Spaceflight Induced Cardiovascular Diseases: Lessons Learned from Space Simulation Models

Introduction: For millennia, humans have watched in awe the unending spectacle of the night skies. As humankind dreams and aims to return to the moon and eventually continue on to Mars, many unanswered questions come to mind regarding the survivability of long duration spaceflight missions to remote destinations. It is, therefore, crucial to consider the wide range of psychological and physiological effects brought about by spaceflight. Methods: This thesis focused on the cardiovascular diseases (CVD) related to human spaceflight and divided the paper in two main parts: the effects of microgravity on the cardiovascular system (CVS) and the effects of radiation on the CVS. This thesis included the health risks related to spaceflight and incorporated the European Space Agency’s (ESA) roadmaps related to human space exploration. An additional experimental study was performed in an isolation and confinement space analog simulation and investigated the effects on the CVS and heartrate recovery (HRR) after a maximal exercise test. Results: This thesis summarized all the CVD related to human spaceflight. Upon entering microgravity, the cephalad fluid shift induces a number of adaptations in the human body, such as an increase in cardiac output and stroke volume. The main microgravity induced effects on the CVS are cardiac atrophy, cardiac arrythmias, arterial stiffness and orthostatic intolerance. The main radiation induced effects on the CVS are fibrotic myocardial remodeling, atherosclerosis and microvascular damage. On a cellular level, spheroid formation in endothelial cells, increased intracellular apoptosis and increased levels of inflammation and oxidative stress were observed leading to microvascular damage and endothelial dysfunction which stimulates the development of atherosclerosis. The one-week isolation and confinement space analog demonstrated no effects of isolation on the HRR at one and five minutes after a maximal exercise test (respectively P=0.1519 and P=0.7561). Conclusion: Spaceflight is associated with several cardiovascular risk factors such as, changes in normal exercise routine, increased psychological stressors and elevated exposure to ionizing radiation, which might promote oxidative stress and inflammation that can impair the normal function of endothelial cells and might accelerate the development of CVD.