astronauts?
Exposure to ionizing radiation is one of the major components of the danger associated with space exploration. The sources of radiation are well defined: solar and galactic radiation are added to the radiation inside the vessel, since it does not benefit from the protection of the terrestrial magnetosphere. On the other hand, the biological risks associated with prolonged exposure to these radiations remain difficult to assess.
Indeed, exposure to space radiation poses complex questions of scientific, medical and societal interest which are, for the most part, identical to those posed by radiodiagnosis. This is particularly the case of risk of radiation-induced cancers, the phenomenon of hypersensitivity to low doses of radiation, the effects of repeated doses and individual radiosusceptibility radiation, which causes cellular transformations.
Psychology and socialization: humans beyond their mechanics
A trip to Mars is expected to last more than 500 days. This new dimension in space and time must be taken into account in future projects, referring to the concept of “self-organized micro-companies”. During interplanetary missions, crews must be fully autonomous. In particular, the life support system (recycling of water, oxygen, carbon dioxide) could have an impact on behavior over time.
In addition, the prospects of interplanetary missions to the Moon or Mars direct research towards new psychological factors, for example isolation, confinement and monotony, and new sociological factors, such as gender, culture, group.
Countermeasures, the key to health in space
From the first space flights, international space agencies became aware of the many negative effects of the environment on the bodies of astronauts. The conquest of space could not be done without maintaining the health of the astronauts in order to ensure their survival and the success of the mission. This is how protocols have been developed to prevent these physiological alterations, which are called “countermeasures”. With the entry of Martian programs into the exploratory phase, which will impose flights of two or three years, develop optimal protocols for maintaining the health of astronauts becomes a top priority.
Current countermeasures are mainly physical exercise, nutritional or pharmacological countermeasures. Recently, vibration, electrical stimulation, or even centrifugation have also been developed. These countermeasures are generally recommended treatments for people on Earth suffering, for example, from osteoporosis, kidney failure, arterial and venous damage, sarcopenia, or insulin resistance. They are first tested on Earth in experiences of prolonged bed rest.
Sedentary lifestyle, a XNUMXst century public health problem in space… and on Earth
Although space is a unique environment, there are obvious parallels between spaceflight, aging and immobilization, but also for us on Earth to reduce the damaging effects of inactivity on general health. WHO has long classified sedentary lifestyle among the top 10 causes of death and disability worldwide.
The beginning of the third millennium will see the exploration projects of the solar system multiply. Unlike the boats that sailed the oceans with crews, the new ships that cross interplanetary space are not currently inhabited by humans but by robots, which makes the missions much less restrictive.
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