Assessing the cardiac function from micro-gravity to hyper-gravity conditions through a validated multiscale modelling approach.

Gravity changes with respect to the 1g terrestrial condition induce several cardiovascular alterations, from fluid shift and blood volume reduction to orthostatic hypotension and venous pooling. Micro-gravity and hyper-gravity exposure characterizes space missions and aeronautical flights, as well as terrestrial analogues such as centrifuges, bed rest studies, and parabolic flights. Despite a growing number of clinical measures becoming available, cardiac function in these extreme conditions is still incomplete and difficult to obtain. Thus, computational haemodynamics provides a powerful and reliable tool to understand the cardiac response. We propose a 0D-1D multiscale cardiovascular model to investigate the steady-state acute cardiac response to gravity changes (from 0g to 3g). The model combines a 1D description of the coronary circulation and arterial tree, with a 0D parameterization of the peripheral microcirculation, the venous return, the cardiopulmonary and the cerebrovascular-ocular circulations. The overall model is equipped with short-term regulation mechanisms, and accounts for gravity and posture changes. After a thorough validation using measured data from literature involving the most common central haemodynamic parameters (i.e. HR, MAP, SV and CO), the model provides an in-depth description of the cardiac response from micro- (0g) to hyper-gravity (3g), highlighting: (i) a different behaviour between left and right heart haemodynamics; (ii) an improvement in cardiac efficiency and cardiac performance in micro-gravity; (iii) a worsening of cardiac efficiency and an energy supply/demand impairment both at heart and coronary levels in hyper-gravity. Therefore, the modelling approach proves to be an important tool in shedding light on space medicine. KEY POINTS: Gravity changes from micro- to hyper-gravity induce several cardiovascular alterations, from fluid shift and blood volume reduction to orthostatic hypotension and venous pooling. Although the overall cardiovascular response is clear, details of the cardiac function in these extreme conditions are still incomplete and difficult to obtain. We propose a validated multiscale cardiovascular model to investigate the steady-state acute cardiac response to gravity changes (from 0g to 3g). After a thorough validation against the most common central haemodynamic parameters in literature, present results show: (i) a different behaviour between left and right heart haemodynamics; (ii) an improvement of cardiac efficiency and cardiac performance in micro-gravity; (iii) an energy supply/demand impairment in hyper-gravity. The computational approach is a useful and reliable tool in exploring the response of cardiac parameters which are difficult to investigate experimentally, aiming to shed light on the cardiac function under altered gravitational force.