In silico study of the posture-dependent cardiovascular performance during parabolic flights

Space exploration plays a crucial role in research and technological advance. Yet, weightlessness entails severe risks for human life that are investigated through both Earth-based and on-orbit experiments. To this aim, parabolic flights are used to study the short-term response of the human cardiovascular system (CVS) to micro- (~0 g) and hypergravity (up to 1.8 g). However, the short flight duration and technical difficulties associated with invasive in vivo measurements allow for the acquisition of a very limited number of hemodynamic variables. To enrich the picture, numerical tools can represent a powerful alternative. In this work, a new validated multiscale model of the CVS is proposed to inquire into global and central hemodynamic alterations – including cardiac mechano-energetic balance – triggered by parabolic flight at different postures (supine, seated and standing). Our analyses show that: (i) gravity-induced CVS changes strongly depend on posture; (ii) central aortic pressure, cardiac work and oxygen consumption indexes are significantly influenced by blood migration between central and lower body regions elicited by gravity variation; and (iii) cardiac efficiency improves during 20 s microgravity, while worsening in both hypergravity phases. Finally, (iv) the role of mildly elevated intracranial pressure (ICP) encountered in 0 g is discussed as a potential risk factor for spaceflight-induced visual impairment.