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अमूर्त

Hemodynamic Changes of Microgravity and Adaptation in Gravity: "Baby Heart Syndrome (BHS)" and Evaluation of New Countermeasures of Microgravity in the Human Body

Simonetta Passarani

In microgravity the human body applies many adaptations to different organs and areas of the body, first of all on the cardiovascular system. The major change observed is fluid redistribution to the upper part of the body that induces an increased preload caused by a peripheral venous system emptying. The increased venous return and the redistribution of blood flow activate a complex neuroendocrine mechanism which reduces the blood volume. According to previous data, the heart volume is reduced by 10%-17% and it continues to steadily reduce for the entire period of time spent in space (weeks or months). The resulting reduced muscle mass of the heart has been wrongly compared to atrophy observed in patients chronically bedridden, geriatric or disabled but it seems to have a different pathophysiological substrate. This phenomenon may be explained by the ability to remodel the left ventricle depending on working conditions; it can reduce its muscle mass as a consequence of hypovolemia and a reduction in peripheral resistance (baby heart).
In order to clarify hemodynamic and neuroendocrine abnormalities and their basis due to microgravity, where hemodynamic and metabolic requirements are reduced, we introduce the concept of Baby Heart Syndrome (BHS).On the contrary, upon their return to earth, astronauts show typical manifestations of heart failure in the upright posture, due to the re-filling of the venous reservoir in gravity. In order to relieve these symptoms, some countermeasures are currently used such as the Head down Tilt (HDT) performed before departure and the Lower Body Negative Pressure (LBNP) in microgravity.
We propose a new measure to improve symptoms during the first days in space and to accelerate the re-adaptation to Earth's gravity. We suggest the creation of a Blood Bank Space in Space (BBSS) for astronauts, which involves a blood sample once they reach the microgravity. This procedure would reduce the volume increase of the heart, and at the same time would constitute a useful reserve of blood to re-infuse to astronauts on their return to the earth, thus reducing orthostatic intolerance. The possibility to re-infuse autologous blood could also remove infective or transfusional risk.