The development of space technology, as well as in various projects to develop a mission to Mars, in addition to programs to return to and eventually inhabit the Moon, and other more exotic plans for planetary travel, pose several medical-biological problems related to life in the extreme conditions of outer space.
Among other conditions, we find the absence of an atmosphere, the existence of extreme temperatures, the adverse effects of microgravity, acceleration and deceleration, the presence of ionizing radiation, in addition to the fact that in the spacecraft or space habitats there may be exposed to toxins in the environment, traumatisms, accidents due to impact with meteorites or, as shown in the movie Gravity, impacts with space debris.
Besides, astronauts' nutrition becomes a real challenge, as well as the management of their psychic condition in isolation and the various alterations they present in their sleep patterns and circadian rhythms, among other medical aspects.
Not so severe medical-biological problems are also produced by the development in modern aeronautics, where pilots are subjected to very high accelerations and decelerations, as well as to various degrees of exposure to radiation and phenomena of loss of orientation due to extreme accelerations and microgravity conditions.
Because of all this, a branch of modern medicine has been developed which is space and aeronautical medicine.
Space medicine addresses the problem of defining the health risks of space flight and developing strategies to prevent and treat various disorders in space. To this end, research tasks are developed to simulate the space environment, very strict processes are carried out for the medical selection of astronauts and risk prevention, protocols are designed for medical treatment in space, and plans are drawn up for emergency and rescue missions for astronauts.
Space can offer an advantageous environment for the treatment of certain medical pathologies, not only to obtain deleterious effects but also some that can be favorable in the medium and long term, such as, for example, the treatment of orthopedic injuries, particularly spinal injuries that produce paraplegia and quadriplegia, which can be treated much better -from the point of view of musculoskeletal mechanics- in space.
Or cases of subjects in a prolonged coma whose care on Earth is complicated and that in space, under microgravity conditions, could be managed in a much simpler and more effective way. It is conceivable that medical care modules could be developed for these patients in space, constituting medical treatment units for specific disorders in extreme cases.
Of all the adverse effects of space travel, the almost total absence of gravitational pull is probably the one that most directly affects the ability of astronauts to perform various activities. Microgravity has adverse cardiovascular, skeletal, muscular, and cognitive effects.
Gravitational attraction is one of the fundamental forces and axis of the development of life. Isaac Newton (1642-1726) described this force that determines that, on Earth, objects fall due to the attraction exerted by the planet on all bodies on its surface, including the air that makes up the atmosphere. Curiously, the force of gravity is one of the few processes whose intensity is essentially constant over time and the evolution of life on the planet (it varies only 0.5% between the poles and the equator).
We can imagine other phenomena such as temperature, which varies widely on the surface of the planet (from -40 to +100 °C); the same happens with the amount of light or solar radiation, which are highly variable; humidity, wind, magnetism, rain, practically all the phenomena of the environment are variable, while there is one that remains practically constant: gravitational attraction. This has led to the proposal that this essential force of nature is an element that contributes to the organization of living beings. Plants are polarized in part thanks to the action of this force, although redwoods seem to defy gravitational attraction because of their height.
Neurobiology and microgravity
In space, the sensitive masses found in the otolithic organs cease to function normally, since these masses, which on Earth are subject to gravitational attraction, in conditions of space travel - whether in a stable orbit around the planet, as in the Space Station, or in travel beyond - are in conditions of microgravity, and the linear accelerations, which on Earth lead to defining the direction of the normal, which is the direction of the gravitational attractive force, cease to be significant.
The subjects then do not have the feeling that there is a direction, of what is up and down; in fact, the objects do not fall, which prevents defining a direction of the normal; it is as if Newton's apple had remained floating in space and he, then, would not have been able to develop the laws of universal gravitation.
In space, astronauts can compensate for the lack of weight sensation by looking around, but in the long term, there are important alterations in the cellular structure of the inner ear, in addition to the fact that the subjects, when they close their eyes, have abnormal sensations, such as spinning, or feel strange the body and its parts and, in extreme cases, feel that they leave their body and do not recognize themselves.
Furthermore, in the long term, plastic changes are produced in the brain that tends to eliminate the vestibular function, producing, as a consequence, that when astronauts return to Earth, they present alterations in the perception of their position and the stabilization of their gaze.
There are currently several research groups around the world working on the development of space medicine products, including the Johns Hopkins University Medical Group in the United States and the Pan-European Vestibular Implant Group based at the Maastricht University Medical Center, among others.
Source: Vega R. and Soto E. Space medicine. Elementos 108 55-60.