Computational Hemodynamic Simulation of Human Circulatory System under Altered Gravity

A computational hemodynamics approach is presented to simulate the blood flow through the human circulatory system under altered gravity conditions. Numerical techniques relevant to hemodynamics issues are introduced to non-Newtonian modeling for flow characteristics governed by red blood cells, distensible wall motion due to the heart pulse, and capillary bed modeling for outflow boundary conditions. Gravitational body force terms are added to the Navier-Stokes equations to study the effects of gravity on internal flows. Six-type gravity benchmark problems are originally presented to provide the fundamental understanding of gravitational 'effects on the human circulatory system. For code validation, computed results are compared with steady and unsteady experimental data for nonNewtonian flows in a carotid bifurcation model and a curved circular tube, respectively. This computational approach is then applied to the blood circulation in the human brain as a target problem. A three-dimensional, idealized Circle of Willis configuration is developed with minor arteries truncated based on anatomical data. Demonstrated is not only the mechanism of the collateral circulation but also the effects of gravity on the distensible wall motion and resultant flow patterns. Introduction Currently, NASA has been challenging long-duration space missions for the International Space Station (ISS) and flight to Mars. During the elongated space mission, astronauts have to adapt themselves to the altered circumstance of microgravity. Blood circulation as well as body fluids distribution undergoes significant adaptation during and after space flight. Much study on physiological changes under weightlessness has been performed since the early days of the space program [ 11. In particular, cardiovascular research in conjunction with the Space Shuttle program has included diverse physiological functions affected by the nervous system such as heart rate, blood pressure, hormone release, and respiration. The altered cardiac output due to adaptation during flight and deconditioning after the flight will impact blood circulation in the human body. Especially, this altered blood supply in the brain and consequent oxygen supply to certain parts of the brain will make nonnegligible impact on long-duration flight. Also gravity over 8G causes unconsciousness, so-called, blackout whereas gravity below -3G makes the retina engorged * RIACS Research Associate, AIAA Member. * Chief, Advanced Supercomputing Applications Branch, AIAA Member. of Aeronautics and Astronautics, Inc. with permission. Research Scientist, AIAA Member. Copyright