مقاله انگلیسی رایگان در مورد جریان خون و جاذبه بسیار کم – الزویر 2018

Blood represents a very challenging fluid medium in terms of theoretical description because of the scale-dependent changes of its properties and its complex mechanical and biochemical structure. Pathologies associated with blood flow and cardiovascular functions are the primary cause of mortality in Europe and the USA. Intense multi-disciplinary research is therefore essential to develop innovative approaches to identify the key elements that promote cardiovascular disorders. A major factor that affects cardiovascular dysfunctions is the absence of gravity during stays in space. It is well known that a long-term mission in space is associated with cardiovascular dysfunctions. For example, heart rhythm disturbances have been seen among astronauts. It is documented that long space missions lead to reduction of plasma volume, as well as left ventricular mass decrease. To give a simple estimate that the absence of gravity should have a clear consequence on blood flow, let us evaluate the pressure due to gravity at the level of the heart and compare it to that of the internal body blood pressure. The first is given typically by ρg h. Taking density ρ to be that of water and g earth gravity and considering that the heart height in the upright position is of about h = 1 m, we obtain 104 Pa = 0.1 bar. An average blood pressure is, in terms of medical common usage, 14/8, which means an extra pressure (in comparison to atmospheric pressure) of 140 mm of mercury in the systolic regime and 80 mm in the diastolic regime. Given the fact that the atmospheric pressure corresponds to 760 mm of mercury, a blood pressure of 14/8 thus corresponds to the range of 0.1–0.18 bar. Interestingly the pressure related to earth gravity is very close to the body internal extra pressure. One expects thus that a long term mission in microgravity should impact physiological functions, that can potentially lead to cardiovascular anomalies. Besides myriads of macroscopic studies (heart rhythm, plasma volume, blood vessel remodeling), other measures performed on astronauts after long missions in space reported several microscopic disturbances. For example it has been reported that space missions are accompanied with anemia, hemolysis and with an increase of amylase activity [1] as well as with variations in Red Blood Cell (RBC) membrane phospholipid composition [2]. Amylase is an enzyme that is known to digest sugar molecules, which are abundant on the glycocalyx as well as on the RBC surface. It is thus an essential goal for studies on blood flow to analyze the far reaching consequences of the impact of microgravity on blood flow, which is our long-term objective. For many years we have been involved in trying to extract the basic elementary blocks that govern the blood flow properties, ranging from the study of single cell dynamics up to collective motions. Other studies consist in functionalizing artificial circuits with polymer brushes and more recently with endothelial cells in order to mimic real blood vessels. In particular an objective is to alter the endothelium, thanks to enzymatic digestion (mimicking the amylase activity in space), and to study the related consequences. In what follows, we shall briefly describe the main achievements of our studies and the various microgravity experiments that have allowed us to extract this information. In particular we shall discuss the lift force on vesicles and on RBCs, experiments performed in parabolic flights where lipid vesicles are simplified models for RBCs.