Understanding post-spaceflight orthostatic intolerance - a simulation study

We have developed a computational model of the cardiovascular system with the aim of analyzing the hemodynamic response to orthostatic stress. Using the model, we investigate the hemodynamic effects of changes in model parameters that are thought to contribute to the syndrome of post-space flight orthostatic intolerance. Our simulations indicate that changes in total blood volume have the largest detrimental effect on arterial blood pressure homeostasis. If the baseline volume status is borderline hypovolemic, changes in other parameters can significantly impact the system´s ability to maintain blood pressure in the upright posture. In particular, any deleterious change in the venous tone feedback impairs blood pressure homeostasis significantly. This result has important implications for countermeasure development as it suggest that an alpha-adrenergic agonist might alleviate the orthostatic syndrome seen post-flight