Microgravity and the respiratory system

Abstract

The structure of the lung, with its delicate network of airspaces and capillaries, means that gravity has a profound influence on its function. Studies of lung function in the absence of gravity provide valuable insight into how, for we Earth-bound individuals, its unavoidable effects shape our lung function. Gravity causes uneven ventilation in the lung through the deformation of lung tissue (the so-called Slinky effect), and uneven perfusion through a combination of the Slinky effect and the zone model of pulmonary perfusion. Both ventilation and perfusion exhibit persisting heterogeneity in microgravity, indicating important other mechanisms. However, gravity serves to maintain a degree of matching of these two processes, so that the ventilation/perfusion ratio, and thus gas exchange, remains efficient. Therefore, while both ventilation and perfusion are more uniform in spaceflight, gas exchange is seemingly no more efficient than on Earth. Despite the changes in lung function when gravity is removed, the lung continues to function well in weightlessness. Unlike many other organ systems, the lung does not appear to undergo structural adaptive changes when gravity is removed, and so there is no apparent degradation in lung function upon return to earth, even after 6 months in space. @ERSpublicationsThe structure of the lung means that gravity has a profound influence on its function

Mechanotransduction as an Adaptation to Gravity

“…However, if the string is stretched further (to simulate inspiration), and due to the elastic recoil forces of the spring, the loops in the lower part of the spring are more distant apart from each other than in the upper part (and by comparison, ventilation is greater in the lower parts of the lung). If the effects of gravity are removed, this model would predict uniform alveolar size, ventilation and perfusion (122). …”

“…In summary, “gravity causes uneven ventilation in the lung through the deformation of lung tissue (Slinky effect), and uneven perfusion through a combination of the Slinky effect and the zone model of pulmonary perfusion” (122). …”

Ergonomic Challenges for Astronauts during Space Travel and the Need for Space Medicine

“…Despite the fact that an early murine model study [19] identified that anti-orthostatic positioning, which is changing the direction of gravity relative to the body vertical axis, may increase water content in the lungs and reduce the properties of pulmonary surfactant, there appears to be little or no effect on lung function in humans in space [20]. Two areas are, however, worthy of further discussion.…”

“…In the early years of space flight, missions were of the period of days and a very restricted number of medicines were carried, some of which are shown in Table 3 Respiratory function Limit number of EVAs and optimise hyperoxia-inducing regime [20,21] Construct 3D human lung models and characterise lung biomarkers under different conditions. [23] Immune function and infection…”

“…The planet is rocky, has a magnetic field and an axial tilt which may provide seasonal variations in climatic conditions. Now in 2017, as we comprehend taking our first steps towards space travel within the solar system which are designed to lead to lunar or planetary colonization within the next [10][11][12][13][14][15][16][17][18][19][20] years, what will we need to know and to develop which will allow such a crew to be safely maintained for these first steps and which may ultimately provide a foundation to permit travel to and permanent colonization of a new world?…”