Cardiovascular deconditioning during long-term spaceflight through multiscale modeling

Abstract

Human spaceflight has been fascinating man for centuries, representing the intangible need to explore the unknown, challenge new frontiers, advance technology, and push scientific boundaries further. A key area of importance is cardiovascular deconditioning, that is, the collection of hemodynamic changes—from blood volume shift and reduction to altered cardiac function—induced by sustained presence in microgravity. A thorough grasp of the 0G adjustment point per se is important from a physiological viewpoint and fundamental for astronauts’ safety and physical capability on long spaceflights. However, hemodynamic details of cardiovascular deconditioning are incomplete, inconsistent, and poorly measured to date; thus a computational approach can be quite valuable. We present a validated 1D–0D multiscale model to study the cardiovascular response to long-term 0G spaceflight in comparison to the 1G supine reference condition. Cardiac work, oxygen consumption, and contractility indexes, as well as central mean and pulse pressures were reduced, augmenting the cardiac deconditioning scenario. Exercise tolerance of a spaceflight traveler was found to be comparable to an untrained person with a sedentary lifestyle. At the capillary–venous level significant waveform alterations were observed which can modify the regular perfusion and average nutrient supply at the cellular level. The present study suggests special attention should be paid to future long spaceflights which demand prompt physical capacity at the time of restoration of partial gravity (e.g., Moon/Mars landing). Since spaceflight deconditioning has features similar to accelerated aging understanding deconditioning mechanisms in microgravity are also relevant to the understanding of aging physiology on the Earth.

Modelling physiology of haemodynamic adaptation in short-term microgravity exposure and orthostatic stress on Earth

“…Moreover, their CVP value in microgravity is lower than in upright and supine position. Trend of our model results in different conditions is in very good agreement with this and other literature data 2 , 18 , 21 , 26 , 33 – 35 , 51 . Moreover, simulated CVP in HDT is higher than in microgravity 53 , 54 ; this result suggests that the upright fluid shift does not contribute to CVP reduction in microgravity, while the gravitational unloading of the P TW plays a key role.…”

“…Gallo et al reported 5.1% reduction for simulated CVP, in accordance with observed early spaceflights data 21 , 26 . Simulated CVP in microgravity condition shows a slight decrease (7.6%) with respect to the simulation in supine position on Earth.…”

“…Therefore, results from Earth-based simulations might not be used to infer conclusions about the microgravity environment 25 . Moreover, the number of clinical studies is limited due to the lack of standard data collection protocol on older missions, the limited number of space missions and studies on humans 18 , 26 . These restrictions, in addition to limitations on Earth-based studies, lead to a poor understanding of the cardiovascular responses to microgravity.…”

“…Many valuable models of the cerebral circulation (like the works of Gisolf et al 12 and Buckey et al 16 ) focused on intracranial segments and related control mechanisms, by providing a simplified description of the main arterial inflow and extracranial venous return. Whole body models such as the one developed by Zhang et al 31 and Gallo et al 26 do not include brain compartments, and only the main outflow routes (IJV and VV) are included in the vascular network. Peripheral vessels play an important role in the brain and head drainage 12 , 32 , so that the choice to neglect them in order to simplify the model is not reasonable.…”

“…Therefore, our overall goal is to make a hemodynamic model able to simulate the main and most reported physiological parameters such as ICP, CVP, IJV-CSA. Noteworthy, the lack of knowledge, discordant literature and measured data about hemodynamic adaptation over time during a spaceflight mission limit the computational approach 26 . To deal with these restrictions, the current model is tuned with literature reporting data of hemodynamic physiology alteration in a short-time space mission or during a parabolic flight, whose experimental conditions and measurement data are compatible.…”