Numerical implementation of Lower Body Negative Pressure in a multiscale mathematical model of the cardiovascular system

A transition from the Earth's gravity to the extraterrestrial microgravity environment causes direct and significant changes to human cardiovascular hemodynamics. Due to the absence of the gravitational pull, a redistribution of body fluids occurs between the upper and lower body. The fluid shift is linked with several changes in cardiovascular functions, for example, reductions in arterial pressure, variations in vascular volumes, and remodeling of carotid baroreflex system. The study of all these challenges related to the manned spaceflight brought to the development of new scientific disciplines known as space medicine and bioastronautics. The main objective of such branches of life sciences is the development of procedures and countermeasures in order to ensure human survival and well-being during and after missions into space. Among these countermeasures, one of the most extensively studied is the Lower Body Negative Pressure (LBNP) which causes pooling of blood in the lower limbs by applying an external negative pressure on the legs. Unfortunately, leading experiment in microgravity in order to study the effect of the countermeasures is not so easy, due to the limited time astronauts can dedicate to these tests and the limited medical equipment available during space missions. For this reason, in the last years numerical models of the cardiovascular system have been realized in order to provide a powerful, non-invasive and cost-effective tool to investigate the changes on the hemodynamics. The present Master Thesis aims to further develop an existing numerical model of the cardiovascular system, incorporating the effect of Lower Body Negative Pressure. We will provide numerical evidence of the effectiveness of Lower Body Negative Pressure, investigating different numerical strategy to implement it, selecting the best mathematical model and comparing the results of the simulation with the effects of a passive standing test on Earth. As the use of computer models presents opportunities to investigate the interaction of a multitude of responses and to vary physiological properties and operating conditions in a strictly controlled manner, this thesis aims to extend the well validated 0D-1D mathematical model to encompass the effects of the LBNP, in order to push further the limit of computational development in the space medicine field.