A Simulation Study On Cardiovascular Responses To Different Kinds Of Orthostatic Stresses

Lower body negative pressure (LBNP) and head-up tilt (HUT) are often used to assess the orthostatic tolerance of astrenauts and pilots. The cardiovascular responses to LBNP or HUT are observed generally. The sustained positive acceleration (+Gz) has a stronger gravitational effect on pilots along the Z-axis of their bodies in the direction of head-to-foot, and induces shift of blood from head and thorax to lower body parts. The cardiovascular system (CVS) response to orthostatic or gravitational stresses shows the function of cardiovascular regulation. If the study relating to orthostatic stresses such as the mechanisms of orthostatic intolerance induced by weightlessness or simulated weightlessness merely depended on human experiment, it would be restricted by many factors such as tolerance limit, methodology, times of experiments, opportunities, and etc. Therefore, it is necessary and of great significance to develop mathematical models to simulate the response to different kinds of orthostatic stresses, and supplement and validate the simulation results by the limited human experimental data. Then we can integrate the present knowledge and discover problems that need to be solved.All the established mathematical models at present for simulating the cardiovascular response to orthostatic or +Gz stresses are stimulus-specific models because one of them could only simulate one kind of orthostatic stress. So first aim of our study was to develop a mathematical model for simulating the cardiovascular responses to LBNP, HUT, or +Gz stress universally and then to provide a more complete model to study the physiological mechanisms of orthostatic or gravitational stresses through comparing the data from simulation and experiments.The mechanisms of orthostatic intolerance induced by real weightlessness or...